Introduction

Winter weather causes significant road impacts. According to the Federal Highway Administration, about 22% of all accidents in the U.S. from 2005-2014 were weather-related. This translates to yearly averages of about 5,900 fatalities, over 445,000 injuries, and nearly 1 million property-damage-only accidents. State, local, and municipal Departments of Transportation (DOTs) implement various strategies to mitigate impacts on the roads. More accurate and timely weather and road weather forecasts, in addition to observations, can better inform DOTs and improve their decision-making capabilities.

In the next section, we will go through an exercise to learn how forecasters can better communicate winter weather threats to the DOT.

Simulation

This simulation will give you a chance to apply what you already know about communicating winter weather information to National Weather Service (NWS) partners. You will take the role of a NWS forecaster communicating winter weather information to a local DOT manager via a teleconference. Your partner’s reaction and decisions will change based on your selections.

Scenario

You are a forecaster at the Weather Forecast Office (WFO) Salt Lake City with responsibility for most of Utah. The Wasatch Front lies west of the Wasatch Mountain Range, stretching from south of Provo to north of Ogden and includes the Salt Lake City metro area (see map). It is Tuesday, January 7th.

A trough along the Oregon coast is forecast to track southeast through northern Utah on Wednesday and bring a chance for snow. Although the trough is not very strong, it does have adequate moisture and lift to generate widespread precipitation across northern Utah throughout Wednesday morning. The snow may begin before sunrise along the Utah/Idaho border before spreading south towards Salt Lake County.

The Storm Scale Ensemble of Opportunity (SSEO) model shows that the snow could arrive in time and in sufficient quantity to slicken the roads during the morning commute. The 24-hour mean quantitative precipitation forecast (QPF) ending early Thursday morning shows 0.10” to 0.25” along the Wasatch Front from Salt Lake City north, and 0.01” to 0.10” in the Provo area. The 6-hour mean QPF ending late Wednesday morning shows that nearly all of the valley precipitation falls on Wednesday between 5:00 AM and 11:00 AM local time.

Traditional snow advisory criteria for Utah’s valleys is 3” to 5” in 12 hours, and 4” to 8” in 24 hours. Snowfall amounts associated with Winter Storm Warning criteria are 6” or more in 12 hours, and 9” or more in 24 hours. However, current NWS philosophy is to adjust these traditional criteria, as needed, based on the level of impact expected with an event.

After looking over all forecast information, it appears that snowfall will begin around 6:00 AM and continue through late morning, although snowfall is expected to be only 1” to 3”.

Another important forecast factor is the road surface temperatures. Tuesday’s road surface temperatures climbed into the mid-30s°F and dropped into the low-30s°F by the time you would be making your forecast. Although road temperatures are expected to stay a little warmer overnight with south winds and increased cloud cover ahead of the cold front, they should still fall well below freezing, which would enable snow to quickly stick to roads.

There are three questions in this simulation. To complete the simulation successfully, you will need to select the correct answer for all three questions. Feedback is available only after you complete the simulation. You will have three attempts to complete the simulation successfully. Launch the simulation when you are ready.

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Communication Simulation

Attempt 1 of 3

Data

• 500 mb Heights
• 24h Mean QPF
• 6h Mean QPF
• Road Temps

500 mb Heights

24h Mean QPF

6h Mean QPF

Road Temps

Question 1.

The local DOT manager notices the advisory issuance, calls you right away, and says “I saw that the NWS has issued a Winter Weather Advisory for our area. Is this going to be a significant weather event? How much snow are we expecting from this storm?”

How would you describe the winter weather threat expected to impact Salt Lake City on Wednesday morning? Choose the best answer.

Although we are not forecasting significant amounts, the storm has enough moisture and energy to produce accumulating snowfall. There is a potential for snowfall totals to reach 1” to 3”.

We are expecting a weak storm system to impact the state. The storm does not have enough moisture to produce heavy snow across the area. The snowfall totals could be around 3” at most.

This impending storm will quickly pass across the state. Although the storm has enough moisture, there will not be enough time for the snow to accumulate on road surfaces.

The correct answers are b, c.

The positive phase of the IOD typically results in drier than normal winter/spring conditions across central and southeast Australia. Temperatures tend to be warmer than normal across the southern part of the country but are typically cooler than normal in the northeast.

Please make a selection.

Question 2.

After you describe the imminent winter weather threat, the local DOT manager says “So, you’re not expecting a strong storm to come in, but the storm could bring a few inches of snow. What is your confidence in this forecast? Are there any specific areas you think are at greatest risk of seeing snow? What time will the worst conditions occur?”

Which of the following statements will you use to answer the question? Choose the best answer.

Yes, you heard me right. We are fairly confident in the potential snowfall totals. However, it is possible that the model guidance is underestimating the strength of this storm. If that is the case, and the storm ends up being stronger than we think, we will see heavier snowfall totals in some spots. Yes, there are specific areas that are at greater risk of getting snow, mainly in northern Utah. The snow will fall near the Utah and Idaho border. As of now, we are thinking that the snow will start tomorrow morning between 8:00 AM and 10:00 AM and somewhere in the risk area. We could see strong snowfall rates, too.

That is what we are thinking. Our confidence is high in the potential snowfall amounts and impacted areas. We expect the greatest risk areas to be along the Wasatch Front from Salt Lake City to north of Ogden and the Logan area. There is also some risk along the southern Wasatch Front, but our confidence in accumulating snow is much lower there. We expect the snow to likely begin between 6:00 AM and 7:00 AM on Wednesday, with the highest snowfall rates occurring between 6:00 AM and 10:00 AM or so. However, the snowfall could begin as early as 4:00 AM. Either way, there is the potential for a messy morning commute.

That is our forecast at the moment. We have low confidence in the potential snowfall totals and impacted areas. This is because we have seen similar storm tracks in the past that had enough moisture for snowfall, but failed to materialize. Although this does not happen for every storm that passes through Utah, it has happened. Considering that we have little trust in our forecast right now, we do not feel comfortable providing you information on high risk areas, or when the precipitation is expected to begin and end. It may be better for you to check back in tomorrow morning. That is when we will have updated model guidance.

Please make a selection.

Question 2.

After you describe the imminent winter weather threat, the local DOT manager says “So, you’re expecting this storm to be a weak one, and it is possible that we may not even see any snow. What is your confidence in this forecast? Are there any specific areas you think are at greatest risk of seeing snow? What time will the worst conditions occur?”

Which of the following statements will you use to answer the question? Choose the best answer.

Yes, you heard me right. We are fairly confident in the potential snowfall totals. However, it is possible that the model guidance is underestimating the strength of this storm. If that is the case, and the storm ends up being stronger than we think, we will see heavier snowfall totals in some spots. Yes, there are specific areas that are at greater risk of getting snow, mainly in northern Utah. The snow will fall near the Utah and Idaho border. As of now, we are thinking that the snow will start tomorrow morning between 8:00 AM and 10:00 AM and somewhere in the risk area. We could see strong snowfall rates, too.

That is what we are thinking. Our confidence is high in the potential snowfall amounts and impacted areas. We expect the greatest risk areas to be along the Wasatch Front from Salt Lake City to north of Ogden and the Logan area. There is also some risk along the southern Wasatch Front, but our confidence in accumulating snow is much lower there. We expect the snow to likely begin between 6:00 AM and 7:00 AM on Wednesday, with the highest snowfall rates occurring between 6:00 AM and 10:00 AM or so. However, the snowfall could begin as early as 4:00 AM. Either way, there is the potential for a messy morning commute.

That is our forecast at the moment. We have low confidence in the potential snowfall totals and impacted areas. This is because we have seen similar storm tracks in the past that had enough moisture for snowfall, but failed to materialize. Although this does not happen for every storm that passes through Utah, it has happened. Considering that we have little trust in our forecast right now, we do not feel comfortable providing you information on high risk areas, or when the precipitation is expected to begin and end. It may be better for you to check back in tomorrow morning. That is when we will have updated model guidance.

Please make a selection.

Question 2.

After you describe the imminent winter weather threat, the local DOT manager says “So, because you’re expecting this storm to blow past us, we shouldn’t expect to see much snow from it or any major impacts. If anything, maybe an inch. What is your confidence in this forecast? Are there any specific areas you think are at greatest risk of seeing snow? What time will the worst conditions occur?”

Which of the following statements will you use to answer the question? Choose the best answer.

Yes, you heard me right. We are fairly confident in the potential snowfall totals. However, it is possible that the model guidance is underestimating the strength of this storm. If that is the case, and the storm ends up being stronger than we think, we will see heavier snowfall totals in some spots. Yes, there are specific areas that are at greater risk of getting snow, mainly in northern Utah. The snow will fall near the Utah and Idaho border. As of now, we are thinking that the snow will start tomorrow morning between 8:00 AM and 10:00 AM and somewhere in the risk area. We could see strong snowfall rates, too.

That is our forecast at the moment. We have low confidence in the potential snowfall totals and impacted areas. This is because we have seen similar storm tracks in the past that had enough moisture for snowfall, but failed to materialize. Although this does not happen for every storm that passes through Utah, it has happened. Considering that we have little trust in our forecast right now, we do not feel comfortable providing you information on high risk areas, or when the precipitation is expected to begin and end. It may be better for you to check back in tomorrow morning. That is when we will have updated model guidance.

That is what we are thinking. Our confidence is high in the potential snowfall amounts and impacted areas. We expect the greatest risk areas to be along the Wasatch Front from Salt Lake City to north of Ogden and the Logan area. There is also some risk along the southern Wasatch Front, but our confidence in accumulating snow is much lower there. We expect the snow to likely begin between 6:00 AM and 7:00 AM on Wednesday, with the highest snowfall rates occurring between 6:00 AM and 10:00 AM or so. However, the snowfall could begin as early as 4:00 AM. Either way, there is the potential for a messy morning commute.

Please make a selection.

Question 3.

As a final follow-up to your responses, the DOT manager says “Given your details, it sounds like you’re confident that the snow will start during the morning commute on Wednesday. And, the Wasatch Range north to Cache County will be primarily impacted, less so further south. This will help me decide where to send my crews and when to start preparing the roads. What are the potential impacts of Wednesday’s winter storm?”

Which of the following statements will you use to answer the question? Choose the best answer.

Happy to hear we can help the DOT. Given that we are going to see up to 3” of snow at most, we are expecting impacts to be minor. You may see some light accumulations on roads, but not something to be overly concerned about. A stronger storm system will come in on Thursday. This system looks to be better organized in the models, and will bring a greater chance for widespread snow.

It is good to know we are giving you useful information. Like I said before, we have low confidence in the snowfall totals and risk areas. The models may be over- or underestimating the strength of the storm and how much snow it can make. Since surface temperatures are cold we may see higher snowfall totals in some spots, but others may just get a trace. Given that we do not have trust in our forecast right now, we cannot tell you what road impacts to expect.

Glad we are able to help you. Since surface temperatures are cold, we expect accumulation on all surfaces including roads. Although there is a potential for low-end snowfall totals of 1” to 3”, the timing of the snowfall will impact the morning commute along the Wasatch Front. Travel impacts could be significant with the slick roadways and reduced visibilities.

Please make a selection.

Question 3.

As a final follow-up to your responses, the DOT manager says “Your answer doesn’t really help me decide where to send my crews out and sufficiently prepare operations for the storm. It sounds like you’re not as confident in how much snow we’ll get, but it’s possible that the model is wrong and we could get much more. So, the best you can do is tell me that some places in northern Utah are likely to get hit sometime Wednesday morning?! This is a pretty wide area. Can you at least tell me what are some of the potential impacts from this storm?”

Which of the following statements will you use to answer the question? Choose the best answer.

There is no need to get angry. If forecasting was easy, everyone could do it. Given that we are going to see up to 3” of snow at most, we are expecting impacts to be minor. You may see some light accumulations on roads, but not something to be overly concerned about. What you need to worry about is Thursday’s storm that looks to be better organized in the models, and will bring a greater chance for widespread snow.

I am telling you all that I know right now! If you call me later, I may know more. So like I said before, we have low confidence in the snowfall totals and risk areas. The models may be over- or underestimating the storm's strength and how much snow it can make. Since surface temperatures are cold we may see higher snow totals in some spots, but others may see just a trace. Given that we do not have trust in our forecast right now, we cannot tell you what road impacts to expect.

I understand your frustration. We need to keep in mind that even though snowfall totals are on the low end, the timing of the snowfall will impact the morning commute along the Wasatch Front. Since surface temperatures are cold, we expect accumulation on all surfaces including roads. Travel impacts could be significant with slick roadways and reduced visibilities.

Please make a selection.

Question 3.

As a final follow-up to your responses, the DOT manager says “So, it sounds like you’re not really confident in the amounts or impacted areas. You really don’t know what is going to happen! It could be a major impact or nothing at all. That doesn’t help me when I need to make decisions on the type of mitigation to do, where to send my crews, and what time they should start preparing the roads. People’s safety is at risk! I can’t wait until tomorrow for your updated forecast. By then it will be too late, the morning commute will be a mess! What are the potential impacts of Wednesday’s winter storm?”

Which of the following statements will you use to answer the question? Choose the best answer.

Don’t get angry at me! If forecasting was easy, everyone could do it. Given that we are going to see up to 3” of snow at most, we are expecting impacts to be minor. You may see some light accumulations on roads, but not something to be overly concerned about. A stronger storm system will come in on Thursday. This system looks to be better organized in the models, and will bring a greater chance for widespread snow.

This is all that I know right now! If you call me later, I may know more. Like I said before, we have low confidence in the snowfall totals and risk areas. The models may be over- or underestimating the strength of the storm and how much snow it can make. We may see higher snowfall totals in some spots and others with just a trace. Given that we do not have trust in our forecast right now, we cannot tell you what road impacts to expect.

I understand why you are angry, this is a difficult forecast situation. We need to keep in mind that even though snowfall totals are on the low end, the timing of the snowfall will impact the morning commute along the Wasatch Front. Since surface temperatures are cold, we expect accumulation on all surfaces including roads. Travel impacts could be significant with slick roadways and reduced visibilities.

Please make a selection.

Feedback

You communicated the winter weather threat very well. As you spoke with the DOT manager, you confidently expressed the range of potential snow amounts, event timing and impacts, and where to expect the worst conditions. The DOT manager decided to send out resources across the Wasatch Range north towards Cache County in advance of the storm. This enabled them to take care of any snowfall accumulations on the roads and efficiently maintain safer road conditions.

You struggled communicating the winter weather threat to the DOT manager. The DOT manager decided not to send out resources to mitigate the road impacts, resulting in numerous accidents and major traffic delays.

Question 1
You described the winter weather threat appropriately by relating it to the partner’s main concerns. You described the expected severity of the storm and provided a range of snowfall totals.

Question 1
Your response did not relate to the partner’s concerns very well. You incorrectly described the forecast weather threat, and provided a deterministic forecast instead of a range of snowfall values. This will not help the DOT adequately prepare for all possible snowfall outcomes.

Question 1
Your response did not relate to the partner’s concerns very well. You incorrectly described the forecast weather threat, and provided a deterministic forecast instead of a range of snowfall values. This will not help the DOT adequately prepare for all possible snowfall outcomes.

Question 2
You expressed the timing, risk areas, and forecast confidence appropriately without going into meteorological jargon. You provided time frames and specific target areas that will be useful for DOT operations. This will help build the DOT manager’s trust in the weather information you communicate.

Question 2
You did not describe the high threat areas using well-known geographic references, and did not show confidence in event timing or in the storm’s intensity. That makes it difficult for the DOT manager to select a course of action. Since the information you provided made it difficult to make a decision, this will increase the frustration level.

Question 2
Your statements undermined your own forecast and did not provide any actionable information. That makes it difficult for the DOT manager to select a course of action. Since the information you provided made it difficult to make a decision, this will increase the frustration level.

Question 3
You communicated to the DOT manager the potential impacts that the storm may bring. This information will help the DOT determine the specific mitigation strategies they will implement and ensure sufficient resources and staffing for the event. You also showed patience for the DOT manager’s concern even though they may have expressed anger in the situation.

Question 3
You took a defensive approach in your response to the DOT. This creates a confrontation instead of partnership in this difficult situation. Also, you selected a statement that is not true for all minor snowfall events. Minor snowfall totals can still impact the road network. These sub-advisory events can have a great impact on DOT strategic planning because the details may not be well known until they are in the tactical time frame.

Question 3
You did not acknowledge the DOT manager’s concern. This places you on opposite sides in the situation instead of being partners. In addition, this response does not provide practical, trustworthy information that a decision-maker can depend on to make good decisions during planning and operations.

Question 3
You communicated to the DOT manager the potential impacts that the storm may bring. This information will help the DOT determine the specific mitigation strategies they will implement and ensure sufficient resources and staffing for the event. You also showed patience for the DOT manager’s concern even though they may have expressed anger in the situation.

Question 3
You took a defensive approach in your response to the DOT. This creates a confrontation instead of partnership in this difficult situation. Also, you selected a statement that is not true for all minor snowfall events. Minor snowfall totals can still impact the road network. These sub-advisory events can have a great impact on DOT strategic planning because the details may not be well known until they are in the tactical time frame.

Question 3
You did not acknowledge the DOT manager’s concern. This places you on opposite sides in the situation instead of being partners. In addition, this response does not provide practical, trustworthy information that a decision-maker can depend on to make good decisions during planning and operations.

Try Again End Simulation

Preseason Coordination

The Traffic Operations Center at the Utah Department of Transportation.

Providing meteorological support to decision-makers does not start with the first event of the season. Pre-season coordination is vital for effective communication whenever a winter weather event unfolds. It will enable you to understand the critical thresholds and decision points of DOT personnel.

Question

Before the winter season begins, you should meet with the DOT to learn about their workflow, concerns, and information needs. Doing so will help you be better prepared to help them when events unfold. Which of the following questions will help you capture this information? Select all that apply.

a) When do you need to make your critical decisions?

b) When would you like to have certain weather information?

c) What are the weather thresholds that you look for when making critical decisions?

d) What potential impacts most concern you?

e) How long does it take you to make your decisions?

f) What are your hours of availability?

The correct answers are a, b, c, d, and f.

Answers to questions like these will help you create a timeline of critical information to help the DOT make important decisions. When providing Impact-Based Decision Support Services (IDSS) to partners, you can create a table that shows the weather conditions, locations at risk, event timing, and road impacts for an impending winter storm (see example below). This is a helpful way of organizing information while keeping it concise, and will give the DOT enough time to implement their preparedness measures.

Table showing expected weather conditions, locations at risk, event timing, and road impacts for an impending Christmas winter storm.

Please make a selection.

Here are additional items to address in pre-season planning with the DOT:

• Find out how they like to be briefed and what information they hope to learn.
• For remote briefings, verify if they have a communication system that you can connect to, and what time window works best for them.
• Become familiar with their planning cycle so you can provide the right information at the right time.
• Ask about their experiences with the previous season’s storms. This will help you understand their perspectives and anticipate some of their concerns with future storms.
• Discuss forecast uncertainties and limitations on what information can (or cannot) be provided at particular phases of an event.
• Identify what their critical decision thresholds are (e.g., snowfall rates and amounts of concern, cross wind speeds that restrict travel).

Keep in mind that the NWS offices will not be forecasting road conditions for DOTs. Private sector and DOT weather providers support DOTs with specialized road surface temperature forecasts and expertise on road treatment options.

You may want to offer short training sessions to the DOT on how to understand and interpret your WFO's winter weather forecast products. Also, conduct integrated warning team exercises with the DOT that simulate actual events. All participants will come away with a better understanding of each other’s needs and roles. A better understanding of how the DOT operates will allow you, as a forecaster, to use your limited time and staffing resources efficiently during significant winter weather events. When partners practice together, everyone benefits.

Question

Winter weather information is viewed differently depending on your role during the event. Use the pull-down menu to select the population that is most interested in the answer for each question.

a) What is the potential snowfall rate we can expect? -- DOT Manager NWS Forecaster General Public

NWS Forecaster

Please make a selection.

b) What type of traffic mitigation strategy should be employed? -- DOT Manager NWS Forecaster General Public

DOT Manager

Please make a selection.

c) Do I leave work early or stay late? -- DOT Manager NWS Forecaster General Public

General Public

Please make a selection.

The correct answers are highlighted above. The following chart describes the focus that decision-makers, meteorologists, and the public have when dealing with a winter weather event.

The main concerns as perceived by decision-makers, meteorologists, and the general public during winter weather events.

Winter weather information is viewed differently depending on your role during the event. As a forecaster, you are likely to focus on the precipitation type, amount, timing, and location. You must determine how to best communicate this information and associated forecast uncertainties. Most of your customers do not know the jargon or science behind the forecast. Also, they have a different perspective on the event according to their responsibility toward the community or their family.

Decision-makers tend to focus on potential impacts. This is typically done through emergency playbooks and disaster plans that have been adapted for the event. These plans contain trigger points based on critical thresholds tailored for the area. Decision-makers need to determine where and when to respond first, what measure of resources are needed, and the type of rescue and recovery actions entailed.

The general public is concerned about potential impacts too, but relative to personal protection and safety. Personal decisions of whether to work from home, send children to school, and stock up on emergency supplies and gas are their primary considerations. They also decide on what can be done to safely limit the impacts of the winter precipitation and when to begin preparation.

Please make a selection.

Next, we explore the ways in which forecasters can best support the DOT during the winter season.

Preseason Coordination » DOT Mitigation Strategies

Snowfall often affects a community’s entire surface transportation system at once such that traffic cannot flow or be directed around the impacted areas. The precipitation type, intensity, and impact on transportation govern many DOT decisions and trigger many actions. Certain actions are taken ahead of potential storms, particularly when Watches are issued and during Advisory and Warning events.

In the DOT, adverse weather impacts on the road can be categorized four ways (Pisano and Goodwin, 2004):

1. Slick roads due to wet, snowy/slushy, or icy pavement.
2. Reduced visibility due to fog, heavy precipitation, or vehicle spray.
3. Obstructed lanes due to snow accumulations, standing water, or road debris.
4. Road damage from potholes or washed out roads.

Road damage usually requires maintenance that can take days or months to complete. The other three impacts can be addressed using mitigation strategies, which will vary from place to place depending on an area’s specific needs.

There are three types of mitigation strategies:

1. Advisory Strategies. Influence drivers and the general public in their decision-making process.
2. Control Strategies. Restrict access to roads by reducing speeds and number of lanes, or completely closing a road to keep drivers safe.
3. Treatment Strategies. Apply resources to the road environment to improve driving conditions.

Preseason Coordination » Supporting the DOT

NWS offices should be flexible in how services are provided to state/local DOTs. For example, if the DOT has no weather support (e.g. in-house or a private sector provider), your IDSS may focus on timing of snowfall, precipitation rates, or your confidence in certain aspects of the event. Your IDSS should not include specialized weather support and customized consulting services to DOTs (e.g. road surface temperature forecasts or advice on which road chemicals are best suited for a particular circumstance).

If the DOT has weather support, a conversation with the DOT site manager should identify the level of service needed from NWS. Service will likely be a collaborative discussion focused on the impacts. The DOT weather support team will likely have expertise in forecasting road conditions and they should be able to help WFO forecasters assess potential event impacts. In this scenario, a brief discussion on the meteorology of the event should quickly shift to expected impacts and joint messaging by the two agencies. This discussion might focus on timing, specific routes, and locations (e.g. mountain passes or traditional trouble spots) that the DOT is most concerned about. Ideally, this interaction would focus on joint messaging strategies (i.e., routes to highlight and verbiage to use in statements) between the WFO and the DOT to ensure that we provide a consistent message to the public and our partners.

Examples of collaboration processes that occur in the DOT can be found here.

DOTs without meteorological staff need information on the evolution, timing, and potential impacts of hazardous weather events. Weather forecasts are useful during the strategic timeframe, 24-48 hours prior to a hazardous weather event (i.e. start of precipitation). During this time, the DOT managers determine the specific mitigation strategies they will implement, ensure they have all of the equipment they need, and begin changing schedules to secure appropriate staffing for the event.

During and just prior to the event (~0-3 hours) is the tactical timeframe. At this point, DOT managers are sending out crews to specific locations and implementing specific advisory, control, and treatment strategies to mitigate the adverse weather impacts. Weather observations are in great demand during the tactical timeframe.

When preparing to provide decision support for a DOT, forecasters need to already be aware of their needs. The mindset of DOT personnel is typically as follows:

• Initiate on magnitude and timing thresholds - DOT managers have critical precipitation types and amounts, and event timing limitations based on the potential road impacts. They use these “trigger points” to initiate actions.
• Plan for threats - once the latest weather assessment is received, including the forecast and its relative uncertainties, default operations are initiated and adapted to the current situation.
• Prepare for impacts - actions are taken according to the active plan in order to ready the community against the potential winter storm impacts.

Collaboration between the NWS and DOT is needed to ensure consistent information is shared between all parties and with the traveling public. Next, we learn about how the NWS and DOT work together to create a unified message.

Collaborate for a Unified Message

Operations area of the Norman, Oklahoma weather forecast office during a winter storm.

Within the NWS, a constant process of coordination and collaboration during a winter weather event is required for a unified message. Interactions need to happen between you and your neighboring local offices. Collaboration between your office and NOAA national centers, such as the Weather Prediction Center, is important to make sure that everyone is communicating a consistent message.

If the DOT that you are working with has weather support, then it presents the opportunity for a much more robust type of collaboration. The NWS Chatroom is one way the NWS and DOT share information. Other common collaboration methods include conference calls and decision-support product development. Prior to the calls, the NWS and DOT weather providers share initial thoughts regarding areas where significant impacts may occur by sharing preliminary informational graphics or via chat.

Conference Calls

Conference calls are key to sharing information between the NWS and DOT weather forecasters. Calls should be short (5-15 minutes) and focus on the expected precipitation type and intensity, event timing, and especially impacts. Subsequent joint messaging should emphasize the most significant impacts.

Weather Graphics

• DOT Graphic
• NWS Graphic

DOT Graphic

NWS Graphic

Both the NWS and DOT weather forecasters share informational graphics that highlight similar forecast weather conditions, event timing, areas of concern, and potential impacts. When user's receive similar information from trusted, authoritative sources, they are more likely to modify their behavior and take protective action.

Snowfall Possibilities

Behavioral research shows that communication of probabilistic information can help end-users make more cost-effective and safer decisions (LeClerc and Joslyn, 2012). The NWS is experimenting with probabilistic snowfall products that show the chances of exceeding specific amounts. Forecasters can show three types of projected scenarios: “Official Snowfall Forecast” (or most likely snowfall), “Expect At Least This Much”, and “Potential For This Much”. The purpose of these products is to provide users with a range of snowfall possibilities, better communicate forecast uncertainties, and further assist decision-makers during winter weather events.

The "Official Snowfall Forecast" is a deterministic representation of a forecaster’s best effort toward absolute accuracy. It is the official forecast within the next one to three days, and the amounts are provided as point and range values.

The “Potential For This Much” forecast represents the “safety margin forecast”, or that 9 out of 10 times the totals will fall below the given forecast value. This product is issued up to 3 days in advance, and helps communities better prepare ahead of the storm based on the storm’s maximum potential snowfall accumulation.

Similarly, the “Expect At Least This Much” forecast can help advance preparations based on the least amount of snow the storm is expected to produce. In a winter weather situation, both "Potential For This Much” and “Expect At Least This Much” scenarios are needed to fully address the array of decisions that need to be made.

The NWS is also experimenting with Exceedance Probability products that represent the likelihood of exceeding a specific snowfall amount (0.1”, 1”, 2”, 4”, 6”, 8”, 12”, and 18”). These products are designed to indicate high or low confidence in the official forecast.

Question

Review the snowfall probabilities below and answer the following question.

• Official Forecast
• Potential for This Much
• Expect at Least This Much
• Percent Exceedance

Official Forecast

Potential for This Much

Expect at Least This Much

Percent Exceedance

Based on the graphics above, what potential snow accumulation amounts could Denver, Colorado experience?

a) The official forecast calls for -- 2-3 4-6 6-8 8-12 inches of snow.

6-8

Please make a selection.

c) The storm can produce as much as -- 6-8 8-12 12-18 18-24 inches of snow.

12-18

Please make a selection.

b) We can expect at least -- <1 2 3 4 inches of snow.

<1

Please make a selection.

d) The chances of exceeding 1 inch of snow is at least -- 68 76 85 94 %. This means that the forecasters have -- high low confidence that it will snow at least 2 inches.

85, high

Please make a selection.

The correct answers are highlighted above.

Please make a selection.

Winter Weather Event Types

Let’s look at NWS support of DOT operations during winter weather. To frame this part of our discussion, it helps to differentiate these winter weather events by perceived severity.

Winter Weather Event Types » Warning-Criteria Events

Events meeting traditional warning-criteria are generally thought of as being more severe. However, forecasters must consider the potential impacts of an event when making watch, warning and advisory decisions. For example, while snowfall totals may reach low-end warning criteria, if it is a late season event with warm ground temperatures and occurring on a Saturday night, perhaps an advisory will be sufficient. Conversely, a snowfall event with snow totals that are below traditional advisory criteria, but which is occurring with cold road surfaces and during a weekday rush hour, might warrant an advisory or warning based on the impacts.

Winter Weather Event Types » Sub-advisory Events

Case: Pennsylvania Winter Storm Event

You are a forecaster at WFO State College with responsibility for central Pennsylvania (PA). It is Sunday, March 12th.

A strong coastal storm is expected to bring significant wintry precipitation across the mid-Atlantic and New England early in the week. Much of central PA is likely to get snow Monday night through Tuesday night. A Winter Storm Watch is in effect.

This storm comes on the heels of another system that brought arctic cold air and snowfall across PA over the weekend. The heaviest snow fell in west-central PA.

Models have converged on the track of the surface low to be east of Maryland early Tuesday. The heaviest snowfall is expected to occur between predawn and early morning on Tuesday, when snowfall rates of 1” to 2” per hour are expected for several hours.

The track of the low will determine where the highest snowfall totals will fall. There is uncertainty in the storm total accumulation, depending on exactly where the deformation zone forms on the northwest side of the surface low. Currently, it looks like the surface low does not strengthen until it passes through New Jersey around midday Tuesday. This scenario would result in the heaviest snow from northeast PA into New England.

• Official Snowfall Forecast
• Potential for This Much
• Expect at Least This Much

Official Snowfall Forecast

Potential for This Much

Expect at Least This Much

After looking over the forecast information, it appears that the official forecast calls for 10”+ of snow over the CWA, with higher amounts over the eastern portions. Overall amounts expected: western counties, 10” to 14"; central counties, 11” to 15"; and eastern counties, 12” to 17". However, uncertainty remains with these amounts and they will be adjusted as the main event approaches.

Case: Pennsylvania Winter Storm Event » Winter Weather Threat

Note: Although NWS State College does not directly communicate with the DOT, this scenario may be applicable to other NWS offices that interact with the DOT.

• Surface Forecast
• Official Snowfall Forecast
• Potential for This Much
• Expect at Least This Much

Surface Forecast

Official Snowfall Forecast

Potential for This Much

Expect at Least This Much

Case: Pennsylvania Winter Storm Event » Confidence and Areas of Concern

• Surface Forecast
• Official Snowfall Forecast
• Potential for This Much
• Expect at Least This Much

Surface Forecast

Official Snowfall Forecast

Potential for This Much

Expect at Least This Much

Case: Pennsylvania Winter Storm Event » Communicate the Impacts

• Surface Forecast
• Official Snowfall Forecast
• Potential for This Much
• Expect at Least This Much

Surface Forecast

Official Snowfall Forecast

Potential for This Much

Expect at Least This Much

Case: Pennsylvania Winter Storm Event » What Happened?

The surface low moved up the U.S. East Coast on March 14th. The strong system produced a large swath of 16”+ of snow over central and northeastern Pennsylvania, and over 32” of snow in northeastern Pennsylvania.

Numerous school closures and 3 fatalities (due to snow shoveling) in Schuylkill County, Pennsylvania were among the notable storm impacts across the State College CWA. The state’s governor signed a “Disaster Emergency” that allowed the state DOT and the Turnpike Commission to restrict speeds on interstate highways and limit traffic. Snowfall rates in eastern areas were 2” to 4” per hour, reducing speeds and closing roads. Blowing and drifting snow on the roads reduced visibility and made it difficult to keep roads passable. Road closings reduced traffic as did advanced warnings.

The map below shows the observed snowfall analysis from the March 13-14 winter storm.

Summary

The DOT implements various strategies to mitigate winter weather impacts on the road network. DOT decision-makers need reliable weather information to make critical decisions and adequately prepare communities at risk. Pre-season coordination enables forecasters to understand the needs, mitigation strategies, and critical time frames of DOT personnel.

Also, the lesson discussed how collaboration between the NWS and DOTs is essential to communicating concise and consistent forecast information. The benefits and appropriate interpretations of probabilistic snowfall forecast products were also highlighted.

The discussion then turned to how warning-criteria events differ from sub-advisory events. Event severity and resulting impacts vary depending on which type of winter weather is at hand. The simulation exercise also provided practice in supporting a DOT manager during a sub-advisory event.

Finally, learners worked through a winter weather case study to practice how to communicate the weather threat, areas at risk, forecast confidence, and potential impacts that are most beneficial to DOT personnel.

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References

Barjenbruch, K., and Coauthors, 2016: Drivers’ Awareness of and Response to Two Significant Winter Storms Impacting a Metropolitan Area in the Intermountain West: Implications for Improving Traffic Flow in Inclement Weather. Wea. Climate Soc., 8,475–491

National Weather Service Winter Safety

COMET MetEd Module: Weather and Road Management

LeClerc, J. and S. Joslyn, 2012: Odds Ratio Forecasts Increase Precautionary Action for Extreme Weather Events. Wea. Climate Soc., 4, 263–270.

NOAA/NWS Warning Decision and Training Division Module: Road Weather Impacts and Surface Transportation Mitigation Strategies

U.S. Department of Commerce National Oceanic and Atmospheric Administration: Guidance for NWS Support for State/Local Departments of Transportation. Retrieved August 11, 2017.

U.S. Department of Transportation Federal Highway Administration: How Do Weather Events Impacts Roads? Last modified: February 1, 2017. Retrieved June 9, 2017.

U.S. Department of Transportation Federal Highway Administration: Another Rain Delay. Last modified: January 31, 2017. Retrieved June 19, 2017.

U.S. Department of Transportation Federal Highway Administration: Collaboration Across the Road Weather Enterprise: The Pathfinder Project. Retrieved August 16, 2017.

Product/Service Description Document - Experimental Probabilistic Snowfall Products Winter 2016-2017

Wisconsin Transportation Bulletin No. 6: Using Salt and Sand for Winter Road Maintenance. Retrieved July 27, 2017.

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