Data Issues in the Mountains

All,

I am still not happy with some of the RTMA data across our higher elevations. When I examined the RTMA Max Temperature information for 3/11/08, I noticed the MaxT for Snowshoe (highest point in our forecast area) on that date was portrayed as 44 degrees. However, the actual MaxT for that location was actually 37 degrees.

The RTMA MaxT information across the lowlands seemed reasonable.

Has anyone else seen these issues?

Jeffrey Hovis

Images attached

[quote=jshovis]All,

I am still not happy with some of the RTMA data across our higher elevations. When I examined the RTMA Max Temperature information for 3/11/08, I noticed the MaxT for Snowshoe (highest point in our forecast area) on that date was portrayed as 44 degrees. However, the actual MaxT for that location was actually 37 degrees.

The RTMA MaxT information across the lowlands seemed reasonable.

Jeffrey Hovis [/quote]

Jeff-

Couple of questions:

1) What exactly do you mean by Max Temperature? Is AWIPS actually somehow generating a max field? The RTMA is an hourly temperature analysis, so there is no max value per se. I'm just trying to figure out exactly what you're viewing.

2) Is there a particular cycle from which your plots were generated? Or is some AWIPS-generated max temp field over a particular time period?

Geoff,

Here are the some answers to your questions:

1) What exactly do you mean by Max Temperature? Is AWIPS actually somehow generating a max field? The RTMA is an hourly temperature analysis, so there is no max value per se. I'm just trying to figure out exactly what you're viewing.

The RTMA MaxT information that I submitted was actually derived by BOIVerify. As far as I understand it, the RTMA MaxT and/or MinT information is derived by looking at the hourly RTMA T information. BOIVerify is also using the baseline version of the RTMA, not the parallel version.

2) Is there a particular cycle from which your plots were generated? Or is some AWIPS-generated max temp field over a particular time period?

I am not entirely sure what you asking here. The observed information was the Maximum temperature between 12 UTC 3/11/08 and 00 UTC 00 UTC 3/12/08.

Here is some additional information about Snowshoe:

Snowshoe is a ski resort which is located at the highest point in our forecast area. It is located at 38.4122N 79.9972W and is approximately 4765 ft MSL. It is one of our Cooperative Observers who give us their 24 hr MaxT, 24 hr MinT, current T and precipitation once a day (every morning).

Thank you,

Jeff

The RTMA terrain at this location is approximately 3600 feet, around 1000 feet lower than the ridge-top observation site. During the afternoon on a day with good mixing, we can expect the downscaling from the 13-km RUC to contribute an adiabatic difference compared to observations over this distance (for instance, if the RUC first guess has the correct potential temperature), which explains most of the difference between the RTMA temperature and the observed temperature in this case.

The RTMA will soon be experimenting (not in the operational version you receive, yet) with a terrain that has sharper relief and happens to fit observation elevations closer in complex terrain. There are also plans (contingent on resources being available, etc.) to move to a 2.5-km product which will use a 2.5-km terrain, which fits the observation elevations even better. I have not checked how those compare specifically for Snowshoe, WV, but in general this is an issue common in the western states which will be helped by these other terrain fields. There will still be a lot of places with terrain differences of around 300 feet, but these newer terrain fields greatly reduce the number of stations with very large differences such as at Snowshoe.

Stephen Jascourt

I should have emphasized the issue of representativeness.
Snowshoe is your peak elevation spot. Is this observation really representative of the area around it on the scale of your NDFD grids? Should the gridded forecast issued by the WFO predict the temperature at Snowshoe where the ski resort is located or should NWS be predicting the temperature in the vicinity, which may be quite different due to the mountainous terrain? Does it make sense to use the Snowshoe observation to verify the gridded forecast?

Even if/when NDFD and RTMA move to 2.5 km grids and the corresponding terrain has closer matches to individual observation spots, there will still be some places with considerable terrain-related temperature variability inside a 2.5 km x 2.5 km area on nearly a daily basis. Under some special conditions such as evening decoupling in calm conditions under clear skies, there can even be amazing micro-scale variability over gently sloping terrain in relatively flat areas, such as at El Reno, Oklahoma which I discuss in the RTMA training you can find on the COMET web page http://www.meted.ucar.edu/nwp/RTMA/ (NOAA employees can get credit for it by taking it through the NWS Learning Center at http://doc.learn.com/noaa/nws )

Stephen