Introduction

The Challenge of Composing a QPF

Where, When, and How Much?

Tracking Regions of Moisture, Lift and Instability

Questions to Ask

Factors Determining the Rainfall Amount

Determining the Areal Extent of the Rainfall

Importance of Pattern Recognition

Metereologocial Considerations

Importance of Large-scale Areas of Lift

Identifying Important Mesoscale Features

Using Model Data to Identify Favorable Patterns

Determining Potential Precipitation Intensity

Estimating Precipation Efficiency

Precipitation Efficiency Factors

Will Convection Occur?

Will Convection Occur?

Assessing Instability

Anticipating Stability Changes

Convective Available Potential Energy

Releasing CAPE

The Importance of CIN

System Movement

System Movement

Cell Movement and Propagation

Outflows Impacts on Propagation

Individual Cell Movement

MBE Movement

System Movement

System Propagation

Thickness Considerations

Quasi-Stationary Convective System: Example

Factors Favorable to Quasi-Stationary Convection

System Evolution: Example

Why Was the System Stationary for 9 Hours?

The Effects of System Shape and Movement

When to Expect 3" or More

Factors Favoring Training or Regeneration

Short Range QPFs/Jets/Tropical Systems

Short Range (0-6 hr) Forecasts

Using radar Data

NEXRAD Limitations

Impact of Upper-level Jets

How the Upper-Level Jet Affects Weather Systems

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Jet streaks have been associated with:

• Variations in strength of the LLJ
• Cyclogenesis and major snowstorms
• Frontogenesis

Remember, curvature and changes in the wind speed are both important.

Upper-level Jet and Cyclones

Jet Streaks and Cyclogenesis

Summer of 1993: Example

Importance of the LLJ

Tropical Storm Conceptual Model

Rainfall with Tropical Systems

More on Tropical Systems

Rules of Thumb for Predicting Heavy Rain

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• The maximum rainfall usually occurs where the center of the strongest inflow intersects a boundary
• The rainfall maximum usually occurs just northeast of the theta-e-ridge
• In summer, the heaviest rainfall often occurs along outflow boundaries south of the warm front

• Inverted isobars along a front can signal heavy rainfall potential
• Heavy rain often falls in an area of thickness difluence
• Beware of thickness lines that hold steady or sink southward in low-level southerly flow
• Heavy rain sometimes occurs in a preferred thickness channel

• MCSs track along of slightly to the right of the 1000-500 thickness lines
• Look for convection along the southern edge of the westerlies
• MCCs often form near the upper-level ridge axis where there is weak inertial stability
• Watch for heavy convection behind a vorticity maximum or near a vorticity minimum when strong thermal and moisture advection is present

More Rules of Thumb

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• A favorable jet structure can enhance the heavy rain potential
• K indices are a good measure of deep moisture; beware of K indices in the upper 30s
• The maximum rainfall is usually with the tropical core of a tropical system at night, rather than the daytime peripheral activity
• Beware of tropical connections as observed from water vapor imagery

• Beware of slow moving synoptic circulation events. They often have warm clouds tops.
• Strong height falls and/or fast moving systems usually preclude very heavy rainfall; instead they produce a large area of more modest rainfall (an inch or two)
• Numerical models usually don't predict the axis of heaviest rainfall far enough south (outflow boundaries)
• The NGM rarely predicts over 3 inches of rain

References

Bosart, L.F. and F.H. Carr, 1978: A case study of excessive rainfall centered around Wellsville, New York, 20-21 June 1972. Mon. Wea. Rev., 106, 348-362.

Chappell, C.F., 1986: Quasi-stationary convective events. Mesoscale Meteorology and Forecasting, P. Ray, Ed., Amer. Meteor. Soc., 289-310.

Corfidi, S.F., J.H. Merritt, and J.M. Fritsch, 1996: Predicting the movement of mesoscale convective complexes. Wea. Forecasting, 11, 41-46.

Doswell, C.A. III, H.E. Brooks, and R.A. Maddox, 1996: Flash flood forecasting: An ingredients-based methodology. Wea. Forecasting, 11, 560-581.

Hovanec, R.D. and L.H. Horn, 1975: Static stability and the 300 mb isotach field in the Colorado cyclogenetic area. Mon. Wea. Rev., 103, 628-638.

Junker, N.W., R.S. Schneider, and S.L. Fauver, 1999: A study of heavy rainfall events during the great Midwest flood of 1993, Wea. Forecasting, 14, 701-712.

Junker, N.W. and R.S. Schneider, 1997: Two case studies of quasi-stationary convection during the 1993 great Midwest flood, Nat. Wea. Dig., 21, 5-17.

Maddox, R.A., 1983: Large-scale meteorological conditions associated with midlatitude mesoscale convective complexes. Mon. Wea. Rev., 111, 1475-1493.

Maddox, R.A., F. Canova, and L.R. Hoxit, 1980: Meteorological characteristics of flash flood events over the Western United States, Mon. Wea. Rev., 108, 1866-1877.

Maddox, R.A., C.F. Chappell, and L.R. Hoxit, 1979: Synoptic and meso-a scale aspects of flash flood events, Bull. Amer. Meteor. Soc., 60, 115-123.

Olson, D.A., N.W. Junker, and B. Korty, 1995: Evaluation of 33 years of quantitative precipitation forecasting at the NMC, Wea. Forecasting, 10, 498-511.

Contributors

The following people have contributed to the development of
Introduction to Quantitative Precipitation Forecasting

Sponsors
National Weather Service (NWS)
Naval Meteorology and Oceanography Command (NAVMETOCCOM)
Air Force Weather Agency (AFWA)

Principal Science Advisor
Wes Junker - National Center for Environmental Prediction (NCEP/HPC)

Additional Scientific Material Provided by
Dr. Charles Chappel - Retired
Dr. Robert Maddox- Chief Editor, Weather and Forecasting
Matthew Kelsch - UCAR/COMET

Instructional Design/Multimedia Authoring
Dr. Sherwood Wang - UCAR/COMET
Lon Goldstein - UCAR/COMET (2007 Revision)

Project Lead/Project Meteorologist
Wendy Abshire - UCAR/COMET

Multimedia Authoring
Seth Lamos - UCAR/COMET

Graphic Interface Design
Heidi Godsil - UCAR/COMET

Illustration/Animation
Steve Deyo - UCAR/COMET
Heidi Godsil - UCAR/COMET

Software Testing/Editing/Quality Assurance
Kay Levesque - UCAR/COMET
Michael Smith - UCAR/COMET

Copyright Administration
Hanne Mauriello - UCAR/COMET

Data Provided By
NOAA/NESDIS
NOAA/NWS
American Meteorological Society (AMS)

COMET HTML Integration Team 2020
Tim Alberta — Project Manager
Dolores Kiessling — Project Lead
Steve Deyo — Graphic Artist
Gary Pacheco — Lead Web Developer
David Russi — Translations
Gretchen Williams — Web Developer
Tyler Winstead — Web Developer

COMET Staff

Director
Dr. Timothy Spangler

Senior Management
Susan Jesuroga (Assistant Director)
Dr. Joe Lamos (Assistant Director)
Hanne Mauriello (Business Manager)

Outreach Program Manager
Dr. Greg Byrd

Administration
Janice Brown
Lorrie Fyffe
Elizabeth Lessard (Budget Analyst)
Bonnie Slagel

Graphics
Steve Deyo
Heidi Godsil

Hardware/Software Support and Programming
Tim Alberta
Steve Drake
Dennis Ward
Carl Whitehurst

Instructional Design
Patrick Parrish (Supervisor)
Dr. Alan Bol
Dr. Vickie Johnson
Dr. Sherwood Wang
Marianne Weingroff

Meteorologists
Dr. Greg Byrd (Supervisor)
Richard Cianflone - NWS
Patrick Dills
Matthew Kelsch
Dolores Kiessling
Anthony Mostek - NWS (National Satellite Training Coordinator)
Lyn Neilley
Elizabeth Mulvihill Page - NWS
Dr. Robert Rozumalski - NWS (SOO/SAC Coordinator)
Wendy Schreiber-Abshire
Dr. Doug Wesley

Software Testing/Quality Assurance
Michael Smith (Coordinator)
Kay Levesque

Systems Administration
Susan Jesuroga (Supervisor)
Karl Hanzel
Willis Piper