March 30, 2003

A Poorly Forecast Frontogenetically Forced Early

Spring Snowstorm

Last year’s storm of the century…

The Christmas 2002 Snowstorm

Unfortunately…Not every storm looks like that…

Consider March 30, 2003.

6-hour Eta forecast pmsl and 850 mb temperature 18z on the 30th.

12-hour Eta forecast pms and 850 mb temperature 00z on the 31st.

6-hour Eta forecast 500 mb heights and vorticity 18z on the 30th.

12-hour Eta forecast 500 mb height and vorticity 00z on the 31st.

6-hour Eta forecast 300 mb heights and wind speed 18z on the 30th.

12-hour Eta forecast 300 mb heights and wind speed 00z on the 31st.

6-hour Eta forecast 700 mb omega (yellow) and frontogenesis (shaded) valid 18 UTC on the 30th.

6-hour Eta forecast cross-section of frontogenesis and EPV valid 18 UTC on the 30th.

00-hour Eta cross section of EPV and frontogenesis valid 1800 UTC on the 30th.

6-hour Eta forecast 600 mb theta-e advection (shaded) and 400 mb theta-e advection (green lines) valid at 18z on the 30th.

6-hour Eta forecast EPV and theta-e advection valid 18z on the 30th.

Water Vapor Imagery at 1450 UTC on the 30th.

Water Vapor Imagery at 1651 UTC on the 30th.

Water Vapor Imagery at 1851 UTC on the 30th.

Water Vapor Imagery at 2050 UTC on the 30th.

12-hour Eta 12-hour QPF valid 00z on the 31st.

Mean SREF QPF from the 21z run on the 29th.

Individual forecasts of 0.5 inches of precipitation (Eta in green, GFS in brown) from the 09z run on the 30th.

Probability of greater than 0.25 inches of precipitation from the 09z run of the SREFs.

6 to 12 inches

4 to 8 inches

1 to 4 inches

In Summary, This Storm Was Associated With…

• Weak surface cyclogenesis• A high amplitude, open mid-level trough• Coupled jets at 300 mb• Strong low-to-mid-level frontogenesis• Reduced stability above the frontal zone

indicating potential for enhanced banding.• Models in good agreement on the

placement of max qpf over the Poconos/Catskills.

Eastern U.S. Radar at 0800 UTC on the 30th.

Eastern U.S. Composite Radar at 1200 UTC on the 30th.

Eastern U.S. mosaic radar at 16 UTC on the 30th.

Eastern U.S. mosaic radar at 2000 UTC on the 30th.

Eastern U.S. mosaic radar at 2200 UTC on the 30th.

KBGM reflectivity at 1208 UTC on the 30th.

KBGM reflectivity at 1558 UTC on the 30th.

KBGM reflectivity at 1957 UTC on the 30th

KBGM reflectivity at 2200 UTC on the 30th.

Observed liquid precipitation March 30, 2003

0.40”0.40”

0.20”

0.20”

1”

1”

4”

4”

6”8”

Observed snowfall 3/30/03

What verified…

• Maximum snowfall and precipitation occurred over the central southern tier of NY (west of the model forecasts).

• Much less precipitation and snowfall occurred over the Poconos and Catskills than what was forecast.

A possible source of model error…

850 mb upper-air plots and Eta 00-hour forecast 12z on the 30th.

700 mb upper-air plot and 00-hour Eta forecast 12z on the 30th.

XX

850 mb

700 mb

FrontogenesisFrontogenesis

Max LiftMax Lift

NW SE NW SE

Eta Initialization Observations

Max snowMax snow

Models underestimate the frontogenesis at 700 mb. Maximum lift is shifted to the northwest.

Another factor to be considered…

AVP

BGM

CONSIDER SOUNDINGS AT AVP AND BGM

Eta forecast time-cross section of snow growth area and omega at AVP

Eta forecast time-section of snow growth area and omega at BGM

Summary

• Models were indicating a significant snowstorm over the Poconos and Catskill Mountains.

• Large-scale forcing was relatively modest.• Models were basing the high qpf on the placement of

strong low-level frontogenesis.• Models were in good agreement.• Observed snowfall maximum was west of the model

forecasts.• One source of model error may have been poor

initialization of the 700 mb temperature gradient associated with the frontogenesis.

• Another factor was less favorable microphysical environment over the Poconos/Catskills.

A WES SIMULATION IS AVAILABLE…

Michael.Evans@noaa.gov