Surprise Snow Storm December 28th 2012

Ben MillerMeteorologist National Weather Service – St. Louis, Missouri

Overview My Midnight Shift Forecast

Model Forecast Data from 00Z December 28th 2012 HPC Snow Forecast My Snowfall Forecast

What Happened? Radar Imagery Total Snowfall Map

Where Did The Forecast Go Wrong? Satellite Imagery Synoptic Analysis An Ageostrophic Response Banded Snowfall Potential

00Z FCST12/28/12

12Z FCST12/28/12

00Z FCST12/29/12

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500 mb Vorticity Maximum fromthe 00Z forecast on 12/28/12

ECMWFGFSNAMSREF

GEMWRF

00Z12/28 12Z

12/28

00Z12/29

12Z12/29

HPC Mid Shift Snowfall FCST for 12/28/12

4-6”

My Snowfall Forecast

So What Happened?

Surprise!

Observed Snowfall from 12/28

How Did That Happen?

00Z 28 December 2012

12Z 28 December 2012

00Z 29 December 2012

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00Z 12/28/12 24 HR FCST of 295KMixing Ratio and Ageostrophic Wind

00Z 12/29/12 00 HR FCST of 295KMixing Ratio and Ageostrophic Wind

12Z NAM FCST on 12/28/12KFAMRed: OmegaYellow: Elevated CAPE

Summary• Shortwave was a little stronger and took on a slightly

negative tilt

• Coupled jet developed

• Ageostrophic flow brought richer moisture farther north/northwest

• Limited instability allowed for banded precipitation

Questions and or Comments…

Except for Fred