Winter '10 / '11 - Snow Storm #5 - Snow Gun

(Updated below)

Tonight's 00z rawindsonde flight launched from OKX observed some major-league instability atop deep low-level moisture.

- Note the strong deep-layer iso-thermal WAA through ~600 mb beneath a layer of CAA near 500mb.
- Snow is indicated b/c the entire column is below zero.
- Specific gravity peaks close to 5g/kg near 750 mb.
- Baroclinic instability indicated with strong increase in wind speed with height.

More importantly is the observed instability AOA 700 mb as indicated by the theta-E plot shown below.  Strong instability is indicated when the trace goes straight up as it does ~700 mb and in the layer between 650 and 500 mb.

Snowfall rates at IAD earlier this evening were quite intense...where less instability was observed.  If I'm the duty forecaster at OKX this evening...I'd be preparing for snowfall rates in excess of 2"/HR over my CWA.

Sounding images courtesy SPC.

UPDATE:

METAR KISP 270656Z 02025KT 1/4SM R06/1800V2200FT +SN BLSN BKN003 OVC008 M01/M03 A2950 RMK AO2 SLP988 SNINCR 5/019

5" / hour!