Northeast Oregon in SLIGHT RISK area today

The Storm Prediction Center has extreme NE Oregon in a “slight risk” area for severe thunderstorms this afternoon/evening.

http://www.spc.noaa.gov/products/outlook/day1otlk.html

This is due to the cool upper-level disturbance moving across the Pacific Northwest producing great lift and shear in the atmosphere.  It’ll be tough to get anything other than a rumble or flash of lightning anywhere west of a Hermiston to Bend line.  But with better lift in Wallowa County and possibly Union/Baker counties some storms may get organized enough to produce strong/damaging wind.  It’s far more likely across northern Idaho and Montana this evening though.  Here is a snippet from their discussion:

...STEEP MID LEVEL LAPSE RATES AND LOW LEVEL DIABATIC HEATING FROM ERN OREGON ACROSS THE NRN ROCKIES AHEAD OF THE ADVANCING COLD FRONT WILL RESULT IN A DEEP SURFACE-BASED MIXED LAYER WITH CAPE REACHING 300-500 J/KG.  CONSENSUS MODEL GUIDANCE INCLUDING CONVECTION-ALLOWING MODELS INDICATE WIDELY SCATTERED HIGH-BASED STORMS WILL DEVELOP ALONG A CORRIDOR FROM NERN OREGON INTO WRN MT DURING THE 21-00Z PERIOD...WITH ACTIVITY SPREADING ENEWD INTO TONIGHT.  STRONG DEEP LAYER SHEAR WILL ENHANCE STORM ORGANIZATION WITH POTENTIAL FOR A FEW BOWING SEGMENTS OR SUPERCELLS TO OCCUR WITH STRONGER STORMSCAPABLE OF PRODUCING DAMAGING WIND GUSTS OR MARGINALLY SEVERE HAIL. 

What is a "severe thunderstorm?".  
Here's the official definition from the SPC folks:  The term severe thunderstorm refers to a thunderstorm producing hail that is at least quarter size, 1 inch in diameter or larger, and/or wind gusts to 58 mph or greater, and/or a tornado. Although lightning can be deadly, the NWS doesn't use it to define a severe thunderstorm. If it did, every thnderstorm would be severe, by definition. Also, excessive rainfall may lead to deadly flash flooding, but heavy rain is not a severe criterion either. The flood threat is handled through a separate set of watches and warnings from your local NWS forecast office.

West of the Cascades we’ll just see some vigorous showers (brief downpours, possible flash of lightning/rumble of thunder) through this evening since most of the action here is to our north up in Washington.  What a change though!  I was just thinking the other day how little of the cold showers & sunbreaks weather we’ve seen since March.

I’ll blog later about the coming payback time…I mean payback for all the warm and dry weather the past three weeks!

Chief Meteorologist Mark Nelsen