A Blustery Spring Day! It’s Payback Time

May 13, 2013

The peak gust of 36 mph at PDX today was the highest (non-easterly) wind gust in about 5 weeks here.  So of course a tree branch fell here or there.

PLOT_Wind_Metro_PeakGusts

Most of the heavier action was to the north in western Washington as mentioned in the previous post.  Take a look at all the lightning strikes in Puget Sound!

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Down here in our area the only cloud to ground strike was up in Cowlitz County.  In fact we didn’t even see much rain, here are the rainfall totals since midnight:

PLOT_Rain_Metro_Autoplot

Severe storms never developed in far NE Oregon and the watch has been cancelled.

So what’s ahead?  Time to make up for all the dry and mild weather.

We’ve seen a very dry late winter and spring with upper level high pressure often sitting just offshore, keeping the storms that do make it inland quite weak.    That changes for the next 7-14 days.  The persistent upper level height anomaly offshore is gone, replaced by weak westerly flow through at least next Sunday-Monday.  Then models are in pretty good agreement that our first chilly “Upper Level Low” we’ve seen in a month or two.   Take a look at the next 4 weeks of the ECMWF, it’s run out to one month twice a week.  Note the below average upper-level heights for the next 2-4 weeks!

500za_week1_bg_NA

500za_week2_bg_NA

500za_week3_bg_NA

500za_week4_bg_NA

Rose Festival and Memorial Day are just around the corner!  You can also see the cooler than average weather on the 12z GFS and ECMWF 850mb ensemble charts.  The green line is average for mid-late May, notice most of the time the temperatures are below average:

tseries_850t_000-360_Portland
tseries_850t_000-384_Portland

Models have attempted to throw up some brief ridging about next Monday, but I didn’t bite on that and only brought up the high temperature into the low 70s that day on our 7 Day Forecast.

Chief Meteorologist Mark Nelsen


Northeast Oregon in SLIGHT RISK area today

May 13, 2013

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

day1otlk_1630
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