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September 2014
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Weekend Wx Outlook

Posted: September 11th, 2014

 

^ Blocking high pressure and clear skies via NWS Enhanced AFD

^ Blocking high pressure and clear skies (image via NWS Enhanced AFD)

 

Strong high pressure off the coast will continue to fend off storm systems and keep high temperatures near or above normal through the weekend. Also, due to “critical combination of wind, low humidity and dry fuels” a NWS Red Flag Warning (fire) is in effect.

 

The National Weather Service currently predicts no rain in the City or Watersheds through Tuesday. Some forecast models hint at rain by next Wednesday.

 

Excerpts from today’s NWS Area Forecast Discussion:

 

HIGH PRES ALOFT COMBINED WITH LOW LEVEL OFFSHORE FLOW WILL RESULT IN DRY AND STABLE WEATHER ACROSS WESTERN WA OVER THE NEXT SEVERAL DAYS. AREAS SHELTERED FROM THE WIND WILL SEE LOWS IN THE MID TO UPPER 30S OVERNIGHT…LIKE OLYMPIA…SHELTON AND ARLINGTON.

THERE IS LITTLE CHANGE IN THE FORECAST FRIDAY THROUGH THE WEEKEND. AN UPPER LEVEL RIDGE WILL CONTINUE TO BRING DRY WEATHER TO THE PAC NW. LOW LEVEL OFFSHORE FLOW WILL PREVAIL WITH A THERMALLY INDUCED TROUGH OF LOW PRES ALONG THE COAST. SKIES WILL REMAIN CLEAR. TEMPS WILL MODERATE A FEW DEGREES WITH HIGH TEMPS ABOVE NORMAL THROUGH THE PERIOD. SUNDAY WILL LIKELY BE THE WARMEST DAY WITH HIGHS IN THE LOW TO MID 80S OVER MUCH OF THE INTERIOR AND COAST.

THE UPPER LEVEL RIDGE AXIS WILL SHIFT EAST OF THE CREST ON MON. MEANWHILE…THE THERMAL TROUGH WILL ALSO WEAKEN AND SHIFT INLAND. THIS WILL BRING A WEAK ONSHORE PUSH WHICH WILL RESULT IN COOLER WEATHER ALONG THE COAST. THE INTERIOR HOWEVER WILL SEE ANOTHER WARM AND SUNNY DAY. MODELS SHOW A WEAK UPPER LEVEL SHORT WAVE TROUGH TRACKING NORTH THROUGH WESTERN WA MONDAY NIGHT OR TUE…BUT THERE IS LITTLE MOISTURE TAP WITH THIS FEATURE. WILL THEREFORE STICK WITH A DRY FORECAST. THIS SHORT WAVE TROUGH WILL KICK THE RIDGE FARTHER INLAND THOUGH. COOLER AND WETTER WEATHER IS EXPECTED WED NIGHT  AND THU AS OUR NEXT SYSTEM ARRIVES. THIS IS A LITTLE SLOWER IN THE MODELS COMPARED TO PREVIOUS SOLUTIONS.

 

References:
GFS 500mb Model Loop (UW)
NWS Area Forecast Discussion
NWS Forecast Table Interface