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October 2014
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Monday Wx Outlook

Posted: October 6th, 2014

 

Our weakening, not so dirty ridge

The not-so-dirty ridge still fending off storms (via NWS EAFD)

 

So much for that “dirty” ridge… Once again, high pressure grew stronger than anticipated and kept us sunnier and warmer than expected. In fact, yesterday’s high temperature of 75 at Seatac was a full 11 degrees above normal.

 

“Clean” high pressure will remain in control through at least the middle of the week. That said, classic October fog will be present when the sun is not. But by Friday, the regime should finally break down and allow the a disturbance to slip by and provide a few sprinkles. Later next weekend, models are suggesting that an atmospheric river will approach the region, though we’ll see how forecast models handle it as the week goes on.

 

Citywide, the NWS currently predicts 0.01″ of foggy drizzle tomorrow morning, followed by no rain until 0.08″ on Friday, then 0.65″ over the 24-hour period ending at 11 AM on Sunday. The ECMWF currently has about 0.20″ on Friday, but then delays more substantial rainfall until next Monday. The latest UW WRF-GFS also leans drier throughout the forecast period.

 

Over SPU’s mountain reservoirs, recent numbers were more notable after this week’s continued dry weather. Early morning NWS forecasts predicted 2.50-3.00″ (south to north) during the 24-hour period ending on Sunday at 11 AM. There’s considerable uncertainty, but SPU will watch developments closely.

 

Excerpts from this morning’s NWS Area Forecast Discussion (emphasis added):

 

UPPER LEVEL RIDGE WILL REMAIN THE PREVALENT WEATHER FEATURE OVER WESTERN WASHINGTON THROUGHOUT THE SHORT TERM PERIOD. FOR MUCH OF THE AREA…THIS WILL MEAN CONTINUED MOSTLY DRY WEATHER. WEAK DISTURBANCES PASSING TO THE NORTH…HOWEVER…WILL BRING THE CHANCE FOR SOME LIGHT PRECIP OVER THE NORTH CASCADES. THESE PASSING DISTURBANCES WILL HELP TO FLATTEN OUT THE RIDGE AS WE MOVE INTO MIDWEEK. COMBINE THIS WITH THE EXPECTED STRENGTHENING OF ONSHORE FLOW AND THE RESULT LOOKS TO BE INCREASING CHANCES OF LOW CLOUDS AND FOG IN THE MORNING ALONG WITH THE CHANCE FOR SOME VERY LIGHT DRIZZLE. WOULD STILL EXPECT ALL THIS TO BURN OFF BY AFTERNOON…BUT GIVEN THE INCREASE…WOULD EXPECT THE TIME THAT IT DOES BURN OFF TO BE PUSHED FURTHER AND FURTHER BACK INTO THE LATE MORNING AND EVEN EARLY AFTERNOON BEFORE THE SUN MAKES ITS WAY THROUGH. TEMPS LOOK TO COOL SOME OVER THE PERIOD…BUT STILL REMAINING ABOVE  SEASONAL NORMALS.

LOOKING FOR THE ABOVE MENTIONED RIDGE TO BREAK DOWN AS WE GET INTO LATE THURSDAY/EARLY FRIDAY…AS AN UPPER LEVEL TROUGH MOVES INTO THE AREA BRINGING WITH IT THE START OF A PROGRESSIVE AND UNSETTLED PATTERN. PRECIP CHANCES RAMP UP INTO THE WEEKEND AND THE PATTERN LOOKS TO KEEP RAIN IN THE FORECAST FOR THE START OF NEXT WEEK. IT IS ALSO POSSIBLE THAT TEMPS MIGHT BE A LITTLE ON THE WARM SIDE FOR THE
END OF THIS PERIOD.

 

Climate Notes:
 

  • Seasonal outlooks continue to show below normal precipitation and above normal temperatures through November, and a very weak El Niño past December.
  • Normal high and low temperature for today: 64 and 48
  • Normal daily and water-year-to-date precipitation: 0.08″ and 0.36″

 

References:

 

NWS Area Forecast Discussion
NWS Forecast Table Interface
Climate Prediction Center El Niño Status
Dirty Ridge Definition