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October 2014
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Splitting Fronts

Posted: October 16th, 2014

 

 

One of the hallmarks of El Niño round these parts are cold fronts that shred to pieces right before they arrive. That’ll often result in storm hype followed by head scratching—not unlike what happened last weekend. While this winter’s (barely) still-forecast El Niño hasn’t yet started, we’ll get to see a few splitting fronts over the next few days, if not beyond that. Like today, which is documented above and as of this post is beautifully headed towards the record high of 70 degrees, this weekend looks to be quiet, partly sunny and warm.

 

Citywide, the NWS currently predicts 0.28″ tomorrow, followed by less than 0.10″ daily through Tuesday. Forecast models hint at more substantial rainfall later next week, but we’ll see how that develops. (Persistence forecasting suggests ridging, splitting, and more warm and relatively dry conditions, as long range outlooks have been consistently predicting.) There may be some gusty winds overnight tonight and tomorrow night, but the weather will at least be comfortable for storm-drain cleaning afterward.

 

Relatively quiet weather is also expected over SPU’s mountain reservoirs. After gusty SE winds, especially tonight, rainfall amounts are only expected to surpass 0.25″ tomorrow and Monday.

 

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

 

A FRONT NEAR 130W WILL SPREAD RAIN TO THE COAST AROUND MIDNIGHT AND INTO THE INTERIOR OF WESTERN WA AROUND DAYBREAK FRIDAY. A STRONG PREFRONTAL SOUTHEASTERLY PRESSURE GRADIENT WILL MOVE INTO THE COASTAL WATERS TONIGHT AND IT MAY BECOME QUITE WINDY ALONG THE COAST BY ABOUT MIDNIGHT TONIGHT. IT SHOULD BE WINDY AROUND THE SAN JUANS AND OVER PARTS OF THE WESTERN PORTION OF WHATCOM COUNTY AS WELL ON FRIDAY. WIND ADVISORIES WERE ISSUED IN  THOSE AREAS…THIS SYSTEM IS A CLASSIC SOUTHEAST SUCKER AND THE WINDIEST PLACES END UP BEING OVER THE MARINE ZONES. THE WINDIEST SPOT IS TATOOSH ISLAND AT THE WEST ENTRANCE TO THE STRAIT AND THE UIL-BLI GRADIENT SHOULD GET UP AROUND -4.5MB OVERNIGHT. THE RAIN WILL MOVE IN OVER ALL OF WESTERN WA FRIDAY…THEN FRONT WEAKEN AND DISSIPATE FRIDAY NIGHT AS IT CROSSES THE CASCADES. THE SHOWERS WILL END PRETTY QUICKLY ON SATURDAY AND SATURDAY AFTERNOON LOOKS DRY WITH AT LEAST PARTLY SUNNY SKIES.

SUNDAY IS LIKELY TO BE A DRY DAY IN OFFSHORE FLOW…ALTHOUGH ANOTHER FRONT WILL BE APPROACHING. THAT FRONT OUGHT TO MOVE THROUGH WRN WA MONDAY AND SHOULD BE FOLLOWED BY ANOTHER BREAK IN THE WEATHER WITH WEAK HIGH PRESSURE ON TUESDAY. OFFSHORE FLOW CONTINUES TO DRY THE AIR TUESDAY NIGHT…BUT THEN ON WEDNESDAY THE 12Z GFS SHOWED RAIN DEVELOPING ON THE COAST…SPREADING INLAND BY AFTERNOON. I THINK IT IS LIKELY TO BE RATHER WET WED-FRI OF NEXT WEEK WITH A FAIRLY IMPRESSIVE UPPER TROUGH DEVELOPING IN THE NE PACIFIC BY MIDWEEK.

 

– JRH

 
References:

 

NWS Area Forecast Discussion
NWS Forecast Table Interface