Seattle.gov Home Page
Seattle Public Utilities Home page

Search Climate Change

October 2014
M T W T F S S
 12345
6789101112
13141516171819
20212223242526
2728293031  

Another Wet and Windy Week

Posted: October 20th, 2014

 

GFS model forecast showing precipitation bullseye toward the coast.

GFS model forecast showing precipitation bullseye toward the coast.

 

Post-frontal showers will continue into this evening, and a clap of thunder with briefly intense rainfall cannot be ruled out. There will then be a lull in activity overnight through most of tomorrow before the arrival of this week’s main event—another meandering atmospheric river expected to hit the coast and parts south more directly.

 

The latest forecast indicates that rainfall will come in two batches, first early Wednesday morning through about midday, and then again late Wednesday night into early Thursday. Post-frontal showers are expected to continue through at least Thursday, if not into the weekend.

 

Citywide, NWS afternoon numbers show 1.27″ Tue-Wed, followed by about 0.25-0.50″ each day thereafter through Saturday. The ECMWF has 1.99″ in 48 hours centered on Wed night, and the UW WRF-GFS is wettest with nearly 2″ in the 36-hour period centered on Wed morning. 15-20mph southwesterly winds with gusts to 35mph are also expected Tuesday PM, which should exacerbate leaf fall and impact drainage inlet performance.

 

Over SPU’s mountain reservoirs about 2.50-3.00″ is forecast Tue-Wed, followed by followed by 0.25-0.50″ daily through Saturday. Southwesterly winds look more favorable than in the lowlands.

 

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

 

SHOWERS ARE LIKELY THIS EVENING AS AN UPPER TROUGH MOVES OVERHEAD IN THE WAKE OF THE FRONT FROM LAST NIGHT. THERE IS ALSO A SLIGHT RISK OF THUNDER NEAR THE COAST WHERE THE AIR WILL BE MOST UNSTABLE. SHOWERS SHOULD BECOME FAIRLY ISOLATED LATER TONIGHT AND TUESDAY MORNING AS THE UPPER TROUGH PUSHES INLAND AND WEAK HIGH PRESSURE ALOFT BRINGS MORE STABLE AIR.

A VIGOROUS FRONTAL SYSTEM WILL BRING RAIN TO THE COAST TUESDAY AFTERNOON AND THEN INLAND TUESDAY NIGHT. THIS SYSTEM WILL BRING A GOOD SHOT OF RAIN…ESPECIALLY TO THE OLYMPICS WHICH COULD PUSH THE SKOKOMISH TO FLOOD WEDNESDAY. THERE WILL ALSO BE SOME WINDY CONDITIONS WITH THIS SYSTEM…MOST NOTABLY FOR THE COAST AND NORTH INTERIOR TUESDAY NIGHT. WIND ADVISORIES MAY EVENTUALLY BE NEEDED FOR THAT.

IT LOOKS LIKE THERE WILL BE A BIT OF A LULL IN THE RAINS FOR AT LEAST PART OF WEDNESDAY…THEN ANOTHER FRONTAL WAVE WILL BRING MORE RAIN LATER WEDNESDAY OR WEDNESDAY NIGHT WITH SHOWERS LINGERING INTO THURSDAY.

FRIDAY WILL BE IN BETWEEN WEATHER SYSTEMS WITH JUST A SMALL CHANCE OF RAIN. THE GFS AND ECMWF ARE IN PRETTY GOOD AGREEMENT SHOWING ANOTHER SHOT OF RAIN FRIDAY NIGHT AND SATURDAY AS A FRONTAL SYSTEM MOVES THROUGH. A WEAK UPPER RIDGE WILL MOVE OVER THE AREA SUNDAY AND MONDAY FOR DRIER AND MORE TRANQUIL WEATHER.

 

– JRH

 

References:

 

NWS Area Forecast Discussion
NWS Forecast Table Interface