Weather Service Report


132 
FXUS66 KSEW 300344
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PDT WED JUL 29 2015

.SYNOPSIS...A STRONG UPPER LEVEL RIDGE WILL BE OVER THE PACIFIC 
NORTHWEST THROUGH THE WEEKEND. THE RIDGE WILL WEAKEN SUNDAY AND 
MONDAY. AN UPPER LEVEL TROUGH WILL MOVE OVER THE AREA BY THE MIDDLE 
OF NEXT WEEK.
 

&&

.SHORT TERM...A STRONG UPPER RIDGE IS OVER THE REGION. HEIGHTS AND 
THICKNESS SHOULD PEAK LATE FRIDAY AFTERNOON...THE 850MB TEMP PEAKS 
AROUND +20C...AND MAX TEMPS OVER THE INTERIOR OF WRN WA SHOULD BE IN 
THE LOWER TO MID 90S FROM THE SEATTLE METRO AREA SOUTH. THE FORECAST 
FOR THE COAST IS FOR HIGHS IN THE 70S. SKIES WILL BE CLEAR TIL LATER 
SATURDAY WHEN SOME HIGH CLOUDS WILL ARRIVE AND HIGHS WILL LIKELY 
FALL OFF A FEW DEGREES.

.LONG TERM...AS THE RIDGE GIVES WAY TO FALLING HEIGHTS AND ONSHORE 
FLOW AND MARINE AIR MOVE BACK INTO THE AREA...TEMPS WILL COOL MON 
AND TUE OF NEXT WEEK. THE 18Z GFS SHOWS AN UPPER TROUGH DIGGING OVER 
THE REGION BY THE MIDDLE OF NEXT WEEK AND IF THIS SOLUTION PANS OUT 
THERE WILL BE COOL TEMPS AND A GOOD CHANCE OF SHOWERS WED AND THU OF 
OF NEXT WEEK. 

&&

.AVIATION...AN UPPER RIDGE WILL REMAIN OVER THE REGION. CONTD WLY 
FLOW ALOFT. LOW LEVEL NW FLOW WILL BECOME NLY LATE TONIGHT. VFR 
CONDITIONS ARE EXPECTED ACROSS MUCH OF THE AREA. THERE WILL LIKELY 
BE PATCHY IFR CIGS/VSBYS ON THE COAST AFTER 0800 UTC.

KSEA...VFR. WINDS WILL REMAIN NLY.

&&

.MARINE... HIGH PRES OFFSHORE WITH LOWER PRES E OF THE CASCADES WILL 
RESULT IN ONSHORE OR NORTHWEST FLOW THROUGH FRI. THERE ARE 
BORDERLINE SMALL CRAFT ADVISORY WINDS IN THE CENTRAL AND EASTERN 
STRAIT THIS EVENING. THE FLOW WILL BECOME BRIEFLY NORTHERLY OR 
OFFSHORE EARLY THU AND FRI MORNINGS DUE TO A THERMALLY INDUCED AREA 
OF LOW PRES TRYING TO SET UP ALONG THE WASHINGTON COAST.

ONSHORE FLOW WILL STRENGTHEN THIS WEEKEND...AND THIS WILL RESULT IN 
THE POSSIBILITY OF GALE FORCE WINDS OVER PARTS OF THE STRAIT OF JUAN 
DE FUCA ON SUNDAY. THE FLOW WILL STRENGTHEN FURTHER ON MON... 
LEADING TO AN INCREASED THREAT OF GALE FORCE WINDS OVER PARTS OF THE 
STRAIT OF JUAN DE FUCA.

&&

.FIRE WEATHER... A VERY DRY AIR MASS ALOFT IS SETTLING OVER WESTERN 
WASHINGTON THROUGH FRIDAY NIGHT. 850-700 MB LAYER AVERAGE RELATIVE 
HUMIDITY WILL BE RUNNING AS LOW 10 PERCENT BETWEEN NOW AND THEN. MID-
 LEVEL HAINES INDEX WILL BE SOLID 5 WITH VALUES REACHING 6 AT TIMES 
OVER THE CENTRAL CASCADES...INDICATING A DRY AND UNSTABLE MID-LEVEL 
AIR MASS. WILL EASILY REACH CRITERIA FOR THE DRY AND UNSTABLE 
CATEGORY OF RED FLAG WARNINGS THROUGH FRIDAY EVENING. AS A RESULT... 
A RED FLAG WARNING WILL SOON BE IN EFFECT. IT WILL BE TARGETED TO 
LOCATIONS ABOVE 2000 FEET ELEVATION...WHICH WILL STICK UP ABOVE THE 
INHIBITING EFFECT OF LOW-LEVEL SUBSIDENCE INVERSIONS. WITH SUCH A 
DRY AIR MASS...LEFTOVER FUEL MOISTURE FROM RECENT RAINS WILL QUICKLY 
BECOME A MEMORY. OVER THE MOUNTAIN ZONES...THIS KIND OF AIR MASS 
SUPPORTS ACTIVE FIRE BEHAVIOR AND RAPID GROWTH ON EXISTING FIRES. 
HANER

&&

.SEW WATCHES/WARNINGS/ADVISORIES... WA...HEAT ADVISORY IN EFFECT 
FROM NOON THURSDAY TIL 9 PM SATURDAY FOR PARTS OF THE PUGET SOUND 
REGION AND SOUTHWEST INTERIOR.

     RED FLAG WARNING IN EFFECT TIL 10 PM PDT FRIDAY FOR THE NORTH 
AND CENTRAL CASCADES AND PARTS OF THE OLYMPIC MOUNTAINS.

PZ...SMALL CRAFT REMAINS IN ADVISORY TIL 11 PM TONIGHT FOR THE       
     COASTAL WATERS FROM JAMES ISLAND TO CAPE SHOALWATER OUT TO 10   
   NM.

&&

$$

WWW.WEATHER.GOV/SEATTLE

AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION CAN BE SEEN AT 
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML

Return to Home page


Western Regional Climate Center, wrcc@dri.edu