Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
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.

&&

$$

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