Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 060235 AAA
AFDSEW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SEATTLE WA
735 PM PDT SUN JUL 5 2015

UPDATED THE AVIATION SECTION.

.SYNOPSIS...WARM WEATHER WILL CONTINUE FOR THE INTERIOR OF WESTERN
WASHINGTON THROUGH MIDWEEK. COOLER WEATHER WILL ARRIVE LATE IN THE
WEEK AS AN UPPER TROUGH NEARS THE AREA AND DEEPER MARINE AIR PUSHES
INTO THE INTERIOR.

&&

.SHORT TERM...A SMOKE LAYER FROM THE B.C. FIRES WORKED SLOWLY SOUTH
TODAY MOVING ACROSS THE STRAIT AND INTO THE OLYMPICS.  WHATCOM
COUNTY HAD SOME HOT BREEZY WEATHER TODAY BUT THE NE WIND DOWN THE
FRASER GAVE OUT BY MID AFTERNOON AND THE BLI-YQL GRADIENT WILL
CONTINUE TO FALL. THE WARM WEATHER WILL LIKELY CONTINUE FOR SEVERAL
MORE DAYS IN THE INTERIOR OF WESTERN WASHINGTON AND THERE IS A HEAT
ADVISORY STILL IN EFFECT FOR THE SEA-TAC METRO AREA. THAT SAID...THE
OTH-SEA GRADIENT AT 3PM IS UP TO +3.7MB AND IF THE MARINE AIR ON THE
COAST DEEPENS OVERNIGHT TEMPS COULD BE A LITTLE COOLER THAN THE
FORECAST. DAY TO DAY VARIATION OF THE COASTAL MARINE LAYER IS PRETTY
TRICKY TO GUESS EXCEPT TO SAY THAT THE COAST WILL HAVE AREAS OF
NIGHT AND MORNING LOW CLOUDS AND FOG WITH COOL TEMPS ALONG THE
BEACHES...AND WARM WEATHER FURTHER INLAND WITH 850MB LEVEL TEMPS
ALOFT OVER SEATTLE THAT WILL CONTINUE TO HOVER AROUND 20C.

.LONG TERM...NIGHT AND MORNING LOW CLOUDS AND FOG MAY TREND TOWARD
AN ALL DAY MARINE LAYER FOR THE COAST BY THE END OF THE WEEK. TEMPS
SHOULD START TO FALL OFF A BIT ACROSS THE INTERIOR OF WRN WA ON
THURSDAY AND THEN DRAMATIC COOLING SHOULD OCCUR ON FRIDAY WITH A
DEEP MARINE PUSH. AN UPPER TROUGH WILL BE NEARING THE AREA AND
ANOTHER UPPER TROUGH WILL KICK OUT OF NRN CALIF AND ACROSS THE
INLAND PORTION OF THE PACNW...THAT WILL INCREASE LOW LEVEL ONSHORE
FLOW INTO WRN WA AND THE AIR ALOFT WILL COOL AS WELL.

&&

.AVIATION... SMOKE EMANATING FROM WILDFIRES IN BRITISH COLUMBIA HAS
BLANKETED THE NW PORTION OF WA. SOME SURFACE OBSERVATIONS IN CANADA
AND WRN WA WERE REPORTING THE SMOKE LAYER DOWN TO 6-7K FT. VSBYS
HAVE ALSO BEEN REDUCED TO 3SM IN SOME PLACES. THE SMOKE WAS
IMPACTING THE FOLLOWING TAFS...KBLI AND KCLM. BASED ON THE STEERING
FLOW...THE DENSEST SMOKE LAYER SHOULD NOT DRIFT MUCH FARTHER S...
HOWEVER A THIN SMOKE LAYER WILL BE VISIBLE AT KPAE...KBFI...AND
KSEA.

A STRONG UPPER LEVEL RIDGE IS OVER THE NE PAC TONIGHT WITH N/NW FLOW ALOFT
OVER WESTERN WA. THE AIR MASS IS DRY. THERE IS STRATUS OVER THE COASTAL
WATERS THAT WILL PUSH INLAND OVERNIGHT...POSSIBLY REACHING THE SOUTH SOUND
EARLY MON MORNING. 33/05

KSEA...VFR CONDITIONS TONIGHT. N WINDS AT THE SURFACE TO 10 KT THIS
EVENING...FLIPPING TO LIGHT S/SW BY 12Z MON. 33

&&

.MARINE...THERMALLY INDUCED TROUGH OF LOW PRES ALONG THE WA COAST
WILL WEAKEN AS IT MOVES INLAND TONIGHT. THE TROUGH OF LOW PRES WILL
SHIFT EAST OF THE CASCADES ON MONDAY FOR A WEAK ONSHORE PUSH.
ONSHORE FLOW WILL INCREASE BY MID WEEK AS STRONG SURFACE HIGH PRES
DEVEOPS OVER THE NE PAC. THE STRONGEST WINDS WILL OCCUR OVER THE
CENTRAL AND EAST STRAIT OF JUAN DE FUCA DURING THE AFTERNOON AND
EVENING HOURS. 33

&&

.FIRE WEATHER...RED FLAG WIND AND HUMIDTY COMBINATIONS CONTINUE AT
ELLIS MTN OVER THE NW OLYMPIC PENINSULA...AS WELL AS INLAND PORTIONS
OF WESTERN WHATCOM COUNTY AS OF 3 PM. KBLI-CYWL PRESSURE GRADIENTS
ARE WEAKENING...SO THE CRITICAL FIRE WEATHER CONDITIONS WILL
DIMINISH IN THE NEXT FEW HOURS. HAVE ENDED THE RED FLAG WARNING
EARLY IN TWO FIRE WEATHER ZONES...AND WILL LET THE OTHER TWO ZONES
EXPIRE ON TIME AT 5 PM.

OTHER FIRE WEATHER CONCERN IS NOW TURNING TO LIGHTNING POTENTIAL
OVER THE NORTH CASCADES ON TUESDAY AFTERNOON. LOOKS LIKE THERE WILL
BE ENOUGH INSTABILITY AT THE TAIL END OF AN UPPER DISTURBANCE DIVING
SE THROUGH B.C. TO TRIGGER A THUNDERSTORM OR TWO. INTRODUCING
ISOLATED THUNDERSTORMS TO THE NORTH CASCADES ON TUE AFTN/EVNG...WITH
THE POTENTIAL FOR SCATTERED COVERAGE. GIVEN HOW DRY FUELS ARE...IF
LATER FORECASTS INCREASE COVERAGE TO SCATTERED...THEN A FIRE WEATHER
WATCH OR RED FLAG WARNING WOULD BE NEEDED FOR ZONE 658 (NORTH
CASCADES) AND 662 (NORTH CASCADES NATIONAL PARK EAST OF THE CREST).
HOWEVER...EVEN ISOLATED LIGHTNING CAN START FIRES WITH THE
HISTORICALLY DRY FUELS. HANER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...HEAT ADVISORY IN EFFECT FOR PARTS OF THE PUGET SOUND REGION
     UNTIL 9 PM MONDAY.

     RED FLAG WARNING IN FIRE WEATHER ZONES 650 AND 656 UNTIL 5 PM.

PZ...NONE.

&&

$$

WWW.WEATHER.GOV/SEATTLE

THE ILLUSTRATED VERSION OF THE DISCUSSION IS UNAVAILABLE AT THIS
TIME.


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