Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 231019
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PDT SAT AUG 23 2014

.SYNOPSIS...HIGH PRESSURE ALOFT WILL MOVE INTO THE PACIFIC
NORTHWEST...BRINGING MAINLY SUNNY AND WARMER WEATHER TO WESTERN
WASHINGTON THIS WEEKEND AND ESPECIALLY EARLY NEXT WEEK. HOWEVER
THERE IS A CHANCE OF SHOWERS NEAR THE CASCADE CREST SUNDAY AFTERNOON
AND EVENING AS A WEAK SYSTEM MOVES INTO EASTERN WASHINGTON.

&&

.SHORT TERM...WE HAVE NORTHWEST FLOW ALOFT OVER WESTERN WASHINGTON
EARLY THIS MORNING...BETWEEN THE UPPER LOW CENTERED OVER SOUTHERN
IDAHO AND THE OFFSHORE UPPER RIDGE ALONG 140W. AT THE SURFACE THE
FLOW IS VERY WEAKLY ONSHORE. MARINE STRATUS OVER THE COASTAL WATERS
HAS SEEPED INLAND OVERNIGHT ABOUT HALF WAY DOWN THE STRAIT OF JUAN
DE FUCA AND INTO THE LOWER CHEHALIS VALLEY.

THE UPPER LOW WILL LIFT NORTHEAST INTO MONTANA TODAY...AND ONSHORE
FLOW WILL REMAIN LIGHT. THE STRATUS IS NOT EXPECTED TO MAKE IT MUCH
FURTHER INLAND THIS MORNING -- PROBABLY TO AROUND PORT ANGELES IN
THE STRAIT -- AND THROUGH THE CHEHALIS GAP TO THE SOUTHWEST END OF
PUGET SOUND AND HOOD CANAL. THE LOW CLOUDS THAT ARE PRESENT THIS
MORNING WILL GIVE WAY TO A MOSTLY SUNNY DAY. THE AIR MASS WILL BE
LESS UNSTABLE OVER THE MOUNTAINS TODAY...SO WE SHOULD NOT SEE A
REPEAT OF THE SHOWERS AND THUNDERSTORMS THAT OCCURRED ALONG THE
CASCADE CREST FRIDAY AFTERNOON.

AN UPPER SHORTWAVE MOVING OVER THE NORTH SIDE OF THE OFFSHORE RIDGE
WILL DIG SOUTHEAST INTO BRITISH COLUMBIA TONIGHT AND THEN OVER
NORTHERN IDAHO OR EASTERN WASHINGTON SUNDAY AFTERNOON. THIS FEATURE
WILL RENEW THE CONVECTIVE ACTIVITY OVER THE CASCADES...BUT FOR NOW
WE WILL LIMIT THE FORECAST TO SHOWERS -- AND OMIT THE MENTION OF
THUNDERSTORMS -- FOR THE AREA WEST OF THE CASCADE CREST. FOR THE
REST OF THE FORECAST AREA...THERE MIGHT BE A BIT MORE LATE NIGHT AND
MORNING STRATUS BUT IT SHOULD AGAIN GIVE WAY TO MOSTLY SUNNY SKIES.

THAT UPPER TROUGH WILL SHIFT EAST LATER SUNDAY NIGHT AND MONDAY.
DRIER NORTHERLY FLOW ALOFT WILL DEVELOP OVER WESTERN WASHINGTON
MONDAY AS THE OFFSHORE UPPER TROUGH PROGRESSES TO AROUND 130W...FOR
ANOTHER SUNNY AND SLIGHTLY WARMER DAY.   MCDONNAL

.LONG TERM...THE UPPER RIDGE WILL PROGRESS INTO THE PACIFIC
NORTHWEST TUESDAY AND WEDNESDAY...BUILDING SLIGHTLY AS IT MOVES
INLAND. THESE WILL BE SUNNY WARM DAYS WITH LITTLE IF ANY MARINE
STRATUS. UPPER HEIGHTS WILL BEGIN TO FALL ON THURSDAY...AS THE UPPER
RIDGE MOVES ACROSS THE ROCKY MOUNTAINS AND AN OFFSHORE UPPER TROUGH
STARTS APPROACHING THE REGION. IT WILL BE ANOTHER DRY DAY...BUT WITH
A STRONGER MARINE INTRUSION. ON FRIDAY THE UPPER TROUGH WILL MOVE
CLOSE ENOUGH FOR A CHANCE OF SHOWERS IN THE NORTH AND OVER THE
CASCADES.   MCDONNAL

&&

.AVIATION...NORTHWESTERLY FLOW ALOFT WITH UPPER LEVEL RIDGE WELL
OFFSHORE. UPPER LEVEL TROUGH MOVING SOUTH THROUGH BRITISH COLUMBIA
REACHING WESTERN WASHINGTON SUNDAY MORNING. LOW LEVEL WEAK ONSHORE
FLOW PATTERN WILL CONTINUE THROUGH TODAY.

SATELLITE IMAGERY SHOWS STRATUS JUST REACHING KSHN AND MOVING DOWN
THE STRAIT OF JUAN DE FUCA TO NEAR NEW DUNGENESS AT 09Z. THE LAYER
IS VERY SHALLOW WITH TOPS 1500 FEET OR LESS AND CEILINGS BELOW 500
FEET. STRATUS MOVING DOWN THE STRAIT COULD GET AS FAR EAST AS KPAE
THIS MORNING WHILE THE STRATUS TO THE SOUTH WILL NOT ADVANCE MUCH
FURTHER EAST. TEMPERATURES/DEW POINT SPREADS ARE SMALL OVER THE
SOUTHWEST INTERIOR WITH LIGHT WINDS SO EXPECT SOME PATCHY FOG WITH
VISIBILITIES LESS THAN A MILE BETWEEN 13Z-16Z. THE STRATUS WILL BURN
BACK TO THE COAST BY 18Z LEAVING JUST A FEW HIGH CLOUDS OVER MOST OF
THE AREA.

KSEA...MOSTLY CLEAR SKIES WITH LIGHT WINDS THIS MORNING. WINDS
BECOMING NORTHWEST 6 TO 10 KNOTS SATURDAY AFTERNOON. FELTON

&&

.MARINE...A LARGE SURFACE HIGH CENTERED NEAR 140W ALONG WITH LOWER
PRESSURE EAST OF THE CASCADES WILL MAINTAIN THE WEAK ONSHORE FLOW
PATTERN INTO THE MIDDLE OF NEXT WEEK. ONSHORE FLOW WILL BE TYPICALLY
STRONGEST DURING THE LATE AFTERNOON AND EVENING HOURS AND WEAKEST
DURING THE MORNING. SMALL CRAFT ADVISORY WINDS ARE EXPECTED IN THE
CENTRAL AND EAST STRAIT EACH EVENING. AN UPPER LEVEL TROUGH WILL
MOVE OVER WESTERN WASHINGTON SUNDAY MORNING. SURFACE PRESSURE
GRADIENTS OVER THE COASTAL WATERS WILL INCREASE AHEAD OF THE TROUGH
AND SHOULD GENERATE SMALL CRAFT ADVISORY WINDS TONIGHT INTO SUNDAY
MORNING FOR THE OUTER COASTAL WATERS. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT OF JUAN DE FUCA
TONIGHT.

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML






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