Avalanche in Washington, May 14, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT WED MAY 14 2014

.SYNOPSIS...AN UPPER RIDGE WILL BRING SUNNY WARM DAYS TO WESTERN
WASHINGTON THROUGH THURSDAY. COOL CLOUDY MARINE AIR REACH THE COAST
LATE THURSDAY AND PUSH INLAND THURSDAY NIGHT AND FRIDAY. AN UPPER
TROUGH WILL MOVE INTO THE PACIFIC NORTHWEST FOR COOL WEATHER AND
SOME SHOWERS THIS WEEKEND AND EARLY NEXT WEEK.

&&

.SHORT TERM...A STRONG 500 MB UPPER RIDGE AXIS WILL REMAIN CENTERED
OVER THE PAC NW TODAY THROUGH THURSDAY MORNING. THE ASSOCIATED
THERMALLY INDUCED TROUGH ALONG THE OREGON COAST WILL NUDGE NWD JUST
OFF THE WASHINGTON COAST MAINTAINING LIGHT OFFSHORE NORTHERLY FLOW.
UPPER HEIGHTS PEAK NEAR 5830M LATE TODAY ACROSS THE GREATER PUGET
SOUND REGION...SO HIGH TEMPERATURES IN THE LOW TO MID 80S SHOULD BE
COMMON. TODAY WILL BE THE WARMEST DAY ALONG THE COAST WITH LOW TO
MID 80S THERE AS WELL. TEMPERATURES WILL REMAINS SOMEWHAT MODERATED
IN THE 70S NEAR THE WATER ALONG THE STRAIT AND N INTERIOR. IT WILL
BE MILD TONIGHT AS GRADIENTS REMAIN LIGHT AND OFFSHORE.

THE UPPER RIDGE AXIS STARTS TO SHIFT E OF THE CASCADES THURSDAY
AFTERNOON. THIS WILL ALLOW A SURGE OF MARINE AIR TO MOVE UP THE
OREGON COAST AND ALONG THE WA COAST BY LATE IN THE DAY. THE SWITCH
TO ONSHORE FLOW ALONG THE COAST WILL RESULT IN HIGHS ABOUT 10
DEGREES COOLER THAN TODAY. BUT MARINE AIR WILL LIKELY NOT MAKE MUCH
PROGRESS INLAND INITIALLY WITH THE THERMALLY INDUCED TROUGH OVER
INTERIOR WRN WA. THIS MIGHT NORMALLY BE THE WARMEST DAY OF THE WARM
SPELL BUT 500 MB HEIGHTS DROP TO AROUND 5750M BY LATE IN THE DAY.
THE CURRENT FORECAST HIGHS SEEM LIKE A GOOD COMPROMISE BETWEEN LOWER
HEIGHTS BUT WITH THE THERMALLY INDUCED TROUGH STILL W OF THE
CASCADES. MOS SHOWS ONLY A COUPLE DEGREES COOLING WITH MORE 80S
ACROSS THE AREA WHICH MAY TURN OUT OK.

SW FLOW ALOFT DEVELOPS THURSDAY EVENING WITH A MARINE PUSH INTO THE
LOWLANDS. MODELS SHOW A PERIOD OF LI'S DOWN AROUND -2C AND SOME WEAK
CAPE AND INSTABILITY. HOWEVER...MOISTURE APPEARS LACKING AND THE
MARINE AIR WILL QUICKLY MODERATE SURFACE BASED INSTABILITY. WILL
LOOK AT THE THREAT OF CONVECTION AGAIN FOR THE AFTERNOON FORECAST
PACKAGE BUT CURRENTLY THE SW FLOW DOES NOT LOOK GOOD FOR
THUNDERSTORMS. THE CASCADE CREST COULD BE THE ONE EXCEPTION.

FRIDAY WILL BE MUCH COOLER WITH MOSTLY CLOUDY SKIES. HIGHS WILL
STRUGGLE TO REACH THE LOW 60S ON THE COAST AND 70 INLAND. THERE
COULD BE SOME MORNING DRIZZLE ALONG THE COAST...THEN A FEW SHOWERS
POSSIBLE FRIDAY AFTERNOON AND NIGHT AS ADDITIONAL MOISTURE AND LIFT
ARRIVES WITH THE UPPER TROUGH.  MERCER

.LONG TERM...FROM 300 AM PDT DISCUSSION...ALL THE MODELS AGREE THAT
AN UPPER TROUGH WILL BE OFFSHORE JUST OUTSIDE 130W ON
SATURDAY...WITH MOIST ONSHORE FLOW AND SOME SHOWERS ACROSS WESTERN
WASHINGTON. THAT WEATHER WILL CONTINUE SUNDAY AS THE UPPER TROUGH
MOVES MORE DIRECTLY OVER THE PACIFIC NORTHWEST. THE THREAT OF
SHOWERS WILL DECREASE MONDAY AND TUESDAY AS THE UPPER TROUGH BEGINS
TO MAKE ITS WAY EAST OF THE CASCADES. HOWEVER FAIRLY STRONG ONSHORE
FLOW WILL CONTINUE AND TEMPERATURES WILL REMAIN ON THE COOL SIDE.
MCDONNAL

&&

.AVIATION...A STRONG UPPER LEVEL RIDGE WILL REMAIN OVER THE PACIFIC
NORTHWEST THROUGH THURSDAY WITH GOOD VFR CONDITIONS EXPECTED TO
CONTINUE IN THE DRY AND STABLE AIR MASS. THE UPPER LEVEL RIDGE WILL
SHIFT E LATE THURSDAY ALLOWING ONSHORE FLOW AND A MARINE PUSH TO
DEVELOP OVER W WA. LOW COASTAL STRATUS WILL SPREAD INLAND THURSDAY
EVENING. THERE IS A VERY SMALL CHANCE THAT ISOLATED HIGH-BASED
THUNDERSTORMS COULD DEVELOP ALONG THE CASCADE CREST LATE THURSDAY.

KSEA...THE STRONG UPPER LEVEL RIDGE OVER THE REGION WILL ALLOW
UNRESTRICTED VFR CONDITIONS TO CONTINUE THROUGH THURSDAY. THE
SURFACE RIDGE OVER BRITISH COLUMBIA WILL KEEP SURFACE WINDS
NORTHERLY OVER KSEA TODAY. WINDS WILL BE N 4-7 KT THROUGH 19Z THEN
INCREASE TO NNW 7-12 KT THROUGH 02Z. KAM

&&

.MARINE...NORTHERLY OFFSHORE FLOW WILL CONTINUE THROUGH TONIGHT
BETWEEN A WEAK SURFACE RIDGE OVER BRITISH COLUMBIA AND A SURFACE
TROUGH ALONG THE OREGON COAST. A SCA IS IN EFFECT FOR THE NEAR
COASTAL WATERS THIS EVENING FOR N WINDS. WINDS STRENGTHENED TO SCA
LEVELS TUESDAY EVENING...AND WARM AFTERNOON TEMPERATURES OVER THE
INLAND COASTAL AREAS TODAY SHOULD ALLOW THIS TO OCCUR ONCE AGAIN.
AFTERNOON HEATING SHOULD ALSO PERMIT N WINDS THROUGH PUGET SOUND TO
RISE TO JUST BELOW SCA LEVELS LATER THIS AFTERNOON.

A CHANGE TO SOUTHERLY ONSHORE FLOW IS STILL EXPECTED TO DEVELOP ON
THURSDAY. A NARROW SURFACE RIDGE WILL PUSH NORTHWARD ALONG THE
OREGON AND WA COASTS THURSDAY CAUSING S-SW ONSHORE FLOW TO DEVELOP.
MESOSCALE MODELS INDICATE THE SHIFT TO S WINDS AND THE ACCOMPANYING
STRATUS/FOG SURGE SHOULD REACH GRAYS HARBOR THURSDAY MORNING AND
CAPE FLATTERY BY LATE THURSDAY AFTERNOON. THERE IS OFTEN A SMALL
AREA OF SCA S WINDS AT THE LEADING EDGE OF THE SURGE THAT THE MODELS
DO NOT HANDLE WELL.

S-SW ONSHORE FLOW WILL SPREAD TO THE INTERIOR OF W WA THURSDAY
EVENING WITH SCA WINDS EXPECTED OVER THE CENTRAL STRAIT OF JUAN DE
FUCA AND PUGET SOUND. LOW END SCA WINDS ARE ALSO LIKELY OVER THE
NEAR-SHORE COASTAL WATERS. THE ONSHORE FLOW APPEARS TO BE TOO
SOUTHERLY FOR SCA WINDS TO REACH THE E ENTRANCE OF THE STRAIT BUT
CONFIDENCE IS LOW HERE. LIKEWISE SPOTTY SCA WINDS ARE POSSIBLE OVER
THE N INLAND WATERS THURSDAY NIGHT...BUT AGAIN CONFIDENCE IS LOW. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY IN EFFECT FROM 5 PM THIS AFTERNOON TIL
     11 PM TONIGHT FOR THE NEAR SHORE WATERS FROM JAMES ISLAND TO
     CAPE SHOALWATER OUT TO 10 NM.

&&

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