Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 232327
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 PM PST SUN NOV 23 2014

.SYNOPSIS...SNOW SHOWERS IN THE CASCADES WILL TAPER OFF THIS
EVENING. THERE WILL BE A BREAK IN THE WEATHER THROUGH MONDAY
MORNING. A WARM FRONT WILL REACH THE AREA LATE MONDAY. WET WEATHER
IS ON TAP FOR TUESDAY WITH A HIGH SNOW LEVEL IN THE MOUNTAINS.
ANOTHER WEATHER SYSTEM WILL DEVELOP OVER THE AREA THURSDAY.

&&

.SHORT TERM...SNOW SHOWERS IN THE CASCADES WILL TAPER OFF AS THE
WESTERLY FLOW ALOFT GIVES OUT THIS EVENING. WEAK HIGH PRESSURE WILL
BUILD INTO THE REGION AND THE CHANCE OF SHOWERS WILL END IN THE
LOWLANDS. A WARM FRONT WILL REACH THE AREA BY ABOUT MONDAY EVENING.
SURGES OF WARM ADVECTION WILL BRING RAIN TO MUCH OF WESTERN WA MON
NITE THRU WED MORNING. AREAS IN THE LEE OF THE OLYMPICS SHOULD NOT
END UP WITH MUCH RAINFALL WHILE THE NORTH CASCADES GET THE BRUNT OF
IT. HEAVY RAINFALL IN PREVIOUS RUNS OF THE GFS GAVE WAY TO A MORE
REASONABLE SOLUTION TODAY WHICH SHOWS A 48 HOUR RAINFALL MAXIMUM
NEAR MT BAKER OF 5.6 INCHES ENDING 18Z WED...MUCH LESS RAIN THAN
EARLIER SOLUTIONS.

.LONG TERM...THE EXTENDED FORECAST INTO NEXT WEEKEND IS CLOSE TO
CLIMO FOR NOW WITH NO ATTEMPT TO SORT OUT THE DIFFERENCES IN THE
MODELS OF LATE. THE GENERAL TREND HAS BEEN TO MAKE THANKSGIVING WET
BUT AFTER THAT THE FCSTS DIVERGE. THE BAROCLINIC ZONE...THE DIRTY
RIDGE WARM FRONT...SHOULD REDEVELOP AND MERGE WITH A SOUTHERN STREAM
SHORTWAVE IN THE CONFLUENCE OF THE UPPER LEVEL FLOW OVER WA...SO
THANKSGIVING COULD BE ANOTHER WET DAY. BEYOND THAT IT IS DIFFICULT
TO SAY WHETHER WRN WA WILL REMAIN WET AND MILD...OR COOL OFF LIKE
THE 12Z ECMWF SOLUTION.

&&

.HYDROLOGY...A HYDROLOGIC OUTLOOK WAS ISSUED FOR WHATCOM TO KING
COUNTY FOR NWRFC FORECASTS THAT SHOW THE RIVERS TO WATCH ARE THE
NOOKSACK...STILLAGUAMISH...AND SNOQUALMIE. HEAVY RAIN IS LIKELY IN
THE MOUNTAINS TUESDAY AND TUESDAY NIGHT. EARLIER RUNS OF THE GFS
WERE EXTREMELY WET IN THE NORTH CASCADES BUT ALL THE MODELS NOW HAVE
MORE BELIEVABLE RAIN TOTALS. FLOODING IS NOT LIKELY IF THE 12Z AND
18Z NAM PRECIP AMOUNTS VERIFY AND THE 12Z EURO HAD MUCH LESS PRECIP
THAN THE OLD 00Z RUN SO THAT IS ENCOURAGING.

&&

.AVIATION...MODERATE NW FLOW ALOFT THIS EVENING...BECOMING MODERATE
SW FLOW ALOFT ON MON. THE LOW-LEVEL AIR MASS IS MOIST AND
UNSTABLE...BUT IT WILL BECOME STABLE ON MON AFTN AS A WARM FRONT
LIFTS NORTH ACROSS WRN WA. SHOWER ACTIVITY HAS ALREADY CONTRACTED IN
COVERAGE TO THE MTNS AND SW INTERIOR...AND IT WILL CONTINUE TO
SHRINK THIS EVNG AS ONSHORE FLOW WEAKENS. LOOKING FOR A DECIDEDLY
DRY PERIOD FROM 12Z-18Z MON...THEN THE WARM FRONT WILL CAUSE SOME
LIGHT RAIN TO BLOSSOM OVER WRN WA ON MON AFTN. CIGS GENERALLY
RUNNING 2000 FEET MSL OR HIGHER FOR THE NEXT 24 HOURS.

KSEA...THE TERMINAL IS LIKELY TO REMAIN RAIN-FREE THROUGH TONIGHT
WITH MAINLY SCATTERED CLOUDS ARND 025-040. SOME LIGHT RAIN WILL
START TO DEVELOP AFT 21Z ON MON. AT THAT POINT...CLOUDS WILL FILL
IN...BECOMING OVERCAST AND SLOWLY LOWERING ON MON EVNG. SW SFC WINDS
WEAKENING THIS EVNG...AND THE CONVERGENCE ZONE WIND SHIFT LINE NEAR
DOWNTOWN SEATTLE SHOULD WASH OUT AND DISSIPATE. SOUTH WIND ON MON...
INCREASING IN SPEED THROUGH THE DAY.        HANER

&&

.MARINE...ONSHORE FLOW WILL CONTINUE TO WEAKEN THIS EVENING. A WARM
FRONT WILL LIFT NORTH THROUGH THE WATERS ON MON AND MON NIGHT...
LEADING TO INCREASING SOUTHERLY WINDS STARTING MONDAY MORNING. THE
FRONT WILL BECOME STATIONARY OVER THE WATERS OR JUST TO THE NORTH OF
THE WATERS ON TUE AND WED. STRONG SW FLOW ON THE ORDER OF 20 TO 30
KT CAN BE EXPECTED TO THE SOUTH OF THIS FRONT. THE FRONT WILL SLIP
BACK SOUTH ON THU...THEN FRASER OUTFLOW AND STRONG OFFSHORE FLOW IS
POSSIBLE NEXT FRI.

HAZARDOUS SWELL WILL CONTINUE ALONG THE COAST THROUGH MON MORNING
AND THEN SUBSIDE A BIT ON MON AFTN.     HANER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...WINTER STORM WARNING CASCADES.
PZ...SMALL CRAFT ADVISORY ALL WATERS EXCEPT PUGET SOUND.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR CONDITIONS.

&&

$$

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