Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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720
FXUS66 KSEW 100408
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
808 PM PST TUE FEB 9 2016

.SYNOPSIS...MOIST SOUTHWEST FLOW ALOFT WILL ALLOW WETTER WEATHER TO
RETURN TO WESTERN WASHINGTON WEDNESDAY THROUGH THE WEEKEND. A WEAK
FRONT WILL BRING LIGHT RAIN TO THE AREA WEDNESDAY AND WEDNESDAY
NIGHT. RAIN WILL INCREASE AS A WARM FRONT REACHES THE AREA
THURSDAY...FOLLOWED BY A COLD FRONT THURSDAY NIGHT AND FRIDAY. AN
UPPER LEVEL TROUGH WILL PRODUCE SHOWERS FRIDAY AFTERNOON THROUGH
SATURDAY. ANOTHER WARM FRONT WILL BRING RAIN THE REST OF THE
WEEKEND.

&&

.SHORT TERM...SW FLOW ALOFT IS IN PLACE OVER THE NE PACIFIC AND W WA
THIS EVENING. MODELS ARE IN BETTER AGREEMENT THIS EVENING REGARDING
THE INITIAL WEAK BAND OF PRECIPITATION EXPECTED TO REACH THE AREA
LATE TONIGHT AND WEDNESDAY MORNING. THE PREVIOUSLY DRY ECMWF AND
CANADIAN HAVE BOTH MIGRATED CLOSER TO THE WETTER SOLUTION THE GFS
HAS HAD THE PAST SEVERAL MODEL RUNS. THIS FEATURE DEVELOPS OUT OF
THE REMNANT OF A OLD NARROW FRONT JUST OFFSHORE ALONG 127W-128W. THE
GFS SHOWS AN E-W ORIENTED 100-110KT JET STREAK W OF THE N CA COAST
THAT PIVOTS N TONIGHT THROUGH WEDNESDAY MORNING. WEAK FRONTOGENESIS
DEVELOPS ALONG THE OLD FRONTAL BAND AS THE NOSE OF THE JET STREAK
APPROACHES. THE GFS BRINGS A LITTLE LIGHT RAIN TO THE COAST AROUND
OR AFTER 12Z/4 AM WEDNESDAY THEN SPREADS IT OVER THE INTERIOR
LOWLANDS BY LATE MORNING. QPF WILL BE LOW WITH ONLY A TRACE TO A FEW
HUNDREDTHS OF AN INCH FALLING.

SW FLOW ALOFT OFFSHORE WILL REALLY BEGIN INCREASING TONIGHT AS THE
JET STREAK PIVOTS N. IT LOOKS LIKE THE INCREASING FLOW ALOFT ALLOWS
THE TRAILING FRONTAL BAND NEAR 42N/136W TO CATCH UP WITH THE INITIAL
FRONT...EVENTUALLY REACHING THE WA COAST LATE WEDNESDAY AFTERNOON.
THIS SECOND FRONT SHOULD MOVE OVER THE CASCADES BY 06Z/10 PM
WEDNESDAY. THE CHANCE OF RAIN WILL DECREASING WEDNESDAY NIGHT BEHIND
THE FRONT. BOTH SYSTEMS ARE WEAK ENOUGH SO THAT POPS ARE ONLY IN THE
CHANCE RANGE FOR THE INTERIOR WITH LIKELY POPS ON THE COAST. QPF
SHOULD BE PRETTY LIGHT WITH UP TO THREE TENTHS OF AN INCH ON THE
COAST AND UP TO A TENTH OVER THE INTERIOR LOWLANDS.

MOIST SW FLOW ALOFT WILL CONTINUE OVER THE NE PACIFIC AND THE PACNW
THURSDAY AND FRIDAY. MODELS HAVE BEEN FAIRLY CONSISTENT...STILL
SHOWING A STRONGER FRONTAL SYSTEM AFFECTING THE AREA DURING THAT
PERIOD. A WARM FRONT APPROACHING FROM THE SW WILL SPREAD RAIN OVER
THE AREA BY THURSDAY AFTERNOON. THE GFS AND ECMWF STILL TAKE THE
STRONGEST PART OF THE WARM FRONT OVER VANCOUVER ISLAND. THE COAST
AND OLYMPICS SHOULD GET A FAIR AMOUNT OF RAIN...WITH LOWER
ACCUMULATIONS OVER THE INTERIOR LOWLANDS. RAIN WILL CONTINUE
THURSDAY NIGHT THROUGH FRIDAY MORNING AS A COLD FRONT PUSHES SLOWLY
EASTWARD ACROSS THE AREA. SNOW LEVELS WILL BE RATHER HIGH AT 5000-
8000 FEET. KAM

.LONG TERM...PREVIOUS DISCUSSION FROM THE 3 PM AFD...AN UPPER TROUGH
MOVES THROUGH THE AREA ON SATURDAY SO THIS DAY WILL BE SHOWERY.
ANOTHER SYSTEM ARRIVES FROM THE WEST ON SUNDAY WITH RAIN LIKELY
THROUGH MONDAY MORNING. MODELS DIVERGE AFTER THAT WITH THE GFS
SENDING SUBSEQUENT SYSTEMS NORTH AND THE EURO STILL AIMING THEM AT
WESTERN WASHINGTON. HAVE KEPT POPS MAINLY IN THE CHANCE CATEGORY
MONDAY AND TUESDAY. THE SNOW LEVEL WILL FALL TO AROUND 3000 FEET
OVER THE WEEKEND THEN RISE TO 7000 FEET OR SO EARLY NEXT WEEK. BURKE

&&

.HYDROLOGY...RIVER FLOODING IS UNLIKELY THROUGH SATURDAY. THERE IS
SOME POTENTIAL FOR HEAVY RAINS OVER THE OLYMPICS BEGINNING SUNDAY
WHICH COULD CAUSE THE FLOOD PRONE SKOKOMISH TO REACH FLOOD STAGE
EARLY NEXT WEEK.

&&

.AVIATION...SW FLOW ALOFT WITH INCREASING MOISTURE FROM A SERIES OF
WEAK FRONTS. THERE WILL BE RAIN AT TIMES ON THE COAST BUT LOW LEVEL
OFFSHORE FLOW SHOULD DRY UP MOST OF THE RAIN FOR THE INTERIOR OF
WESTERN WA ON WEDNESDAY...WITH JUST SOME SPRINKLES.

KSEA...CURRENT TAF LOOKS FINE WITH MID AND HIGH CLOUDS SLOWLY
DROPPING INTO A TYPICAL CLOUDY DAY TUESDAY WITH A CHANCE OF RAIN
IN THE AFTERNOON.

&&

.MARINE...A WEAK WARM FRONT WILL BRUSH MAINLY THE COASTAL WATERS ON
WED. THIS FRONT WILL GIVE AREAS OF SMALL CRAFT ADVISORY SOUTH TO
SOUTHEAST WINDS TO PORTIONS OF THE COASTAL WATERS LATER WED.
ANOTHER FRONTAL SYSTEM WILL STALL JUST OFFSHORE THU AND FRI...MOVING
INLAND SAT.


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

WWW.WEATHER.GOV/SEATTLE

AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION CAN BE SEEN AT
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