Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 042233
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
333 PM PDT MON MAY 4 2015

.SYNOPSIS...AN UPPER LOW OFF THE COAST WILL MOVE OVER THE PACIFIC
NORTHWEST OVERNIGHT AND THEN REMAIN OVER THE REGION ON TUESDAY.
LOOK FOR UNSETTLED CONDITIONS TONIGHT AND TUESDAY...ALONG WITH A
RISK OF THUNDERSTORMS. THE LOW WILL MOVE SLOWLY EAST ON WEDNESDAY
AND WILL BE FOLLOWED BY HIGH PRESSURE ALOFT ON THURSDAY.

&&

.SHORT TERM...
THE COLD FRONT WAS MOVING A LITTLE SLOWER THAN ANTICIPATED AND WAS
ON THE COAST AT THIS TIME. EXPECT THE FRONT TO REACH THE CASCADES
LATE TODAY. THERE WAS A NARROW BAND OF SHOWERS ASSOCIATED WITH THE
WEAK FRONT. THE SHOWER BAND WILL LIKELY BREAK UP A BIT AS IT
CROSSES THE OLYMPIC RANGE.

MEANWHILE...THE UPPER LOW WILL MOVE OVER THE PACIFIC NORTHWEST
OVERNIGHT FOR AN INCREASED THREAT OF SHOWERS. THE SHOWERS SHOULD
BE MORE NUMEROUS OVER THE COAST...MOUNTAINS...AND SNOHOMISH
COUNTY NORTHWARD. THE UPPER LOW WILL REMAIN OVER THE REGION ON TUE
FOR COOL AND UNSETTLED CONDITIONS. THE AIR MASS WILL BECOME
UNSTABLE OVER THE CWA ON TUE FOR A RISK OF TSTMS. IT LOOKS LIKE
THE BEST CHANCE OF TSTMS WILL BE OVER WHATCOM COUNTY AND WITHIN
THE PUGET SOUND CONVERGENCE ZONE /PSCZ/. THE STRONGER TSTMS WILL
LIKELY CONTAIN SMALL HAIL AT THE LOWER ELEVATIONS.

THE UPPER LOW WILL REMAIN OVER THE REGION TUE NIGHT BUT IT WILL BE
MOVING SLOWLY EAST. THE SHOWERS WILL LIKELY BE DIURNALLY DRIVEN BY
THIS TIME...THUS HAVE SHOWN THE HIGHEST POPS DURING TUE EVENING.
LOOK FOR THE UPPER LOW TO MOVE INTO EASTERN WASHINGTON/EASTERN
OREGON ON WED. THIS WILL PLACE THE CWA UNDER DRIER NORTHERLY FLOW
ALOFT. THE BEST CHANCE OF SHOWERS ON WED WILL BE OVER THE INTERIOR.

AN UPPER RIDGE WILL BUILDING INTO THE AREA FROM THE WEST WEDNESDAY
NIGHT AND THU FOR DRIER AND WARMER WEATHER.

.LONG TERM...
AN UPPER RIDGE WILL PREVAIL OVER THE REGION ON FRI FOR DRY AND
WARM CONDITIONS. BEYOND FRI...IT LOOKS LIKE A HIGH LATITUDE BLOCK
WILL DEVELOP...AND THIS WILL RESULT IN AN UPPER LOW DEVELOPING OFF
OUR COAST. THIS LOW WILL EVENTUALLY BECOME CUT-OFF AND BECOME A
WEATHER PERSONS WOE. CONSEQUENTLY...HAVE KEPT A THREAT OF SHOWERS
IN THE FORECAST DURING MUCH OF THIS PERIOD.

&&

.AVIATION...A COLD FRONT MOVING ONSHORE THIS AFTERNOON WILL PUSH
THROUGH THE INTERIOR VALLEYS EARLY THIS EVENING. AN UPPER LEVEL LOW
OFF THE NW TIP OF VANCOUVER ISLAND WILL DROP SE INTO THE AREA ON
TUE. MODERATE SW FLOW ALOFT WILL WEAKEN ON TUE AS THE UPPER LOW
MOVES INTO THE AREA. A STABLE AND SOMEWHAT MOIST AIR MASS THIS
EVENING WILL BECOME MOIST AND UNSTABLE LATE TONIGHT INTO TUE
EVENING.

A BAND OF SHOWERS ASSOCIATED WITH THE INCOMING COLD FRONT IS ALONG
THE WASHINGTON COAST AND WILL PUSH E INTO THE CASCADES THIS EVENING.
CIGS ARE GENERALLY 030-040 WITH THE FRONT AND THESE CIGS WILL PUSH
INTO THE INTERIOR BY 00Z.

THE AIR MASS WILL DESTABILIZE STARTING AROUND 06Z. LIFT ASSOCIATED
WITH THE APPROACHING UPPER LOW WILL REDUCE CIGS TO 025-035
OVERNIGHT. EXPECT SHOWERS AND A RISK OF TSTMS TUE WITH TSTM ACTIVITY
BEING MOST LIKELY IN A PUGET SOUND CONVERGENCE ZONE BETWEEN KSEA AND
KPAE 18Z-06Z. ALBRECHT

KSEA...EXPECT INCREASING CLOUDS TO BECOME BKN AT FL030-040 AROUND
00Z WITH ABOUT A 40 PERCENT CHANCE OF 6SM -SHRA. BKN030-035 TONIGHT
AND TUE WITH -SHRA...THERE IS ABOUT A 30 PERCENT CHANCE OF -TSRA
18Z-06Z TUE WITH A PUGET SOUND CONVERGENCE ZONE NEAR OR JUST NORTH
OF THE TERMINAL. SW WIND 12-16 KT WITH GUSTS TO 20-24 KT THROUGH
ABOUT 05Z WILL EASE TO S 10-14KT TONIGHT INTO TUE. ALBRECHT

&&

.MARINE...A WEAK COLD FRONT ON THE WASHINGTON COAST WILL PUSH
THROUGH THE INLAND WATERS BY EARLY THIS EVENING. MODERATE ONSHORE
FLOW WILL FOLLOW THE FRONT TONIGHT THEN WILL DECREASE ON TUE AS A
WEAK SURFACE TROUGH MOVES ACROSS THE AREA. EXPECT SMALL CRAFT
ADVISORY CONDITIONS OVER PUGET SOUND AND HOOD CANAL TO EASE TO 20 KT
OR LESS AFTER 9 PM AND SMALL CRAFT ADVISORY WESTERLY WINDS IN THE
STRAIT TO EASE AFTER 3 AM TUE MORNING.

A WLY SWELL AROUND 10 FT WILL MOVE INTO THE COASTAL WATERS LATER
THIS EVENING...THIS HAS PROMPTED THE ISSUANCE OF A SMALL CRAFT
ADVISORY FOR HAZARDOUS SEAS FOR LATE TONIGHT INTO TUE AND A SMALL
CRAFT ADVISORY FOR A ROUGH GRAYS HARBOR BAR FROM LATE TONIGHT INTO
MIDDAY TUE.

A SURFACE TROUGH AND UPPER LEVEL LOW PRES SYSTEM WILL GIVE LIGHT TO
MODERATE ONSHORE FLOW FOR SHOWERS AND A PUGET SOUND CONVERGENCE ZONE
ON TUE. THERE IS A THREAT OF AFTERNOON AND EVENING SHOWERS...
ESPECIALLY IN THE INLAND WATERS FROM ADMIRALTY INLET SOUTHWARD TUE
AFTERNOON AND EVENING.

EXPECT W TO NW FLOW THROUGH THE STRAIT OF JUAN DE FUCA TO APPROACH
SMALL CRAFT ADVISORY CRITERIA DURING THE LATE AFTERNOON AND
OVERNIGHT HOURS TUE AFTERNOON THROUGH THE END OF THE WEEK. NWLY FLOW
WILL BECOME MODERATE OVER THE COASTAL WATERS STARTING WED AS A RIDGE
OF HIGH PRES BUILDS ALONG ABOUT 130W WITH SMALL CRAFT ADVISORY
CONDITIONS POSSIBLE AT TIMES...ESPECIALLY DURING THE LATE AFTERNOON
AND EVENING HOURS. ELSEWHERE...NLY WINDS WILL DOMINATE OVER THE
INLAND WATERS WITH WINDS BELOW 20 KT. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE COASTAL WATERS...
     CENTRAL/EASTERN STRAIT OF JUAN DE FUCA...AND THE PUGET
     SOUND/HOOD CANAL.

     SMALL CRAFT ADVISORY IN EFFECT FOR ROUGH BAR FROM MIDNIGHT
     TONIGHT TIL NOON TUESDAY FOR THE GRAYS HARBOR BAR.

&&

$$

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