Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 291028
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
328 AM PDT FRI MAY 29 2015

.SYNOPSIS...NO SIGNIFICANT CHANGES ARE ANTICIPATED IN THE OVERALL
WEATHER PATTERN OVER THE REGION THROUGH THIS WEEKEND. TEMPERATURES
WILL REMAIN ABOVE NORMAL FOR THIS TIME OF THE YEAR. LOOK FOR A
CHANGE TO AN UNSETTLED AND COOLER PATTERN NEXT WEEK.

&&

.SHORT TERM...
THERE WAS CIRROSTRATUS STREAMING ACROSS THE CWA AT THIS TIME...
AND THIS WAS MAKING IT DIFFICULT TO SEE THE TRUE EXTENT OF THE
LOW CLOUDS. NOTE...THE ECHOES BEING DETECTED ON KATX WSR- 88D
OVER THE CENTRAL STRAIT OF JUAN DE FUCA WAS NOT PRECIPITATION.

MEANWHILE...NOT EXPECTING ANY SIGNIFICANT CHANGES TO THE SYNOPTIC
SCALE PATTERN OVER THE PACIFIC NORTHWEST THROUGH SATURDAY. THE CWA
WILL REMAIN BETWEEN A CUT-OFF LOW OVER WESTERN CANADA AND AN UPPER
LEVEL RIDGE CENTERED OVER NORTHERN MEXICO.

LOOK FOR A VERY WARM DAY AGAIN ACROSS MUCH OF THE CWA TODAY. THERE
WILL ALSO BE A RISK OF TSTMS OVER THE MOUNTAINS AGAIN LATE THIS
AFTERNOON THROUGH EARLY EVENING. THE THETA-E RIDGE EXTENDED WEST
ACROSS THE PUGET SOUND INTO THE OLYMPIC RANGE EARLY THIS MORNING.
THE SREF SUGGESTED THAT THERE WILL NOT BE MUCH CHANGE IN THE
POSITION OF THIS FEATURE...SO WENT ON AHEAD AND ADDED A MENTION OF
TSTMS TO THE CASCADE FOOTHILLS ZONE.

THE SURFACE ONSHORE PRESSURE GRADIENT WILL TIGHTEN SOME LATER
TODAY AND EVEN MORE ON SATURDAY. THUS ANTICIPATE LOW CLOUDS TO
BLANKET MUCH OF THE INTERIOR LOWLANDS SATURDAY MORNING. IT
APPEARED THAT THE RISK OF ANY SHOWERS OR TSTMS WILL BE EAST OF THE
CASCADE CREST ON SATURDAY...SO THE DRY FORECAST STILL LOOKED GOOD.

HIGH PRESSURE ALOFT WILL STRENGTHEN SOME OVER THE REGION SATURDAY
NIGHT AND SUNDAY AHEAD OF AN UPPER LEVEL TROF APPROACHING FROM THE
SOUTHWEST. THIS WILL RESULT IN A WEAKER ONSHORE PRESSURE GRADIENT.
THERE WILL ALSO BE AN INCREASE IN PRIMARILY HIGH CLOUDS ACROSS THE
CWA IN ADVANCE OF THE TROF. OVERALL...TEMPS ON SUNDAY SHOULD NOT
BE TOO MUCH DIFFERENT THAN ON SATURDAY.

.LONG TERM...
NO MAJOR CHANGES TO THE PREVIOUS THINKING. AN UPPER LEVEL TROUGH
WILL DOMINATE THE WEATHER PATTERN OVER THE PACIFIC NORTHWEST
DURING THIS PERIOD FOR COOL AND UNSETTLED CONDITIONS. DAYTIME
TEMPS WILL BE BELOW NORMAL FOR THIS TIME OF THE YEAR.

&&

.AVIATION...AN UPPER LOW OVER WEST CENTRAL BRITISH COLUMBIA WILL
GIVE LIGHT WESTERLY FLOW ALOFT TO THE AREA. AT THE SURFACE...HIGH
PRESSURE OFFSHORE AND LOWER PRESSURE TO THE EAST OF THE CASCADES
WILL GIVE LIGHT TO MODERATE ONSHORE FLOW. THE AIR MASS IS DRY AND
STABLE WITH A MARINE LAYER ALONG THE COAST...AROUND THE STRAIT OF
JUAN DE FUCA...AND THROUGH THE CHEHALIS GAP. THE STRATUS WILL BURN
BACK TO THE COASTLINE BY 18Z THEN THE AIR MASS WILL DESTABILIZE IN
THE INTERIOR DURING THE AFTERNOON HOURS.

AT 10Z...MARINE STRATUS HAD REACHED THE WESTERN SHORES OF WHIDBEY
ISLAND IN THE NORTH INTERIOR AND KSHN IN THE SOUTH INTERIOR. THE
STRATUS WILL SNEAK SE FROM THE STRAIT OF JUAN DE FUCA TO AROUND KPAE
13Z-16Z AND AROUND THE SAN JUANS. IN THE SOUTH PUGET SOUND AREA
EXPECT SOME STRATUS TO REACH KPWT AND THE PUGET SOUND W OF
KSEA...BUT IT IS EXPECTED TO REMAIN TO THE WEST OF THE KSEA AND KBFI
TERMINALS. THE STRATUS IS LOW AND SHALLOW WITH BASES 004-008 AND
TOPS 010-014. THE STRATUS WILL BURN BACK TO THE PACIFIC COASTLINE BY
ABOUT 19Z. EXPECT STRATUS TO MOVE BACK INLAND 10Z-18Z SATURDAY WITH
ABOUT THE SAME EXTENT AS THIS MORNING.

THE AIR MASS WILL BE SLIGHTLY MORE UNSTABLE ALOFT ACROSS THE AREA
TODAY THAN IT WAS ON THU WITH LATE AFTERNOON AND EARLY EVENING
LIFTED INDEX VALUES -1 TO -3. MID LEVEL MOISTURE AND ORGANIZED LIFT
IS GENERALLY LACKING...SO THE THREAT FOR TSTMS WILL BE LIMITED TO
THE CASCADE CREST AREA 21Z-04Z WITH ONLY A 10 PERCENT CHANCE THAT A
BUILDUP OVER THE OLYMPICS WILL GIVE AN ISOLD TSTM THERE. THE
LOWLANDS ARE EXPECTED TO BE DRY THIS AFTN. ALBRECHT

KSEA...SCT-BKN CIRRUS WITH VARIABLE WIND TO 5 KT. LOW STRATUS AND
FOG WILL VERY LIKELY REMAIN TO THE WEST OF THE TERMINAL OVER PUGET
SOUND SOUTHWESTWARD THROUGH THE CHEHALIS GAP. WIND WILL BECOME NW
10KT AFTER 19Z. ALBRECHT

&&

.MARINE...HIGH PRESSURE CENTERED OFFSHORE WITH LOWER PRESSURE INLAND
WILL GIVE LIGHT TO MODERATE ONSHORE FLOW THROUGH THE WEEKEND. SMALL
CRAFT ADVISORY CONDITIONS CAN BE EXPECTED DURING THE LATE AFTERNOON
AND OVERNIGHT HOURS IN THE CENTRAL AND EASTERN PORTIONS OF THE
STRAIT OF JUAN DE FUCA.

AREAS OF FOG IN THE STRAIT OF JUAN DE FUCA AND PATCHY FOG IN
ADMIRALTY INLET AND THE FAR NORTH AND SOUTH REACHES OF PUGET SOUND
WILL BURN BACK TO THE PACIFIC COASTLINE MIDDAY. THE FOG AND LOW
CLOUDS WILL PUSH BACK INLAND LATE TONIGHT INTO SATURDAY MORNING.

IT APPEARS THAT THE WEATHER PATTERN WILL CHANGE SUNDAY NIGHT OR
MONDAY AS AN UPPER LEVEL DISTURBANCE MOVES THROUGH THE AREA FROM THE
SOUTHWEST. LOW LEVEL FLOW WILL LIKELY BECOME MORE SOUTHERLY STARTING
SUNDAY NIGHT AND THERE WILL BE A THREAT OF SHOWERS AND
THUNDERSTORMS. STRONG WESTERLY FLOW IS POSSIBLE EARLY NEXT WEAK
DURING THE AFTERNOON AND OVERNIGHT HOURS IN THE STRAIT OF JUAN DE
FUCA.  ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY IN EFFECT FOR THE CENTRAL AND EASTERN
     STRAIT OF JUAN DE FUCA.

&&

$$

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