| SEATTLE FORECAST DISCUSSION |
FXUS66 KSEW 221750
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
910 AM PST SUN NOV 22 2009
.SYNOPSIS...A LOW PRESSURE CENTER OVER WASHINGTON WILL SHIFT INLAND
AND HIGHER PRESSURE WILL BUILD INTO THE REGION TODAY. THIS WILL GIVE
RATHER BLUSTERY WINDS...ESPECIALLY ON THE COAST AND IN THE STRAIT OF
JUAN DE FUCA. SNOW SHOWERS WILL BE HEAVY AT TIMES IN THE MOUNTAINS.
A WARM FRONT WILL MOVE THROUGH THE AREA MONDAY AND MONDAY
NIGHT...FOLLOWED BY ANOTHER WARM FRONTAL SYSTEM LATER IN THE WEEK.
&&
.SHORT TERM...ANOTHER BLUSTERY DAY FOR WRN WA...WINDY ON THE COAST
AND THRU THE CHEHALIS GAP...AND WESTERLY GALES SHUD DVLP IN THE
STRAIT BY NOON. THE WIND ADVISORY SHUD PROBABLY BE EXTENDED NORTH
THRU THE METRO AREA AND HOOD CANAL FOR RATHER BLUSTERY WEATHER DVLPG
THRU THE MORNING AND PEAKING MIDDAY. WHEN I DO THAT I WILL HAVE THEM
ALL EXPIRE AT 3PM. SHOULD BE A GOOD PSCZ WIND PATTERN BY
AFTERNOON...SO AFTER THE SURGE OF SW 20-30MPH WINDS THIS MORNING
THRU THE SEATTLE METRO AREA THE WIND WILL SETTLE DOWN AS THE PSCZ
SETS UP. THE WINTER STORM WARNING FOR THE CASCADES PROBABLY NEEDS A
REFRESH AS WELL...IT EXPIRES AT 1PM AND AS THE WESTERLY OROGRAPHIC
SNOW KICKS IN BY AFTERNOON SO THAT NEED TO BE EXTENDED INTO THE
EARLY EVENING. WINDS IN THE CASCADE PASSES INCREASING TO WESTERLY
20-30 MPH BY AFTERNOON AND GUSTS TO 50 ON THE RIDGETOPS...A LOT LESS
THAN THE PEAK WINDS OVERNIGHT: AT THE VERY TOP OF CRYSTAL MOUNTAIN
ARND 1AM LAST NITE STRONG SE WINDS OF 50 MPH GUSTED TO ARND
95MPH...QUITE A WINTER STORM UP HIGH. THE SYSTEM FOR MONDAY WILL BE
WEAKER AND WARMER...ALTHOUGH IT WILL PROBABLY MUSTER SSE GALES JUST
AHEAD OF THE FRONT OVER THE COASTAL WATERS MON MORNING....BY MON
NITE THE GRADIENT OVER WRN WA IS QUITE LIGHT. IN FACT THE WEATHER
PATTERN NEXT WEEK LOOKS A LOT LIKE WHAT EL NINO IS SUPPOSED TO
BRING...WARMTH AND FAIRLY WEAK SYSTEMS. 19
.LONG TERM...ANOTHER WARM FRONT WILL BRUSH THE NORTHWEST CORNER OF
THE AREA AS IT MOVES INTO BRITISH COLUMBIA. THE TRAILING COLD FRONT
WILL DRAG SLOWLY ACROSS THE FORECAST AREA WEDNESDAY NIGHT THROUGH
THURSDAY FOLLOWED BY ITS UPPER TROUGH THURSDAY NIGHT AND FRIDAY.
MCDONNAL
&&
.HYDROLOGY...THE ONLY CURRENT RIVER FLOOD PROBLEM IS THE SKOKOMISH
RIVER. IT IS JUST ABOVE FLOOD STAGE THIS MORNING AND WILL LIKELY
REMAIN ABOVE FLOOD STAGE INTO MONDAY. THIS IS DUE PRIMARILY TO
RELEASES OF WATER FROM CUSHMAN DAM #2. THE SYSTEM MOVING THROUGH
WESTERN WASHINGTON TODAY IS NOT A FLOOD-PRODUCING RAIN SYSTEM BUT
RATHER A HEAVY MOUNTAIN SNOW SYSTEM.
THE FRONTAL SYSTEMS EXPECTED TO ARRIVE DURING THE COMING WEEK WILL
BE ACCOMPANIED BY HIGHER SNOW LEVELS -- PROBABLY IN THE 5000 TO 7000
FT RANGE. ONE FRONT IS FORECAST TO MOVE THROUGH MONDAY AND MONDAY
NIGHT WITH ANOTHER SYSTEM MOVING SLOWLY THROUGH WEDNESDAY NIGHT
THROUGH THURSDAY NIGHT. THEY ARE NOT EXPECTED TO PRODUCE ENOUGH
PRECIPITATION TO CREATE FLOODING CONCERNS.
NO FLOODING IS EXPECTED AT ANY TIME ON THE GREEN RIVER.
&&
.AVIATION...SURFACE LOW PRES THAT MOVED ONSHORE EARLIER THIS MORNING
IS NOW SHIFTING INTO WRN WA ALONG WITH THE UPPER TROUGH. ONSHORE
FLOW WILL PERSIST TODAY WITH STRONG WLY FLOW ALOFT. THE ATMOSPHERE
WILL REMAIN MOIST AND SLIGHTLY UNSTABLE THIS MORNING WITH WRAP
AROUND MOISTURE KEEPING LOWER CIGS AND RAIN AROUND A LITTLE LONGER
THAN EXPECTED. CIGS SHOULD IMPROVE TO VFR AFTER 21Z WITH DECREASING
MOISTURE. WITH PARTIAL CLEARING TONIGHT...EXPECT AREAS OF FOG TO
FORM...MOSTLY IN FAVORED SHELTERED VALLEYS.
A PUGET SOUND CONVERGENCE ZONE /PSCZ/ WILL DEVELOP N OF THE
SNOHOMISH/KING COUNTY BORDER LATER THIS MORNING AND THEN MOVE S
DURING THE AFTERNOON...BECOMING QUASISTATIONARY OVER THE N CENTRAL
PUGET SOUND. AT THIS TIME...IT LOOKS LIKE THE PSCZ WILL REMAIN N OF
KBFI. WINDS WILL BACK TONIGHT AS THE PRES GRADIENT BECOMES SLY...
THUS EXPECT THE PSCZ TO DRIFT BACK TO THE N AND THEN DISSIPATE LATER
TONIGHT.
KSEA...CIGS 1-2K FT AND VIS 3-5SM MAY HOLD IN A LITTLE LONG THAN
EXPECTED DUE TO WRAP AROUND MOISTURE. STILL EXPECT IMPROVEMENT TO
VFR CONDITIONS BY 21Z. SW WIND 10-15 KT W/ GUSTS TO 30 KT
TODAY...BECOMING S 3-6 KT THIS EVENING. DTM
&&
.MARINE...STRONG ONSHORE FLOW TODAY BEHIND A LOW PRESSURE SYSTEM
WHICH IS NOW SHIFTING INTO ERN WA. GALES ALONG THE COAST SHOULD
CONTINUE THROUGH MOST THE DAY BEFORE EASING. THE WINDS IN THE STRAIT
TOOK A LITTLE LONGER THAN EXPECTED TO COME AROUND WLY...BUT SHOULD
STILL POP UP TO GALE FORCE BY NOON. WINDS HAVE COME UP SLIGHTLY
AROUND PUGET SOUND BUT OBS SO FAR ARE FAR SHORT OF GALES...SO I WILL
KEEP A SMALL CRAFT IN EFFECT TODAY. DTM
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...A FLOOD WARNING REMAINS IN EFFECT FOR THE SKOKOMISH RIVER
IN MASON COUNTY.
A WINTER STORM WARNING REMAINS EFFECT FOR THE CASCADES TODAY.
WIND ADVISORIES ARE IN EFFECT FOR THE STRAIT OF JUAN DE FUCA
AND THE ADMIRALTY INLET AREAS...SOUTHWEST INTERIOR...LOWER
CHEHALIS VALLEY...SEATTLE TACOMA BREMERTON METRO AREA...HOOD
CANAL.
PZ...GALE WARNINGS ARE IN EFFECT FOR ALL WATERS EXCEPT PUGET SOUND
TODAY.
SMALL CRAFT ADVISORY PUGET SOUND TODAY.
A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR ROUGH GRAYS
HARBOR BAR CONDITIONS TIL 4 PM MON.
$$
WWW.WEATHER.GOV/SEATTLE
FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.
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SEA TRACON WEATHER IMPACTS ISSUED: 11/22/2009 2:01:36 PM |
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| PSCZ | CONF | TIME | WIND SHIFT INFO |
| BFI | |||
| SEA | |||
| WIND (>40KT AOB 050) | DIR/SPD/LEVEL | ||
| SEA | |||
| TS (WITHIN 10 MILES) | |||
| BFI | |||
| SEA | |||
| FOG (VIS < 1 MILE) | |||
| BFI | |||
| SEA | |||
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ZSE ARTCC PIREP REQUIREMENTS |
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| Issued: 11/22/2009 2:01:39 PM | ||||
| AREAS | ||||
| HAZARDS | A | B | C | D |
| ICING | X | X | X | |
| LO-TURB | X | X | X | X |
| LLWS | ||||
| HI-TURB | X | X | X | X |
| TSTM | ||||
| CIG <050 | X | X | X | X |
| IFR | X | |||
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