Snow Advisory 16, NWS Seattle, WA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SEATTLE WA
314 PM PDT FRI OCT 19 2007

UPDATED THE AVIATION AND HEADLINE SEGMENTS

.SYNOPSIS...LOW LEVEL ONSHORE FLOW...COMBINED WITH A COLD UPPER
LEVEL TROUGH OF LOW PRESSURE MOVING IN FROM OFFSHORE...WILL PRODUCE
SHOWERS AND ISOLATED THUNDERSTORMS THROUGH SATURDAY. SNOW SHOWERS
ARE EXPECTED IN THE MOUNTAINS ABOVE ABOUT 3500 FEET. SHOWER ACTIVITY
WILL END LATE SATURDAY NIGHT AS AN UPPER LEVEL RIDGE BUILDS OVER THE
AREA. A WEAK WARM FRONT WILL BRUSH THE NORTH PART OF THE AREA SUNDAY
AND SUNDAY NIGHT. HIGH PRESSURE AT THE SURFACE AND ALOFT WILL GIVE
DRY WEATHER TO THE AREA EARLY NEXT WEEK...WITH LATE NIGHT AND
MORNING FOG IN THE INTERIOR VALLEYS.

&&

.SHORT TERM...A RATHER STRONG ONSHORE FLOW OF COOL AND UNSTABLE AIR
OFF THE PACIFIC IS PRODUCING SHOWERS AND ISOLATED THUNDERSTORMS THIS
AFTERNOON. EXPECT LITTLE CHANGE FOR THE NEXT 24-30 HOURS AS A LARGE
BATCH OF COLD AIR ALOFT IS SEEN EXTENDING FROM JUST OFF THE
COASTLINE OUT TO 140W. THE COLD POOL ALOFT...WITH M38C TO M40C AT
500 MB...IS EXTENSIVE. WHILE THERE COULD BE AN ISOLATED THUNDERSTORM
AT ANY TIME ON THE COAST AS AIR ASCENDS AGAINST THE TERRAIN...THE
BEST CHANCE FOR THE ISOLATED THUNDERSTORMS IN THE INTERIOR WILL BE
DURING THE DAYTIME HOURS WHEN INSTABILITY IS MAXIMIZED. BREEZY
CONDITIONS WILL ALSO CONTINUE UNTIL THE UPPER TROUGH PASSES SAT
EVENING.

SNOW LEVELS IN THE MOUNTAINS NEAR 4000 FEET THIS AFTERNOON WILL
GRADUALLY FALL TO ABOUT 3500 FEET...WITH SNOW AFFECTING THE HIGHER
PASSES. EXPECT AMOUNTS GENERALLY TO RANGE FROM 3 TO 5 INCHES PER 12
HOUR PERIOD TONIGHT AND SATURDAY...A BIT BELOW SNOW ADVISORY
CRITERIA.

SHOWER ACTIVITY WILL COME TO AN END LATE SAT NIGHT OR EARLY SUN AS
THE AIR MASS RAPIDLY STABILIZES IN A BUILDING UPPER RIDGE ALONG THE
WEST COAST. MODELS ARE TRENDING TOWARD A SOLUTION THAT WOULD BRING A
WEAK WARM FRONT TO THE COAST AND NORTH INTERIOR LATER SUN AND SUN
NIGHT. HAVE TRIMMED BACK POPS...EXCEPT ON THE NORTH COAST...FOR
LATER IN THE WEEKEND...AND IF TRENDS CONTINUE LATER SHIFTS MAY BE
ABLE TO TRIM THEM BACK FURTHER. ADDED SOME PATCHY FOG MON MORNING
FOR THE SOUTH INTERIOR WHERE THERE MAY BE A LITTLE MORE CLEARING
LATE SUN NIGHT.

TEMPERATURES IN THE SHORT TERM WILL CONTINUE TO RUN BELOW
NORMAL...BUT WILL SLOWLY MODERATE STARTING MON. ALBRECHT

.LONG TERM...RIDGING AT THE SURFACE AND ALOFT WILL PROVIDE DRY
CONDITIONS TUE AND INTO EARLY WED. 500 MB HEIGHTS CLIMB TO AROUND
588 DAM WHILE A 1030 MB HIGH SETS UP JUST TO OUR NORTH. ITS OCTOBER
AND THE GROUND IS WET...THEREFORE IT LOOKS LIKE ITS GOING TO FOG. I
TRIMMED MAX TEMPERATURES IN THE LOWLANDS BELOW GUIDANCE AS FOG
POSSIBLY HANGS TOUGH INTO THE EARLY TO MID AFTERNOON HOURS BEFORE
BREAKING OUT. LATER WED OR WED NIGHT...BOTH THE GFS AND EURO IN
RESPONSE TO STRONG DEVELOPMENT IN THE CENTRAL PACIFIC...START
BUILDING A RIDGE AROUND 150W AND DIG TROUGHING INTO THE PAC NW.
MODELS ARE CONSISTENT IN THESE TRENDS BUT ARE VARYING A BIT FROM RUN
TO RUN. SO WILL INTRODUCE A CHANCE OF SHOWERS FOR WED NIGHT THROUGH
THE END OF THE WEAK BEFORE FLOW GOES OFFSHORE FOR DRYING ONCE AGAIN
TOWARD THE NEXT WEEKEND. ALBRECHT

&&

.AVIATION...THE AIR MASS WILL BE REMAIN COOL AND UNSTABLE OVER THE
AREA THRU TONIGHT...ALTHOUGH THE RISK OF TSTMS WILL END ABOUT SUNSET
ACROSS THE ENTIRE AREA EXCEPT THE PAC COASTAL WATERS. ANTICIPATE
SMALL HAIL WITH THE STRONGER TSTMS. CIGS WILL GENERALLY BE AT OR
ABOVE 4K FT...EXCEPT NEAR 2K FT WITH SHOWERS. AFTERNOON...OTHERWISE
THE MOST UNSTABLE AIR MASS WILL REMAIN OVER THE OLYMPICS WWD. CIGS
WILL GENERALLY BE NEAR 5K FT...EXCEPT BETWEEN 1K AND 2K FT WITH THE
HEAVIER SHOWERS. MODERATELY STRONG...LOW LEVEL...ONSHORE FLOW WILL
PERSIST.

CASCADE PASS FROM KSEA-KELN...BASES GENERALLY 4-6K FT MSL WITH TOPS
BETWEEN 10K AND 15K FT. CASCADES OBSCURED BY CLOUDS AND/OR
PRECIPITATION.

AT KSEA...EXPECT CIGS TO GENERALLY BE AT OR ABOVE 5K FT...EXCEPT
DOWN TO NEAR 2K FT WITH ANY HEAVY SHOWERS. THERE IS A 20 PERCENT
CHANCE OF A TSTM WITHIN THE AIRPORT COMPLEX BETWEEN 22Z AND 01Z.
AFTER 01Z...THE TSTM THREAT WILL BECOME NIL. WINDS WILL REMAIN SLY
10-15 KT...WITH GUSTS TO 25 KT TIL 02Z.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
1. HIGH SURF ADVISORY COAST.
2. SMALL CRAFT ADVISORY COASTAL WATERS...W ENTRANCE TO THE STRAIT OF
JUAN DE FUCA...NORTHERN INLAND WATERS...AND PUGET SOUND/HOOD CANAL.

WEATHER.GOV/SEATTLE

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
421 PM PDT FRI OCT 19 2007

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0417 PM     HAIL             4 WNW CINEBAR           46.61N 122.62W
10/19/2007  E0.25 INCH       LEWIS              WA   TRAINED SPOTTER

            CALLED SPOTTER FOR STORM REPORT. SAID HAIL WAS ABOUT
            1/4-3/8 INCH IN DIAMETER AND COVERED THE GROUND.

&&

DDAMICO