AREA FORECAST DISCUSSION
NWS SEATTLE WA
AFDSEW 315 PM PST SAT JAN 12 2002
.SYNOPSIS...A COOL SHOWERY UNSTABLE AIR MASS WILL BE OVER THE REGION
TONIGHT. SNOW SHOWERS MAY BE HEAVY AT TIMES IN THE MOUNTAINS. A
TEMPORARY RIDGE OF HIGH PRESSURE WILL MOVE ACROSS THE AREA SUNDAY. A
WEAK WEATHER SYSTEM WILL BRUSH THE STATE SUNDAY NIGHT. A STRONGER
RIDGE OF HIGH PRESSURE WILL BUILD OVER WESTERN WASHINGTON MONDAY.
.DISCUSSION...SATELLITE IMAGERY SHOWS WEAK CONVERGENCE ZONE OVER
NORTH SEATTLE EXTENDING INTO THE CENTRAL CASCADES WITH RAIN SHADOW
EFFECT FROM THE OLYMPICS KEEPING THE CENTRAL AND SOUTHERN PUGET SOUND
PARTLY CLOUDY. PLENTY OF COOL UNSTABLE AIR OFFSHORE WITH WEAK UPPER
LEVEL RIDGE BUILDING NEAR 130W. ACARS SOUNDINGS CONTINUE TO SHOW WEST
WINDS AROUND 30 KT WHICH WILL KEEP THE OROGRAPHIC PRECIPITATION GOING
IN THE CASCADES OVERNIGHT. WILL KEEP THE SNOW ADVISORY GOING IN THE
CASCADES TONIGHT. AIR MASS STABILIZING LATER TONIGHT INTO SUNDAY WITH
WEAK UPPER LEVEL RIDGE MOVING ACROSS THE AREA. 18Z MODELS RUNS
CONTINUE TO SHOW DIFFERENCES IN THE SOLUTION FOR SUNDAY NIGHT WITH
THE AVN TRACKING A WEAK UPPER LEVEL LOW INSIDE OF 130W SOUTHEASTWARD
TO NEAR KOTH BY 12Z...CLOSE ENOUGH TO BRING PRECIPITATION TO THE
COAST AND POSSIBLY THE SOUTH INTERIOR. MESOETA HAS A SIMILAR TRACK
PUT PRODUCES NO PRECIP OVER THE AREA. BOTH MODELS SHOW WEAK NORTHERLY
SURFACE GRADIENTS AND LIGHT EASTERLY FLOW ALOFT. NOT A GOOD SCENARIO
FOR PRECIPITATION. WILL KEEP THE POPS IN THE CHANCE CATEGORY FOR NOW
AND DROP THE MENTION OF PRECIP FROM THE NORTHERN PORTION OF WESTERN
WASHINGTON INTERIOR. UPPER LEVEL RIDGE BUILDING INTO BRITISH COLUMBIA
ON MONDAY WITH DRY NORTHEASTERLY FLOW ALOFT. MODEL RUNS HAVE BEEN
GRADUALLY INCREASING THE AMPLITUDE OF THE RIDGE WITH EACH RUN WITH
THE RIDGE FIRMLY IN PLACE OVER THE AREA ON TUESDAY.
.EXTENDED...12Z AVN MUCH WEAKER WITH THE SHORTWAVE MOVING DOWN THE
BACKSIDE OF THE RIDGE FOR WEDNESDAY. EXTENDED MODELS HINTING AT MORE
RETROGRESSION OF THE RIDGE WHICH WOULD ALLOW THE NEXT SHORTWAVE
MOVING OVER THE TOP OF THE RIDGE TO EACH THE AREA LATE THURSDAY. IF
THE RIDGE DOES NOT RETROGRADE THURSDAY COULD END UP BEING A DRY TOO.
TROUGH SLOWLY BEING CARVED OUT IN THE LAST COUPLE DAYS OF THE
EXTENDED AS THE RIDGE CONTINUES TO RETROGRADE. FELTON
UIL 6131 SEA 4111 OLM 4121
.SEW...GALE WARNING STRAIT.
SMALL CRAFT ADVISORY REMAINDER OF THE WATERS EXCEPT PUGET
SOUND SEATTLE NORTHWARD AND HOOD CANAL.
SNOW ADVISORY TONIGHT CASCADES.
.KATX...VCP21/CSR21...OPERATIONAL.
AREA FORECAST DISCUSSION
NWS SEATTLE WA
AFDSEW 920 AM PST SAT JAN 12 2002
.SYNOPSIS...A COLD FRONT MOVED THROUGH WESTERN WASHINGTON EARLY THIS
MORNING. A COOL SHOWERY UNSTABLE AIR MASS WILL BE OVER THE REGION
THROUGH THIS EVENING. SNOW SHOWERS MAY BE HEAVY AT TIMES IN THE
MOUNTAINS THROUGH THIS EVENING. A WEATHER SYSTEM MAY BRUSH THE STATE
SUNDAY NIGHT.
.DISCUSSION...SURFACE OBS INDICATE COLD FRONT REACHED COAST AROUND
11Z...KSEA 13Z...KSMP 15Z. STRONG PUSH THROUGH THE STRAIT BEHIND THE
FRONT WITH KUIL-KBLI OVER PLUS 6 MB AT 16Z. ACARS SOUNDINGS SHOW WEST
WINDS 30-40 KNOTS AT 850 MB. CONVERGENCE ZONE DEVELOPING NEAR KPAE
WITH CALM WINDS ON THE 17Z OB. STRONG SOUTHERLY GRADIENTS BEHIND THE
FRONT ALSO WITH KOLM-KBLI GRADIENTS ALSO OVER PLUS 6 MB. WITH THE
STRONG FLOW ALOFT EXPECT THE CONVERGENCE ZONE TO GET PUSHED INTO THE
CASCADES THIS AFTERNOON. THIS COMBINED WITH THE OROGRAPHICS WILL KEEP
SNOW ADVISORY UP. TEMPORARY UPPER LEVEL RIDGE MOVING ACROSS THE AREA
ON SUNDAY TO DRY THINGS OUT. ONCE AGAIN MODELS DIFFER ON THE SOLUTION
FOR THE WEAK UPPER LEVEL THAT DEVELOPS OFF VANCOUVER ISLAND ON
SUNDAY. MESOETA KEEPS THE LOW FAR ENOUGH TO WEST AS IT MOVES BY
OFFSHORE SUNDAY NIGHT TO KEEP PRECIP OUT OF THE STATE WHILE THE AVN
HAS A MORE EASTERLY TRACK TO THE LOW WITH PRECIP ALONG THE COAST AND
JUST NICKING THE WESTERN INTERIOR. SURFACE HIGH PRESSURE OVER THE
AREA SUNDAY NIGHT AND FLOW ALOFT NORTHEAST OR EASTERLY...NOT GOOD FOR
PRECIP. WILL LEAVE THE CHANCE POPS FOR THE AREA FOR NOW. MONDAY LOOKS
LIKE A DRY DAY WITH OFFSHORE FLOW AT THE LOWER LEVELS. LITTLE CHANGE
TO THE CURRENT FORECAST PACKAGE. FELTON
UIL 841 SEA 441 OLM 841
.SEW...GALE WARNING COAST AND STRAIT.
SMALL CRAFT ADVISORY REMAINDER OF THE WATERS.
SNOW ADVISORY THROUGH TONIGHT CASCADES.
SNOW ADVISORY TODAY OLYMPICS.
.KATX...VCP21/CSR21...OPERATIONAL.