AREA FORECAST DISCUSSION
NWS SEATTLE WA
AFDSEW 925 AM PST SAT JAN 19 2002
.SYNOPSIS...COOL ONSHORE FLOW AND A TROUGH OF LOW PRESSURE ALOFT WILL
GIVE SHOWERS TO THE LOWLANDS AND LOCALLY HEAVY SNOW TO THE MOUNTAINS
TODAY. A STRONGER AND WETTER PACIFIC FRONT WILL PUSH RAPIDLY THROUGH
THE AREA LATE TONIGHT AND SUNDAY MORNING BRINGING MORE RAIN AND
LOCALLY WINDY CONDITIONS TO THE LOWLANDS. THE FRONT WILL BRING HEAVY
SNOW TO THE MOUNTAINS AND STRONG ONSHORE FLOW WILL KEEP THE SNOW IN
THE MOUNTAINS GOING ON SUNDAY. ANOTHER TROUGH OF LOW PRESSURE ALOFT
WILL GIVE COOL AND SHOWERY ONSHORE FLOW SUNDAY NIGHT THROUGH TUESDAY.
.DISCUSSION...WSR-88D SHOWS CONVERGENCE ZONE NOW MOVING OUT OF THE
METRO AREA AND INTO THE CASCADES. SATELLITE IMAGERY SHOWS SHOWER
ACTIVITY OFFSHORE MOVING SE IN THE NORTHWESTERLY FLOW ALOFT. ALSO
WARM AIR ADVECTION OUT AHEAD OF THE NEXT SYSTEM BEGINNING TO OVERTAKE
THE COLD AIR POOL OFF THE COAST. THIS COMBINATION WILL DIMINISH THE
SHOWER ACTIVITY SOMEWHAT OVER WESTERN WASHINGTON THIS AFTERNOON.
ACARS SOUNDINGS THIS MORNING INDICATING WNW WINDS BETWEEN 5000 AND
10000 FEET GIVING THE METRO AREA A LITTLE BIT OF A RAIN SHADOW. CALL
FROM LOCAL MEDIA WITH REPORT OF SNOW SHOWERS EAST OF BELLINGHAM. VERY
SHALLOW LAYER OF COOL AIR TOUGH TO SCOUR OUT. CYXX STILL ONLY 34
DEGREES AT 17Z. WILL ADD SOME MIXED PRECIPITATION SHOWERS TO THE
NORTHWEST INTERIOR ZONE. NEXT SYSTEM CURRENTLY EXTENDING FROM THE
QUEEN CHARLOTTES TO ABOUT 50/134 TO 45/140 BEING PUSHED ALONG BY A
STRONG 160 KT JET. 12Z MODELS HAVE THE PRECIP ASSOCIATED WITH THIS
SYSTEM ALONG THE COAST AFTER 00Z AND OVER THE INTERIOR OF WESTERN
WASHINGTON BEFORE MIDNIGHT. 12Z RUNS INDICATING THE POSSIBILITY OF A
WEAK WAVE FORMING ON THE BACK SIDE OF THE FRONT WHICH WOULD SLOW IT
DOWN A LITTLE BUT STILL THE FRONT SHOULD BE THROUGH WESTERN
WASHINGTON BY 15Z SUN. BEHIND THE FRONT GOOD WESTERLY FLOW ALOFT...40
KT AT 850 MB...WILL KEEP THE SNOW GOING IN THE MOUNTAINS. FLOW ALOFT
BEGINS TO WEAKEN OVER THE NORTH CASCADES IN THE AFTERNOON AS THE JET
SLOWLY SAGS SOUTH OVER OREGON. WILL INDICATE HEAVIER SNOW AMOUNTS IN
THE CENTRAL CASCADES. COOL UPPER LEVEL TROUGH DIGGING OFFSHORE
BEGINNING LATE SUNDAY WITH THE TROUGH NOT MOVING INLAND UNTIL MONDAY
NIGHT/TUE MORNING. AVN 850 MB TEMPS OF -6 TO -8C BUT GOOD ONSHORE
FLOW AT THE SURFACE SHOULD KEEP THE SNOW LEVEL OFF THE SURFACE. OTHER
THAN WHAT IS MENTIONED ABOVE...LITTLE CHANGE TO THE FORECAST. FELTON
UIL 8++ SEA 499 OLM 799
.SEW...SNOW ADVISORY TODAY FOR THE CASCADES AND OLYMPICS.
.WINTER STORM WARNING TONIGHT/SUNDAY CASCADES/OLYMPICS.
.GALE WARNING COAST AND STRAIT OF JUAN DE FUCA.
.SMALL CRAFT ADVISORY ADMIRALTY INLET...N INLAND WATERS...
PUGET SOUND/HOOD CANAL.
.KATX...VCP21/CSR21...OPERATIONAL.