AREA FORECAST DISCUSSION
NWS SEATTLE WA
AFDSEW 230 AM PDT WED APR 5 2000
.OVERVIEW...THE UPPER FLOW HAS BECOME MORE ZONAL AND PROGRESSIVE OVER
THE PAST 24 HOURS. GIVEN THE SPEED OF THE JET OVER THE CENTRAL/ERN
PAC WITH AIRCRAFT OBSERVATIONS NEAR 52N/160W REPORTING 155KT AT
300MB...EXPECT PROGRESSIVE SHORT WAVE TROUGHS TO SWEEP THRU THE STATE
A LITTLE FASTER THAN EVEN THE FASTER AND PREFERRED 00Z AVN SOLUTION.
THEN AFTER WARM ADVECTION PCPN BRUSHES THE COAST AND N INTR THU NIGHT
AND EARLY FRI MORNING...STRONG RIDGING ALF WITH LIGHT OFFSHORE FLOW
BRINGS ANOTHER BOUT OF FINE SPRING WEATHER TO THE AREA IN TIME FOR
THE WEEKEND.
.SHORT TERM...SATELLITE IMAGERY SHOWS A DIGGING SHORT WAVE TROUGH
NEARING 50N/130W AT 08Z. THIS WILL PUSH THROUGH THE CWFA DURING THE
MORNING HOURS. GIVEN THE COLDER BOUNDARY CONDITIONS AND MORE ZONAL
NATURE TO THE FLOW...EXPECT INSTABILITY TO BE INSUFFICIENT FOR
THUNDERSTORMS TODAY. BUT DO EXPECT A POST TROUGH CONVERGENCE ZONE TO
SET UP THIS AFTN WITH 30KT INFLOW THROUGH THE STRAIT...THEN SOME
ADDED LIFT THIS EVENING AS THE STRONG JET NOW NEAR 52N/155W NOSES
ESE. POPS WILL BE HIGHEST IN UPSLOPE AREAS AND VICINITY OF
CONVERGENCE ZONES AT LEE OF OLYMPICS AND VANCOUVER ISLAND. BUT SOME
LOCATIONS SUCH AS KSEA AND THE SAN JUANS MAY MISS OUT ON MEASURABLE
PCPN AS A RAIN SHADOW AND SUBSIDENCE AROUND CONVERGENCE ZONES LOCALLY
SUPPRESSES ACTIVITY. WARM ADVECTION PCPN THU NIGHT AND EARLY FRI
SHOULD BE MAINLY CONFINED TO COAST AND N INTR. WILL ADJUST PREVIOUS
FORECASTS FOR NEW TIMING OF SYSTEMS.
.EXTENDED...WARMING AND CLEARING FROM THE S FRI WILL USHER IN MOSTLY
SUNNY AND MILD CONDITIONS SAT AND SUN. WILL SPLIT OUT FRI TO INDICATE
THE WARMING/DRYING TREND THAT DAY.
UIL 786 SEA 554 OLM 354
.KATX...VCP21/CSR21...OPERATIONAL.
.SEW...SMALL CRAFT ADVISORY COAST AND STRAIT OF JUAN DE FUCA.
N