FXUS66 KSEW 170421
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
915 PM PDT WED APR 16 2003

.SYNOPSIS...A WEAK UPPER LEVEL TROUGH WILL BRING SCATTERED SHOWERS TO
THE AREA TONIGHT. ANOTHER STRONGER UPPER LEVEL TROUGH APPROACHING THE
AREA WILL INCREASE THE SHOWER ACTIVITY THURSDAY AFTERNOON AND NIGHT.
A TEMPORARY RIDGE OF HIGH PRESSURE WILL GIVE DRY WEATHER TO THE AREA
DURING THE DAY FRIDAY. A FRONTAL SYSTEM WILL SPREAD RAIN INTO THE
REGION LATE FRIDAY NIGHT THROUGH SATURDAY.

.DISCUSSION...SCATTERED SHOWERS ARE DECREASING IN INTENSITY OVER THE
AREA THIS EVENING. HAD A FEW ISOLATED THUNDERSTORMS OVER THE CASCADES
AND FOOTHILLS LATE THIS AFTERNOON. SCATTERED SHOWERS TONIGHT LOOKS
FINE EVEN WITH THE AIR MASS STABILIZING SOME OVERNIGHT.

BACK EDGE OF NEXT APPROACHING UPPER TROUGH HAS REACHED 133W AND IS
HANDLED WELL BY THE 00Z GFS AND MESOETA. 700MB OMEGA STARTS
INCREASING ON THE COAST BY LATE MORNING THURSDAY...AND IN THE
AFTERNOON OVER THE INTERIOR. 00Z MESOETA SOUNDINGS INDICATE THAT THE
AIR MASS WILL BE JUST AS UNSTABLE THURSDAY AFTERNOON AS LATE THIS
AFTERNOON. LI'S AND CAPE ARE THE SAME. A FEW ISOLATED THUNDERSTORMS
AGAIN THURSDAY AFTERNOON ARE PROBABLY A GOOD BET. 

WEAK CONVERGENCE IS UNDERWAY OVER PUGET SOUND...BUT HAVEN'T DETECTED
ANY INCREASE OR FOCUS IN THE SHOWER ACTIVITY YET. GRADIENT THROUGH
THE STRAIT HAS GONE FLAT AND GFS INDICATES IT WILL GO NEGATIVE
BRIEFLY AS THE UPPER/SURFACE TROUGH APPROACHES LATE TONIGHT/THURSDAY.
AM NOT SURE THE SURFACE WINDS THROUGH THE STRAIT WILL GO EASTERLY...
BUT WILL PROBABLY GO VARIABLE FOR A WHILE EARLY THURSDAY. MESOETA
SHOWS THE 925 MB WINDS STAY WEST THE ENTIRE TIME. WESTERLIES THROUGH
THE STRAIT STRENGTHEN THURSDAY NIGHT BEHIND THE UPPER TROUGH AND
SMALL CRAFT ADVISORY IS A DECENT BET...SO THERE IS SOME SUPPORT FOR A
CONVERGENCE ZONE ALL THE WAY THROUGH THURSDAY NIGHT.

LATEST GFS HAS BACKED OFF A LITTLE ON THE NEXT SYSTEM DUE LATE
FRIDAY. IF THE LATEST RUN IS CORRECT...WE COULD PROBABLY TAKE OUT
PRECIP OVER THE INTERIOR FROM THE FRIDAY PERIOD AND CUT FRIDAY NIGHT
BACK TO CHANCE POPS. ONCE FRONT SLIDES OVER WESTERN WASHINGTON
SATURDAY ANOTHER UPPER TROUGH DEEPENS DOWN THE COAST...WHICH BACKS
THE WINDS ALOFT AND HOLDS THE DECAYING FRONT OVER THE AREA THROUGH
THE WEEKEND. LOOKS KIND OF DRIPPY. KAM
UIL 7867  SEA 5763  OLM 5763

.KSEW...NONE.

.KATX...VCP21/CSR21...OPERATIONAL.

$$