AREA FORECAST DISCUSSION
NWS SEATTLE WA
AFDSEW 215 AM PST SAT FEB 19 2000
.OVERVIEW...THE BLOCKING PATTERN THAT HAS BEEN SO PERSISTENT OVER THE
AREA FOR THE PAST SEVERAL DAYS IS NOW SHOWING SIGNS OF PROGRESSING
EWD. THIS PROMISES A GRADUAL PATTERN CHANGE AS ALL GUIDANCE MOVES THE
BLOCK INTO THE MIDWEST AND DEVELOPS A MEAN LONG WAVE TROUGH ALONG THE
PACIFIC COAST BY THE MIDDLE OF NEXT WEEK. MODELS ARE GENERALLY
CONSISTENT AND ARE SHOWING GOOD CONTINUITY. WITH ALL NCEP GUIDANCE
SIMILAR AND ACCEPTED WILL USE AVN IN SHORT TERM AND MRF IN EXTENDED.
.SHORT TERM...IN RESPONSE TO THE UPPER RIDGE SHIFTING INTO ERN WA AND
A STRETCHING FRONT APPROACHING 135W...ELY GRADIENTS ARE ON THEIR WAY
UP WITH KSEA-KEAT M6.1MB AT 08Z. AS A RESULT EXPECT LITTLE OR NO FG
ON THE COAST TODAY...PATCHY AM FG IN SHELTERED RIVER VALLEYS KSEA
NWD...AND AREAS OF FG IN THE MORE SHELTERED S INTR. WITH INSOLATION
TODAY AND INCRG ELY GRADIENTS...WARMING SHOWN BY MOS GUIDANCE LOOKS
GOOD AND WILL BE FOLLOWED. WEAK STAGNATION SHOWN ON ACARS SOUNDINGS
FROM KSEA THIS MORNING SHOULD BREAK BY THIS AFTN AS ELY GRADIENTS AND
LAPSE RATES INCREASE. AS THE UPPER FLOW TURNS SLY LATER TONIGHT AND
SUN AND E/SE GRADIENTS WILL CONTINUE TO INCR. AS A RESULT EXPECT A
GOOD DEAL OF TEMPERATURE VARIABILITY TONIGHT BETWEEN WIND SHELTERED
LOCATIONS AND LOCATIONS EXPOSED TO ELY FLOW SUCH AS KSEA. THEN
FURTHER WARMING IS EXPECTED SUN DESPITE INCR IN HIGH CLOUDS. RA
CHANCES SHOULD BE MINIMAL THRU SUN. BUT PER THE FASTER 00Z GUIDANCE
THE COAST MAY FLIRT WITH A FEW SPRINKLES LATE SUN AFTERNOON.
.EXTENDED...MRF CONSISTENT WITH PREVIOUS SOLUTIONS SHOWING PASSAGE OF
A WEAK SPLITTING SYS MON...A STRONGER/WETTER FRONT TUE...THEN SHOWERS
WED. THE PREVIOUS FORECAST WILL BE FOLLOWED BUT WITH SLIGHTLY FASTER
TIMING MON/TUE PER NEW GUIDANCE.
UIL 002 SEA 001 OLM 001 ALBRECHT
.KATX...VCP32/CSR31...OPERATIONAL.
.SEW...SCA W ENTRANCE STRAIT OF JUAN DE FUCA.