AREA FORECAST DISCUSSION
NWS SEATTLE WA
AFDSEW 830 PM PDT WED APR 4 2001
SATELLITE AND UIL SOUNDING INDICATE SOME WARM ADVECTION...POSSIBLE
DISSIPATING WARM FRONT NEAR WESTERN VANCOUVER ISLAND EARLY THIS
EVENING. SPOTTY TRACE PRECIPITATION NOTED W WA PROBABLY ASSOCIATED
WITH THE DISSIPATING WARM FRONT. THE COLD FRONT AT 5 PM WAS FROM THE
SOUTHERN TIP OF THE QUEEN CHARLOTTES SW INTO THE PACIFIC. MOST OF THE
COLD AIR AND UPPER LOW ARE JUST SOUTH OF THE ALEUTIANS. A POSITIVELY
TILTED 5H RIDGE AND A SURFACE HIGH REST OVER WA THIS EVENING.
THE NGM AND ETA LOOK REASONABLY INITIALIZED. BUT BY 06Z THEY HAVE A
DIFFERENCE OF OPINION ON HOW FAR SOUTH THE PRECIP DIPS. THE ETA
BRINGS PRECIPITATION TO THE NORTH CASCADES BY 12Z THU WHILE THE NGM
KEEPS ANY PRECIPITATION TO THE NORTH NEAR CENTRAL VANCOUVER ISLAND.
BY 18Z THE ETA HAS SPREAD RAIN DOWN INTO SOUTHERN PUGET SOUND WHILE
THE NGM HAS IT JUST NICKING THE NW TIP OF THE OLYMPIC PENINSULA. BY
LATE THU AFTERNOON...THE TWO ARE TOGETHER AGAIN. THE VORTICITY
PATTERN ALSO DIVERGES SOME. AT 12Z THU THE NGM HAS A VORT MAX NEAR
134W/52N. THE ETA HAS IT ABOUT 131W/48N. GIVEN THE FACT THAT THE
ACARS DATA SHOWS 100 KT JET APPARENTLY ASSOCIATED WITH THE VORT MAX
SEEN IN THE ETAS POSITIONING OF THE VORT MAX...WILL LEAN MORE TOWARD
THE ETA SOLUTION IN THE SHORT TERM. CURRENT FORECAST TIMING LOOKS
GOOD. WITH COLD FROPA THU EVE.
MODELS DIG UPPER TROF SOUTHWARD OFF THE COAST AND THE COLDEST AIR BY
PASSES WA WELL OFFSHORE. NO STRONG WESTERLY WIND AT 850 MB...MORE NLY
SO NO CONVERGENCE ZONE DEVELOPMENT BEHIND THE COLD FRONT. EVEN THOUGH
SOME PRECIPITATION WILL OCCUR ALL PERIODS...PREVIOUS FORECASTERS
THOUGHT THAT NO SNOW ADVISORIES NEEDED FOR MOUNTAINS LOOKS GOOD.
WHITNEY
UIL 3999 SEA 0697 OLM 0597
.SEW...SMALL CRAFT ADVISORY FOR THE STRAIT OF JUAN DE FUCA.
.KATX...VCP31/CSR31...OPERATIONAL.