AREA FORECAST DISCUSSION
NWS SEATTLE WA
AFDSEW 830 PM PST TUE MAR 27 2001
.OVERVIEW...
ACARS DATA...WATER VAPOR IMAGERY AND MODELS SHOW A STRONG 150KT WLY
JET AT 300 MB CENTERED NEAR 48N/143W PUSHING A WARM OCCLUSION INTO
THE CASCADES AT 04Z. 12Z SHORT TERM FORECASTS AND 00Z INITIALIZATIONS
APPEAR REASONABLE OVER THE EASTERN PACIFIC SHOWING A WEAK WAVE NEAR
41N/151W...OLD/DECAYING LOWS NEAR 39N/170W AND NEAR PANC...AND A
NORTHERN STREAM UPPER LEVEL TROUGH S OF THE ALEUTIANS. SHORT TERM
MODELS ARE CONSISTENT WITH PREVIOUS RUNS IN SHOWING LOW LEVEL ONSHORE
FLOW CONTINUING THRU WED NIGHT WITH WNW FLOW ALOFT. US MODELS AND
UKMET CONTINUE TO SHOW A SHORT WAVE TROUGH MOVING THRU WRN WA THU
WHILE THE ECMWF SHOWS MORE SHORT WAVE RIDGE. THEN THE MODELS ARE
SHOWING TWO CONTRADICTORY SOLUTIONS OVER THE WEEKEND WITH THE MRF/AVN
FAMILY SHOWING MORE RIDGE IN NNW FLOW ALOFT AND THE
ECMWF/NOGAPS/CANADIAN SOLUTIONS SHOWING A DEEP TROUGH ALONG 128W.
WITH ENSEMBLE SPREAD LARGE OVER THE NE PAC...CONFIDENCE IN ANY
SOLUTION IS QUITE LOW FRI AND BEYOND.
.SHORT TERM...
FRONT NOW MOVING INTO THE CASCADES WITH CHANGEOVER PCPN FROM SN TO
FZRA AT KSMP. EXPECT RA TO TAPER OFF OVERNIGHT THEN SCATTERED SHOWERS
WED AND WED NIGHT MAINLY CONFINED TO UPSLOPE AREAS AND CONVERGENCE
ZONES. GIVEN SN AMOUNTS IN THE PASSES AND MOUNTAINS OF 4 OR 5 INCHES
THIS AFTN/EVENING AND CONTINUED SN IN UPSLOPE CONDITIONS OVERNIGHT
WILL ISSUE A MARGINAL SNOW ADVISORY OVERNIGHT. AMOUNTS WED AND WED
NIGHT SHOULD BE BELOW ADVISORY CRITERIA. THU COULD SEE MORE RA WITH
ANOTHER PASSING SHORT WAVE TROUGH. WILL LET LATER SHIFTS REFINE ONCE
ALL NEW 00Z GUIDANCE IS IN.
.EXTENDED...
NO CONFIDENCE AS SOLUTIONS DIVERGE. NO CHANGES FOR NOW.
UIL +556 SEA 6436 OLM 7536 ALBRECHT
.SEW...SMALL CRAFT ADVISORY ALL WATERS.
.SNOW ADVISORY TONIGHT FOR THE WEST SLOPES OF THE NORTH AND
CENTRAL CASCADES AND PASSES.
.KATX...VCP21/CSR21...OPERATIONAL.