Small Craft Advisory 319, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
130 PM ADT TUE APR 3 2007

.DISCUSSION...

ANALYSIS...SATELLITE IMAGERY SHOWS A STRONG NEAR ZONAL UPPER JET
STREAMING ALONG AT AROUND 40N TO A LARGE CLOSED LOW AT 46N 160W.
TWO LOWS ARE EMBEDDED IN THE CYCLONIC ROTATION TO THE EAST OF THE
SURFACE LOW ROTATING NORTH AND THEN WEST...AND REMAINING SOUTH OF
THE ANCHORAGE FORECAST AREA. THE GRADIENT AHEAD OF THE OCCLUDED FRONT
CONNECTING THESE TWO LOWS IS VERY TIGHT. THE JET IS BEGINNING TO
CURVE NORTHWARD AROUND THE EAST SIDE OF THIS LOW...WHICH WILL BEGIN
TO FORCE THIS FRONTAL BOUNDARY NORTHWARD TOWARD THE GULF TONIGHT...
RESULTING IN INCREASING WINDS ACROSS THE GULF WATERS. BACK WEST ALONG
THE UPPER TROUGH AXIS IS A WEAK SURFACE LOW NEAR ATKA. AS PER WATER
VAPOR...LOT OF MOISTURE IS STREAMING WESTWARD ACROSS THE ALEUTIANS
AND THERE IS A BAND OF GALE FORCE WINDS FROM THE EASTERN ALEUTIANS
TO JUST NORTH OF THE CENTRAL ALEUTIANS. AS THE UPPER JET CURVES
TOWARD THE GULF TONIGHT AND WEDNESDAY FLOW ACROSS THE BERING WILL
BACK TO THE NORTH AND PUSH EVERYTHING SOUTHWARD. FINALLY...A WEAK
UPPER LOW OVER BRISTOL BAY COMBINED WITH A TROUGH DROPPING DOWN
THROUGH NORTHWEST ALASKA ARE COMBINING TO PROVIDE CLOUDS OVER MOST
OF THE MAINLAND AND EVEN SOME VERY LIGHT PRECIP OVER BRISTOL BAY.

MODEL DISCUSSION...THE FRONT THAT APPROACHES THE GULF FROM THE SOUTH
TONIGHT IS STRONGER THAN PREVIOUSLY FORECAST...SO WILL INCREASE THE
WINDS ACROSS THE GULF WATERS FOR THE NEXT COUPLE DAYS. 12Z GFS HAS
COME BACK IN LINE WITH 12Z SOLUTION FROM YESTERDAY WITH REGARD TO
SURFACE TROUGH MOVING ACROSS GULF ON THURSDAY. NAM...WHICH IS OFTEN
IN CATCH-UP MODE WITH THE GFS NOW SHOWS A MUCH SHARPER
TROUGH...CLOSER TO THE PREVIOUS GFS SOLUTION...SO WILL BE
DISREGARDED. UKMET AND ECMWF MATCH UP WELL WITH GFS SOLUTION. MODELS
DIVERGE SIGNIFICANTLY WITH LOW TRACKING TO GULF AT THE END OF THE
WEEK. GFS IS FASTEST OF THE MODELS AND WITH STRONG UPPER JET DRIVING
THE LOW NORTHWARD THIS MAKES SENSE. HOWEVER...THERE IS LARGE VARIANCE
IN THE GFS ENSEMBLES AND THE OPERATIONAL RUN IS FASTER THAN THE
ENSEMBLE MEAN. SO FOR NOW WILL STICK WITH THE CURRENT FORECAST
(BEGINNING AT ABOUT 72 HOURS).

SHORT-TERM FORECAST...EXPECT GRADUALLY IMPROVING CONDITIONS OVER THE
ALEUTIANS AS THE LOW NEAR ATKA TRACKS SOUTH AND DISSIPATES TONIGHT
AND WEDNESDAY. MEANWHILE WINDS WILL INCREASE RAPIDLY ACROSS THE
SOUTHERN GULF WATERS TONIGHT TO AROUND 40 KT AS THE FRONT APPROACHES
FROM THE SOUTH. THIS FRONT WILL VERY SLOWLY MOVE INTO THE GULF
WEDNESDAY CAUSING WINDS ALONG THE ENTIRE GULF COAST AS WELL AS ALONG
THE AKPENN TO REACH OR COME CLOSE TO GALE FORCE. THE FRONT WILL STALL
OVER THE GULF AND BEGIN TO WEAKEN BY LATE WEDNESDAY...BUT A SURFACE
TROUGH APPROACHING FROM THE SOUTH WILL MAINTAIN A TIGHT PRESSURE
GRADIENT. THE TROUGH WILL MOVE ACROSS THE GULF THURSDAY AND THEN FALL
APART AS IT REACHES LAND THURSDAY NIGHT. KODIAK AND THE SOUTHERN
AKPENN CAN EXPECT TO SEE PRECIP WITH THE FRONT BEGINNING LATE
TONIGHT. WHEN THE TROUGH MOVES THROUGH THURSDAY PRECIP WILL SPREAD
TO THE REST OF THE GULF COAST WHILE INLAND AREAS WILL CONTINUE TO
REMAIN MOSTLY DRY.

MEANWHILE...THE TROUGH DROPPING THROUGH NORTHWEST ALASKA WILL MOVE
INTO THE BERING SEA AS A CLOSED LOW. COMING FROM THE NORTH...THERE
IS NOT A LOT OF MOISTURE TO WORK WITH...SO DONT EXPECT MORE THAN
A BIT OF LIGHT PRECIP OVER SOUTHWEST ALASKA AND THE BERING AS THIS
FEATURE MOVES ACROSS THROUGH.

EXTENDED FORECAST...MAIN UPPER LOW CIRCULATION WILL MOVE NORTHWARD
INTO THE ANCHORAGE FORECAST AREA. THIS WILL LIKELY LEAD TO WETTER
CONDITIONS ACROSS MOST OF THE FORECAST AREA...ESPECIALLY INLAND
AREAS WHICH HAVE BEEN VERY DRY OF LATE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 120 130 132 138 150 155.
FIRE WEATHER...NONE.

SEB APR 07