Small Craft Advisory 278, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT TUE APR 19 2011

.MODEL DISCUSSION...
THE MODELS ARE GENERALLY IN GOOD AGREEMENT THROUGH THU MORNING.
MODELS THEN DIVERGE ON SOLUTIONS...MAINLY WITH THE LOW COMPLEX SOUTH
OF THE AK PEN AND GULF OF ALASKA. THE GFS AND ECMWF MODELS HAVE BOTH
BEEN INTERNALLY CONSISTENT ON THE LAST COUPLE OF RUNS THROUGH THE
SHORT TERM BUT VARY CONSIDERABLY FROM EACH OTHER. AFTERNOON PACKAGE
(THRU 84 HRS) WILL BE BASED ON MINOR BLENDS OF THE 12Z GFS AND 00Z
ECMWF WITH THE CHANGES MINOR OVERALL.

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVELS SHOW A STRING OF CLOSED LOWS THAT LIE JUST SOUTH OF
SHEMYA TO ABOUT 600 NM SOUTH OF KODIAK. THERE IS ALSO AN UPPER LOW
OVER FAR NORTHERN CANADA THAT WILL MOVE SOUTHWESTWARD OVER ALASKA
OVER THE NEXT FEW DAYS. OTHERWISE...A LARGE AREA OF HIGH PRESSURE
OVER BERING IS KEEPING WEATHER RELATIVELY BENIGN ACROSS THE AREA. THE
MAIN SURFACE LOW THAT IS AFFECTING THE FORECAST AREA IS JUST SOUTH OF
ATKA...AND REMAINS NEARLY STATIONARY.

.SHORT TERM...
SOUTHCENTRAL...CONDITIONS WILL GET PROGRESSIVELY MORE CLOUDY AND
UNSTABLE OVER THE NEXT COUPLE OF DAYS AS UPPER LEVEL TROUGH DIGS
SOUTHWEST OVER THE WESTERN MAINLAND. THE SURFACE TROUGH EXTENDING
ACROSS THE COPPER RIVER BASIN TO OVER COOK INLET WILL REMAIN
RELATIVELY STATIONARY THROUGH THU. PRESSURE GRADIENTS INCREASE THU AS
A RIDGE BUILDS ACROSS THE NORTH GULF COAST IN ADVANCE OF AN
APPROACHING FRONTAL TROUGH. THE RESULTANT CHANGE WILL PRODUCE BRISK
AND GUSTY GAP FLOWS OVER SOUTHCENTRAL...ESPECIALLY EAST WINDS ACROSS
TURNAGAIN ARM...SE WINDS THROUGH KNIK VALLEY...AND GUSTY SOUTH WINDS
ALONG THE COPPER RIVER.

SW ALASKA...GENERALLY DRY CONDITIONS WILL CONTINUE THROUGH WED. MAY
SEE INCREASING CHANCES OF SHOWERS THU/THU NIGHT OVER BRISTOL BAY AS
SOUTHERLY FLOW IN THE MID/LOW LEVEL BRINGS IN MOISTURE WHICH COMBINE
WITH INSTABILITY OF UPPER TROUGH.

ALEUTIANS/BRISTOL BAY/EASTERN BERING SEA...A SERIES OF LOWS WILL
CONTINUE SOUTH OF THE ALEUTIANS OVER THE NEXT COUPLE OF DAYS AND
BRING PERIODS OF SHOWERS/RAIN TO MUCH OF THE ALEUTIANS/AK PEN. BRISK
EAST TO NE WINDS...GENERALLY BELOW GALES...CAN ALSO BE EXPECTED
ACROSS THE ALEUTIANS...AK PEN...AND EASTERN BERING SEA INTO THU.

.LONG TERM FORECAST...
THE RAIN AND SNOW SHOWER CHANCES WILL CONTINUE FOR MUCH OF THE AREA
THROUGH THE END OF THE WEEK. WHILE CONFIDENCE IS MODERATE TO HIGH FOR
THE END OF THE WEEK...CONFIDENCE DECREASES SIGNIFICANTLY BY THE
WEEKEND...WHEN MODEL DIFFERENCES ARE GREATEST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 172 175.
FIRE WEATHER...NONE.

RMC APR 11