Small Craft Advisory 795, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
131 PM AKDT SUN OCT 12 2014

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL LOW OVER THE SOUTHWEST GULF OF ALASKA. AN
ASSOCIATED (STRONG) SURFACE LOW IS LOCATED OVER THE CENTRAL GULF.
AN UPPER LEVEL HIGH IS OVER THE WESTERN AND CENTRAL
BERING/ALEUTIANS...WITH ANOTHER (WEAK) HIGH OVER NORTHEAST AND
NORTH CENTRAL ALASKA.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE ONLY IN FAIR AGREEMENT...EVEN EARLY IN
THE FORECAST. THE STRONG SURFACE LOW IN THE GULF PROVIDES THE
FIRST AREA OF DISAGREEMENT. THE GFS...ECMWF...AND NAM ARE IN
FAIRLY GOOD AGREEMENT ON THE LOCATION/STRENGTH AT 00Z (12 HOURS
INTO THE FORECAST) BUT THEN THE ECMWF DEEPENS THE LOW FURTHER THAN
THE NAM AND GFS. THE CANADIAN MODELS (GEM REGIONAL AND GEM NH) ARE
FURTHER EAST AND STRONGER WITH THE LOW INITIALLY. THEY CONTINUE TO
BE FURTHER EAST WITH THE LOW INTO MONDAY (WHEN THE LOW MOVES OUT
OF OUR AREA OF CONCERN) AND CONTINUE JUST A LITTLE DEEPER THAN THE
ECMWF. THE ECMWF IS THE PREFERRED MODEL AS OT HAS BEEN PERFORMING
BETTER WITH THIS LOW THAN THE OTHER MODELS AND HAS GOOD RUN-TO-RUN
CONSISTENCY. OVER-ALL CONFIDENCE IN THE FORECAST IS NEAR TO A BIT
BELOW NORMAL.

&&

.SHORT TERM FORECAST...

FOR SOUTH CENTRAL ALASKA...THE STRONG SURFACE LOW OVER THE GULF
WILL RAPIDLY MOVE SOUTH/SOUTHWEST TONIGHT THEN SOUTH/SOUTHEAST
EARLY MONDAY...BEING WELL SOUTH OF THE GULF BY MONDAY AFTERNOON.
MOST OF THE SIGNIFICANT WEATHER WITH THIS SYSTEM WILL BE OVER THE
WESTERN GULF...THE KENAI PENINSULA (MAINLY THE SOUTHERN PORTION)
AND KODIAK ISLAND. FAIRLY SIGNIFICANT WINDS AND PRECIPITATION ARE
EXPECTED IN THESE AREAS. TO THE NORTH OF THIS THE GRADIENTS IN
PRECIPITATION AND WINDS WILL DROP OFF SHARPLY AND LITTLE OR NO
IMPACTS ARE EXPECTED...WITH THE EXCEPTION OF SOME GAP WINDS. WE
THEN ENTER A PERIOD OF WEAK FLOW ALOFT COMBINED WITH SURFACE HIGH
PRESSURE OVER LAND AND SURFACE LOW PRESSURE OVER THE GULF. THIS
WILL CREATE LOW LEVEL OFFSHORE FLOW. A FEW SHOWERS COULD LINGER
INTO EARLY TUESDAY...BUT MAINLY DRY CONDITIONS ARE EXPECTED
THROUGH WEDNESDAY.

FOR SOUTHWEST ALASKA...THE GENERAL TREND IS FOR LOW LEVEL
NORTHERLY FLOW TO SPREAD OVER THE AREA AND CONTINUE THROUGH
WEDNESDAY. SOME SHOWERS ARE POSSIBLE THROUGH THE LOWER KUSKOKWIM
VALLEY AND DELTA INTO TUESDAY WITH A WEAK TROUGH ALOFT.
ALSO...SOME SHOWERS ARE POSSIBLE ALONG THE ALEUTIAN RANGE LATER
TONIGHT AND MONDAY ASSOCIATED WITH THE GULF LOW. OTHERWISE
CONDITIONS ARE EXPECTED TO BE MAINLY DRY.

FOR THE BERING SEA/ALEUTIANS...HIGH PRESSURE OVER THE WESTERN AND
CENTRAL BERING/ALEUTIANS WILL SLOWLY DRIFT EAST INTO THE EASTERN
BERING ON TUESDAY AND REMAIN THERE THROUGH WEDNESDAY. A SOMEWHAT
WEAK FRONTAL SYSTEM/UPPER LEVEL TROUGH WILL SLIDE INTO THE WESTERN
ALEUTIANS AND BERING SEA BY LATE MONDAY...PUSHING RAPIDLY
EASTWARD INTO THE CENTRAL ALEUTAINS/BERING EARLY TUESDAY...THEN
SLOWING AS IT REACHES THE EASTERN ALEUTIANS TUESDAY NIGHT THEN
BREAKS APART ON WEDNESDAY. A STRONGER SYSTEM (CONTAINING THE
EXTRA-TROPICAL REMNANTS OF FORMER TYPHOON VONGFONG) WILL THEN
MOVE INTO THE WESTERN ALEUTIANS ON WEDNESDAY.

&&

.LONG TERM FORECAST...
A LONGWAVE TROUGH EXTENDING FROM THE KAMCHATKA PENINSULA TO
PACIFIC COAST OF THE CONTINENTAL UNITED STATES WILL CONTINUE TO
AMPLIFY THROUGH THE FORECAST PERIOD AS THE EXTRATROPICAL REMNANTS
OF TYPHOON VONGFONG GET ABSORBED INTO THE UPPER LEVEL FLOW. IN
RESPONSE TO THE AMPLIFIED TROUGHING...LONGWAVE RIDGING WILL BUILD
OVER THE WESTERN BERING SEA ON THE WESTERN EDGE OF THE UPPER LEVEL
TROUGH. THE POST-TROPICAL REMAINS OF VONGFONG WILL PUSH ACROSS
ATTU AND THE WESTERN ALEUTIANS LATE WEDNESDAY NIGHT AND THEN BEGIN
AN EASTWARD PATH THAT TRACKS IT ACROSS THE CENTRAL AND WESTERN
ALEUTIANS ON THURSDAY BEFORE FINALLY DIVING SOUTH INTO THE NORTH
PACIFIC EARLY FRIDAY MORNING. THIS WILL BRING A PERIOD OF MODERATE
TO HEAVY RAINFALL ALONG THE ALEUTIANS ISLANDS DURING THIS TIME
FRAME...AS WELL AS GALE FORCE WINDS ACROSS THE COASTAL WATERS AND
SOUTHERN BERING SEA. HIGH PRESSURE WILL BEGIN TO BUILD ACROSS THE
FAR WESTERN BERING SEA ON FRIDAY AND GRADUALLY SHIFT TOWARD THE
SOUTHEAST INTO THE NORTH PACIFIC BY LATE SATURDAY AS AN AREA OF
LOW PRESSURE PUSHES OFF THE KAMCHATKA PENINSULA AND INTO THE
BERING SEA.

FOR SOUTHWEST AND SOUTHCENTRAL ALASKA...IT APPEARS THAT THE
MAJORITY OF THE EXTENDED PERIOD SHOULD BE MOSTLY DRY AS THE
AMPLIFYING UPPER LEVEL TROUGH SHUNTS ALL SHORTWAVE ENERGY AND
SIGNIFICANT UPPER LEVEL SYSTEMS TOWARD THE ALASKA PANHANDLE. THE
ONE EXCEPTION WILL NORTHERN GULF COAST THAT WILL BE UNDER BROAD
CYCLONIC FLOW WHICH WILL CREATE SCATTERED TO NUMEROUS SHOWERS
THROUGH FRIDAY MORNING. BY MIDDAY ON FRIDAY...A WEAK LOW OFF THE
ALASKA PANHANDLE WILL MERGE WITH A NORTH PACIFIC LOW. MOST OF THE
ENERGY WILL BE SHUNTED INTO THE PANHANDLE...BUT BY FRIDAY
EVENING...THE REMAINS OF THE LOW WILL PUSH INTO THE NORTHERN GULF
AND BRING STRATIFORM RAINFALL TO THE GULF COAST. AT THE SAME
TIME...THE REMNANTS OF VONGFONG WILL BEGIN PHASING WITH THE LOW IN
THE NORTHERN GULF. ONCE AGAIN...MOST OF THE ENERGY WILL BE SHUNTED
INTO THE PANHANDLE...BUT RAIN CHANCES WILL PERSIST ALONG THE GULF
COAST ONCE AGAIN DUE IN LARGE PART TO BROAD CYCLONIC FLOW.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 150.
     GALE WARNING 120 130 131 132 136 137 138 155 160 165 170 172
             176 177 180.
FIRE WEATHER...NONE.

&&

LUDWIG/MCLAY OCT 14