Gale Warning 354, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 AM AKDT MON APR 13 2009

.ANALYSIS AND UPPER LEVELS...
THE LOW IN THE NORTHERN GULF HAS DISSIPATED THIS MORNING...ALTHOUGH
SCATTERED SHOWERS ARE STILL IMPACTING COASTAL PORTIONS OF
SOUTHCENTRAL. WEAK SURFACE RIDGING BUILDING BEHIND THIS LOW IS
CURRENTLY OVER SOUTHWEST ALASKA AND KODIAK ISLAND. A LARGE 996 MB LOW
IS LOCATED JUST NORTH OF ATKA. THIS LOW IS EXPECTED TO MOVE EAST INTO
THE GULF OF ALASKA ON TUESDAY...AND WILL BE THE MAIN WEATHER FOCUS
OVER THE NEXT SEVERAL DAYS.

IN THE UPPER LEVELS...A ROBUST CLOSED LOW IS LOCATED OVER THE
KUSKOKWIM DELTA...WITH A BROAD LONGWAVE TROUGH OVER MAINLAND ALASKA.
RIDGING IS LOCATED OVER THE BERING SEA AND EASTERN ALEUTIANS...BUT IS
BEING UNDERCUT BY ANOTHER UPPER LOW ASSOCIATED WITH THE SURFACE LOW
NEAR ATKA.

.MODEL DISCUSSION...
MODELS ARE CONTINUING TO HAVE DIFFICULTY RESOLVING THE EVOLUTION OF
THE LOW CURRENTLY NORTH OF ATKA AFTER TUESDAY. ALL SOLUTIONS DO AGREE
ON A COMPLEX LOW CENTER BECOMING NEARLY STATIONARY IN THE GULF BY
TUESDAY NIGHT...BUT THE POSITIONING OF THE INDIVIDUAL CENTERS IS THE
MAIN POINT OF CONTENTION. A NAM AND GFS BLEND WAS USED ONCE AGAIN FOR
CONSTRUCTING THE MORNING FORECAST PACKAGE THROUGH THE SHORT
TERM...WITH ONLY RELATIVELY MINOR CHANGES.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...SNOW HAS BROKEN OUT ACROSS PORTIONS OF SOUTHCENTRAL
THIS MORNING...AS THE UPPER LOW OVER SOUTHWEST AK AND AN ASSOCIATED
TROUGH SWING ACROSS THE AREA. GOOD ISENTROPIC LIFT IS EXPECTED TO
CONTINUE ACROSS THE ANCHORAGE BOWL AND VICINITY THROUGH THIS
AFTERNOON. AS A RESULT...SNOW SHOWERS WILL PERSIST TODAY AS THE UPPER
LOW PASSES TO THE NORTHWEST. ONSHORE FLOW WILL ALSO BE INCREASING
THROUGHOUT THE DAY...AS A FRONT ASSOCIATED WITH THE LOW NEAR ATKA
MOVES INTO SOUTHCENTRAL. ANTICIPATE SNOW AND RAIN TO OVERSPREAD
KODIAK THIS AFTERNOON...MOVING INTO THE REST OF THE AREA BY TONIGHT.
EXPECT HEAVIEST PRECIPITATION ASSOCIATED WITH THIS FRONT TO FALL
ALONG THE COAST...WITH UPSLOPE SNOW ALONG THE SUSITNA VALLEY...AND
LIGHTER SNOW ELSEWHERE. RAIN AND SNOW SHOWERS UNDER SOUTHERLY FLOW
WILL CONTINUE THROUGH TUESDAY AS THE LOW BECOMES NEARLY STATIONARY
SOUTH OF KODIAK ISLAND.

.SOUTHWEST...THE DEEP UPPER LOW WILL CONTINUE TO RESULT IN SNOW
ACROSS PORTIONS OF THE KUSKOKWIM VALLEY TODAY DUE TO STRONG DYNAMICS.
AS THE UPPER LOW MOVES INTO INTERIOR ALASKA...EXPECT SHOWERS TO
GRADUALLY DIMINISH THIS EVENING. THE LOW OVER THE ALEUTIANS WILL BE
SPREADING MOISTURE BACK OVER THE AKPEN AND BRISTOL BAY TODAY INTO
TONIGHT. WARM AIR ASSOCIATED WITH THIS SYSTEM WILL EVENTUALLY BRING A
RAIN AND SNOW MIX TO THESE AREAS. THE KUSKOKWIM DELTA IS EXPECTED TO
REMAIN DRY WITH THIS SYSTEM...ALTHOUGH SNOW SHOWERS WILL BE ON THE
INCREASE ALONG THE KUSKOKWIM VALLEY DUE TO FAVORABLE UPSLOPE FLOW.

.BERING SEA AND ALEUTIANS...THE LOW NEAR ATKA WILL MOVE EASTWARD INTO
THE WESTERN GULF OF ALASKA BY TUESDAY. RAIN AND SNOW ASSOCIATED WITH
THIS LOW WILL BE MOST WIDESPREAD ACROSS THE EASTERN ALEUTIANS TODAY.
COLD ADVECTION AND NORTHERLY FLOW ON THE BACK SIDE OF THE LOW WILL
CHANGE SCATTERED SHOWERS BACK OVER TO SNOW. HIGH PRESSURE WILL BE
BUILDING OVER THE WESTERN AND CENTRAL ALEUTIANS TUESDAY...HELPING TO
CLEAR OUT ANY REMAINING PRECIPITATION.

.LONG TERM FORECAST...
AS PREVIOUSLY MENTIONED...THE LOW PRESSURE CENTER IS EXPECTED TO PARK
ITSELF OVER THE CENTRAL AND SOUTHERN GULF OF ALASKA THROUGH THE END
OF THE WEEK. THIS WILL KEEP PRECIPITATION CHANCES CONFINED MAINLY TO
COASTAL LOCATIONS. HIGH PRESSURE WILL BUILD OVER THE BERING SEA AND
ALEUTIANS WITH GENERALLY FAIR WEATHER AS WE HEAD THROUGH THE END OF
THE WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE...132 165 170 172 179
         HEAVY FREEZING SPRAY...179
FIRE WEATHER...NONE

NRH APR 09