Gale Warning 824, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
240 PM AKST MON NOV 2 2009

.ANALYSIS AND UPPER LEVELS...
AN UPPER TROF PERSISTS OVER THE EASTERN HALF OF THE STATE ALONG THE
ALCAN BORDER. THE HIGH AMPLITUDE UPPER LEVEL RIDGE THAT HAS BEEN IN
PLACE OVER THE WESTERN INTERIOR IS BEING UNDERCUT BY A DEEPENING TROF
OVER THE CENTRAL BERING SEA. THE RESULT IS A LARGE COL OVER THE LOWER
YUKON VALLEY. A 210 KT JET IS FLOWING OUT OF THE NORTHWEST PACIFIC
AND ACROSS THE ALEUTIANS AND SOUTHERN BERING SEA. THIS JET WILL BE
THE CATALYST FOR A VERY BUSY WEEK WEATHER WISE.

AT THE SURFACE...AN AREA OF LOW PRESSURE IS SLOWLY WEAKENING EAST
OF MIDDLETON ISLAND...SPREADING SHOWERS MAINLY OVER THE COASTAL
WATERS. CLEAR SKIES CAN BE FOUND OVER THE INTERIOR...WITH THE
EXCEPTION OF SOME STRATUS AND FOG ALONG THE ALASKA RANGE AND THE
LOWER KUSKOKWIM VALLEY. THERE IS A WEAK AREA OF LOW PRESSURE OVER THE
EASTERN BERING SEA THAT THE MODELS DID NOT RESOLVE WELL. A 975 MB LOW
IN THE CENTRAL BERING SEA AND ITS ASSOCIATED FRONTAL BOUNDARY HAVE
REACHED THEIR MAXIMUM INTENSITY.

.MODEL DISCUSSION...MANY CHALLENGES IN THIS AFTERNOONS FORECAST
PACKAGE...AND IT BEGINS WITH THE MODELS NOT INITIALIZING WELL ON THE
UPPER LEVEL FEATURES OVER THE CENTRAL AND WESTERN BERING SEA. THE
MODELS DIVERGE IN THE FIRST 24 HOURS AS THE WEAKENING FRONT IN THE
CENTRAL BERING BECOMES AN ELONGATED TROF OVER BRISTOL BAY. THE MORE
SIGNIFICANT DIFFERENCES ARISE BETWEEN 48 AND 84 HOURS WHEN A STRONG
LOW DEVELOPS IN THE SOUTHERN GULF. THE DEVELOPING LOW DEEPENS RAPIDLY
TO 954 MB WEDNESDAY AFTERNOON AS ANOTHER NORTH PACIFIC LOW ROTATES
AROUND ITS PERIPHERY AND BECOMES ABSORBED LATER ON THURSDAY INTO ONE
LARGE CONCENTRIC LOW...WITH CENTRAL PRESSURE ABOUT 945 MB. THE GFS IS
THE OUTLIER WITH THIS SOLUTION...INSTEAD DEVELOPING ONE LARGE
CONCENTRIC LOW AT 60 HOURS WITH CENTRAL PRESSURE AT 939 MB...NOT
IMPOSSIBLE BUT NOT LIKELY. THE INHERITED FORECAST WAS STILL
ADVERTISING A DEEP LOW JUST SOUTHEAST OF KODIAK ISLAND INSTEAD OF THE
DOUBLE BARRELED LOW AT THAT TIME. GIVEN THE POOR
INITIALIZATION...CONFIDENCE REMAINS LOW IN THE EXACT TIMING AND
POSITION OF THE LOW ALTHOUGH FEEL LIKE WE ARE GETTING A BETTER HANDLE
ON IT.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...IN THE FIRST 24 HOURS...ANTICIPATE SOUTHWESTERLY FLOW
ALOFT TO INCREASE AS A RESULT OF THE UPPER TROUGH OVER THE EASTERN
INTERIOR SAGGING TOWARD THE ALASKA RANGE THIS EVENING. THE ISENTROPIC
ANALYSIS DEPICTS WARM AIR OVERRUNNING THE COOLER AIR AT THE SURFACE
BEGINNING TONIGHT. IT WILL TAKE SOME TIME TO SATURATE THE COLUMN AS
THE ATMOSPHERE IS INITIALLY VERY DRY...BUT BELIEVE CLOUDS WILL
DEVELOP QUICKER OVERNIGHT THAN THE MODELS ARE DEPICTING. THE
OVERRUNNING MOISTURE WILL CONTINUE THROUGH TUESDAY...RESULTING IN
LIGHT SNOW DEVELOPING ACROSS PRINCE WILLIAM SOUND AND POSSIBLY
SPREADING INLAND OVER THE COPPER RIVER BASIN. THE INITIAL FRONT WILL
BRING STRONG GALE FORCE WINDS TO THE COASTAL ZONES...WITH 75 MPH
POSSIBLE THROUGH PORTAGE VALLEY AND EASTERN TURNAGAIN ARM TUESDAY
NIGHT. THE DOWN-INLET GRADIENT WILL PREVENT THE STRONGEST WINDS FROM
REACHING WESTERN TURNAGAIN ARM AND THE ANCHORAGE HILLSIDE. WINDS AT
ALL LEVELS WILL BECOMING SOUTHEASTERLY BY TUESDAY NIGHT RESULTING IN
A RAIN SHADOW DEVELOPING ON THE LEE SIDE OF THE MOUNTAINS.
STILL...THIS LOW IS DYNAMIC ENOUGH THAT LIGHT RAIN AND SNOW COULD
SPILL OVER THE RANGE AND FALL IN THE ANCHORAGE BOWL AND THE MATSU
VALLEY.

.SOUTHWEST INTERIOR AND BERING SEA/ALEUTIANS...THE 200+ KT JET
FLOWING PARALLEL TO THE ALEUTIAN CHAIN WILL BRING VERY ACTIVE WEATHER
TO THE REGION. SOUTHEASTERLY GAP WINDS WILL INCREASE...EVENTUALLY
TURNING NORTHEAST AND FINALLY NORTHWEST AS LOW PRESSURE MOVES SOUTH
OF THE ALASKA PENINSULA AND INTO THE GULF. PLACES LIKE DILLINGHAM
COULD SEE A PERIOD OF FREEZING RAIN AS WARM AIR ALOFT WILL BE SLOW TO
ERODE THE COLD ARCTIC AIR AT THE SURFACE. STRONG LOW LEVEL WIND SHEAR
IS AN INDICATION THAT COLD AIR WILL CONTINUE TO DRAIN FROM THE NORTH
WHILE STRONG SOUTHEASTERLY WINDS AT 2000 FT PUMP IN WARMER AIR JUST
ABOVE THE SURFACE. COLD AIR WILL ADVECT SOUTH BACK ACROSS THE REGION
WEDNESDAY NIGHT RESULTING IN NUMEROUS SNOW SHOWERS...SIGNIFICANT
ACCUMULATION AT THIS POINT WILL BE LIMITED TO THE UPSLOPE MOUNTAIN
RANGES. A BROAD TROF WITH AXIS JUST EAST OF THE SOUTHWEST INTERIOR
WILL STALL OVER THE REGION...RESULTING IN BLUSTERY BUT RELATIVELY
NORMAL FOR THIS TIME OF YEAR.

BUOY 35 WEST OF THE PRIBILOF ISLANDS IS ALREADY REPORTING WINDS THAT
ARE EXCEEDING THE STRONGEST MODEL WINDS AT THIS POINT...ANOTHER
INDICATOR THAT THE INITIALIZATION OF THE WESTERN FEATURES IS POOR.
WINDS WILL INCREASE ON THE COLD ADVECTION SIDE OF THE LOW IN THE
CENTRAL BERING SEA TONIGHT...REACHING STORM FORCE WINDS. THESE WINDS
WILL SKIRT SOUTH OF THE PRIBILOFS AND IMPACT THE EASTERN ALEUTIANS
OVERNIGHT...BRINGING STORM FORCE GUSTS TO UNALASKA AND DUTCH HARBOR
LATE TONIGHT AND TUESDAY MORNING.

STRONG NORTHWESTERLY FLOW WILL PERSIST THROUGH THE REMAINDER OF THE
WEEK ACROSS THE BERING SEA...WITH WIDESPREAD GALES AND STORM FORCE
GUSTS LIKELY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WATCH 125
MARINE...STORM 172 175 176 411 412 413 414
         GALES 120 125 130 132 138 140 141 155 160 165 180 170 171
               172 179 185 414.
FIRE WEATHER...NONE.

AB NOV 09