Gale Warning 812, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKST TUE NOV 24 2009

.ANALYSIS/UPPER LEVELS...
LONG WAVE TROUGH REMAINS ENTRENCHED OVER ALL OF ALASKA...KEEPING THE
REGION IN A VERY ACTIVE PATTERN. THERE ARE THREE AREAS OF LOW
PRESSURE...THE MOST IMPRESSIVE HAS MATURED OVER THE NORTH PACIFIC
ALONG THE 150W MERIDIAN AND IS MOVING NORTH TOWARD THE GULF. A SECOND
AREA OF LOW PRESSURE IS MUCH SMALLER...LOCATED JUST WEST OF THE
PRIBILOF ISLANDS. AN ELONGATED AND QUITE POTENT SHORTWAVE IS
ASSOCIATED WITH THIS LOW WHICH WILL BE A CRITICAL COMPONENT TO THE
SOUTHCENTRAL FORECAST TOMORROW. THE LAST LOW OUT WEST IS A VERTICALLY
STACKED LOW THAT IS STRENGTHENING OVER THE WESTERN BERING SEA.

.MODEL DISCUSSION...NO MAJOR CHANGES TO THE SHORT TERM FORECAST.
MODELS HAVE COME INTO AGREEMENT AND REMAIN CONSISTENT WITH THE
OCCLUDED LOW MOVING TOWARD THE GULF. THE INCREASED CONFIDENCE IS
GOING TO RESULT IN AN INCREASED CHANCE OF SNOW FOR ANCHORAGE AND THE
MATANUSKA VALLEY WEDNESDAY AFTERNOON. DIFFERENCES ARISE IN THE MID
TERM REGARDING THE EVOLUTION OF THE LOW DEVELOPING OUT WEST. AS THE
LOW OCCLUDES...THE MAIN ENERGY IS EXPECTED TO MOVE EAST TOWARD THE
ALASKA PENINSULA IN RESPONSE TO A NORTH PACIFIC SHORTWAVE BEING
EJECTED FROM THE JET AND WRAPPING AROUND THE BROAD CYCLONIC
CIRCULATION. THIS IS A MAJOR DEPARTURE FROM 24 HOURS AGO WHEN ALL THE
MODELS...EXCEPT THE ECMWF...PLACED A 966 MB LOW AT 00Z FRIDAY NEAR
BETHEL. NOW WE ARE LEANING TOWARD THE LATEST ECMWF SOLUTION WHICH HAS
A DOUBLE HEADED LOW...THE WEAKER LOW OVER BRISTOL BAY AND THE SECOND
STRONGER ONE DEVELOPING SOUTH OF KODIAK AND MOVING INTO THE
NORTHWESTERN GULF THURSDAY NIGHT. SO FEW CHANGES WERE MADE TO THE
SHORT TERM AND THE MID TERM LEANED HEAVILY TOWARD THE 12Z ECMWF.

.SHORT TERM FORECAST...
SOUTHCENTRAL...SHOWER ACTIVITY IS PERSISTING THROUGH EARLY THIS
AFTERNOON MAINLY ALONG THE GULF COAST WHILE ONLY A FEW SHOWERS MAKE
IT INLAND. THIS ACTIVITY WILL CONTINUE TO DIMINISH IN COVERAGE
OVERNIGHT AS THE AREA OF LOW PRESSURE MOVES INTO THE GULF AND WINDS
BECOMING MORE NORTHEASTERLY. THE OLD OCCLUSION FROM THE DISSIPATING
LOW WILL MOVE INTO THE NORTHERN GULF TONIGHT...SPREADING SNOW FROM
KODIAK ISLAND TO THE EASTERN PRINCE WILLIAM SOUND. A DEFORMATION ZONE
WILL ESTABLISH ITSELF OVER THE SOUTHERN KENAI PENINSULA...WHICH WILL
RESULT IN ACCUMULATING SNOW FROM HOMER TO ANCHORAGE AND THE SOUTHERN
SUSITNA VALLEY BY AFTERNOON. THE AFOREMENTIONED POTENT WAVE MOVING
ACROSS THE ALASKA PENINSULA WILL PUSH THROUGH THE REGION WEDNESDAY
EVENING...BRIEFLY BRINGING AN END TO THE SNOW BEFORE THE NEXT SYSTEM
APPROACHES THURSDAY MORNING.

AT THIS TIME...SNOWFALL TOTALS WILL RANGE FROM 1 TO 4 INCHES IN THE
AREAS MENTIONED WITH MORE EXPECTED IN THE POPULAR WINTER RECREATIONAL
HOT SPOTS OF TURNAGAIN PASS AND GIRDWOOD. LIMITING FACTORS OF THIS
STORM WILL BE THE WEAK COLD AIR ADVECTION AND ITS SPEED...OTHERWISE
MORE SIGNIFICANT SNOW WOULD BE ANTICIPATED. THE LOW WILL MOVE INLAND
WEDNESDAY EVENING...NOT BEFORE BRINGING SIGNIFICANT SNOW TO VALDEZ.

SOUTHWEST...RELATIVELY BENIGN WEATHER CONTINUES ACROSS SOUTHWEST
ALASKA. ONSHORE FLOW IS BRINGING SCATTERED SNOW SHOWERS AND AREAS OF
FOG TO THE REGION. A DEFORMATION ZONE WILL EXTEND ACROSS THE ALASKA
PENINSULA TONIGHT...RESULTING IN LIGHT SNOW ALONG THE ALASKA RANGE
FROM ILIAMNA NORTHWARD. SNOW ENTERS THE PICTURE AREA WIDE AGAIN ON
THURSDAY AFTERNOON AS THE DOUBLE HEADED LOW MOVES INTO BRISTOL BAY
AND ACROSS THE ALASKA PENINSULA.

ALEUTIANS/BERING SEA...POTENT SURFACE LOW IS APPROACHING THE
PRIBILOFS EARLY THIS AFTERNOON. GUSTY NORTHWEST WINDS ARE EXPECTED ON
THE BACKSIDE OF THIS LOW AS BUOY 35 AND 70 REPORTED GALE FORCE GUSTS
AFTER FROPA. BEHIND THIS LOW...EYES TURN WEST TOWARD THE DEVELOPING
LOW AND ITS ASSOCIATED FRONTAL BOUNDARY NEAR SHEMYA. GALE FORCE WINDS
ARE EXPECTED WITH THIS SYSTEM WITH STORM FORCE GUSTS LIKELY ALONG AND
BEHIND THE BOUNDARY. NOT FEELING CONFIDENT ENOUGH AT THIS POINT TO
ISSUE ANY WATCHES OR WARNINGS WITH THIS SYSTEM ALTHOUGH IT WILL BRING
STRONG WINDS TO ENTIRE ALEUTIAN CHAIN THROUGH THURSDAY. THE POTENTIAL
FOR SHORT LIVED BLIZZARD CONDITIONS EXISTS AS THE FRONT PASSES
THROUGH...ESPECIALLY THE PRIBILOFS WHERE TEMPERATURES WILL REMAIN
BELOW FREEZING AND WINDS WILL REACH 40 TO 45 MPH. THE LIMITING FACTOR
FOR THE SPEED OF THE SYSTEM...AT THIS TIME WE ARE ONLY ANTICIPATING A
SHORT PERIOD OF VISIBILITY BELOW ONE MILE SO WILL WORD THE FORECAST
TOWARD THAT WITHOUT ISSUING A WATCH OR WARNING. IF THE SPEED CHANGES
WITH SUBSEQUENT RUNS...THE EVENING OR NIGHT SHIFT MAY NEED TO ISSUE
THE WATCH/WARNING BASED ON THE NEW MODEL DATA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM 172 175 176
         GALES 120 130 132 150 155 179 180 185
         HEAVY FREEZING SPRAY 180
FIRE WEATHER...NONE

AB NOV 09