High Wind in Alaska, December 31, 2012

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1215 PM AKST MON DEC 31 2012

.ANALYSIS AND UPPER LEVELS...
A LONGWAVE TROUGH REMAINS CENTERED OVER THE EASTERN BERING SEA WITH
FAIRLY WEAK HIGH PRESSURE RIDGES OVER THE EASTERN GULF AND WESTERN
BERING. THE THIRD MAJOR LOW IN FOUR DAYS IS INTENSIFYING RAPIDLY OVER
THE NORTH PACIFIC AND HEADED DUE NORTH TOWARD THE ALASKA PENINSULA.
THIS LOW IS BEING FUELED BY A 140 KT DUE SOUTHERLY JET BRINGING WARM
AIR NORTHWARD FROM THE TROPICS. PRESSURE GRADIENTS ACROSS SOUTHERN
ALASKA HAVE BEGUN TO COME UNDER THE INFLUENCE OF THIS APPROACHING
LOW...AND HAVE THUS RECENTLY SWITCHED TO NORTHERLY ACROSS COOK INLET
FROM KENAI TO ANCHORAGE AND THE MAT-SU VALLEY. GAP WINDS...ESPECIALLY
THROUGH TURNAGAIN ARM...ARE BEGINNING TO INCREASE AS WELL. OUT
WEST...NORTHWESTERLY FLOW PREVAILS ACROSS MUCH OF THE BERING AS THE
REGION IS CAUGHT BETWEEN HIGH PRESSURE TO THE WEST AND LOWER
PRESSURES TO THE EAST.

.MODEL DISCUSSION...
THE MODELS ARE IN FAIRLY GOOD AGREEMENT ON THE POSITIONS/TIMING OF
THE APPROACHING LOW CENTER. THE MOST GLARING DISCREPANCY IS WITH THE
NAM MODEL THAT IS NEARLY 10 MB WEAKER THAN ALL OTHER MODEL SOLUTIONS
WITH THE STRENGTH OF THE LOW. MEANWHILE...THE ECMWF IS A TAD SLOWER
THAN THE MODEL CONSENSUS WITH THE NORTHWARD PROGRESSION OF THE
LOW...AND HAS BEEN PLAYING CATCH-UP FOR SEVERAL RUNS. ALL OF THIS
LEADS TO A PREFERENCE TOWARD THE GFS SOLUTION FOR UPDATES TO THE 0-48
HOUR FORECAST THIS AFTERNOON. BEYOND 48 HOURS...A COMPLEX LOW
REDEVELOPS ACROSS THE EASTERN ALEUTIANS/AKPEN...WITH THE GFS
SPREADING THE ENERGY BETWEEN TWO MAIN LOWS...WHILE THE ECMWF AND
OTHER GLOBAL MODELS FOCUS MORE OF THE ENERGY ON A SINGLE LOW SOUTH OF
THE ALASKA PENINSULA ON WEDNESDAY. WITH THE JET STAYING FAR TO THE
SOUTH...IT SEEMS MOST LIKELY THE FURTHER SOUTH AND EAST LOWS WILL
HAVE THE BEST CHANCE TO STRENGTHEN. THUS THERE IS A PREFERENCE TOWARD
THE ECMWF SOLUTION BEYOND 48 HOURS.

.SHORT TERM FORECAST...
SOUTHCENTRAL...HIGH WIND WATCHES ARE ONCE AGAIN IN EFFECT FOR THE
ENTIRE LENGTH OF TURNAGAIN ARM...PORTAGE VALLEY...AND THE UPPER
HILLSIDE OF ANCHORAGE. THIS STORM WILL FOLLOW A SIMILAR TRACK TO THE
STORM YESTERDAY. HOWEVER...THIS LOW WILL REACH PEAK INTENSITY JUST
SOUTH OF KODIAK ISLAND THIS EVENING...SIGNIFICANTLY FURTHER NORTH
THAN THE PREVIOUS STORM. THIS MEANS THE STRONGEST WINDS ASSOCIATED
WITH THE FRONT WILL LIKELY STILL BE LOCATED IN THE LOWER LEVELS OF
THE ATMOSPHERE...UNLIKE THE STORM YESTERDAY WHERE THE STORM WAS
WEAKENING AND STRONGEST WINDS WERE MOVING ALOFT BY THE TIME THE STORM
CAME THROUGH SOUTHCENTRAL. AS SUCH...THE WATCHES WILL BE UPGRADED TO
WARNINGS WITH THE AFTERNOON FORECAST PACKAGE...WITH THE STRONGEST
WINDS EXPECTED TO DEVELOP BY LATE THIS EVENING. ANOTHER DIFFERENCE
WITH THIS STORM WILL BE THAT THE ATMOSPHERE WILL BE A BIT COOLER THAN
THE PREVIOUS STORMS. WHILE RAIN WILL STILL FALL AT LOWER
ELEVATIONS...HIGHER ELEVATIONS IN THE MOUNTAINS...INCLUDING TURNAGAIN
PASS...WILL LIKELY SEE HEAVY WET SNOW DEVELOP AS THE FRONT APPROACHES
TONIGHT.

SOUTHWEST...AS WITH THE LAST STORM...EXPECT WIDESPREAD PRECIP TO MOVE
THROUGH THE REGION ASSOCIATED THE FRONTAL PASSAGE FOLLOWED BY SHOWERY
PRECIP AND SOUTHERLY WINDS ONCE THE FRONT AND LOW MOVE PAST. AS
MENTIONED ABOVE...THE ATMOSPHERE SHOULD BE A FEW DEGREES COOLER WITH
THIS STORM THAN THE LAST...SO THINK ANY AREAS OF FREEZING
RAIN/DRIZZLE AROUND THE KUSKOKWIM DELTA WILL BE ISOLATED AND
RELATIVELY SHORT-LIVED. OVER BRISTOL BAY...VERY STRONG WINDS WILL
ONCE AGAIN DEVELOP THROUGH CHANNELED AREAS OF THE NORTHERN ALEUTIAN
RANGE...PRIMARILY AROUND LAKE ILIAMNA. WINDS IN THE AFTERNOON
FORECAST WILL BE TRENDED SLIGHTLY UPWARD BUT SHOULD REMAIN BELOW
WARNING-LEVEL.

BERING AND AND ALEUTIANS...GALE-FORCE FRONT MOVING SLOWLY ACROSS THE
WESTERN ALEUTIANS WILL DEVELOP INTO A LOW PRESSURE SYSTEM WEST OF
ADAK BY TUE MORNING. THIS LOW WILL THEN DROP INTO THE BASE OF A VERY
LARGE BUT FAIRLY WEAK CYCLONIC CIRCULATION OVER THE EASTERN BERING BY
TUE EVENING. OVERALL...UNSETTLED WEATHER WILL CONTINUE ACROSS THE
BERING SEA REGION FOR THE NEXT SEVERAL DAYS...THOUGH INDIVIDUAL LOWS
THAT WILL AFFECT THE AREA WILL REMAIN RELATIVELY WEAK AND
SHORT-LIVED.

.LONG TERM FORECAST...
BY THE END OF THE WEEK THE LONG RANGE MODELS ARE SUGGESTING THE
LONGWAVE TROUGH WILL PULL SLIGHTLY WESTWARD INTO THE WESTERN TO
CENTRAL BERING SEA. THIS WILL SHIFT MEAN FLOW ACROSS MAINLAND ALASKA
FROM SOUTHERLY TO SOUTHWESTERLY. WHILE THIS SHOULD BRING AN END TO
THE RAPID-FIRE WINDSTORMS ACROSS SOUTHCENTRAL...IT WILL LEAVE THE
MAINLAND IN A FAIRLY MILD PATTERN. WHILE TEMPERATURES WILL GRADUALLY
SINK BACK CLOSER TO NORMAL...NO SIGNIFICANT COOL DOWNS ARE ON THE
HORIZON.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 101 125
MARINE...STORM 120 130 132 138 150
         GALE 125 128 129 140 141 155 160 175 176
         HEAVY FREEZING SPRAY 179 185
FIRE WEATHER...NONE

AMD DEC 12