High Wind Warning 52, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1245 PM AKST TUE DEC 13 2011

.ANALYSIS AND UPPER LEVELS...A HURRICANE FORCE LOW JUST NORTH OF
THE CENTRAL ALEUTIANS IS THE DOMINANT FEATURE ON SATELLITE THIS
MORNING. THE LOW HAS BOTTOMED OUT AND IS BEGINNING TO VERY SLOWLY
WEAKEN AS IT TRACKS OFF TO THE NORTHWEST. A HIGH AMPLITUDE RIDGE
IS LOCATED DOWNSTREAM OF THIS SYSTEM OVER SOUTHWEST ALASKA AND THIS
IS HELPING TO SLOW THE PROGRESSION OF THE OCCLUDED FRONT. THE FRONT
IS ALSO ELONGATING AND WEAKENING ALONG THE WEST SIDE OF THIS RIDGE.
HEADING FURTHER DOWNSTREAM A WEAK UPPER TROUGH IS MOVING THROUGH
SOUTHCENTRAL ALASKA PRODUCING SOME SNOW SHOWERS FROM EASTERN PRINCE
WILLIAM SOUND TO THE COPPER RIVER BASIN. PATCHY STRATUS AND FOG
HAVE DEVELOPED IN THE WAKE OF THIS TROUGH.

THE NEXT MAJOR STORM TO AFFECT THE ALASKA REGION IS TAKING SHAPE
OVER THE NORTH CENTRAL PACIFIC IN THE LEFT EXIT REGION OF A 180 KT
JET.

.MODEL DISCUSSION...THERE CONTINUES TO BE MODEL DIFFERENCES WITH
TRIPLE POINT DEVELOPMENT SOUTH OF KODIAK ISLAND THIS AFTERNOON. THE
ECMWF IS AN OUTLIER WITH A STRONGER FURTHER SOUTH LOW WHILE THE NAM
IS THE WEAKEST SOLUTION. WILL GO RIGHT DOWN THE MIDDLE CLOSE TO THE
GFS/EKMET/GEM SOLUTIONS. DIFFERENCES REMAIN EARLY ON WITH DEVELOPMENT
OVER THE NORTH PACIFIC. THE GFS/UKMET CONTINUE TO DEPICT A SINGLE
LOW SOLUTION WHILE THE OTHER MODELS DEVELOP A SECONDARY LOW AT THE
BASE OF THE UPPER TROUGH WHICH RAPIDLY DEEPENS AND BECOMES THE MAIN
LOW CENTER. IN CASES OF STRONG UPPER LEVEL SUPPORT LIKE THIS IT IS
COMMON TO SEE SECONDARY LOW DEVELOPMENT SO BELIEVE THAT IS THE MOST
LIKELY SCENARIO. EVEN WITH THIS MODEL DIFFERENCE EARLY ON ALL MODELS
COMMON INTO GOOD AGREEMENT ON LOW POSITION AND STRENGTH BY 42
HOURS...SO CONFIDENCE IS ABOVE AVERAGE WITH THIS SYSTEM.

.SHORT TERM FORECAST...

TRIPLE POINT LOW WILL DEVELOP SOUTH OF KODIAK ISLAND THIS AFTERNOON
WHICH WILL HASTEN THE DEMISE OF THE FRONT OVER THE EASTERN BERING
SEA AS FLOW OVER SOUTHWEST ALASKA BACKS TOWARD THE NORTH. AN UPPER
LEVEL SHORT-WAVE TROUGH WILL QUICKLY LIFT NORTHEASTWARD ACROSS THE
GULF WEDNESDAY TAKING THE LOW WITH IT. KODIAK ISLAND AND THE
GULF COAST WILL SEE MOST OF THE PRECIP AND WINDS WITH THIS WEAK
SYSTEM. THE OCCLUDED FRONT WILL REMAIN OVER THE GULF WHICH MEANS
PRECIP-TYPE WILL REMAIN ALL SNOW WITH THE EXCEPTION OF THE SOUTH TO
EAST SIDE OF KODIAK ISLAND WHICH MAY WARM JUST ENOUGH TO MIX WITH
RAIN BRIEFLY.

MEANWHILE THE LOW CURRENTLY OVER THE SOUTHERN BERING WILL EXIT TO
THE WESTERN BERING WHILE THE NEW LOW OR LOWS APPROACH THE EASTERN
ALEUTIANS AND SOUTHERN ALASKA PENINSULA TONIGHT INTO WEDNESDAY.
THERE IS STILL SOME UNCERTAINTY IN WHETHER THERE WILL BE ONE LOW
OR TWO AND THE EXACT TRACK OF THE SYSTEM. BOTTOM LINE THOUGH...
EXPECT THE END RESULT TO BE A VERY STRONG LOW BOTTOMING OUT IN
THE 940S. WILL ISSUE HIGH WIND WATCHES FOR THE EASTERN ALEUTIANS
AND SOUTHERN ALASKA PENINSULA WITH STORM TO HURRICANE FORCE WINDS
EXPECTED ALONG THE FRONTAL BOUNDARY. THE FRONT WILL BE MOVING AT
A PRETTY GOOD CLIP SO THE STRONGEST WINDS SHOULD NOT LAST FOR MORE
THAN ABOUT 6 HOURS OR SO. THE FRONT WILL HAVE OCCLUDED BY THE TIME
IT REACHES SOUTHWEST ALASKA WEDNESDAY NIGHT SO EXPECT PRECIP TO
BE MAINLY IN THE FORM OF SNOW WHICH WHEN COMBINED WITH THE WINDS
CREATES POTENTIAL FOR BLIZZARD CONDITIONS. WILL WAIT ONE MORE
MODEL CYCLE AND IF THINGS DON'T CHANGE APPRECIABLY WILL LIKELY
ISSUE BLIZZARD WATCHES FOR PORTIONS OF BRISTOL BAY AND THE KUSKOKWIM
DELTA. WITH A SOUTHERLY JET ALOFT THE FRONT WILL MOVE FAIRLY QUICKLY
ACROSS THE SOUTHERN MAINLAND WEDNESDAY NIGHT AND THURSDAY. AT THIS
POINT IN TIME IT DOESN'T LOOK LIKE ANY ADVISORIES OR WARNING WILL
BE NEEDED FOR SOUTHCENTRAL ALASKA...BUT THERE IS STILL LOTS OF TIME
TO WORK OUT THE DETAILS.

.LONG TERM FORECAST...MODELS ARE FAIRLY CONSISTENT IN DEPICTION OF
A LONG-WAVE TROUGH OVER THE BERING AND A RIDGE ALONG SOUTHEAST ALASKA
UP TO NEAR THE ALASKA/CANADA BORDER. A PERSISTENT STRONG UPPER JET
ACROSS THE NORTH PACIFIC AND UP THE WEST SIDE OF THIS RIDGE TOWARD
MAINLAND ALASKA WILL MAINTAIN AN ACTIVE AND FAST MOVING PATTERN.
MODELS DIFFER ON THE MOVEMENT OF INDIVIDUAL SYSTEMS WHICH CAN BE
EXPECTED IN THIS SET-UP.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...HURRICANE FORCE WIND WARNING...155.
         STORM WARNING...150 160 165 170 172 175 176 179 185.
         GALE WARNING...120 130 132 138 171.
         HEAVY FREEZING SPRAY WARNING...180 185.
FIRE WEATHER...NONE.

SEB DEC 11