Gale Warning 213, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...BLOCKING RIDGE OVER MAINLAND ALASKA
IS SLOWLY BEING PUSHED EASTWARD AS STRONG SYSTEMS RIDE UP ITS
WESTERN SIDE. THE RIDGE AXIS CURRENTLY EXTENDS FROM THE NORTH
CENTRAL PACIFIC NORTHEAST TO THE ALASKA/CANADIAN BORDER. THIS IS
PROVIDING ANOTHER CLEAR AND CALM DAY OVER SOUTHCENTRAL ALASKA.
A SHORT-WAVE OVER SOUTHWEST ALASKA IS PRODUCING A FAIRLY NARROW
BAND OF SNOW FROM THE SOUTHERN KUSKOKWIM SOUTHEAST TO BRISTOL BAY.
THE MAJOR STORY OF THE DAY IS A HURRICANE FORCE SURFACE LOW ALONG
THE WESTERN ALEUTIANS. THE SHORT-WAVE TROUGH ALOFT IS NOT TERRIBLY
IMPRESSIVE...AND THE SURFACE PRESSURE IS ONLY DOWN INTO THE 980S.
HOWEVER...ARCTIC AIR IS FEEDING INTO THE BACK SIDE OF THE
SYSTEM...THE LOW IS IN AN IDEAL POSITION FOR STRENGTHENING BETWEEN
TWO UPPER JET STREAKS...AND THERE IS A VERY TIGHT PRESSURE GRADIENT
BETWEEN THE LOW AND A 1040 MB SURFACE HIGH OVER THE NORTH PACIFIC.
THIS IS PRODUCING A FAIRLY SMALL AREA OF STORM TO HURRICANE FORCE
WINDS NEAR THE LOW CENTER. AN 18Z QUIKSCAT WIND IMAGE VERIFIES THE
PRESENCE OF STORM FORCE WINDS ON THE BACK SIDE OF THE SYSTEM. THIS
STORM IS EXPECTED TO BRING WIDESPREAD WARNING CONDITIONS AS IT
TRACKS ACROSS THE BERING TO SOUTHWEST ALASKA. THE PROBLEM OF THE
DAY IS IDENTIFYING THESE WARNING TIMES AND LOCATIONS.

.MODEL DISCUSSION...THE GFS IS STRONGEST WITH THE ALEUTIAN LOW...BUT
IS HAS BEEN CONSISTENTLY SO. WEAKEST SOLUTION IS THE ECMWF WHICH IS
UP TO 10 MB WEAKER AS THE LOW TRACKS NORTH OF THE PRIBILOFS. WITH
SPARSITY OF OBSERVATIONS OVER THE WESTERN ALEUTIANS IT IS VERY
DIFFICULT TO VERIFY THE CURRENT CENTRAL PRESSURE. BUT SATELLITE
IMAGERY SHOWS THE LOW REALLY BEGINNING TO WIND UP. THERE ARE ENOUGH
SUPPORTIVE FACTORS OF DEEPENING IN PLACE TO GO CLOSER TO THE GFS
SOLUTION. THE ECMWF IS ALSO THE OUTLIER WITH REGARD TO TRACK TO THE
SOUTHWEST COAST...SO WILL GO WITH CONSISTENT GFS ON THAT AS WELL.

.SHORT TERM FORECAST...

BERING SEA/ALEUTIANS/SOUTHWEST ALASKA...THE PRIBILOF ISLANDS WILL BE
RIGHT IN THE LINE OF FIRE OF THE MAJOR ALEUTIAN STORM. TEMPERATURES
WILL WARM SLIGHTLY THIS AFTERNOON AND EVENING AS STRONG SOUTHERLY
FLOW DEVELOPS. HOWEVER...BY LATE EVENING THE COLD FRONT WILL MOVE
THROUGH AND THE VERY COLD AIR ALOFT WILL QUICKLY CHANGE PRECIPITATION
TO ALL SNOW. THE AREA OF STRONGEST WINDS (60 TO 70 KT) WILL ACCOMPANY
THE COLD AIR...SO EVEN WITH TEMPERATURES INITIALLY NEAR FREEZING
THERE SHOULD BE ENOUGH FALLING SNOW AND WIND TO PRODUCE BLIZZARD
CONDITIONS. THEREFORE...WILL UPGRADE TO A BLIZZARD WARNING.
MEANWHILE...DUE TO A FAIRLY FAST STORM TRACK WARNING BACK OVER
THE CENTRAL AND WESTERN ALEUTIANS WILL END THIS EVENING. DOWNSTREAM
OVER SOUTHWEST ALASKA THERE WILL BE LITTLE IN THE WAY OF ANY WARM-UP
IN TEMPERATURES WITH WARM FRONT OCCLUDING BEFORE IT REACHES THE
COASTLINE. THEREFORE...EXPECT BLIZZARD CONDITIONS TO QUICKLY DEVELOP
LATE TONIGHT INTO WEDNESDAY MORNING FROM THE WESTERN CAPES OF
BRISTOL BAY NORTHWARD ACROSS THE KUSKOKWIM DELTA. THE SECONDARY BUT
SIGNIFICANT THREAT IS WARNING LEVEL WINDS WHICH WILL LIKELY AFFECT
THESE SAME COASTAL AREAS DURING THE DAY WEDNESDAY AS COLD ADVECTION
KICKS IN. STRONG WINDS ARE ALSO EXPECTED TO MAKE IT INTO THE REST OF
THE BRISTOL BAY ZONE AND THE KUSKOKWIM VALLEY BY WEDNESDAY AFTERNOON.
SO THERE IS POTENTIAL THAT BLIZZARD CONDITIONS COULD SPREAD TO THESE
AREAS...BUT WITH SOME UNCERTAINTY IN WHERE SNOW WILL FALL...IT IS
TOO EARLY TO ISSUE ANY WATCHES OR WARNINGS.

HURRICANE FORCE WESTERLIES WILL QUICKLY BUILD UP 30 FEET PLUS
WAVEHEIGHTS OVER THE EASTERN BERING LATE TONIGHT. AS THESE SOUTHWEST
WINDS CONTINUE ACROSS THE ICE PACK TO SOUTHWEST ALASKA EXPECT MINOR
COASTAL FLOODING AS WELL AS SOME MINOR SEA ICE PULE-UPS ALONG THE
SOUTHWEST COAST. A COASTAL FLOOD ADVISORY HAS BEEN ISSUED FOR THIS.
THE POTENTIAL FOR COASTAL FLOODING IN BRISTOL BAY WILL ALSO NEED TO
BE WATCHED.

SOUTHCENTRAL ALASKA...THE UPPER WAVE OVER SOUTHWEST ALASKA WILL
CROSS SOUTHCENTRAL ALASKA TONIGHT. WITH RIDGING TO THE SOUTH AND
EAST THERE IS NO ACCESS TO PACIFIC MOISTURE AND THE TROUGH WILL BE
MOVING INTO A DRY AIRMASS. THEREFORE...IT WILL ONLY HAVE ITS OWN
DYNAMICS AND MOISTURE TO WORK WITH...WHICH ARE NOT VERY UNIMPRESSIVE.
THEREFORE...EXPECT ONLY CLOUDS AS THE TROUGH MOVES THROUGH. THERE
WILL BE SOME INCREASE IN LOW LEVEL MOISTURE...SO AS MID TO HIGH
CLOUDS EXIT WITH THE TROUGH LATE TONIGHT INTO WEDNESDAY MORNING
CONDITIONS WILL BECOME A LITTLE MORE CONDUCIVE TO FOG.
HOWEVER...DONT EXPECT ANY WIDESPREAD PROBLEMS...JUST SOME PATCHY
FOG. MOISTURE ASSOCIATED WITH THE LOW CROSSING THE BERING WILL MOVE
INTO SOUTHCENTRAL WEDNESDAY NIGHT AND THURSDAY...BUT WITH A LOW
TRACK ACROSS INTERIOR ALASKA DONT EXPECT ANY SIGNIFICANT SNOW.
THE PRIMARY IMPACT WILL BE COLD ADVECTION WINDS THROUGH THE KODIAK
ISLAND REGION. THE UPPER RIDGE WILL BE COMPLETELY GONE BY FRIDAY
WITH THE REMNANTS OF THE STORM OVER INTERIOR ALASKA AND A RIDGE
BUILDING OVER THE BERING. THIS WILL BE TEMPORARY THOUGH...AS A MORE
PROGRESSIVE PATTERN DEVELOPS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING...155 161 191 195.
         HIGH WIND WARNING 187.
MARINE...HURRICANE FORCE WIND WARNING...172 175 179.
         STORM WARNING...160 165 170 176 180 185.
         GALE WARNING...130 132 138 140 150 155 171.
         HEAVY FREEZING SPRAY WARNING...185.
FIRE WEATHER...NONE.

SEB FEB 09