Heavy Freezing Spray Warning 237, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1230 PM AKST TUE DEC 18 2012

.ANALYSIS AND UPPER LEVELS...
THE MAIN FEATURE ON THE MORNING WEATHER MAP IS A VERTICALLY STACKED
LOW IN THE SOUTHWEST GULF OF ALASKA. A DEFORMATION BAND ON THE
NORTHWEST SIDE OF THE LOW IS BRINGING MODERATE SNOW TO THE BRISTOL
BAY ZONE AND KODIAK ISLAND. A RIDGE BUILDING ACROSS THE BERING SEA IS
HELPING TO GENERATE STRONG NORTHWEST WINDS ACROSS MUCH OF THE
SOUTHWEST MAINLAND AND ALASKA PENINSULA. A HIGH WIND WARNING REMAINS
IN EFFECT FOR THE ALASKA PENINSULA AS THE STRONG WINDS ARE
ACCELERATED BY GAPS IN THE TERRAIN. FURTHER EAST...THE WINDS ARE
COMBINING WITH FALLING SNOW TO PRODUCE BLIZZARD CONDITIONS AROUND
KODIAK ISLAND. THE JET STREAM REMAINS WELL SOUTH OF THE
MAINLAND...WHICH IS SOUTHCENTRAL ALASKA UNDER DRY CONDITIONS...WITH
THE ONLY IMPACT FROM THE GULF LOW BEING MIDLEVEL CLOUDS.

.MODEL DISCUSSION...
THE MODELS REMAIN IN ABOVE AVERAGE AGREEMENT...BUT HAVE ALL CHANGED
SLIGHTLY SINCE YESTERDAY. THE MODEL RUNS YESTERDAY HAD SHOWN THE LOW
NEAR KODIAK STALLING BRIEFLY DURING THE DAY TODAY OVER THE SOUTHERN
GULF. BY CONTRAST...THE MODELS TODAY ARE ALL SHOWING THE LOW SLOWING
BUT NOT STALLING. ADDITIONALLY...THE EC AND GFS ARE SUGGESTING THE
CONSOLIDATED LOW CENTER WILL BREAK APART INTO MULTIPLE WEAKER LOW
CENTERS. THIS SEEMS LIKELY SINCE THE JET IS REMAINING FAR TO THE
SOUTH...AND CURRENT SATELLITE APPEARANCE OF THIS STORM SEEMS A BIT
RAGGED. THE NET EFFECT OF THESE CHANGES SINCE YESTERDAY ARE THAT THE
DEFORMATION BAND OF MODERATE TO HEAVY SNOW MAY SHIFT OFFSHORE OF
KODIAK ISLAND EARLY THIS EVENING RATHER THAN OVERNIGHT...WHICH COULD
BRING A PREMATURE END TO THE BLIZZARD CONDITIONS. THIS SCENARIO IS
LOOKING INCREASINGLY LIKELY...AND THE FORECAST WILL BE UPDATED TO
REFLECT THIS LIKELIHOOD.

.SHORT TERM FORECAST...
SOUTHCENTRAL...THE MAIN STORY TODAY AND TONIGHT WILL BE THE BLIZZARD
CONDITIONS AFFECTING PORTIONS OF KODIAK ISLAND. AS MENTIONED
ABOVE...THERE IS INCREASING CONCERN THE MODERATE SNOWFALL WILL
DIMINISH A BIT FASTER THAN EXPECTED YESTERDAY...WHICH MAY RESULT IN
THE EARLY TERMINATION OF BLIZZARD CONDITIONS. REGARDLESS...THE STRONG
NORTHWEST WINDS WILL BE DEVELOPING THROUGHOUT THE AFTERNOON AS SNOW
CONTINUES TO FALL AND TEMPERATURES DROP. THUS THE BOTTOM LINE REMAINS
THAT CONDITIONS WILL GET WORSE BEFORE THEY GET BETTER. WIDESPREAD
CLOUDINESS WILL DIMINISH LATE TONIGHT AS THE GULF LOW MOVES OFF TO
THE SOUTHEAST. AS THIS HAPPENS...COLD AIR ADVECTION AND NORTHERLY
FLOW WILL INTENSIFY...WHICH WILL ALLOW STRONG WINDS TO ONCE AGAIN
DEVELOP THROUGH FAVORED TERRAIN GAPS AND CONTINUE THROUGH THE END OF
THE WEEK.

SOUTHWEST...WITH THE STRONG LOW NOW WELL INTO THE WESTERN GULF...MOST
OF THE REGION IS CLEARING OUT FROM WEST TO EAST AS STRONG
NORTHWESTERLY WINDS DEVELOP WITH DROPPING TEMPERATURES. THE EXCEPTION
IS IN EASTERN PORTIONS OF THE BRISTOL BAY ZONE AND LOWER KUSKOKWIM
VALLEY WHERE A BAND OF MODERATE TO HEAVY SNOW IS CREATING A BRIEF
PERIOD OF NEAR-BLIZZARD CONDITIONS AT MANY LOCATIONS. THIS WILL
CONTINUE TO PULL OFF TO THE EAST EARLY THIS EVENING...AT WHICH POINT
SKIES WILL CLEAR AND NORTHWEST WINDS WILL GET EVEN STRONGER. THE
REMAINDER OF THE WEEK WILL BE DRY AND COLD AS HIGH PRESSURE MOVES IN
FROM THE BERING SEA.

BERING SEA AND ALEUTIANS...A SHORTWAVE TROUGH DROPPING DOWN THE FRONT
SIDE OF THE BERING RIDGE IS ENHANCING STRONG WINDS AND SNOW SHOWER
ACTIVITY AROUND THE PRIBILOFS AND EASTERN ALEUTIANS. THIS FEATURE
WILL CONTINUE EASTWARD THIS EVENING AND ENHANCE WINDS THAT ARE
ALREADY GUSTING AROUND HURRICANE FORCE THROUGH THE CHANNELED TERRAIN
OF THE ALASKA PENINSULA. THE EASTERN BERING WILL STAY IN A COLD
ADVECTION REGIME WITH SNOW SHOWER ACTIVITY CONTINUING THROUGH
WEDNESDAY NIGHT. FURTHER WEST...SOUTHERLY FLOW WILL BEGIN TO INCREASE
IN ADVANCE OF A PACIFIC FRONT THAT MOVES INTO THE WESTERN ALEUTIANS
LATE TONIGHT AND SLOWLY SPREADS GALE FORCE WINDS AND WARMER
TEMPERATURES EASTWARD FOR THE REST OF THE WEEK.

.LONG TERM FORECAST...
THE ZONAL PATTERN WITH PROGRESSIVE EMBEDDED DISTURBANCES OVER THE
LAST WEEK IS SLOWING DOWN AND TRANSITIONING INTO A MODIFIED BLOCKING
HIGH PRESSURE OVER NORTHERN ALASKA...SLIGHTLY REMINISCENT OF LATE
NOVEMBER AND EARLY DECEMBER. THE MAIN DIFFERENCE THIS TIME WILL BE
THAT THE POSITION OF THE HIGH WILL BE MUCH FURTHER NORTH...ALLOWING
LOW PRESSURE SYSTEMS TO RETROGRADE ACROSS THE STATE FROM CANADA. IN
PRACTICAL TERMS...THIS WILL KEEP MOST OF MAINLAND ALASKA IN
BELOW-NORMAL TEMPERATURES...WITH A CHANCE OF SNOW AND MODERATING
TEMPERATURES AS WE HEAD INTO THE LATTER HALF OF THE UPCOMING WEEKEND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 171
         HIGH WIND WARNING 181
MARINE...STORM WARNING 130 132 150 155 176
         GALE WARNING 120 121 126 127 128 160 165 170 171 172 175 185
         HEAVY FREEZING SPRAY WARNING 121 126 126 127 128 129 130 132
                                      138 140 141
FIRE WEATHER...NONE

AMD DEC 12