Heavy Freezing Spray Warning 10, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1145 AM AKST SAT JAN 21 2012

.ANALYSIS AND UPPER LEVELS...STRONG BLOCKING HIGH OVER EASTERN
SIBERIA IS SINKING SOUTHWARD THIS MORNING TOWARD THE FAR WESTERN
BERING SEA WHILE A STRONG SHORT-WAVE CONTINUES TO DIVE SOUTHWARD
ACROSS MAINLAND ALASKA ALONG THE EASTERN PERIPHERY OF THE HIGH.
MEANWHILE...A STRONG LOW OVER THE EASTERN GULF IS BEGINNING TO
WEAKEN AS IT BECOMES VERTICALLY STACKED. MOISTURE ON THE NORTHERN
PERIPHERY OF THIS SYSTEM IS BEING PULLED NORTH AND WEST TOWARD
SOUTHCENTRAL AS SHORT-WAVE DROPS SOUTHWARD THROUGH SOUTHWEST ALASKA.
IN FACT MIDDLETON ISLAND RADAR IS SHOWING SIGNIFICANT RETURNS FROM
MIDDLETON ISLAND EASTWARD. OFFSHORE FLOW IS KEEPING CONDITIONS DRY
FOR THE MOMENT IN CORDOVA...BUT EXPECT SNOW TO DEVELOP AS WE HEAD
THROUGH THE AFTERNOON HOURS. WINDS ACROSS SOUTHCENTRAL ARE TRENDING
SLOWLY DOWNWARD AS PRESSURE GRADIENTS SLACKEN AND UPPER FLOW SHIFTS
TO SOUTHERLY AHEAD OF THE SOUTHWEST ALASKA SHORTWAVE. HOWEVER...
COLDER AIR INLAND IS CONTRIBUTING TO STRONGER WINDS THROUGH MOUNTAIN
GAPS. ARCTIC AIR IS SURGING SOUTHWARD ACROSS SOUTHWEST ALASKA THIS
MORNING RESULTING IN STRENGTHENING WINDS AND FALLING TEMPERATURES.
THE STRONGEST WINDS ARE CURRENTLY BEING OBSERVED ALONG THE KUSKOKWIM
DELTA COAST WHERE WIDE OPEN SPACE IS ALLOWING FOR BLIZZARD CONDITIONS
IN BLOWING SNOW. EXPECT WIDESPREAD SNOW SHOWERS TO DEVELOP AS THIS
AIR MASS MOVES OVER THE OPEN WATERS OF THE CENTRAL TO EASTERN BERING
SEA THIS AFTERNOON.

.MODEL DISCUSSION...MODELS ARE IN FAIRLY CLOSE WITH SYNOPTIC FEATURES
THROUGH MONDAY AFTERNOON. NOTABLE DIFFERENCES ARISE ON TUESDAY WITH
SYSTEM TRACKING FROM THE NORTHEAST PACIFIC INTO THE GULF. THERE ARE
TWO CAMPS OF SOLUTIONS. THE ECMWF/UKMET/GEMGLB SHOW A 960S MB LOW
MOVING TO THE FAR EASTERN GULF WHILE THE GFS/NAM SHOW A 940S LOW
TRACKING FURTHER WEST. WITH A HIGHLY AMPLIFIED PATTERN AND ARCTIC
AIR FEEDING INTO THE BACK SIDE OF THE SYSTEM TEND TO BELIEVE THE
STRONGER SOLUTION. HOWEVER...THERE IS QUITE A BIT OF SPREAD IN THE
GFS ENSEMBLE AND CURRENT FORECAST WAS BASED OFF THE ECMWF SOLUTION.
THEREFORE...WILL STICK CLOSE TO INHERITED FORECAST FOR NOW.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...AN UPPER LOW WILL DEVELOP OVER SOUTHWEST
ALASKA THIS AFTERNOON AND DROP SOUTH OF THE ALASKA PENINSULA AND
KODIAK ISLAND ON SUNDAY. THIS WILL AID IN DEVELOPMENT OF A SURFACE
LOW OVER THE NORTHWEST GULF WHICH WILL BE PULLED WESTWARD BY THE
ROTATION AROUND THE UPPER LOW. THE COMBINATION OF THE UPPER LOW
AND SURFACE LOW WILL HELP SPREAD SNOW WESTWARD ACROSS SOUTHCENTRAL
TONIGHT AND SUNDAY. EXPECT THE BULK OF ACCUMULATING SNOW ALONG
THE COAST. WITH A LACK OF ANY SIGNIFICANT DYNAMICAL FORCING ANY
SNOW THAT FALLS INLAND WILL BE LIGHT WITH LITTLE OR NO ACCUMULATION.

AS UPPER LOW CONTORTS AND SHIFTS EASTWARD INTO THE GULF ON MONDAY
EXPECT ANOTHER WEAK LOW TO DEVELOP OVER THE GULF AND MORE LIGHT
SNOW TO SPREAD TO THE COAST. FLOW WILL BACK TO THE NORTH INLAND
AND MAINTAIN DRY CONDITIONS. A MUCH STRONGER SYSTEM IS EXPECTED
TO MOVE OUT OF THE PACIFIC MONDAY NIGHT AND ACROSS THE GULF TUESDAY
BUT THERE IS SOME UNCERTAINTY IN THE TRACK AND STRENGTH OF THIS LOW.
ULTIMATELY IT LOOKS LIKE IT SHOULD END UP IN PRINCE WILLIAM SOUND
AND BRING SNOW TO MUCH OF SOUTHCENTRAL.

SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...WINDS WILL CONTINUE TO BLOW
ACROSS SOUTHWEST ALASKA THROUGH SUNDAY NIGHT AND THEN GRADUALLY
DIMINISH SUNDAY NIGHT AND MONDAY. MEANWHILE...AIR TEMPERATURES
WILL CONTINUE TO FALL AS ARCTIC AIR MASS SETTLES IN. THIS WILL
PRODUCE VERY WIND CHILL READINGS AS LOW AS 55 DEGREES BELOW ZERO
IN SOME PLACES. ONCE THE WINDS DIE DOWN ACTUAL AIR TEMPERATURES
WILL CONTINUE TO FALL EVEN FURTHER WITH -30 DEGREE READINGS LIKELY
BY MONDAY NIGHT. THE AMOUNT OF TRANSPORTABLE SNOW ALONG THE KUSKOKWIM
DELTA COAST SHOULD GRADUALLY DIMINISH AND BRING AND END TO BLIZZARD
CONDITIONS BY SOMETIME ON SUNDAY. MEANWHILE CONDITIONS WILL
DETERIORATE OVER THE EASTERN BERING...EASTERN ALEUTIANS...AND
SOUTHERN ALASKA PENINSULA THIS AFTERNOON THROUGH TONIGHT AS ARCTIC
AIR ARRIVES AND THE SNOW MAKING MACHINE THAT IS THE BERING SEA KICKS
INTO HIGH GEAR. SNOW SHOWERS WILL BE ENHANCED BY WAVES ROTATING
AROUND THE BACK SIDE OF THE UPPER LOW....ESPECIALLY ALONG THE
SOUTHERN ALASKA PENINSULA. THIS WILL RESULT IN STEADIER SNOW AND
LOW VISIBILITIES THAN IS TYPICALLY THE CASE WITH RUN OF THE MILL
COLD ADVECTION SNOW SHOWERS. THUS...THE CURRENT BLIZZARD WATCH FOR
THE SOUTHERN ALASKA PENINSULA WILL BE UPGRADED TO A WARNING WITH
THE AFTERNOON FORECAST. WINDS WILL BECOME MARGINALLY WEAKER AS COLD
ADVECTION WEAKENS MONDAY AND TUESDAY. HOWEVER...SNOW SHOWERS WILL
CONTINUE.

.LONG TERM FORECAST...WAVES MOVING DOWN THE EASTERN SIDE OF THE
BLOCKING HIGH WILL CAUSE IT TO GRADUALLY WEAKEN AND RETROGRADE
WESTWARD AS WE HEAD THROUGH NEXT WEEK. THE TROUGH OVER MAINLAND
ALASKA WILL GRADUALLY BROADEN AND COVER THE BERING SEA BY THE END
OF NEXT WEEK. THE LOW THAT MOVES TO PRINCE WILLIAM SOUND TUESDAY
WILL LIKELY SIT THERE FOR THE REMAINDER OF THE WEAK AND WORK WITH
THE UPPER LOW TO PRODUCE PERIODS OF SNOW ACROSS SOUTHCENTRAL.
ARCTIC AIR WILL REMAIN FIRMLY ENTRENCHED ACROSS THE ALASKA REGION.
MODELS INDICATE THE POSSIBILITY OF A CHANGE IN THIS PATTERN AS WE
HEAD THROUGH NEXT WEEK...BUT UNCERTAINTY IS VERY LARGE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WATCH 181.
MARINE...GALE WARNING...127 130 150 155 160 165 170 171 172 179 185.
         HEAVY FREEZING SPRAY WARNING...121 125 126 127 128 130 132
                                        138 140 141 150 155 165 170
                                        171 179 185.
FIRE WEATHER...NONE.

SEB JAN 12