Heavy Freezing Spray Warning 9, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1215 PM AKST FRI JAN 20 2012

.ANALYSIS AND UPPER LEVELS...STRONG BLOCKING HIGH IS CENTERED
OVER EASTERN SIBERIA WITH A CORRESPONDINGLY STRONG LOW OVER
NORTHERN CANADA. A SPOKE OF THE RIDGE IS MOVING SOUTHWARD ACROSS
THE NORTHERN MAINLAND OF ALASKA. A SHORT-WAVE DROPPING OUT OF
THE ARCTIC BEHIND IT WILL BE THE KEY FEATURE OVER THE NEXT COUPLE
DAYS. SOUTH OF THE RIDGE AXIS IS ANOTHER UPPER LEVEL LOW. THERE
ARE TWO UPPER CENTERS BUT THE STRONGER ONE BY FAR IS ASSOCIATED
WITH A STRONG STORM JUST SOUTH OF THE GULF OF ALASKA. BASED ON
NEARBY SHIP AND BUOY OBSERVATIONS THE CENTRAL PRESSURE AT THE
SURFACE IS AROUND 958 MB. THE BRUNT OF THIS STORM IS CURRENTLY
BEING FELT OVER THE SOUTHERN GULF WHERE STORM FORCE WINDS AND
NEARLY 30 FT SEAS ARE BEING OBSERVED. THERE ARE NEARLY 100 MB
DIFFERENCE BETWEEN THE PRESSURE OF THE PACIFIC LOW AND THE
SIBERIAN HIGH. THE TIGHT PRESSURE GRADIENT IS SUPPORTING AREAS
OF STRONG AND GUSTY WINDS ACROSS THE BERING SEA AND SOUTHERN
MAINLAND OF ALASKA. WATER VAPOR IMAGERY ALSO SHOWS A STRONG ARE
OF SUBSIDENCE FROM INTERIOR SOUTHCENTRAL TO NEAR ADAK WHICH IS
CONTRIBUTING TO EVEN STRONGER WINDS IN SOME LOCATIONS...INCLUDING
VALDEZ...THE MATANUSKA VALLEY...AND THE KUSKOKWIM DELTA.
RE-SUSPENDED SNOW IS ALSO PRODUCING BLIZZARD CONDITIONS THROUGH
THOMPSON THIS MORNING.

.MODEL DISCUSSION...MODELS ARE IN FAIR AGREEMENT THROUGH THE NEXT
FEW DAYS. THE MAIN DIFFERENCES CONTINUE TO BE WITH POSITION OF
SURFACE LOW IN THE GULF IN THE SUNDAY TO MONDAY TIME FRAME. THIS
PRIMARILY WILL AFFECT WHETHER SNOW WILL SPREAD INLAND OR REMAIN
ALONG THE GULF COAST. THE POSITION OF THESE LOWS WILL LARGELY
DEPEND ON THE EXACT POSITION OF THE UPPER LEVEL CUT-OFF LOW...
WHICH THE MODELS TYPICALLY STRUGGLE WITH. BASED ON THE LEVEL OF
CONFIDENCE AT THIS POINT CURRENT SYNOPTIC FORECAST LOOKS GOOD AND
ONLY MINOR ADJUSTMENTS WILL BE MADE.

.SHORT TERM FORECAST...AS THE RIDGE AXIS OVER NORTHERN ALASKA
ROTATES SOUTHWESTWARD AROUND THE HIGH CENTER THE SHORT-WAVE OVER
THE ARCTIC WILL DIVE SOUTHWARD ACROSS MAINLAND ALASKA TONIGHT AND
SATURDAY. AN UPPER LEVEL LOW WILL FORM AS TROUGH MOVES ACROSS THE
SOUTHERN MAINLAND AND THIS LOW WILL SET UP SHOP SOMEWHERE SOUTH OF
KODIAK ISLAND SUNDAY AFTERNOON. THE FORMATION OF THIS LOW WILL SPARE
SOUTHCENTRAL ALASKA FROM A STRONG BORA WIND EVENT BECAUSE MID TO
UPPER LEVEL FLOW WILL BECOME SOUTHERLY AND THE COLDEST AIR WILL BE
SHUNTED TO THE WEST SIDE OF THE UPPER LOW ACROSS SOUTHWEST ALASKA
AND THE EASTERN BERING SEA.

WILL ISSUE WIND CHILL ADVISORIES FOR SOUTHWEST ALASKA BEGINNING
SATURDAY NIGHT AND CONTINUING THROUGH AT LEAST MONDAY. MEANWHILE...
WINDS OVER SOUTHCENTRAL SHOULD BEGIN TO DIMINISH FROM CURRENT
LEVELS TONIGHT AS UPPER RIDGE AXIS MOVES INTO THE AREA AND PRESSURE
GRADIENTS BEGIN TO SLACKEN IN RESPONSE TO WEAKENING OF THE NORTHEAST
PACIFIC LOW AS IT TRACKS TOWARD SOUTHEAST ALASKA. THE TYPICAL GAP
WINDS WILL PERSIST ALONG THE GULF COAST AND LESS SO THROUGH THE
ALASKA RANGE WITH COLDER AIR REMAINING ON THE NORTH SIDES OF THE
RANGES THAN ON THE SOUTH SIDES. A SERIES OF SURFACE LOWS WILL FORM
OVER THE GULF SATURDAY THROUGH MONDAY AS THE UPPER LOW SETTLES IN
AND MEANDERS AROUND. A SERIES OF FRONTS WILL SPIN OFF FROM THESE
LOWS AND BRING SNOW TO COASTAL LOCATIONS. DEPENDING ON THE POSITION
OF THE LOWS SOME LIGHT SNOW MAY MAKE IT INLAND...BUT WOULD EXPECT
ANY ACCUMULATION TO BE VERY MINOR. SO THE GENERAL TREND THE NEXT
FEW DAYS WILL BE CONTINUED COLD AND DRY INLAND AND MARGINALLY WARMER
AND LESS WINDY ALONG THE COAST WITH PERIODS OF SNOW.

AS THE ARCTIC AIR CROSSES INTO THE OPEN WATERS OF THE EASTERN BERING
SEA SNOW SHOWERS WILL RATCHET UP AND WILL BE ACCOMPANIED BY STRONG
GUSTY WINDS. THIS WILL PRODUCE BLOWING SNOW AND PERIODS OF WHITE-OUT
CONDITIONS ALONG THE SOUTHERN ALASKA PENINSULA AND EASTERN ALEUTIANS
AS HEAVIER SNOW SHOWERS MOVE THROUGH. THESE LOW VISIBILITIES ARE
GENERALLY NOT LONG ENOUGH IN DURATION TO WARRANT A BLIZZARD
WARNING...BUT IT IS SOMETHING TO KEEP AN EYE ON.

.LONG TERM FORECAST...AS IS TYPICAL MODELS STRUGGLE WITH THE
BREAKING DOWN OF A BLOCKING HIGH. SPREAD AMONG THE SOLUTIONS IS
QUITE HIGH RIGHT NOW...ESPECIALLY AS WE HEAD THROUGH THE MIDDLE
TO END OF NEXT WEEK OVER THE NORTH PACIFIC AND BERING SEA REGIONS.
UNTIL THEN EXPECT ARCTIC AIR MASS TO REMAIN FIRMLY ENTRENCHED
ACROSS MAINLAND ALASKA WITH MOSTLY DRY CONDITIONS WITH THE EXCEPTION
OF THE GULF COAST WHICH WILL SEE PERIODS OF SNOW. MEANWHILE...COLD
ADVECTION WINDS AND SNOW SHOWERS WILL GRADUALLY DIMINISH AS WE
HEAD THROUGH NEXT WEEK WITH THE POSSIBILITY OF A PACIFIC STORM
MOVING INTO THE AREA LATE IN THE WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 131.
MARINE...GALE WARNING...121 127 130 150 155 160 165 170 171 179 180
                        185.
         HEAVY FREEZING SPRAY WARNING...121 126 127 128 129 130 138
                                        140 141 150 155 165 179 185.
FIRE WEATHER...NONE.

SEB JAN 12