Heavy Freezing Spray Warning 9, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
410 PM AKST WED JAN 19 2011

.ANALYSIS AND UPPER LEVELS...
A SIGNIFICANT PATTERN CHANGE IS UNDERWAY ACROSS SOUTHCENTRAL ALASKA.
AN ELONGATED UPPER LEVEL RIDGE STRETCHING FROM THE NORTHEASTERN
PACIFIC TO THE KAMCHATKA PENINSULA IS GRADUALLY WEAKENING AND
SPLITTING INTO TWO SEPARATE ENTITIES...A HIGH OVER FAR EASTERN RUSSIA
AND AN EASTWARD MIGRATING RIDGE OVER THE NORTHEASTERN PACIFIC. THIS
IS ALLOWING A SURFACE LOW PRESSURE SYSTEM AND ASSOCIATED OCCLUDED
FRONT TO MOVE ONSHORE OVER THE NORTH GULF COAST AND BRING THE FIRST
WIDESPREAD SNOW IN QUITE SOME TIME TO SOUTHCENTRAL ALASKA. A
STACKED UPPER LEVEL LOW IS MEANDERING SEVERAL HUNDRED MILES SOUTHWEST
OF SHEMYA. THE WEAKENING 960 MB SURFACE LOW IS ALSO ESSENTIALLY
STATIONARY SOUTHWEST OF THE WESTERN ALEUTIANS...THOUGH MULTIPLE
SHORTWAVES ARE ROTATING AROUND THIS SYSTEM. THE STRONGEST OF THESE
WAVES IS THE AFOREMENTIONED WEATHER SYSTEM CURRENTLY IMPACTING THE
NORTHERN GULF.

.MODEL DISCUSSION...
MODELS REMAIN IN FAIR AGREEMENT ON THE GENERAL SYNOPTIC WEATHER
ELEMENTS OUT THROUGH THE SHORT TERM...BUT THEY HAVE BEEN STRUGGLING
TO CAPTURE THE DETAILS OF THE UPCOMING SYSTEMS AS WE TRANSITION INTO
A MORE ACTIVE PATTERN. THERE IS RELATIVELY GOOD CONSISTENCY WITH THE
FIRST TWO SHORTWAVES THAT MOVE INTO THE GULF IN THE NEXT 48
HOURS...BUT THE MODELS THEN QUICKLY FALL APART WITH A THIRD WEAK
SHORTWAVE THAT ENTERS THE GULF OUT AROUND 72 HOURS. HOWEVER...THE
MODELS DO REGROUP AND BRING THE MEAN LOW PRESSURE SYSTEM OUT FROM
SOUTHWEST OF THE ALEUTIANS INTO THE BRISTOL BAY AREA BY MONDAY
MORNING. GIVEN THE CURRENT VOLATILE MODEL SOLUTIONS...TODAY'S
FORECAST PACKAGE USED THE 00Z RUN OF THE ECMWF SINCE THE NEWEST RUN
IS SUBSTANTIALLY DIFFERENT COMPARED TO THE PREVIOUS SOLUTIONS AND THE
INHERITED GRIDS.

.SHORT TERM FORECAST...
.SOUTHCENTRAL ALASKA...SNOW WILL CONTINUE TO SPREAD INLAND ACROSS THE
REGION AS THE OCCLUDED FRONT SURGES ONSHORE LATE THIS AFTERNOON AND
INTO THE EVENING HOURS. LITTLE SNOW ACCUMULATION IS EXPECTED FROM
THIS SYSTEM...BUT PERSISTENT SOUTHWESTERLY FLOW AND A THICK CLOUD
DECK WILL HELP TO RAISE TEMPERATURES BACK TO NEAR CLIMATOLOGICAL
NORMS FOR THIS TIME OF YEAR. THE SNOW WILL TAPER OFF TO SCATTERED
SHOWERS LATE TONIGHT AS THE FRONT MOVES INLAND AND DISSIPATES. THERE
WILL BE A BRIEF LULL IN THE ACTION THURSDAY BEFORE ANOTHER
MOISTURE-LADEN SHORTWAVE PUSHES ONSHORE LATE THURSDAY NIGHT AND
FRIDAY.

.SOUTHWEST ALASKA...THE SHORTWAVE AFFECTING MUCH OF SOUTHCENTRAL
ALASKA IS ALSO BRINGING AREAS OF SNOW AND BLOWING SNOW TO SOUTHWEST
ALASKA THIS AFTERNOON...WITH BLIZZARD CONDITIONS TODAY IN KOLIGANEK
AND NEAR BLIZZARD CONDITIONS IN TOOKSOK BAY. SNOW SHOWERS
WILL LINGER ACROSS THE REGION THROUGH THE WEEKEND AS A SERIES OF
SHORTWAVES WRAP AROUND NORTH PACIFIC LOW AND INTO SOUTHERN ALASKA.
TEMPERATURES WILL GRADUALLY MODERATE IN THE INTERIOR PORTIONS OF
SOUTHWEST ALASKA AS MILD SOUTHWESTERLY FLOW BECOMES MORE ESTABLISHED.

.BERING SEA AND ALEUTIANS...BROAD SOUTHERLY TO EASTERLY FLOW WILL
PERSIST BEHIND THE OCCLUDED FRONTAL BAND THAT PUSHED THROUGH THE
ALEUTIANS LAST NIGHT. WINDS WILL REMAIN GENERALLY LIGHT WITH
SCATTERED SHOWERS POSSIBLE INTO THE WEEKEND AS SEVERAL WEAK
SHORTWAVES ROTATE AROUND THE MAIN UPPER LEVEL LOW IN THE NORTH
CENTRAL PACIFIC.

.LONG TERM FORECAST...
AN ACTIVE WEATHER PATTERN WILL CONTINUE INTO NEXT WEEK OVER SOUTHWEST
AND SOUTHCENTRAL ALASKA...WITH ADDITIONAL SHORTWAVES DEVELOPING
AROUND THE UPPER LEVEL LOW SOUTH OF THE ALEUTIANS AND ROTATING INTO
THE REGION.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...120 127 130 138 140 176 180 185.
         HEAVY FREEZING SPRAY WARNING...127 128 140 141 185.
FIRE WEATHER...NONE.

KS JAN 11