Heavy Freezing Spray Warning 20, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
125 PM AKST MON JAN 2 2012

UPDATE

A LOOK AT THE 18Z RUNS SHOWS CONTINUING RUN-TO-RUN INCONSISTENCIES
IN THE EASTERN GULF WHICH COULD GREATLY AFFECT WHEN PRECIP MOVES
INTO SOUTHCENTRAL. THEREFORE...WILL HOLD OFF ON ISSUING A THOMPSON
PASS BLIZZARD WATCH. HOWEVER...WITH MODELS BEGINNING TO HONE IN ON
TRACK OF LOW ACROSS BERING WILL ISSUE A BLIZZARD WATCH FOR THE
PRIBILOFS AS THE LOW PASSES BY TO THE SOUTH ON TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT.

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PREVIOUS DISCUSSION

.ANALYSIS AND UPPER LEVELS...CLOSED UPPER LOW IS CENTERED OVER THE
SEWARD PENINSULA WITH SHORT-WAVES ROTATING AROUND MAINLAND ALASKA.
WATER VAPOR IMAGERY SHOWS ONE WAVE EXITING THROUGH THE COPPER RIVER
BASIN INTO INTERIOR ALASKA WHILE ANOTHER ENTERS SOUTHCENTRAL FROM
THE SOUTHWEST. AREAS OF SNOW CONTINUE ACROSS THE COPPER BASIN BUT
WILL BEGIN TO TAPER TO SCATTERED SHOWERS AS THE TROUGH EXITS. AREAS
OF LIGHT SNOW OR SHOWERS HAVE DEVELOPED IN THE WESTERN KENAI/COOK
INLET REGION ALONG WITH AREAS OF STRATUS OR STRATO-CU. COLD
ADVECTION BEHIND THE SECOND SHORT-WAVE HAS BEEN PRODUCING GUSTY
WINDS ALONG THE KUSKOKWIM DELTA WHERE A WIND CHILL ADVISORY IS IN
EFFECT. HOWEVER...WINDS ARE DIMINISHING SO EXPECT WIND CHILLS TO
RISE THROUGH THIS AFTERNOON.

A LOW HAS FORMED IN THE BACK SIDE OF THE TROUGH OVER THE WESTERN
BERING. WITH WEAK STEERING FLOW IT IS MOVING VERY SLOWLY OFF TO
THE EAST. THE FLOW OVER THE NORTH PACIFIC HAS BECOME MUCH MORE
AMPLIFIED THE PAST COUPLE DAYS WITH A TROUGH CENTERED AROUND 165W
EXTENDING SOUTHWARD TO AROUND 30N. THERE IS A COMPLEX SERIES OF
LOWS WITHIN THE TROUGH WITH DOWNSTREAM LOWS BEGINNING TO ROTATE
NORTHEASTWARD TOWARD THE GULF OF ALASKA.

.MODEL DISCUSSION...AS HAS BEEN THE CASE IN THIS PATTERN MODELS
DID NOT INITIALIZE WELL WITH THE MULTIPLE LOW CENTERS OVER THE
NORTH-CENTRAL PACIFIC AND ARE STRUGGLING WITH CONSISTENCY AS THIS
COMPLEX MOVES NORTHEASTWARD TOWARD THE GULF. THE UPPER TROUGH WILL
LIFT NORTHEASTWARD TO THE EASTERN GULF AND SOUTHEAST ALASKA...SO
THAT WILL BE THE BIGGEST PROBLEM AREA. FOR THE CENTRAL GULF UP
TO SOUTHCENTRAL WILL SEE THE TYPICAL INVERTED TROUGH EXTENDING
BACK TO PRINCE WILLIAM SOUND. THE MODELS ARE MUCH CLOSER AND
CONSISTENT WITH THIS FEATURE SO ONLY MINOR ADJUSTMENTS WILL BE
MADE TO CURRENT FORECAST.

MODELS ARE ALSO STRUGGLING WITH LOW MOVING ACROSS THE BERING
SEA...ESPECIALLY AS IT REACHES THE BRISTOL BAY REGION MID WEEK
AND INTERACTS WITH A PACIFIC SYSTEM MOVING TOWARD THE WESTERN
GULF LATE IN THE WEEK. GFS/ECMWF DID TREND TOWARD A SIMILAR
SOLUTION WITH THESE TWO LOWS...SO WILL TREND FORECAST IN THAT
DIRECTION.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE SHORT-WAVE ENTERING SOUTHCENTRAL THIS
MORNING WILL SWING NORTHWARD TONIGHT AS THE UPPER LOW TO THE
NORTH TAKES A WESTWARD JOG. THE VORTICITY FIELD WILL BECOME VERY
ELONGATED...SO EXPECT VERTICALLY MOTION AHEAD OF IT TO BE WEAK
AND OVER A SMALL AREA. THUS...ANY SNOW THAT DOES FALL WILL BE
VERY LIGHT WITH NO ACCUMULATION. THE ONE EXCEPTION WILL BE SNOW
SHOWERS IN THE PRINCE WILLIAM SOUND REGION WHICH CONTINUE TO BE
FED BY LOW LEVEL INSTABILITY AS ARCTIC AIR MOVES OVER THE WARMER
WATERS OF THE GULF. AS MID TO UPPER LEVELS DRY OUT BEHIND THE
TROUGH CONDITIONS WILL BECOME FAVORABLE FOR STRATUS AND
FOG...ESPECIALLY IN THE COOK INLET/SUSITNA VALLEY CORRIDOR.

STRONG OFFSHORE FLOW WILL DEVELOP AS SYSTEMS FROM THE PACIFIC
BEGIN TO MOVE INTO THE GULF TUESDAY AFTERNOON THROUGH WEDNESDAY.
WITH A STRONGER UPPER TROUGH MOVING IN FROM THE WEST THAN THE MOST
RECENT STORM PRECIPITATION WILL MAKE IT FURTHER WEST...PERHAPS
AS FAR WEST AS ANCHORAGE AND THE MAT-SU IN THE WEDNESDAY/WEDNESDAY
NIGHT TIME FRAME. PRINCE WILLIAM SOUND AND THE COPPER BASIN WILL
AGAIN SEE THE BULK OF PRECIPITATION. WITH STRONG GAP WINDS ALONG
THE COASTAL RANGE BLOWING SNOW WILL ONCE AGAIN BE AN ISSUE THROUGH
THOMPSON PASS....SO WILL ISSUE A BLIZZARD WATCH WITH THE AFTERNOON
FORECAST. AS THIS SYSTEM EXITS WEDNESDAY NIGHT AND THURSDAY EXPECT
ANOTHER SYSTEM TO THE SOUTH AND WEST TO MOVE IN RIGHT BEHIND IT.
FORECAST CONFIDENCE IN THE TRACK OF THIS SYSTEM IS LOW...BUT WITH
AN ARCTIC AIR MASS IN PLACE WIDESPREAD SNOW IS LIKELY.

SOUTHWEST ALASKA...THE UPPER LOW WILL WANDER WESTWARD AND THEN
SOUTHWARD TOWARD THE KUSKOKWIM DELTA ON TUESDAY...ENSURING ARCTIC
AIR REMAINS FIRMLY ENTRENCHED ACROSS SOUTHWEST ALASKA. DRY
CONDITIONS WILL DOMINATE UNTIL LATE WEDNESDAY AND THURSDAY WHEN
THE LOW CROSSING THE BERING SEA ARRIVES. THERE IS UNCERTAINTY IN
WHERE THIS LOW WILL ULTIMATELY TRACK...BUT WITH ARCTIC AIR IN
PLACE CLIMATOLOGY FAVORS A SOUTHERN TRACK. BASED ON THIS...BRISTOL
BAY WOULD HAVE THE BEST CHANCE OF SNOW AND A BRIEF WARM-UP AS THIS
SYSTEM MOVES THROUGH.

BERING SEA/ALEUTIANS...THE BERING LOW WILL TAKE A SIMILAR TRACK TO
THE ONE WHICH MOVED ACROSS THE REGION LAST WEEK. HOWEVER...THIS ONE
DOES APPEAR TO BE STRONGER...WITH GALE FORCE WINDS EXPECTED ALONG
ITS PATH. NORTHERLY FLOW AND SNOW SHOWERS WILL RETURN BEHIND THIS
SYSTEM.

.LONG TERM FORECAST...MODELS INDICATE THE SAME LARGE SCALE EVOLUTION
THROUGH THE BEGINNING OF NEXT WEEK...WITH THE UPPER LOW RETROGRADING
NORTHWESTWARD TOWARD EASTERN RUSSIA. THIS WILL ALLOW THE UPPER JET
TO LIFT NORTHWARD CLOSER TO ALASKA AND SET UP A MORE NORTHERLY STORM
TRACK. EXPECT SYSTEMS TO BEGIN TO TRACK JUST SOUTH OF THE ALEUTIANS
AND THEN NORTHEASTWARD TOWARD SOUTHCENTRAL ALASKA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...130 132 150 155 165 170 171 172 179.
         HEAVY FREEZING SPRAY WARNING...121 129 130 132 138 140 141
                                        150 155 160 165 179 185.
FIRE WEATHER...NONE.

SEB JAN 12