Blizzard and High Wind in Alaska, January 3 to 4, 2012

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1215 PM AKST TUE JAN 3 2012

.ANALYSIS AND UPPER LEVELS...COLD UPPER LOW IS DRIFTING SOUTHWARD
THIS MORNING ACROSS NORTON BAY. A SHORT-WAVE EXTENDS SOUTHWARD
FROM BRISTOL BAY INTO THE NORTH PACIFIC ALONG 160W. ITS EASTWARD
PROGRESSION HAS SLOWED TO A CRAWL AS RIDGE BUILDS OVER THE GULF
AND SOUTHCENTRAL AHEAD OF LOW COMPLEX MOVING OUT OF THE NORTHEAST
PACIFIC. SINCE IT IS BEING BLOCKED FROM MOVING EASTWARD EXPECT IT
TO BEGIN LIFTING DUE NORTH TODAY. THERE ARE SOME LOW TO MID LEVEL
CLOUDS RIGHT AHEAD OF IT ALONG THE NORTHERN END OF THE ALASKA
PENINSULA WHICH SHOULD ALSO LIFT NORTHWARD TOWARD THE KUSKOKWIM
VALLEY. ELSEWHERE ACROSS THE SOUTHERN MAINLAND CONDITIONS ARE
VERY QUIET THIS MORNING. A SMALL BUT POTENT LOW IS MOVING EASTWARD
ACROSS THE CENTRAL BERING SEA. SNOW AND BLOWING SNOW IS INTENSIFYING
ON THE PRIBILOF ISLANDS THIS MORNING JUST AHEAD OF THE FRONT. EXPECT
BLIZZARD CONDITIONS TO DEVELOP BY LATE THIS MORNING AND CONTINUE
THROUGH EARLY WEDNESDAY MORNING AS THE LOW PASSES JUST TO THE
SOUTH WITH OCCLUDED FRONT REMAINING IN THE VICINITY OF THE ISLANDS
THE ENTIRE TIME. A MUCH WEAKER LOW IS NOTED SOUTH OF THE ALEUTIANS...
PERHAPS JUST CLOSE ENOUGH TO BE PICKED UP AND ABSORBED INTO THE
BERING SEA SYSTEM. THE NORTHEAST PACIFIC TROUGH IS LIFTING
NORTHEASTWARD...WITH MULTIPLE LOWS PINWHEELING AROUND EACH OTHER
AS THEY HEAD FOR THE EASTERN GULF AND SOUTHEAST ALASKA. THE MAIN
IMPACT ON SOUTHCENTRAL AHEAD OF THESE SYSTEM IS A TIGHTENING
PRESSURE GRADIENT WITH GAP WINDS BEGINNING TO DEVELOP ALONG THE
NORTH GULF COAST.

.MODEL DISCUSSION...CONTINUE TO DEAL WITH RUN-TO-RUN INCONSISTENCIES
AMONG ALL THE MODELS. THEY MIGHT COME INTO GOOD AGREEMENT FOR A
SINGLE MODEL CYCLE BUT THEN ONE OR TWO SOLUTIONS DIVERGE THE NEXT
RUN. THEY ALL DEAL SIMILARLY WITH THE LOWS MOVING OUT OF THE
PACIFIC...BUT 12Z ECMWF IS NOW NOTABLY FASTER THAN OTHER SOLUTIONS
LIFTING EVERYTHING NORTHEASTWARD INTO CANADA. ALTHOUGH THE ECMWF
HAS GENERALLY BEEN PERFORMING VERY WELL IN RECENT WEEKS IT IS THE
OUTLIER AT THE MOMENT...SO WILL STICK WITH SPEED OF THE OTHER
SOLUTIONS. THIS WILL AFFECT TIMING OF PRECIPITATION...ESPECIALLY
IN THE PRINCE WILLIAM SOUND AND COPPER RIVER BASIN AREAS.

MODELS ARE A BIT MORE PROBLEMATIC ON TRACK OF THE BERING LOW. THE
ECMWF/UKMET NOW SHOW A FARTHER SOUTH SOLUTION RIGHT WHICH STRADDLES
THE ALASKA PENINSULA/KODIAK ISLAND AREA WHILE THE GFS/NAM/GEMGLB
NOW DEPICT A MORE NORTHERLY TRACK SIMILAR TO WHAT THE ECMWF SHOWED
YESTERDAY MORNING. WILL STICK CLOSE TO THE NORTHERLY TRACK WHICH
IS WHAT THE CURRENT FORECAST IS BASED OFF OF WITH RECOGNITION THAT
ADJUSTMENTS MAY NEED TO BE MADE. SOLUTIONS CONTINUE TO DIVERGE
FURTHER ON THURSDAY/THURSDAY NIGHT AS ANOTHER LOW MOVES UP OUT OF
THE PACIFIC AND INTO THE GULF. PREFER THE NAM/GFS SOLUTION FOR NOW
BECAUSE IT CREATES THE BEST TEMPORAL CONTINUITY WITH EVOLUTIONS OF
OTHER SYSTEMS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...INVERTED TROUGH AND ASSOCIATED PRECIP WILL
BACK ITS WAY INTO PRINCE WILLIAM SOUND AND THE COPPER RIVER BASIN
ON WEDNESDAY. THE NORTH-SOUTH PRESSURE GRADIENT WILL PEAK TONIGHT
AND THEN SLOWLY WEAKEN ON WEDNESDAY...SO WINDS IN THE EASTERN
PRINCE WILLIAM SOUND AREA WILL DIMINISH AS SNOW ARRIVES. STILL...
THERE SHOULD BE SOME WIND IN THOMPSON PASS...SO PLAN TO ISSUE A
BLOWING SNOW ADVISORY TOMORROW AFTERNOON AND INTO THE EVENING AT
WHICH POINT WINDS WILL BECOME LIGHT. WESTERN EDGE OF PRECIPITATION
WILL BE NEAR ANCHORAGE AND THE MAT-SU ON WEDNESDAY NIGHT. SNOW FOR
ANCHORAGE IS THE MOST QUESTIONABLE WITH HIGHER PROBABILITIES AS
YOU HEAD NORTH AND EAST OF ANCHORAGE. UPPER TROUGH WILL KICK
EVERYTHING OFF TO THE NORTHEAST ON THURSDAY...BUT A NEW STORM WILL
BE TAKING SHAPE IMMEDIATELY BEHIND IT. A STRONG SHORT-WAVE ROUNDING
AN UPPER LOW OVER SOUTHWEST WILL COMBINE WITH A LOW MOVING UP FROM
THE PACIFIC TO PRODUCE A WIDESPREAD SNOW EVENT ACROSS SOUTHCENTRAL
ON THURSDAY AFTERNOON THROUGH EARLY FRIDAY MORNING. THERE IS QUITE
A BIT OF UNCERTAINTY IN THE TRACK OF THE PACIFIC LOW...BUT THERE IS
HIGHER CONFIDENCE IN THE UPPER SHORT-WAVE MOVING THROUGH...SO SNOW
IS LIKELY NO MATTER WHERE THE LOW TRACKS. WITH SUCH A FOCUSED AND
STRONG UPPER FEATURE AND LOW LEVEL COLD ADVECTION EXPECT A PERIOD
OF MODERATE TO HEAVY SNOWFALL AS IT MOVES THROUGH. CONDITIONS WILL
DRY OUT FRIDAY WITH YET ANOTHER SYSTEM HEADED UP FROM THE PACIFIC
ON SATURDAY.

SOUTHWEST ALASKA...THE BERING SEA LOW WILL MOVE TO BRISTOL BAY
WEDNESDAY NIGHT AND THURSDAY BRINGING SNOW AND A TEMPORARY WARM-UP
OF TEMPERATURES TO THE REGION. PRIOR TO THE ONSET OF SNOW IN THE
KUSKOKWIM VALLEY THERE IS A GOOD CHANCE WIND CHILLS WILL DROP TO
MINUS 40 OR LOWER...SO WILL LIKELY ISSUE AN ADVISORY BEGINNING
DURING THE DAY WEDNESDAY. THEN...AS SNOW ARRIVES WEDNESDAY AFTERNOON
OR EVENING THERE IS THE THREAT OF LOW VISIBILITIES IN BLOWING SNOW.
WINDS DO NOT LOOK STRONG ENOUGH FOR BLIZZARD CONDITIONS SO WILL
HAVE TO CONSIDER A BLOWING SNOW ADVISORY. SNOW WILL TAPER OFF
ACROSS SOUTHWEST ALASKA FRIDAY AS SURFACE LOW DISSIPATES AND UPPER
LOW HEADS NORTHWARD. COLD AND DRU CONDITIONS WILL THEN SETTLE BACK
IN WITH THE PRIMARY STORM TRACK REMAINING OFF TO THE SOUTH AND EAST.

BERING SEA/ALEUTIANS...LOW OVER THE CENTRAL BERING WILL STRENGTHEN
AS IT CONTINUES EASTWARD TONIGHT. STRONG WINDS ON THE BACK SIDE OF
THE LOW WILL PROVIDE WHITE-OUT CONDITIONS AT TIMES ON THE PRIBILOF
ISLANDS. THE EFFECTS OF THESE WINDS WILL EXTEND SOUTHWARD TO THE
EASTERN ALEUTIANS AND EVENTUALLY THE ALASKA PENINSULA AS THE LOW
OVER THE PACIFIC IS ABSORBED AND A WELL DEFINED COLD FRONT DEVELOPS.
DON'T EXPECT BLIZZARD CONDITIONS IN THESE LOCATIONS...BUT VERY BRIEF
PERIODS OF WHITE-OUT CONDITIONS IN SNOW SHOWERS IS LIKELY. BROAD
NORTHERLY FLOW AND SNOW SHOWERS WILL SETTLE BACK IN BEHIND THIS
SYSTEM AND THROUGH THE WEEKEND.

.LONG TERM FORECAST...AS UPPER LOW RETROGRADES TO THE NORTH AND
WEST THE JET WILL LIFT NORTHWARD RESULTING IN A VERY ACTIVE PATTERN
FROM THE NORTH CENTRAL PACIFIC TO SOUTHCENTRAL ALASKA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 195.
MARINE...STORM WARNING 179.
         GALE WARNING...130 132 150 160 155 165 170 171 172 180.
         HEAVY FREEZING SPRAY WARNING...121 129 130 138 140 141
                                        150 160 165 179 185.
FIRE WEATHER...NONE.

SEB JAN 12