Blizzard in Alaska, January 7, 2012

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
300 PM AKST FRI JAN 6 2012

.ANALYSIS AND UPPER LEVELS...POLAR VORTEX OVER THE WESTERN HEMISPHERE
ELONGATED FROM JUST NORTH OF HUDSON BAY BACK INTO EASTERN RUSSIA.
THIS SETS UP A SOUTHWEST FLOW OVER MUCH OF THE STATE. THE STORM TRACK
WILL BE FROM THE NORTH PACIFIC INTO THE GULF OF ALASKA FOR THE NEXT
FEW SYSTEMS THROUGH EARLY NEXT WEEK.

THE JET STREAM IS STRONG ALONG THE NORTH PACIFIC OFF THE ASIAN COAST
TO 160W. THIS IS WHY THE LOWS ARE TURNING INTO THE GULF OF ALASKA.
STRONG SHORT WAVE TROUGHS ARE RIDING ALONG THIS JET AND INTO THE
GULF. ONE OF THESE TROUGHS IS ROTATING THROUGH SOUTH CENTRAL THIS
MORNING WITH SNOW TO FINALLY TAPER OFF LATE THIS AFTERNOON OVER THE
COPPER RIVER BASIN. THE NEXT WAVE TO CURVE INTO THE WESTERN GULF
TONIGHT. RIGHT NOW THE EFFECTS OF THIS WAVE HAS DEVELOPED A 964 MB
LOW SOUTH OF COLD BAY. COMBINED WITH THE HIGH PRESSURE OVER WESTERN
ALASKA...A STRONG PRESSURE GRADIENT HAS DEVELOPED OVER THE ALASKA
PENINSULA AND EASTERN ALEUTIANS. THE EFFECT HAS BEEN THE ISSUANCE OF
BLIZZARD WARNINGS FOR THE ALASKA PENINSULA STARTING NOW NEAR COLD BAY
AND INCREASING TO THE NORTHEAST THIS EVENING. WITH THE PASSAGE OF
LAST NIGHTS LOW ACROSS SOUTH CENTRAL ALASKA...THE WINDS WERE QUITE
IMPRESSIVE WITH A MODERATE WESTERLY GRADIENT ALLOWING FOR AREAS OF
BLOWING SNOW AND BLIZZARD CONDITIONS NEAR VALDEZ TODAY. OVER THE
BERING IN OPEN WATER...THE COLD AIR ALOFT IS CONDUCIVE FOR CONVECTIVE
SNOW SHOWERS. VISIBILITIES ARE REDUCED HEAVILY IN THESE SHOWERS.

.MODEL DISCUSSION...MODELS WERE NOT TOO BAD IN CONSENSUS OF MOVING
THE LOW IN THE GULF INLAND THIS AFTERNOON AND WERE IN THE SAME
VICINITY FOR THE NORTH PACIFIC LOW. THE CURRENT NORTH PACIFIC LOW
WILL ROTATE INTO THE GULF WITH THE 12Z EC AND 18Z GFS BEING THE
DEEPEST NOW. THIS WILL MEAN A MODERATE BARRIER JET IN THE NORTHERN
GULF COAST AREA AND SOME SNOW FOR SOUTH CENTRAL AGAIN SATURDAY AND
SUNDAY AND KODIAK TONIGHT. THE BIGGER DISCUSSION ON MODEL CONSENSUS
WAS WITH THE NEXT LOW ON MONDAY REACHING THE ALEUTIAN CHAIN. THE 12Z
GFS WAS MUCH FASTER THAN THE 06Z ENSEMBLES AND ECMWF SOLUTIONS. THE
18Z RUN THOUGH HAS SLOWED THIS FEATURE DOWN NOW.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE LOW IN THE NORTH PACIFIC TO MOVE INTO THE
WESTERN GULF TONIGHT. AS THIS HAPPENS...PRECIPITATION AND STRONG
NORTHEAST FLOW WILL MOVE IN OVER THE GULF. WE EXPECT BLIZZARD
CONDITIONS TO REACH KODIAK BEFORE MIDNIGHT AND REMAIN THROUGH MUCH OF
THE DAY TOMORROW AS THE LOW WRAP UP EAST OF THEM AND INTO THE SOUND
SATURDAY NIGHT. AHEAD OF THE LOW...A MODERATE BARRIER JET CAN BE
EXPECTED. AN 850 MB INVERTED TROUGH WILL SWING THROUGH SOUTH CENTRAL
SATURDAY BEFORE THE LOW SETTLES INTO THE SOUND SATURDAY NIGHT. THIS
WILL SPREAD SNOWFALL OVER THE INLAND AREAS WITH NORTH GULF COAST
STATIONS RECEIVING PRECIP LATER TONIGHT. WITH HIGH PRESSURE OVER
WESTERN ALASKA...THE GRADIENT WILL SHARPEN UP SATURDAY NIGHT AND
SUNDAY FOR STRONG WESTERLY GAP FLOWS THROUGH THE COOK INLET AND KENAI
PENINSULA REGIONS BY SUNDAY. THE MAIN FACTOR WILL BE WHETHER
PRECIPITATION IS STILL PRESENT AND MAY WARRANT A BLIZZARD WARNING FOR
SUNDAY. WILL HAVE TO WAIT TIL IT GETS MORE RUN TO RUN CONSISTENCY TO
DETERMINE LIKELIHOOD OF BLIZZARD CONDITIONS NEAR HOMER OR WHITTIER
AND PORTAGE SUNDAY BEFORE THE SNOW SHUTS OFF.

SOUTHWEST ALASKA...A LOW SOUTH OF THE EASTERN ALEUTIAN CHAIN THIS
AFTERNOON HAS PROVIDED ENOUGH GRADIENT FOR STRONG NORTHERLY WINDS
ALONG THE CHAIN. WITH PERSISTENT SNOWFALL ALONG THE ALASKA PENINSULA
DEVELOPING...BLIZZARD CONDITIONS HAVE BEGUN NEAR COLD BAY. THESE
CONDITIONS WILL SPREAD INTO THE AKPEN AREA OF BRISTOL BAY THIS
EVENING. INLAND...THE LOW MOVING TOWARD KODIAK THIS EVENING WILL
INCREASE THE NORTHERLY FLOW OVER THE AREA. THIS WILL BRING THE COLD
CONDITIONS TO WIND CHILL ADVISORY AND WARNING LEVELS TONIGHT. THE
COLDEST AIR TO REMAIN IN PLACE OVER THE YK DELTA AND WARNING LEVELS
WILL BE EXPERIENCED THERE LATER TONIGHT. THE ADVISORIES AND WARNINGS
FOR WIND CHILL WILL DIMINISH AS THE WINDS DROP OFF AGAIN BY TOMORROW
EVENING IN SOUTHWEST ALASKA. AS THE WINDS BEGIN TO PICK UP AGAIN ON
MONDAY THE TEMPERATURES ARE EXPECTED TO PICK UP A BIT WITH THE NEXT
LOW. THIS LOW WILL BRING SNOW TO THE AREA MONDAY NIGHT AND TUESDAY.

BERING SEA/ALEUTIANS...WEAK TROUGH MOVING THROUGH THE BERING TONIGHT
AND TOMORROW FOR SNOW SHOWERS. WITH THE COLD AIR AS WELL...CONVECTIVE
SHOWERS CAN BE EXPECTED OVER THE OPEN WATER AREAS. THE LOW ON MONDAY
WILL BRING SOME WARMER TEMPERATURES TO THE CENTRAL AND EASTERN
ALEUTIANS SUNDAY NIGHT INTO MONDAY. HOWEVER...PRECIPITATION SHOULD
REMAIN ALL SNOW. DEFINITELY WILL EXPERIENCE GALE FORCE WINDS WITH
THIS LOW ON MONDAY. SO THE POTENTIAL FOR BLIZZARD CONDITIONS COULD
ARRIVE AGAIN BY LATE SUNDAY/MONDAY FOR THE CENTRAL AND EASTERN
ALEUTIAN CHAIN.

.LONG TERM FORECAST...THE UPPER LEVEL LOW WILL RETROGRADE BACK TO
WEST OF THE KAMCHATKA PENINSULA LATE THIS WEEKEND. THIS WILL CHANGE
THE LONG WAVE PATTERN FOR THE STORM TRACK TO BE FARTHER WEST.
SO...THE NEXT LOW ON MONDAY WILL MOVE INTO BRISTOL BAY RATHER THAN
THE GULF. THIS COULD MEAN A WIND EVENT ONCE AGAIN FOR SOUTH CENTRAL
ALASKA WITH TEMPERATURE BECOMING ABOVE NORMAL FOR MONDAY AND TUESDAY.
THIS LOW WILL SWING ACROSS THE MAINLAND WEDNESDAY WITH A RETURN TO
COLDER AIR OVER THE MAINLAND. THE NEXT LOW WILL BE EVEN FARTHER WEST
WEDNESDAY IN THE WESTERN BERING WITH A FRONT EXTENDING INTO THE
EASTERN BERING BY FRIDAY. THE TIMING AS WOULD BE EXPECTED IS STILL UP
FOR DEBATE. HOWEVER...THE BIG PICTURE IS THAT THE STORM TRACK WILL BE
PROGRESSIVELY FARTHER WEST THROUGH THE WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 161 171 181.
         WIND CHILL WARNING 155.
MARINE...GALE WARNING...120 130 132 138 140 150 155 165 170 171.
         HEAVY FREEZING SPRAY WARNING...121 129 130 132 138 140 141
                                        160 165 179 185.
FIRE WEATHER...NONE.

JN JAN 12