Blizzard in Alaska, February 16, 2016

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
453 PM AKST TUE FEB 16 2016

.ANALYSIS AND UPPER LEVELS...A SLIGHT CHANGE IN OUR LONG-LIVED
PATTERN IS UNDERWAY. THE JET HAS FINALLY MOVED FAR ENOUGH NORTH
TO IMPACT THE MAINLAND OF AK. IT IS CURRENTLY MOVING FROM
SOUTHWEST TO NORTHEAST ACROSS THE CENTRAL ALEUTIANS AT ABOUT
150KTS. THIS IS PROVIDING THE SUPPORT FOR A DEVELOPING LOW
PRESSURE CENTER THIS AFTERNOON JUST WEST OF THE PRIBILOF ISLANDS.
DETERIORATING CONDITIONS ARE ALREADY APPARENT AT THE PRIBILOF ISLANDS
AS RAIN HAS DEVELOPED. SOUTHEAST WINDS ARE ALSO INCREASING ACROSS
THE EASTERN ALEUTIANS THROUGH THE WEST COAST OF THE YK-DELTA IN
RESPONSE TO THIS SYSTEM DEVELOPING. MEANWHILE...A TRANSIENT RIDGE
OVER THE MAINLAND BROUGHT ENOUGH STABILITY TO ALLOW WIDESPREAD FOG
AND STRATUS TO FORM OVER BRISTOL BAY. AS THOSE INCREASING WINDS
START TO SPREAD INLAND...THERE WILL BE ENOUGH MIXING TO CAUSE SOME
OF THIS LOW LEVEL MOISTURE TO LIFT.

IN THE EAST...THE SAME TRANSIENT RIDGE IS MAKING FOR ANOTHER SUNNY
DAY FOR JUST ABOUT ALL AREAS. THE LONE EXCEPTION IS SOME LOW
STRATUS HUNG UP IN THE COPPER RIVER BASIN COURTESY OF A VERY WEAK
SHORTWAVE PASSING THROUGH THE AREA FROM THE NORTHWEST. OUTFLOW
WINDS THROUGH THE USUAL PLACES...THOMPSON
PASS...WHITTIER...SEWARD...ARE ALSO STARTING TO INCREASE SOME
THIS AFTERNOON AS HIGHER PRESSURE INLAND WORKS IN TANDEM WITH A
WEAK TROUGH ALONG THE NORTH GULF COAST.

&&

.MODEL DISCUSSION...MODELS REMAIN IN RELATIVELY GOOD AGREEMENT ON
THE SYNOPTIC SCALE FOR THE FIRST 40 HRS OR SO. AFTER THAT...WE
START TO SEE FAIRLY BROAD DISAGREEMENT WITH ANOTHER DEVELOPING LOW
OVER THE WESTERN ALEUTIANS LATE WED INTO THU. WE ALSO SEE SOME
MINOR ISSUES WITH HOW A TRIPLE POINT LOW FORMS ALONG THE FRONT
OVER THE SOUTHWEST AND SUBSEQUENTLY...HOW IT TRACKS INTO THE GULF.
A GFS/EC BLEND WAS USED TO TAKE AN AVERAGE OF THE LOW OVER THE
WESTERN ALEUTIANS. THERE IS A DECENT LIKELIHOOD THAT THIS SYSTEM
COULD SPLIT INTO TWO SYSTEMS...SO THERE IS LOW CONFIDENCE IN
EXACTLY WHERE ANY STORM-FORCE WINDS MAY OCCUR. AS FOR THE LOW
TRACKING INTO THE GULF WED INTO THU...MOST MODELS TAKE IT OVER THE
SOUTHERN TIP OF KODIAK. ONLY THE GEM SEEMED TO SHOW A TRACK AS
FAR NORTH AS THE NORTHERN HALF OF KODIAK. SO WE LEANED AWAY FROM
THE GEM AND TRIED TO ENSURE THAT SOME SHELIKOF WINDS WERE
INCORPORATED. FINALLY...THERE IS SLIGHT DISAGREEMENT ON EXACTLY
HOW MUCH WARM AIR WILL COME UP INTO THE YK-DELTA COAST. THE NAM IS
THE COLDEST AT THIS POINT. BUT EVEN WITH 60 KTS OF -3 TO -4C
850MB FLOW...THERMAL PROFILES IN THE AREA SUPPORT MOSTLY SNOW
THROUGH THE EVENT.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

THE UPPER LEVEL RIDGE OVER WESTERN ALASKA WILL SHIFT EAST OVER
CENTRAL ALASKA TONIGHT AS A FRONTAL SYSTEM PUSHES ONSHORE AND INTO
SOUTHWEST ALASKA. FOR MUCH OF SOUTH CENTRAL ALASKA THE RIDGE WILL
BRING CLEAR SKIES WITH THE POTENTIAL FOR SOME LOCALIZED AREAS OF
PATCHY FOG OR LOW STRATUS FORMING IN WIND SHELTERED LOCATIONS. THE
BREEZY WEST TO NORTHERLY OUTFLOW WINDS THROUGH TERRAIN GAPS NEAR
THE COAST WILL DIMINISH OVERNIGHT AS THE OFFSHORE PRESSURE
GRADIENT RELAXES. THE FRONTAL SYSTEM COMING IN FROM THE WEST WILL
REACH KODIAK ISLAND ON WEDNESDAY THEN STALL IN THAT GENERAL
LOCATION THROUGH THROUGH THURSDAY. WINDS ALONG AND OUT AHEAD OF
THE FRONT WILL INCREASE TO EAST TO NORTHEASTERLY GALES WEDNESDAY
THEN GRADUALLY DIMINISH WEDNESDAY NIGHT AND THURSDAY AS THE FRONT
WEAKENS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...

A STRONG AND MOIST WARM FRONT WILL RAPIDLY MOVE INTO SOUTHWEST
TONIGHT AND EARLY TOMORROW...MOVING FROM THE COAST EASTWARD
THROUGH WEDNESDAY BEFORE STALLING ACROSS THE LOWER KUSKOKWIM
VALLEY AND INLAND BRISTOL BAY. THIS WILL BRING STRONG SOUTHEAST
WINDS AND POTENTIAL PERIODS OF HEAVY SNOW...ESPECIALLY ALONG THE
KUSKOKWIM DELTA COAST. SOME MIXING WITH RAIN MAY OCCUR FROM THE
COAST OF BRISTOL BAY TO THE SOUTHERN PORTION OF THE DELTA...WITH
THE BEST CHANCE FOR HEAVY ACCUMULATING SNOW AND STRONG WINDS ALONG
THE COAST MAINLY FROM TOKSOOK BAY NORTH. THIS WILL OCCUR LATE THIS
EVENING...WITH THE SNOW BAND MOVING INLAND BY TOMORROW
MORNING...BRINGING AN END TO ANY POTENTIAL BLIZZARD CONDITIONS. AS
THE FRONT MOVES INLAND...SNOW WILL CONTINUE TO FALL INTO THURSDAY
AS THE FRONT STALLS. COLD AIR WILL WRAP IN AS A COLD FRONT MOVES
INLAND WEDNESDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

A POWERFUL GALE FORCE FRONT WILL MAKE EASTWARD PROGRESS TO THE
SOUTHWEST COAST BY THIS EVENING...WITH AN EQUALLY STRONG COLD
FRONT CURRENTLY CROSSING THE WESTERN BERING RAPIDLY FOLLOWING ON
ITS HEELS. WINDS WILL QUICKLY TURN WEST SOUTHWEST WITH STRONG COLD
AIR ADVECTION AND INSTABILITY SNOW SHOWERS MOVING ACROSS THE
BERING SEA THROUGH WEDNESDAY. ANOTHER STRONG LOW WILL MOVE INTO
THE WESTERN BERING SEA WEDNESDAY EVENING THROUGH THURSDAY
BRINGING RAIN AND SNOW AND STRONG GALE FORCE TO NEAR STORM FORCE
WINDS...STALLING OVER THE CENTRAL BERING.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE 500MB 5-WAVE GEOPOTENTIAL HEIGHTS ARE SHOWING THE SAME
WEATHER PATTERN THAT WE HAVE BEEN EXPERIENCING FOR THE LAST
MONTH. THEREFORE...LOOK FOR WARMER TEMPERATURES AND DRIER
CONDITIONS FOR THE SOUTHCENTRAL REGION WITH AN AMPLIFIED RIDGE
OVER THE SOUTHEAST PANHANDLE EXTENDING THROUGH THE SOUTHCENTRAL
INTERIOR. WHILE THE BERING SEA...SOUTHWEST AND THE ALEUTIANS WILL
BE DOMINATED BY AN UPPER LEVEL TROUGH THROUGH THE WEEKEND. THIS
SYNOPTIC FEATURE WILL BRING A SHOWERY WEATHER REGIME FOR THE MOST
PART AS WE HEAD INTO THE WEEKEND. THE MODELS IN GENERAL AT THE
SURFACE ARE GENERATING A BROAD AREA OF LOW PRESSURE DEVELOPING
JUST SOUTH OF THE EASTERN ALEUTIANS BY THE WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...BLIZZARD WARNING 155 AND WINTER WEATHER ADVISORY FOR SNOW
161.
MARINE...STORMS 177 180 181. GALES 130 132 138 150 155 160 165
170 171 172 173 174 175 176 178 179 185 411 412 413 414.

&&

SYNOPSIS AND MODEL DISCUSSION...MO
SOUTHCENTRAL ALASKA...JR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...PD