Storm Surge and Blizzard in Alaska, December 23 to 28, 2015

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
507 PM AKST WED DEC 23 2015

.ANALYSIS AND UPPER LEVELS...

UPPER LEVELS...A BUILDING UPPER LEVEL RIDGE WITH AXIS OVER THE
EASTERN BERING IS MOVING NORTH AND EASTWARD TOWARDS MAINLAND
SOUTHERN ALASKA THIS AFTERNOON. THIS RIDGE IS BUILDING DUE TO A
STRONG STORM MOVING ACROSS THE WESTERN ALEUTIANS. A DIGGING TROUGH
IS SWINGING ACROSS THE WESTERN BERING AND NORTH PACIFIC. THE COLD
AIR ASSOCIATED WITH THE TROUGH IS MOVING EASTWARD AND
STRENGTHENING THE GRADIENT WITH THE WARMER AIR MOVING UP FROM THE
SOUTH IN THE EASTERN PORTION OF THE STORM. THIS STRENGTHENED
TEMPERATURE GRADIENT IS HELPING TO CAUSE THE STORMS RAPID
DEEPENING.

SURFACE...WITH REGARDS TO THE BERING STORM...ITS MOVEMENT WEST OF AMCHITKA
IS KEEPING THE STRONGEST WINDS ON THE WARM SIDE OF THE STORM
LARGELY WEST OF ADAK AND ATKA...BOTH OF WHOM HAVE ONLY SEEN GUSTS
UP TO 60 MPH THUS FAR. HOWEVER...THE PRECIPITATION SHIELD EXTENDS
WELL AWAY FROM THE STORM...WITH DUTCH HARBOR GETTING RAIN AND
SHEMYA GETTING SNOW.

THE WARM AIR ASSOCIATED WITH THE SOUTHERLY WINDS EAST OF
THE BERING STORM IS MOVING OVER THE COLD AIR NEAR THE SURFACE.
THE STRONG INVERSION IS CAPPING ANY MIXING FROM
OCCURRING...KEEPING MOIST AIR TRAPPED. THIS HAS RESULTED IN
WIDESPREAD FOG...WITH LOCALLY DENSE AREAS TO PERSIST OVER NEARLY
ALL OF THE BRISTOL BAY AREA. THE 12Z KING SALMON SOUNDING AFFIRMS
THIS SCENARIO...WITH A SATURATED STRONG NEAR-SURFACE INVERSION
NOTED. THE FOG/MIST IS ALSO WIDESPREAD ACROSS THE KUSKOKWIM DELTA
AREA...THOUGH IT IS NOT AS DENSE DUE TO MUCH DRIER AIR BEING
PRESENT ABOVE THE INVERSION...AS NOTED ON THE 12Z BETHEL SOUNDING.

FOG HAS ALSO BEEN THE PRIMARY HAZARDOUS WEATHER FEATURE ACROSS
SOUTHCENTRAL FOR THE PAST COUPLE DAYS. WHILE ALL OF THE TREES ARE
FESTOONED WITH HOAR FROST FROM THE FREEZING FOG OF PREVIOUS
DAYS...IT HAS LARGELY DISSIPATED OVER SOUTHCENTRAL DUE TO A
WEAKENING INVERSION AND A BIT MORE WIND ABOVE THE INVERSION TO
PROMOTE MIXING. FOR THE FOURTH DAY IN A ROW...ANCHORAGES SOUNDING
CONTINUES TO SHOW LARGE SCALE COOLING OF THE LOWER HALF OF THE
ATMOSPHERE.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN GOOD AGREEMENT IN THE NEAR-TERM...BOTH WITH THE
TRACK AND POSITION OF THE BERING STORM...AND TRACKING THE SMALLER
UPPER LEVEL DISTURBANCES MOVING ACROSS SOUTHCENTRAL. SUBSTANTIAL
DISAGREEMENT BETWEEN THE MODELS OCCURS FOR THE DAY TOMORROW
REGARDING HOW THE BERING STORM INTERACTS WITH A SECONDARY LOW THAT
FORMS ALONG THE BERING STORMS COLD FRONT OVER THE NORTH PACIFIC.
WHILE THE SECONDARY LOW FORMS IN THE LEFT EXIT REGION OF A JET
STREAK IN THE SUBTROPICAL JET...THE JET STREAK QUICKLY LEAVES THE
SECONDARY LOW BEHIND AS IT TRANSLATES EASTWARD TOWARDS THE
SOUTHERN GULF BY CHRISTMAS MORNING. WHILE THE MODELS AGREE ON THAT
SCENARIO FOR THE UPPER LEVELS...THE DISAGREEMENT IS WHERE THE
TRACK OF THE SURFACE LOW GOES ONCE THE JET STREAK HAS MOVED AWAY.
THE GFS WAS THE MODEL OF CHOICE...KEEPING THE SECONDARY LOW
FURTHER SOUTH AND EAST...CLOSER TO THE JET STREAK AND THE BEST
UPPER LEVEL DIVERGENCE. CONFIDENCE IS BELOW AVERAGE GIVEN THE
LARGE MODEL SPREAD IN THE TRACK OF THE STORM.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
ONE MORE DAY OF RELATIVELY QUIET CONDITIONS IS IN STORE FOR
SOUTHCENTRAL AK BEFORE MORE ACTIVE WEATHER RETURNS ON CHRISTMAS
DAY WITH THE ARRIVAL OF A STRONG FRONT OVER THE GULF OF ALASKA. IN
THE MEANTIME...OUTFLOW WINDS ALONG THE GULF COAST WILL PEAK IN
INTENSITY TONIGHT AS A 130 KT UPPER LEVEL JET STREAK MOVES
OVERHEAD IN ADVANCE OF A RIDGE BUILDING IN FROM THE SOUTHWEST.
WINDS WILL THEN GRADUALLY DIMINISH THROUGH THE DAY ON THURSDAY.
THE RIDGE MOVING OVERHEAD WILL ALSO CONTINUE TO SUPPORT PATCHY FOG
OVER THE UPPER COOK INLET REGION THROUGH THURSDAY MORNING AS SKIES
CLEAR AND WINDS REMAIN LIGHT AT THE SURFACE. A WEAKENING FRONT
ASSOCIATED WITH A LOW OVER THE WESTERN BERING WILL BRING A ROUND
OF LIGHT RAIN AND SNOW TO KODIAK ISLAND THURSDAY MORNING AND THEN
POSSIBLY CLIP THE SOUTHERN TIP OF THE KENAI PENINSULA WITH A FEW
SNOW SHOWERS BEFORE DISSIPATING IN THE AFTERNOON.

CONDITIONS WILL THEN RAPIDLY DETERIORATE BEGINNING THURSDAY NIGHT
AS A MUCH STRONGER FRONT ENTERS THE SOUTHWESTERN GULF ACCOMPANIED
BY GALE TO STORM FORCE WINDS AND HEAVY PRECIPITATION. LOCATIONS IN
THE VICINITY OF THE EASTERN KENAI PENINSULA/WESTERN PRINCE WILLIAM
SOUND WILL LIKELY BEAR THE BRUNT OF THE IMPACTS FROM THIS SYSTEM
AS THE FRONT ARRIVES ALONG THE GULF COAST ON FRIDAY...WITH THE
MAIN FORECAST CHALLENGES REVOLVING AROUND HOW QUICKLY THESE
LOCATIONS WARM TO NEAR OR ABOVE FREEZING. THIS WILL HAVE LARGE
IMPLICATIONS ON POTENTIAL SNOW AMOUNTS AND ALSO THE POTENTIAL FOR
BLOWING SNOW OVER THE PORTAGE VALLEY AND EASTERN TURNAGAIN ARM. IT
APPEARS AT THIS TIME AS THOUGH MOST INLAND LOCATIONS WILL REMAIN
COLD ENOUGH FOR ALL SNOW THROUGH FRIDAY EVENING WITH RAIN
BEGINNING TO MIX IN ALONG THE COAST BY LATE FRIDAY
AFTERNOON...WITH THE HIGHEST SNOW AMOUNTS OVER INLAND LOCATIONS.
POTENTIAL ACCUMULATIONS AND BLOWING SNOW WILL CONTINUE TO BE
CLOSELY MONITORED OVER THE NEXT 24-36 HOURS. INLAND LOCATIONS
INCLUDING THE ANCHORAGE BOWL WILL INITIALLY REMAIN DOWNSLOPED AS
STRONG CROSS BARRIER FLOW DEVELOPS WITH THE ARRIVAL OF THE FRONT.
&&

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

A POTENT WARM FRONT ATTACHED TO THE STRONG LOW IN THE WESTERN
BERING SEA WILL PUSH INLAND ACROSS SOUTHWEST ALASKA THURSDAY
MORNING. WITH AN OFFSHORE PRESSURE GRADIENT (EAST TO NORTHEAST
WINDS)...TEMPERATURES WILL BE SLOW TO RESPOND TO THE IMPENDING
WARM AIR ADVECTION (NOT TO MENTION THE FRONTAL OCCLUSION). THE
WARM FRONT WILL ADVECT A MOISTURE RICH AIR MASS NORTHWARD WHICH
WILL BRING SNOW TO MUCH OF SOUTHWEST ALASKA. THE STRONGEST
PRESSURE GRADIENT AND POTENTIAL FOR HEAVIEST SNOW WILL BE ACROSS
THE KUSKOKWIM DELTA LATE THURSDAY NIGHT THROUGH THURSDAY MORNING.
THIS WILL SUPPORT PERIODIC BLIZZARD CONDITIONS ALONG THE COAST
FROM KIPNUK NORTHWARD...WITH REGIONS OF BLOWING SNOW INLAND AS
WELL...ALTHOUGH NOT AS SEVERE. SNOW ACROSS THE BRISTOL BAY AREA
WILL BE SHORT-LIVED AS TEMPERATURES QUICKLY WARM ABOVE FREEZING
LEADING TO A TRANSITION TO RAIN. THE FRONT WILL LIFT NORTH
THURSDAY AFTERNOON...WITH MOST AREAS ACROSS SOUTHWEST DRYING OUT
AND WARMING UP BEFORE ANOTHER FRONT MOVES IN THURSDAY NIGHT AND
EARLY FRIDAY.

A SECOND LOW IN THE NORTH PACIFIC WILL RAPIDLY SPIN UP ON THURSDAY
AS IT QUICKLY PUSHES NORTHWARD TOWARD THE ALASKA PENINSULA. MODEL
GUIDANCE HAS BEEN EXTREMELY POOR IN HANDLING THE EXACT TRACK OF
THIS LOW ON FRIDAY IN WHETHER IT PUSHES INTO THE BERING SEA OR
NOT. THE TRACK PLAYS IN IMPORTANT ROLE ON HOW STRONG THE WINDS
ACROSS THE ALASKA PENINSULA WILL BE ON FRIDAY. AT THIS TIME IT
APPEARS THE LOW WILL STAY JUST SOUTH OF THE PENINSULA AND THE PRESSURE
GRADIENT WILL BE QUITE FAVORABLE FOR THE SOUTHEASTERLY WINDS
ASSOCIATED WITH THE FRONT TO SCREAM THROUGH THE GAPS ALONG THE
PENINSULA. WIND GUSTS WILL LIKELY MAX OUT IN THE 65 TO 70 MPH
RANGE BUT A FEW ISOLATED STRONGER GUSTS WILL BE POSSIBLE. AS THIS
FRONT SHIFTS ACROSS BRISTOL BAY FRIDAY EVENING...WINDS WILL BEGIN
TO INCREASE WITH THE STRONGEST WINDS COMING THROUGH LAKE CLARK PASS
ALONG THE ALASKA RANGE. THESE STRONGER WINDS WILL LIKELY PUSH ALL
THE WAY INTO THE DELTA WITH HEAVY PRECIPITATION POSSIBLE AT TIMES
IN THE BRISTOL BAY AREA.

&&

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

A STORM FORCE LOW CONTINUES TO STRENGTHEN OVER THE WESTERN BERING
SEA THIS AFTERNOON. THIS IS EVIDENT FROM MULTIPLE SATELLITE IMAGES
AS WELL AS MULTIPLE SURFACE OBSERVATIONS THROUGHOUT THE WESTERN
AND CENTRAL ALEUTIANS. RAIN AND SNOW WILL QUICKLY TURN TO ALL
RAIN AS A STRONG WARM FRONT MOVES THROUGH THE REGION. THE ONLY
LOCATION TO REMAIN COLD ENOUGH FOR SNOW AND SNOW SHOWERS WILL BE
ACROSS THE FAR WESTERN ALEUTIANS WHERE COLDER ARCTIC AIR WILL WRAP
AROUND THIS LOW. THIS LOW WILL SLOWLY MEANDER EASTWARD DURING THE
OVERNIGHT HOURS WITH THE STRONGEST WINDS REMAINING ON THE
WEST/NORTHWEST SECTORS OF THE LOW. THE STRONGEST CORE OF WINDS
WILL PASS JUST TO THE EAST OF SHEMYA TOMORROW MORNING AND
EVENTUALLY PUSH OVER ADAK AND ATKA FRIDAY MORNING. THIS LOW WILL
MERGE WITH ANOTHER STORM FORCE LOW MOVING IN FROM THE NORTH
PACIFIC ON FRIDAY. THIS WILL KEEP RAIN (MIXED WITH SNOW OVER THE
WESTERN HALF OF THE BERING SEA) IN THE FORECAST AND THE STRONGEST
WINDS AFTER THE MERGER WILL BE SEEN OVER THE CENTRAL AND EASTERN
ALEUTIANS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE STRONG LOW WHICH WILL BE OUT NEAR THE TIP OF THE ALASKA
PENINSULA FRIDAY EVENING WILL TRACK SLOWLY TO THE EAST AND INTO
THE WESTERN GULF FRIDAY NIGHT AND SATURDAY. THE ASSOCIATED FRONTAL
SYSTEM WHICH WILL BE STRETCHED ACROSS THE KENAI PENINSULA AND
NORTHERN GULF FRIDAY EVENING WILL LIFT NORTH AND INLAND SATURDAY
MORNING...HOWEVER SEVERAL ADDITIONAL TROUGHS ASSOCIATED WITH THE
SURFACE LOW WILL SWING ONSHORE THROUGH THE WEEKEND AND KEEP
PRECIPITATION GOING ALONG AND NEAR THE COAST WITH MINIMAL BREAKS.
FURTHER INLAND PRECIPITATION WILL TAKE THE FORM OF ISOLATED TO
SCATTERED SNOW SHOWERS WITH INCREASED COVERAGE ALONG THE
MOUNTAINS.

THE NEXT FRONTAL SYSTEM WILL TRACK INTO THE WESTERN ALEUTIANS
SATURDAY. A DEVELOPING FRONTAL WAVE WILL SPIN UP INTO A CLOSED
LOW SOUTH OF THE CENTRAL ALEUTIANS THEN TRACK EAST ALONG 50N
SATURDAY NIGHT THROUGH SUNDAY. THE ASSOCIATED FRONT WILL REACH
THE SOUTHWESTERN AND SOUTH CENTRAL GULF SUNDAY NIGHT WITH A
SURFACE LOW ROTATING UP INTO THE GULF ON MONDAY. ADDITIONAL
SYSTEMS WILL TRACK INTO THE ALEUTIANS THROUGH MIDWEEK WITH TRIPLE
POINTS AND FRONTAL WAVES DEVELOPING INTO CLOSED LOWS THAT SWING IN
FROM THE SOUTHWEST TOWARDS THE ALASKA PENINSULA AND THEN SPIN UP
ADDITIONAL SURFACE LOWS WHICH SUBSEQUENTLY ROTATE INTO THE GULF.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...BLIZZARD 155.
MARINE...STORM 132 150 155 160 165 178 177 176 180 352 411 412.
         GALE 127 129 130 131 136 137 138 139 170 172 173 174
              175 179 181 185 413 414
         HEAVY FREEZING SPRAY 180 181 185 &&

SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...JR