Ice Storm and Avalanche in Alaska, February 11, 2016

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
442 PM AKST WED FEB 10 2016

.ANALYSIS AND UPPER LEVELS...

A BROAD UPPER LEVEL TROUGH SPANS FROM THE GULF TO THE EASTERN
BERING AND IS CENTERED 800 MILES SOUTH OF THE ALASKA PENINSULA. A
STRONG SHORT WAVE IS PINWHEELING AROUND THE CENTER...HEADING
NORTHWEST TOWARD KODIAK ISLAND. ACROSS SOUTHCENTRAL...AN AMPLIFIED
RIDGE IS BEGINNING TO BREAK DOWN AS THE STRONG SHORTWAVE PUSHES
ENERGY TOWARD THE NORTHEAST COAST. RAIN SHOWERS CONTINUE TO
DEVELOP ALONG THE GULF THIS AFTERNOON ALONG A FRONT THAT MOVED
TO THE NORTHERN GULF EARLIER TODAY WITH ISOLATED SNOW SHOWERS
INLAND.

TO THE WEST...A SNOW BAND DEVELOPED ALONG A WEAK FRONT MOVING
ACROSS BRISTOL BAY WITH MOST OF THE ACTIVITY NORTH OF KING SALMON.
THE LOW THAT MOVED THE FRONT TO SOUTHWEST ALASKA AND THE GULF IS
NOW WEAKENING SOUTH OF THE ALASKA PENINSULA. RAIN AND SNOW SHOWERS
CONTINUE TO DEVELOP ALONG THE EASTERN BERING AS THE SURFACE LOW
DRIFTS SLOWLY WEST. RIDGING ACROSS THE CENTRAL ALEUTIANS IS
SHUNTING PROGRESS OF A NORTH PACIFIC LOW. WITH THE RIDGE
HOLDING...NORTHERLY WINDS ARE BEGINNING TO INCREASE AS THE
PRESSURE GRADIENT IS TIGHTENING ACROSS THE WESTERN BERING AND
ALEUTIANS.

&&

.MODEL DISCUSSION...
AN ACTIVE WEATHER PATTERN CONTINUES TO MOVE UP FROM THE PACIFIC
AS THE MAIN UPPER LOW SOUTH OF THE ALASKA PENINSULA SLOWLY LIFTS NORTH
INTO FRIDAY. THE NAM AND GFS MODELS WERE IN BEST AGREEMENT FOR THE
12Z RUN THIS MORNING WITH THE ECMWF RUNNING A BIT FASTER ON THE LOW
TRACKING INTO THE GULF ON FRIDAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
MOIST ONSHORE FLOW WILL KEEP ABUNDANT PRECIPITATION FOCUSED ALONG
THE GULF COAST THROUGH THE END OF THE WORK WEEK AS VARIOUS
EMBEDDED DISTURBANCES MOVE INTO THE GULF. THE NEXT IN A SERIES OF
FRONTS WILL ARRIVE ALONG THE COAST LATE TONIGHT AND SERVE TO
ENHANCE PRECIPITATION...WITH RAIN ALONG THE IMMEDIATE COAST AND
THE POTENTIAL FOR A FEW INCHES OF WET SNOW ACCUMULATION FROM
VALDEZ TO EASTERN PORTIONS OF TURNAGAIN ARM AND THE PORTAGE
VALLEY. A TRAILING UPPER LEVEL WAVE WILL MOVE OVER SOUTHCENTRAL
AK ON THURSDAY AND BRING THE POSSIBILITY FOR A FEW SHOWERS TO THE
COOK INLET AND MAT-SU REGIONS. OTHERWISE...PERSISTENT DOWNSLOPE
FLOW WILL KEEP THESE AREAS MOSTLY DRY THROUGH FRIDAY. THE NEXT
FRONT WILL APPROACH THE GULF COAST THURSDAY NIGHT INTO FRIDAY
AHEAD OF A SURFACE LOW AND ASSOCIATED UPPER TROUGH MOVING THROUGH
THE EASTERN GULF...BRINGING ANOTHER ROUND OF POTENTIALLY HEAVIER
PRECIPITATION TO AREAS ALONG THE COAST.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THERE IS A NORTH PACIFIC LOW TRACKING JUST SOUTH OF THE EASTERN
ALEUTIANS THIS EVENING RESULTING IN GALE FORCE NORTHEASTERLY WINDS
ALONG THE SOUTHWEST ALASKA COASTLINE. WHILE THE GRADIENT IS
SLIGHTLY WEAKER INLAND ACCOMPANIED BY OFFSHORE FLOW. THE BULK OF
THE PRECIPITATION WILL SPILL-OVER THE ALASKA PENINSULA AND THE
ALEUTIAN RANGE THROUGH TONIGHT. THIS WILL PRODUCE SCATTERED SNOW
SHOWERS THROUGH THE AOR...EXCEPT FOR A MIXTURE OF RAIN/SNOW ALONG
THE ALASKA PENINSULA DUE TO THE WARMER TEMPERATURES. BY THURSDAY
MORNING A SECOND LOW WILL TRACK NEAR KODIAK ISLAND WHICH WILL
RESULT IN ANOTHER SWATH OF MOISTURE SPREADING ACROSS THE ALEUTIAN
RANGE BEFORE EXTENDING INTO THE BRISTOL BAY INLAND AREAS. THIS
MOISTURE WILL MOVE INTO THE KUSKOKWIM DELTA REGION BY LATE
THURSDAY NIGHT AND WILL FALL AS ALL SNOW THROUGH THE AREA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE MAJORITY OF THE BERING SEA WILL WE UNDER A SHOWERY WEATHER
REGIME WITH THE NORTHEASTERLY FLOW. THE COLDEST TEMPERATURES WILL
OCCUR FROM THE CENTRAL TO NORTHERN BERING. THIS IS RESULTING FROM
A GALE FORCE LOW PRESSURE SYSTEM TRACKING TOWARD DUTCH HARBOR
TONIGHT FROM THE PACIFIC SIDE OF THE CHAIN. THIS IS BRINGING A
SWATH OF RAIN AND STRATUS TO THE EASTERN ALEUTIANS BEFORE
SPREADING TO THE CENTRAL ALEUTIANS HEADING INTO THURSDAY. THE
WESTERN ALEUTIANS WILL SEE COOLER TEMPERATURES WITH ANY
PRECIPITATION FALLING AS LIGHT SNOW SHOWERS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

THE MIDTERM IS HIGHLIGHTED BY A COMPLEX AREA OF LOW PRESSURE
HOVERING ALONG THE CENTRAL AND EASTERN ALEUTIANS WITH ANOTHER AREA
OF LOW PRESSURE MOVING INTO THE NORTHERN GULF OF ALASKA. THE
COMPLEX LOW NEAR THE ALEUTIANS WILL BE ON A WEAKENING TREND AS IT
SLOWLY DRIFTS NORTHWARD INTO BRISTOL BAY OVER THE WEEKEND AS THE
JET ENERGY (STEERING CURRENTS) REMAINS MUCH FURTHER SOUTH IN THE
NORTH PACIFIC. THIS WILL CONTINUE TO BRING RAIN SHOWERS (MAYBE
MIXED WITH SNOW TOWARD THE WESTERN ALEUTIANS) AS WELL AS ANOTHER
PUSH OF WARMER AIR FROM THE SUBTROPICS. THE LOW AND ITS ASSOCIATED
FRONT IN THE NORTHERN GULF WILL BRING RAIN SHOWERS TO THE NORTHERN
GULF COAST AND SOME SNOW SHOWERS FURTHER INLAND TO LOCATIONS LIKE
VALDEZ AND THOMPSON PASS. ANCHORAGE AND THE MAT-SU VALLEYS LOOK TO
REMAIN ON THE DRY SIDE AS THE FRONT WEAKENS AS IT APPROACHES THE
GULF COAST AND ENOUGH CROSS BARRIER FLOW SHOULD KEEP THE LOW
LEVELS TOO DRY TO SUPPORT PRECIPITATION.

HEADING INTO THE EXTENDED PERIOD THE FORECAST BECOMES MUCH MORE
COMPLICATED AS MODEL SOLUTIONS BEGIN TO DIVERGE DUE TO THE
LOCATION AND STRENGTH OF THE UPPER LEVEL JET. THE GFS IS BY FAR
THE STRONGEST OF ALL DETERMINISTIC GUIDANCE AS IT PLACES THE JET
FURTHER NORTH AND ALLOWS THIS JET ENERGY TO SPIN UP A STRONG LOW
IN THE WESTERN BERING SEA BEHIND THE DEPARTING TROUGH ON TUESDAY.
THE ECMWF LOOKS TO KEEP THIS JET ENERGY FURTHER SOUTH WHICH CAUSES
THE LOW IN THE BERING TO BE A GOOD BIT WEAKER AND FASTER AS THE
FURTHER SOUTH JET CAUSES THE SYNOPTIC PATTERN TO BE MORE
PROGRESSIVE. REGARDLESS OF THE SOLUTION...A MUCH MORE ACTIVE
PATTERN LOOKS IN STORE FOR NEXT WEEK ACROSS MUCH OF ALASKA.
TEMPERATURES LOOK TO REMAIN A GOOD BIT ABOVE NORMAL THROUGH
WEDNESDAY BUT MODELS HINT AT COOLER TEMPERATURES TAKING OVER BY
THE END OF NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 120 130 138 139 160 180 181 185.
		 HEAVY FREEZING SPRAY 180 185.

&&