Avalanche in Alaska, March 14, 2015

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
538 AM AKDT SAT MAR 14 2015

.ANALYSIS AND UPPER LEVELS...

LONGWAVE TROUGHING CONTINUES TO RESIDE ACROSS THE ALASKA MAINLAND
THIS MORNING...WHICH HAS CONTINUED TO SUPPLY COLD AIR FROM THE
ARCTIC TO MUCH OF ALASKA. OVERNIGHT TEMPERATURES ACROSS SOUTHWEST
AND SOUTHCENTRAL ALASKA ONCE AGAIN DROPPED INTO THE SINGLE DIGITS
TO THE NEGATIVE TEENS. IT LOOKS LIKE A PATTERN SHIFT IS BEGINNING
TO TAKE PLACE OVER THE CENTRAL ALEUTIANS AS A QUICKLY EVOLVING
AREA OF LOW PRESSURE SOUTH OF THE ALEUTIANS AND ITS ASSOCIATED
UPPER LEVEL LOW HAVE SHIFTED EASTWARD OVERNIGHT. THE 500 MB
HEIGHTS HAVE BEEN ON THE RISE ACROSS THE ALASKA PENINSULA AS A
RESULT OF THE DEEPENING AREA OF LOW PRESSURE. THIS DEVELOPING
RIDGE HAS BEGUN TO PUT PRESSURE ON THE TROUGH OVER ALASKA AND IS
EXPECTED TO SHIFT THE TROUGH EASTWARD IN THE COMING DAYS. BACK TO
THE PRESENT...GALE FORCE WINDS AND BLOWING SNOW HAVE BEEN SEEN
ACROSS THE PRIBILOF ISLANDS OVERNIGHT AS A FRONT PIVOTS OVER THE
PRIBILOFS. SOME WARMER AIR IS BEING ADVECTED NORTHWARD IN
ASSOCIATION WITH THE LOW IN THE NORTH PACIFIC WHICH HAS TRANSITIONED
THE PRECIPITATION TYPE OVER DUTCH HARBOR TO RAIN AND BUMPED UP THE
TEMPERATURES OVER THE PRIBILOF ISLANDS TO NEAR FREEZING.

TOWARD THE NORTHERN GULF OF ALASKA...A WEAK AREA OF LOW PRESSURE
JUST TO THE SOUTH OF PRINCE WILLIAM SOUND CONTINUES TO SPARK SNOW
SHOWERS ACROSS THE NORTHERN GULF COAST WITH OCCASIONAL SNOW
SHOWERS PUSHING ACROSS CORDOVA...VALDEZ AND GULKANA. WITH THE
PROXIMITY OF THE LOW NEAR PRINCE WILLIAM SOUND...THE GRADIENT
CONTINUES TO BE FAVORABLE TO PUSH SOME GUSTY WINDS THROUGH
TURNAGAIN ARM AND PORTAGE VALLEY. AS THE LOW CONTINUES TO SHIFT
EASTWARD DURING THE MORNING HOURS...THE GRADIENT SHOULD WEAKEN AND
BECOME LESS FAVORABLY ORIENTED FOR STRONGER WINDS.

&&

.MODEL DISCUSSION...

MODELS INITIALIZED WELL FOR THE MOST PART FOR THE 00Z SYNOPTIC
RUNS...WITH THE EXCEPTION OF THE LOW SOUTH OF PRINCE WILLIAM
SOUND. SCATTEROMETER DATA FROM 05Z SHOWED THE LOW ABOUT 25 NM
WEST OF WHERE THE MODELS INITIALIZED THE LOW CENTER. OVERALL
IMPACTS FROM THIS WILL BE MINIMAL WITH SHOWERS POSSIBLY PERSISTING
A FEW HOURS LONGER AS WELL AS THE GUSTY WINDS THROUGH TURNAGAIN
ARM AND PORTAGE VALLEY. THE GFS SEEMS TO HAVE THE BEST GRASP ON
THE WARMER AIR BEING ADVECTED FROM THE NORTH PACIFIC NEAR DUTCH
HARBOR. WHILE THE NAM/ECMWF ARE HINTING AT A RAIN/SNOW MIX...THE
GFS HAS THEIR PRECIPITATION TYPE AS RAIN AND AS OF 04Z THE PRECIPITATION
TYPE TRANSITIONED TO RAIN. THE HIGHER RESOLUTION NAM WAS UTILIZED
THROUGH THE FIRST 36 HOURS OF THE FORECAST FOR HELP WITH GAP WINDS
OVER SOUTHCENTRAL ALASKA AND ALONG THE TERRAIN OF THE ALEUTIAN
ISLANDS. THE GFS WAS UTILIZED THROUGH THE REMAINDER OF THE SHORT-
TERM.

&&

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

THE SURFACE LOW OVER THE NORTHERN GULF WILL RAPIDLY MOVE EAST
TODAY. THIS WILL RELAX THE GRADIENTS AND THUS THE OFFSHORE WINDS
WILL DIMINISH TODAY. THE PATTERN WILL UNDERGO AN ABRUPT CHANGE
BEGINNING LATE TONIGHT. THE UPPER LOW THAT HAS BEEN ANCHORED OVER
SOUTHERN ALASKA WILL BE SHUNTED NORTH AS A LOW SOUTH OF THE
ALASKA PENINSULA SENDS A FRONTAL SYSTEM NORTHWARD ACROSS THE
GULF. THE WARM FRONT WILL REACH KODIAK EARLY SUNDAY AND THEN TO
THE GULF COAST LATER IN THE DAY. MOISTURE AND WARM AIR WILL SURGE
NORTHWARD. SOME BLOWING SNOW IS POSSIBLY WITH THE ARRIVAL OF THE
WARM FRONT AT KODIAK...BUT SHOULD END QUICKLY. THE SAME STORY
GOES FOR PORTAGE VALLEY AND EASTERN TURNAGAIN ARM...THOUGH IT MAY
TAKE A LITTLE LONGER FOR THE AIR TO WARM. NORTHERLY SURFACE WINDS
AND SOUTH/SOUTHEAST FLOW ALOFT WILL KEEP PRECIPITATION AT A
MINIMUM NEAR ANCHORAGE...WITH THE PROBABILITY OF PRECIPITATION
FINALLY HITTING "LIKELY" (MORE THAN 50 PERCENT) LATE SUNDAY NIGHT.

&&

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

ONE MORE DAY OF CLEAR AND COLD WEATHER IS EXPECTED OVER THE
SOUTHWEST MAINLAND TODAY. BY THIS EVENING...A NORTH PACIFIC LOW
MOVING TOWARDS THE EASTERN BERING WILL BRING INCREASING WINDS AND
CLOUD COVER TO COASTAL AREAS THAT WILL CONTINUE INTO SUNDAY. WITH
THE COLD AIR MASS CURRENTLY IN PLACE OVER THE KUSKOKWIM
DELTA...WIND CHILLS OVERNIGHT TONIGHT ARE EXPECTED TO
APPROACH...BUT NOT QUITE REACH ADVISORY CRITERIA AS THE OFFSHORE
FLOW INCREASES. STRONG WINDS WILL ALSO SPREAD UP BRISTOL BAY FROM
THE SOUTH BEGINNING LATE TONIGHT...WITH STRONG WINDS EXPECTED
THROUGHOUT BRISTOL BAY BY SUNDAY MORNING. THESE WINDS WILL CREATE
DOWNSLOPING CONDITIONS AND KEEP MUCH OF THE AREA DRY THROUGH
SUNDAY MORNING. AS THESE WINDS DIMINISH BY SUNDAY
AFTERNOON...LIGHT SNOW IS EXPECTED TO DEVELOP OVER BRISTOL
BAY...AND LIKELY CONTINUE INTO SUNDAY EVENING.

&&

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

THE LOW CURRENTLY APPROACHING THE EASTERN ALEUTIANS WILL BE THE
FOCAL POINT OF FOR THE WEATHER THROUGHOUT THE REGION THIS
WEEKEND. THE LARGEST AREA OF CONCERN WITH THIS SYSTEM CENTERS
AROUND A RETURN TO BLIZZARD CONDITIONS TO THE PRIBILOF ISLANDS.
ANOTHER ROUND OF ACCUMULATING SNOW WILL MOVE INTO THE AREA WITH
STORM FORCE WINDS BY THIS AFTERNOON...AND WITH THE ROUGHLY 2
INCHES OF FRESH SNOW RECEIVED YESTERDAY...THIS IS EXPECTED TO
CREATE NEAR WHITEOUT CONDITIONS THAT SHOULD CONTINUE INTO SUNDAY
MORNING. AS A RESULT A BLIZZARD WARNING WAS ISSUED WITH THE
MORNING PACKAGE. BLOWING SNOW WILL LIKELY CONTINUE OVER THE AREA
THROUGH SUNDAY...BUT WITH SNOW SHOWERS AND WINDS DIMINISHING THIS
IS NOT EXPECTED TO BRING BLIZZARD CONDITIONS AFTER SUNDAY
MORNING. TO THE SOUTH...WARM AIR ASSOCIATED WITH THIS SYSTEM HAS
ALREADY CAUSE SNOW OVER THE EASTERN ALEUTIANS TO TURN TO
RAIN...AND THIS WARMING WILL CONTINUE TO SPREAD EASTWARD INTO THE
THE ALASKA PENINSULA BY THIS AFTERNOON. CONDITIONS OVER THE
ALEUTIANS WILL ALSO IMPROVE THROUGHOUT THE DAY ON SUNDAY AS THE
LOW CONTINUES TO SLOWLY DISSIPATE AND WINDS DIMINISH.

&&

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

A BROAD UPPER LEVEL LOW CENTERED OVER THE ALASKA PENINSULA AND
EASTERN ALEUTIANS AND A LARGE UPPER LEVEL RIDGE STRETCHING FROM
WESTERN CANADA INTO INTERIOR ALASKA WILL PERSIST FOR MUCH OF THE
NEXT WEEK. THE POSITION OF THESE TWO FEATURES WILL STEER A SERIES
OF LOW PRESSURE SYSTEMS UP INTO THE GULF OF ALASKA AND BRISTOL
BAY...BRINGING WARMER AND MOISTURE SOUTH TO SOUTHEAST FLOW TO
SOUTHWEST AND SOUTHCENTRAL ALASKA.

THE FIRST OF MANY FRONTS WILL BE STRETCHED ACROSS THE KENAI
PENINSULA AND NORTHERN GULF COAST MONDAY MORNING WITH A SURFACE
LOW AROUND THE BARREN ISLANDS. THIS FRONTAL SYSTEM WILL LIFT NORTH
AND INLAND THROUGH THE DAY WHILE ANOTHER DEEPENING LOW APPROACHES
THE ALASKA PENINSULA FROM THE SOUTH. THIS SECOND LOW WILL CROSS
THE PENINSULA MONDAY NIGHT TRACKING INTO BRISTOL BAY AND SIGNIFICANTLY
INCREASING EASTERLY WINDS ACROSS SOUTHWEST ALASKA. SEVERAL
ADDITIONAL LOWS WILL ALSO FOLLOW SIMILAR TRACKS THROUGH THE
WEEK...WHILE A SERIES OF LOWS FORMING AND SWINGING THROUGH THE
EASTERN GULF WILL LIFT NORTH ACROSS THE NORTHERN GULF COAST.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...BLIZZARD WARNING FOR THE PRIBILOF ISLANDS FROM 4 PM THIS
         AFTERNOON TO 10 AM SUNDAY.
MARINE...GALE WARNING 119 120 131 132 139 150 155 160 165 170 172
                      173 174 175 180 351 352 411 412 413.
         STORM WARNING 130 138 179 414.
         HEAVY FREEZING SPRAY WARNING 121 126 127 128 129
               130 131 139 160 179 180 185 412 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MC
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...JER