Storm Warning 223, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
552 AM AKST TUE DEC 29 2015

.ANALYSIS AND UPPER LEVELS...
THE PATTERN ALOFT FEATURES AN AMPLIFIED RIDGE OVER THE GULF
EXTENDING THROUGH THE SOUTHCENTRAL REGION NORTHWARD INTO THE NORTH
SLOPE. THIS IS BRINGING STRONG SOUTHERLY FLOW WITH WARMER
TEMPERATURES BEING ADVECTED INTO ALASKA REGION. THE KENAI
PENINSULA...ANCHORAGE BOWL...PRINCE WILLIAM SOUND AND THE
MATANUSKA VALLEY ALL HAVE TEMPERATURES IN THE 40S THIS MORNING.
THE JET STREAK ALSO REFLECTS THIS WARMER PATTERN WITH A STRONG 100
KNOT SOUTHERLY JET STREAM OVER THE EASTERN ALEUTIANS EXTENDING
THROUGH THE SOUTHWEST INTERIOR BEFORE TRANSITIONING TO A ZONAL
WEST TO EAST FLOW OVER THE EASTERN BROOKS RANGE TERRITORY. FARTHER
UPSTREAM THE VERY STRONG 185 KNOT NORTHWESTERLY SUBTROPICAL JET
LOCATED SOUTH OF THE WESTERN ALEUTIAN CHAIN...CONTINUES TO DIG
INTO THE BASE OF THE LONGWAVE TROUGH SOUTH OF THE CENTRAL
ALEUTIANS. THIS IS SETTING UP FOR THE AFOREMENTIONED LONGWAVE
TROUGH TO BECOME NEGATIVELY TILTED IN THE NORTHERN PACIFIC. THE
WATER VAPOR IMAGERY IS SHOWING A WAVE FORMING NEAR 44N 164W THIS
MORNING. ALSO WITH A LARGE PLUME OF MOISTURE STREAMING NORTHWARD
INTO THE EASTERN ALEUTIANS AND EXTENDING INTO THE
SOUTHWEST/SOUTHCENTRAL ALASKA REGION. THE WEATHER FRONT THAT WENT
THROUGH OUR AREA YESTERDAY HAS THE WATER VAPOR IMAGERY SHOWING
THIS FRONT OVER THE NORTH SLOPE. WHILE ON THE BERING SIDE THE
OCCLUDED LOW AT THE SURFACE IS POSITIONED JUST SOUTH OF THE
PRIBILOF ISLANDS. THE SCATTEROMETER WIND IMAGERY IS SHOWING THE
SOUTHERLY FLOW AHEAD OF THIS SYSTEM WITH SMALL CRAFT WINDS OVER
THE EASTERN BERING SEA AND EASTERN ALEUTIANS. THIS SOUTHERLY FETCH
WILL CONTINUE TO BRING WARMER TEMPERATURES TO THE EASTERN BERING
SEA AND SOUTHWEST ALASKA. THE SURFACE TEMPERATURES IN BRISTOL BAY
THIS MORNING ARE IN THE MID 30S TO LOWER 40S. THE REST OF THE
BERING SEA IS UNDER A SHOWERY WEATHER REGIME WITH GALE FORCE
NORTHEASTERLY WINDS IN THE NORTHERN BERING.

&&

.MODEL DISCUSSION...
THE MODELS HAVE COME INTO BETTER AGREEMENT WITH THE NEXT MAJOR
NORTH PACIFIC LOW PRESSURE SYSTEM THAT WILL BE TRACKING TOWARD THE
EASTERN ALEUTIANS BY TUESDAY NIGHT. THE NAM WAS THE PREFERRED
MODEL OF CHOICE IN THE SHORT TERM DUE TO IT HIGHER RESOLUTION.
BY EARLY WEDNESDAY MORNING THIS STORM FORCE LOW WILL CROSS THE
OVER THE EASTERN ALEUTIANS INTO THE BRISTOL BAY AREA. THE ECMWF IS
THE OUTLIER WITH IT MOVING THIS SYSTEM FASTER THAN THE OTHER
MODELS. THE GFS MODEL IS THE STRONGEST OUT OF THE OTHER MODELS IN
SHOWING HURRICANE FORCE WINDS ON THE PACIFIC SIDE ALONG THE
EASTERN ALEUTIANS AND THROUGH THE BRISTOL BAY INTERIOR FOR
WEDNESDAY MORNING. THE BOTTOM LINE...THERE WILL BE VERY STRONG
PRESSURE GRADIENTS RESULTING IN VERY STRONG GAP WINDS WHICH WILL
LIKELY MEET HIGH WIND WARNING THRESHOLD WITH THIS STORM. THE
FORECAST CONFIDENCE IS ABOVE AVERAGE AND WILL INCREASE AS WE GET
CLOSER TO THE TIME OF THE STORM EVENT.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A MAJOR STORM SYSTEM FORMING OVER THE PACIFIC WILL BRING SIGNIFICANT
WINDS TO KODIAK ISLAND AND THE GULF AS WELL AS NEARLY ALL OF
SOUTHCENTRAL ALASKA TONIGHT THROUGH WEDNESDAY. THERE IS STILL SOME
UNCERTAINTY IN EXACTLY HOW DEEP THE LOW CENTER WILL GET...BUT
OVERALL FORECAST CONFIDENCE IN THE TRACK OF THE LOW AND ASSOCIATED
FRONTAL SYSTEM IS HIGH. THEREFORE...HAVE UPPED WINDS BASED ON THE
AVERAGE STRENGTH OF AVAILABLE GUIDANCE. IT IS WORTH NOTING THAT
WINDS WITH THIS SYSTEM WILL BE A LEVEL HIGHER THAN THE FRONT
WHICH CROSSED THE REGION SUNDAY NIGHT AND MONDAY. IN
ADDITION...THE TRACK OF THE LOW NORTHWESTWARD ACROSS SOUTHWEST
ALASKA AND NORTH OF 60N LATITUDE IS VERY FAVORABLE FOR STRONG
WINDS IN GENERAL FOR MUCH OF SOUTHCENTRAL...INCLUDING THE
POPULATION CENTERS OF ANCHORAGE AND THE MATANUSKA VALLEY. BESIDES
THE NORMAL WINDS ALONG AND AHEAD OF THE FRONTAL BOUNDARY...STRONG
PRESSURE RISES BEHIND THE LOW AND FRONT WILL LEAD TO CONTINUING
STRONG SOUTHERLY WINDS AS THE SYSTEM MOVES AWAY FROM SOUTHCENTRAL.

HAVE UPGRADED TO HIGH WIND WARNINGS FOR THE TYPICAL AREAS FROM
PORTAGE VALLEY TO TURNAGAIN ARM AND HIGHER ELEVATIONS OF
ANCHORAGE. CONSIDERED THE POSSIBILITY OF REACHING HIGH WIND
WARNING THRESHOLDS FOR LOWER ELEVATIONS OF ANCHORAGE NEAR THE
CHUGACH (60 MPH) DUE TO THE FAVORABLE PATTERN FOR STRONG CHINOOK
WINDS. HOWEVER...MODEL SOUNDINGS DO NOT SHOW A CRITICAL LEVEL
ABOVE MOUNTAIN TOP SO EXPECT STRONGEST WINDS WILL TEND TO ESCAPE
UPWARDS INTO THE ATMOSPHERE. ALSO...THE SURFACE FRONT WILL MOVE
THROUGH BEFORE PRESSURE GRADIENTS BECOME REALLY FAVORABLE FOR
TURNAGAIN WINDS TO BEND INTO ANCHORAGE. WILL CONTINUE TO EVALUATE
THIS POTENTIAL. FOR NOW HAVE HIGHLIGHTED THE EXPECTED STRONG
(SUB-WARNING LEVEL WINDS) VIA A HEADLINE FOR MANY OF THE FORECAST
ZONES...INCLUDING ANCHORAGE...THE MAT VALLEY...THE KENAI
PENINSULA...AND PRINCE WILLIAM SOUND.

LASTLY ON WINDS...IF THE DEEPEST OF THE AVAILABLE SOLUTIONS WAS TO
VERIFY WOULD NEED TO CONSIDER A HIGH WIND WARNING FOR PORTIONS OF
KODIAK ISLAND WITH THE LOW PASSING JUST SOUTH OF THE ISLAND. WILL
CLOSELY MONITOR THE LOW DEVELOPMENT TODAY TO SEE WHICH SOLUTION IS
VERIFYING BEST.

AS FAR AS PRECIPITATION WITH THIS EVENT...TEMPERATURES HAVE
WARMED ABOVE FREEZING FOR MUCH OF SOUTHCENTRAL TO PRECIP WILL
BE PRIMARILY RAIN OR A RAIN/SNOW MIX...EVEN UP INTO THE SUSITNA
VALLEY WHICH SAW MOSTLY SNOW OUT OF THIS PAST EVENT. THE ONLY
PRECIP RELATED CONCERN IS THOMPSON PASS...WHICH AT NEARLY 3000
FEET MAY SEE ANOTHER BLIZZARD AS THE FRONT MOVES THROUGH ON
WEDNESDAY.

BEHIND THIS SYSTEM (WEDNESDAY NIGHT AND BEYOND) FORECAST CONFIDENCE
QUICKLY DROPS TO LOW WITH LARGE SPREAD IN MODEL GUIDANCE. IT DOES
LOOK LIKE ACTIVE WEATHER WILL PERSIST.

&&

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

THE PRIMARY QUESTION MARK FOR TODAY IS THE POTENTIAL FOR
ACCUMULATING SNOWFALL FOR INLAND PARTS OF THE KUSKOKWIM DELTA...AS
AN UPPER TROUGH REMAINS NEARLY STATIONARY ALONG THE COAST AND
MOISTURE MOVES NORTH FROM THE BRISTOL BAY REGION. THE CURRENT
THINKING IS THAT THERE WILL BE ACCUMULATIONS WILL BE
LIGHT...GENERALLY AN INCH OR TWO OR LESS...BUT THERE IS THE
POTENTIAL FOR UP TO 4 INCHES SHOULD THE MORE MOIST GFS SCENARIO
PLAY OUT.

THE NEXT STRONG AREA OF LOW PRESSURE WILL LIFT UP FROM THE SOUTH
TONIGHT...CROSSING THE ALASKA PENINSULA AND MOVING INTO BRISTOL
BAY WEDNESDAY MORNING. THE GFS AND THE 06Z GEM REGIONAL MODELS RAPIDLY
STRENGTHENS THE LOW THIS MORNING INTO QUITE THE IMPRESSIVE
CYCLONE THROUGH PHASING OF TWO SIGNIFICANT PIECES OF UPPER LEVEL
ENERGY...WHILE ALL OF THE OTHER MODELS SHOW A MORE GRADUAL
STRENGTHENING OF THE LOW (THOUGH STILL IMPRESSIVE) WITH ONLY
PARTIAL PHASING OF THE TWO VORT MAXES. THE MODEL DIFFERENCE
BETWEEN THE TWO SOLUTIONS FOR TONIGHT INTO WEDNESDAY FOR SOUTHWEST
ALASKA...PARTICULARLY BRISTOL BAY...IS SIGNIFICANT. IF THE GFS AND
06Z GEM REGIONAL MODEL SCENARIO WERE TO PAN OUT...A POTENTIALLY
HIGH-IMPACT HIGH WIND EVENT IS IN STORE FOR THE BRISTOL BAY
REGION...WITH THE POTENTIAL FOR GUSTS EXCEEDING 100 MPH THROUGH
THE GAPS OF THE ALEUTIAN RANGE. FOR THIS FORECAST PACKAGE HAVE
OPTED TO LEAN TOWARD A MODEL CONSENSUS BLEND (WHICH EXCLUDES THE
GFS AND 06Z GEM REGIONAL) BUT WHICH STILL BRINGS A POTENTIALLY
IMPACTFUL HIGH WIND EVENT FOR BRISTOL BAY LATE THIS EVENING INTO
EARLY WEDNESDAY...WITH WINDS WELL BELOW THE MAXIMUM GUST POTENTIAL
DEPICTED BY THE GFS AND GEM REGIONAL MODELS.

FOR THIS EVENING INTO THE OVERNIGHT...EAST WINDS ALONG THE
WESTERN SLOPES OF THE ALEUTIAN RANGE WILL BE FAVORED ESPECIALLY
NEAR GAPS AND PASSES. ONCE THE LOW PASSES BY EARLY WEDNESDAY WINDS
WILL RAPIDLY SHIFT TO THE SOUTH TO SOUTHWEST WITH A TIGHT PRESSURE
GRADIENT AND STRONG PRESSURE RISES FAVORING THE STRONGEST WINDS TO
OCCUR ALONG AND NEAR THE NORTHERN BRISTOL BAY COAST. WHILE THE
STRONGEST WINDS WILL BE FAIRLY SHORT LIVED AT ANY GIVEN
LOCATION...DUE TO THE RAPID PROGRESS OF THE LOW THEY ARE EXPECTED
TO IMPACT MOST ALL OF THE BRISTOL BAY ZONES DURING SOME PORTION OF
THE LOW'S PASSAGE.

TO ACCOUNT FOR THE UNCERTAINTY IN MAXIMUM WIND GUSTS FOR THIS
STORM...A LARGER THAN TYPICAL GUST SPREAD OF 80 TO 100 MPH WILL BE
MENTIONED. WE WILL CLOSELY WATCH THIS SYSTEM AND MAKE SIGNIFICANT
UPWARD REVISIONS TO THE FORECAST IF MODEL AGREEMENT INTENSIFIES.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
INDIVIDUAL AREAS OF LOW PRESSURE CONTINUE TO ROTATE AROUND THE
LARGE UPPER LEVEL LOW CENTERED OVER THE BERING. THE LOW CURRENTLY
JUST SOUTH AND WEST OF THE PRIBILOFS WILL FILL AND WEAKEN AS IT
TRACKS INTO THE CENTRAL BERING THROUGH TONIGHT. ADDITIONAL COOL
SHOWERY TROUGHS WILL ROTATE ACROSS THE ALEUTIANS THROUGH MIDWEEK
BUT REMAIN LESS ORGANIZED.

&&

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

AN UNSEASONABLE WEATHER PATTERN LOOKS TO CONTINUE THROUGH THE
REMAINDER OF THE WEEK AS A HIGHLY AMPLIFIED TROUGH OVER THE BERING
SEA CONTINUES TO PUSH WARM SYSTEMS FROM THE SUBTROPICS UP TOWARD
THE ALASKA MAINLAND. THIS IS DUE IN LARGE PART TO MULTIPLE UPPER
LEVEL DISTURBANCES AND THEIR ASSOCIATED JET ENERGY COMING OFF THE
COAST OF RUSSIA AND WILL CONTINUE TO HELP DIG OUT THE TROUGH OVER
THE BERING SEA. WHILE A FEW SYSTEMS TRY TO FLATTEN AND WEAKEN THE
TROUGH...THE MERIDIONAL PATTERN IS JUST TOO STRONG. A COMPLEX AND
BROAD AREA OF LOW PRESSURE WILL ENCOMPASS MUCH OF THE BERING SEA
THROUGH THE WEEKEND AS ADDITIONAL WEAK LOW PRESSURE SYSTEMS
CONTINUE TO PHASE WITH THE BROAD LOW OVER THE BERING SEA. THIS
WILL KEEP SOUTHWEST AND SOUTHCENTRAL IN THE STORM TRACK LEADING TO
AN ACTIVE PERIOD OF WEATHER. HOWEVER...AS MENTIONED EARLIER THE
SYNOPTIC PATTERN WILL CONTINUE TO USHER WARMER AIR FROM THE
SUBTROPICS UP TOWARD THE MAINLAND. WHILE TEMPERATURES ARE NOT
EXPECTED TO REMAIN ABOVE FREEZING THROUGHOUT THE EXTENDED
FORECAST...PERIODS OF ABOVE FREEZING TEMPERATURES ARE LIKELY
ACROSS MUCH OF THE AREA.

ALL HOPE IS NOT LOST FOR SNOW HOWEVER AS THE ACTIVE STORM PATTERN
SHOULD BRING SEVERAL CHANCES OF SNOW TO SOUTHWEST AND SOUTHCENTRAL
ALASKA ON THURSDAY AND AGAIN OVER THE WEEKEND. HOWEVER...DOWNSLOPING
WILL ONCE AGAIN BE A BIG CONCERN AS LOWS WEST OF THE KENAI
PENINSULA OFTEN PUSH A WARM FRONT THAT KEEPS PORTIONS OF THE KENAI
PENINSULA...ANCHORAGE AND THE MATANUSKA ON THE DRY SIDE DUE TO
CROSS BARRIER FLOW. HOWEVER...PATTERN RECOGNITION FAVORS THAT AS
THESE LOWS SHIFT EASTWARD TOWARD PRINCE WILLIAM SOUND THAT UPPER
LEVEL FLOW SHIFTS TO THE SOUTHWEST AND A SHOT OF SNOW WOULD BE
POSSIBLE. THIS SCENARIO EXISTS FOR BOTH THURSDAY AND SATURDAY BUT
IS HIGHLY DEPENDENT ON LOW TRACK. MODELS ARE STRUGGLING WITH
DEVELOPING THESE LOW PRESSURE SYSTEMS IN THE GULF OF ALASKA DUE TO
THE COMPLEX NATURE AND ATYPICAL SYNOPTIC PATTERN FOR THIS TIME OF
THE YEAR...SO THE CHANCES FOR SNOW COULD EITHER DECREASE OR
INCREASE IN THE COMING DAYS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 101 125 161.
         BLIZZARD WATCH 131.
         WINTER WEATHER ADVISORY FOR SNOW 145.
MARINE...HURRICANE 128 129 130 131.
         STORM 119 120 125 132 136-139 141 150 155 160.
         GALE 140 165 170 172 180 181 185.
         HEAVY FREEZING SPRAY 185.

&&

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC
LONG TERM...MC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
145 PM AKST TUE DEC 29 2015

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1032 AM     SNOW             18 NNW CHASE            62.70N 150.23W
12/29/2015  E8.0 INCH                           AK   DEPT OF HIGHWAYS

            DOT ESTIMATES 8 INCHES SNOW FELL OVERNIGHT.

1032 AM     SNOW             8 NNW CHASE             62.55N 150.24W
12/29/2015  E4.0 INCH                           AK   DEPT OF HIGHWAYS

            DOT CHULITNA ESTIMATES 4 INCHES OF SNOW FELL NEAR MM 121
            ON PARKS HIGHWAY OVERNIGHT

&&

RDUELL