High Surf Advisory 6, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...

THE OVERALL ACTIVE WEATHER PATTERN CONTINUES TO AMPLIFY. A
LONGWAVE TROUGH OVER THE BERING SEA AND NORTH PACIFIC IS BECOMING
INCREASINGLY NEGATIVELY TILTED UPSTREAM OF A BUILDING BLOCKING RIDGE
OVER THE EASTERN PACIFIC AND GULF OF ALASKA. EMBEDDED WITHIN THE
LONGWAVE TROUGH ARE MULTIPLE SHORTWAVES SOUTH OF THE ALEUTIANS. A
WEAKENING VERTICALLY STACKED LOW IS SLOWLY DRIFTING NORTHWARD
THROUGH THE CENTRAL BERING SEA. STRONG ONSHORE SOUTHERLY AND
SOUTHEASTERLY FLOW THROUGHOUT THE SOUTHERN AND INTERIOR MAINLAND
IS ADVECTING WARMER...MOISTER AIR NORTHWARD. THIS IS VISIBLE ON
THE WATER VAPOR SATELLITE IMAGERY AS A LARGE MOISTURE PLUME OVER
THE MAJORITY OF THE MAINLAND. AN UPPER LEVEL JET STREAK STRETCHING
NORTHWARD FROM THE NORTH PACIFIC SOUTH OF THE ALASKA PENINSULA TO
THE WESTERN MAINLAND AND THEN EASTWARD OVER THE BROOKS RANGE IS
AIDING IN THE RAPID TRANSPORT OF MOISTURE NORTHWARD. THE NET
RESULT OF THE UPPER AND LOWER LEVEL STRONG SOUTHERLY FLOW IS
SEASONABLY WARM AND MOIST CONDITIONS THROUGHOUT THE SOUTHERN
PORTION OF THE STATE AS EVIDENT ON 12Z SOUNDINGS. THESE EARLY
MORNING SOUNDINGS SHOWED TOTAL PRECIPITABLE WATER AMOUNTS AT NEAR
OR OVER 150 PERCENT OF NORMAL VALUES OVER SOUTHCENTRAL INTO THE
SOUTHERN INTERIOR AND SURFACE TEMPERATURES 10 TO 20 DEGREES
FAHRENHEIT ABOVE NORMAL OVER SOUTHWEST AND SOUTHCENTRAL ALASKA.

SOUTH OF THE ALASKA PENINSULA...THE NEXT SYSTEM TO IMPACT THE
FORECAST AREA IS RAPIDLY DEEPENING AS IT TRACKS NORTHWARD THROUGH
THE NORTH PACIFIC. THE RAPID INTENSIFICATION OF THE SYSTEM IS
ATTRIBUTED IN PART TO THE FAVORABLE LOCATION OF THE LOW IN THE
LEFT EXIT REGION OF A STRONG ZONAL JET AT THE BASE OF THE LONGWAVE
TROUGH. THE STRONG FRONTAL BOUNDARY ASSOCIATED WITH THE SYSTEM IS
JUST APPROACHING THE SOUTHERN GULF WHILE PREFRONTAL WINDS BEGIN TO
RAMP UP IN SOUTHERN KODIAK ISLAND AND THE SOUTHERN ALASKA
PENINSULA AHEAD OF THE BOUNDARY. GUSTY SOUTHEASTERLY WINDS OVER
THE MAJORITY OF THE SOUTHERN MAINLAND CONTINUE AS THE EAST-WEST
ORIENTED SURFACE PRESSURE GRADIENT REMAINS STRONG ACROSS THE
STATE. OVER THE KUSKOKWIM DELTA...A DEFORMATION BAND MOVING
NORTHWEST IS BRINGING PRIMARILY SNOW TO THE REGION AS TEMPERATURES
HOVER NEAR FREEZING.

&&

.MODEL DISCUSSION...

NUMERICAL GUIDANCE HAS CONTINUED TO STEADILY COME INTO BETTER
AGREEMENT ON THE STRONG STORM EXPECTED TO IMPACT SOUTHERN ALASKA
TONIGHT AND WEDNESDAY. THE OVERALL TREND HAS BEEN TOWARD A
STRONGER SOLUTION THAT HAS BEEN DEPICTED CONSISTENTLY BY THE GFS
FOR SEVERAL RUNS. THE LOW IS NOW EXPECTED TO TRACK ACROSS THE
ALASKA PENINSULA EARLY WEDNESDAY MORNING AND REACH PEAK INTENSITY
NEAR CAPE NEWENHAM LATE WEDNESDAY MORNING IN THE MID 950S MB
RANGE. THE ASSOCIATED STRONG FRONT WILL SWEEP ACROSS SOUTHCENTRAL
AND THE BRISTOL BAY ZONE OF SOUTHWEST ALASKA AS THE LOW MOVES INTO
THE BERING BASIN...WITH VERY STRONG WINDS EXPECTED IN MANY AREAS.

WHILE MODELS HAVE HAD SOME DISCREPANCIES OVER THE LAST DAY WITH
POSITIONS AND INTENSITY, WHAT HAS BEEN COMMON ACROSS ALL GUIDANCE
IS A VERY LARGE AND IMPRESSIVE AREA OF SIGNIFICANT PRESSURE RISES
BEHIND THE LOW CENTER ITSELF. THIS BULLSEYE OF PRESSURE RISES WILL
TRACK GENERALLY ACROSS KODIAK ISLAND...THE BRISTOL BAY ZONE...AND
PORTIONS OF THE ALASKA PENINSULA WEDNESDAY MORNING. THESE ABRUPT
PRESSURE RISES WILL CAUSE A SUDDEN ACCELERATION OF WINDS FROM A
MORE SOUTHERLY DIRECTION...WHICH WILL BE MOST EXAGGERATED IN AREAS
OF COMPLEX TERRAIN. MOST CHANGES TO THE FORECAST TODAY WERE DONE
WITH MANUAL EDITS THAT REFERENCED THE HIGHER RESOLUTION
MODELS...THOUGH NO MODELS WERE COMPLETELY DISCARDED TODAY DURING
FORECAST PREPARATION.
&&

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

AS THE WEATHER FRONT MOVES ACROSS THE GULF TONIGHT AND REACHES THE
NORTH GULF COAST BY MIDDAY WED...IT WILL BRING DANGEROUS WINDS TO
SEVERAL PARTS OF SOUTHCENTRAL AK. THESE WINDS WILL AFFECT THE
ENTIRE LENGTH OF TURNAGAIN ARM TONIGHT THROUGH MIDDAY
WEDNESDAY...AS WELL AS KACHEMAK BAY. WIND WILL ALSO AFFECT HIGHER
ELEVATIONS AROUND ANCHORAGE AND WILL WORK THEIR WAY DOWN THE LOWER
HILLSIDE TO EAST ANCHORAGE. ELSEWHERE SOMEWHAT WEAKER WINDS
ASSOCIATED WITH THE FRONT WILL AFFECT CHANNELED TERRAIN OVER MUCH
OF THE REGION THROUGH MIDDAY WEDNESDAY. COLD AIR WITH THIS SYSTEM
WILL BE LIMITED TO THOMPSON PASS...WHERE PRECIPITATION WILL FALL
AS SNOW...COMBINE WITH STRONG WIND AND PRODUCE BLIZZARD CONDITIONS
LATE TONIGHT THROUGH WED.

AFTER THIS FRONT PASSES CONDITIONS WILL IMPROVE ACROSS THE AREA
BENEATH WEAK RIDGING BEFORE THE NEXT FRONT MOVES INTO THE GULF THU
AFTERNOON WITH SOME WIND AND RAIN.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
CURRENTLY THE DEFORMATION BAND STRETCHED ACROSS THE WESTERN
KUSKOKWIM DELTA AND THE POTENTIAL FOR A FEW MORE HOURS FOR SNOW OR
MIXED RAIN AND SNOW ALONG THE WESTERN MOST COAST REMAINS THE MAIN
IMMEDIATE TERM FORECAST CHALLENGE. TEMPERATURES SHOULD CONTINUE TO
WARM GRADUALLY THROUGH THE EVENING AND OVERNIGHT HOURS AS THE
NEXT LOW RAPIDLY DEEPENS AS IT APPROACHES THE ALASKA PENINSULA.
SO EXPECTING TO SEE PRECIPITATION TYPE SWITCH ENTIRELY OVER TO
RAIN BY AROUND MIDNIGHT AND CONTINUE THAT WAY UNTIL FRONTAL
PASSAGE MIDDAY WEDNESDAY WHEN COLDER AIR WILL START PUSHING BACK
IN FROM THE SOUTH.

WITH REGARDS TO THE UPCOMING SIGNIFICANT WIND EVENT IN
ASSOCIATION WITH THE POWERFUL LOW CROSSING INTO BRISTOL BAY LATE
TONIGHT AND THEN TRACKING NORTH ACROSS CAPE NEWENHAM AND ALONG THE
KUSKOKWIM DELTA COAST...MODELS CONTINUE TO TREND TOWARDS THE
STRONGER DEEPER LOW SOLUTION. THUS INCREASING CONFIDENCE IN
WIDESPREAD HIGH WINDS IMPACTING MUCH OF THE BRISTOL BAY AREA AND
STRONG WINDS OVER MUCH OF THE REMAINDER OF SOUTHWEST ALASKA.

EAST WINDS WHICH HAVE ALREADY STARTED TO INCREASE IN SOUTHWEST
ALASKA WILL CONTINUE TO INCREASE THROUGH THE EVENING...PEAKING
AROUND MIDNIGHT THROUGH THE GAPS AND PASSES IN THE ALEUTIAN AND
ALASKA RANGES AS THE DOWNSLOPE/GAP WIND PHASE OF THE STORM
DOMINATES THROUGH THE EARLY MORNING HOURS. WINDS WILL SHIFT MORE
SOUTHEASTERLY ALONG THE COAST AROUND 1 OR 2 AM CONTINUE TO
INCREASE THE FRONT APPROACHES. THE STRONGEST SOUTHERLY WINDS WILL
PUSH IN ALONG THE NORTHERN BRISTOL BAY COAST BETWEEN 6 TO 7 AM
IMMEDIATELY BEHIND THE LOW AND FRONTAL PASSAGE. VERY STRONG
ISALLOBARIC PRESSURE RISES IN BRISTOL BAY WILL ADDITIONALLY
STRENGTHEN THE ONSHORE SOUTHERLY FLOW MAKING GUSTS 60 TO 80 MPH
LIKELY IN COASTAL COMMUNITIES AND BRING GUSTS UP TO 100 MPH TO
THE MORE EXPOSED COASTAL HEADLANDS.

&&

.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
NORTH OF THE PRIBILOFS WILL FILL AND WEAKEN AS IT CONTINUE NORTH
THROUGH TONIGHT. ADDITIONAL COOL SHOWERY TROUGHS WILL ROTATE
ACROSS THE ALEUTIANS THROUGH MIDWEEK BUT REMAIN LESS ORGANIZED.
THE NEXT LARGER LOW WILL APPROACH THE EASTERN ALEUTIANS FROM THE
THE SOUTH THURSDAY AFTERNOON.

&&

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

THE EXTENDED FORECAST WILL CONTINUE WITH AN UNSETTLED WEATHER PATTERN
AS THE UPPER LOW OVER THE BERING SENDS CONTINUOUS SHORTWAVES FROM
THE PACIFIC TO THE SOUTHERN MAINLAND. AN AMPLIFIED RIDGE OVER THE
SOUTHEAST BREAKS DOWN AND SHIFTS FURTHER EAST ON FRIDAY WHICH ALLOWS
A SURFACE LOW TO TRACK NORTH INTO THE WESTERN GULF FRIDAY NIGHT
BEFORE LIFTING ACROSS THE SOUTHWEST ON SATURDAY. THIS SYSTEM WILL
BRING GUSTY WINDS ALONG THE FRONT AND WIDESPREAD RAIN ACROSS THE
GULF AND SURROUNDING COAST. A SURGE OF WARM AIR PUSHES INLAND
ACCOMPANIED BY SCATTERED RAIN AND SNOW SHOWERS. RIDGING BUILDS
BACK INTO THE SOUTHEAST ON MONDAY AS THE NEXT PACIFIC WAVE ROUNDS
THE BASE OF THE LONGWAVE TROUGH. THIS SENDS THE NEXT ORGANIZED
SYSTEM TOWARD THE ALASKA PENINSULA ON MONDAY WHICH PULLS ANOTHER
WARM AND MOIST PACIFIC AIR MASS INTO THE SOUTHWESTERN MAINLAND AS
IT TRACKS TO THE EASTERN BERING.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNINGS 101 121 125 161. BLIZZARD WARNING 131.
MARINE...HURRICANE FORCE 130 131. STORM WARNING 119 120 129 132
136 137 138 139 141 150 160 180. GALES 128 140 155 165.

&&

SYNOPSIS AND MODEL DISCUSSION...AD
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...KH

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