Small Craft Advisory 241, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 PM AKDT TUE MAR 17 2015

.ANALYSIS AND UPPER LEVELS...

A FAMILIAR PATTERN IS IN PLACE WITH AN UPPER LOW SOUTH OF THE
ALASKA PENINSULA ANCHORING A BROAD LONGWAVE TROUGH THAT ENCOMPASSES
VIRTUALLY ALL OF THE NORTH PACIFIC. THIS SETS MAINLAND ALASKA UP
UNDER WARM SOUTHERLY FLOW WITH SENSIBLE WEATHER GOVERNED LARGELY
BY EMBEDDED SHORTWAVE FEATURES. CURRENTLY...SOUTH CENTRAL ALASKA
IS UNDER THE INFLUENCE OF SHORTWAVE RIDGING (BETWEEN STORMS) WITH
A VERY SPRING-LIKE DAY UNFOLDING WITH SUNSHINE AND ABOVE-FREEZING
TEMPERATURES. A SHORTWAVE TROUGH IS LOCATED IN THE EASTERN GULF
AND IS MOVING TO THE NORTHWEST AND THE BEGINNINGS OF THE
PRECIPITATION SHIELD ARE JUST BEGINNING TO SHOW UP ON THE FRINGES
OF THE MIDDLETON ISLAND RADAR.

WEST OF THE ALASKA RANGE...A WARM FRONT IS PUSHING WESTWARD AND
HAS CLEARED MOST OF THE SOUTHWEST MAINLAND EXCEPT THE DELTA
COAST...WHERE SNOW CONTINUES TO FALL AT THIS TIME. THIS SAME FRONT
IS PUSHING SNOWFALL TOWARD THE PRIBILOF ISLANDS WHERE PLENTY OF
IN- PLACE COLD AIR AND STRONGER NORTH WINDS ARE PRODUCING SNOW AND
BLOWING SNOW. ALONG THE CHAIN...A WARMING AIRMASS HAS CHANGED A
RAIN/SNOW MIX TO ALL RAIN IN DUTCH HARBOR...BUT WILL HAVE A HARD
TIME PUSHING THE RAIN/SNOW LINE MUCH FURTHER TO THE WEST THAN
THAT. THE WESTERN HALF OF THE BERING/ALEUTIANS ARE DOMINATED BY
COLD NORTHERLY FLOW AND ONGOING CONVECTIVE SNOW SHOWER ACTIVITY.

&&

.MODEL DISCUSSION...

MODELS REMAIN IN GOOD SYNOPTIC AGREEMENT. THIS IS NOT A HUGE
SURPRISE GIVEN A SLOWLY CHANGING LONGWAVE PATTERN THROUGHOUT THE
REMAINDER OF THE WEEK. MINOR CHANGES IN THE TIMING AND PLACEMENT
OF SHORTWAVES MOVING NORTHWARD THROUGH THE GULF GROW OVER
TIME...AND FOR FORECAST GENERATION TODAY THE GLOBAL MODELS (AND
SPECIFICALLY THE ECMWF) WERE PREFERRED...THOUGH SOME OF THE
CANADIAN RDPS (GEM-REGIONAL) WAS UTILIZED IN THE FIRST 36 HOURS OF
THE FORECAST TO TAKE ADVANTAGE OF SUPERIOR RESOLUTION. BY THE END
OF THE WEEK THE ANCHORING UPPER LOW WILL HAVE DRIFTED EASTWARD
INTO THE GULF...THOUGH DETAILS OF THE INDIVIDUAL SURFACE LOWS ARE
VERY JUMBLED BY THIS POINT.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2...WED AND
THU)...THE AIRMASS HAS BEEN REPLACED OVER THE PAST 36-48 HRS AND
WE ARE NOW EXPERIENCING THE WARMEST DAY OF 2015 SO FAR IN
ANCHORAGE. 850 MB TEMPERATURES ON SATURDAY AFTERNOON'S SOUNDING
WERE NEARLY -24 C AND THIS AFTERNOON WE ARE ALL THE WAY UP TO
NEARLY 0 C. THE PATTERN FOR THE NEXT COUPLE OF DAYS WILL BE
DOMINATED BY FLOW AROUND THE BROAD UPPER LEVEL LOW SOUTH OF DUTCH
HARBOR. THIS WILL CONTINUE TO SPIN WEAK TRANSIENT AREAS OF LOW
PRESSURE FROM THE NORTH PACIFIC TOWARD THE GULF COAST. AND FOR THE
MOST PART...THE GULF COAST IS REALLY WHERE MOST OF THE IMPACTS
WILL REMAIN. THE FIRST FRONT IS ALREADY STARTING TO SHOW UP ON
THE MIDDLETON RADAR. PRECIPITATION SHOULD REACH CORDOVA FIRST
LATER THIS EVENING BEFORE STRETCHING WESTWARD TOWARD KACHEMAK BAY.
COASTAL LOCATIONS SHOULD STAY ALL RAIN WHILE INLAND LOCATIONS WILL
LIKELY SEE A MIX OF RAIN AND SNOW AS TEMPERATURES COOL OVERNIGHT.
THE EXCEPTION IS VALDEZ WHERE THINGS SHOULD REMAIN ALL SNOW. AS
THE UPPER LEVEL SUPPORT PASSES THROUGH THE COOK INLET
REGION WEDNESDAY MORNING...THERE IS A BRIEF WINDOW WHERE THE
DOWNSLOPING WINDS SLACK OFF JUST ENOUGH AND THE ANCHORAGE
HILLSIDE COULD SEE A BURST OF SNOW SHOWERS. CERTAINLY NOT LOOKING
LIKE MUCH IN THE WAY OF ACCUMULATION. THE NEXT FRONT FOLLOWS A
NEARLY IDENTICAL TRACK LATE WEDNESDAY INTO THURSDAY. THIS WILL
KEEP THINGS WET FOR COASTAL LOCATIONS AND RELATIVELY WARM (FOR
MID-MARCH) OVER INLAND AREAS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE FIRST FRONTAL BOUNDARY IS EXITING THE KUSKOKWIM DELTA EARLY
THIS EVENING WHERE SNOW WILL DISSIPATE. ANOTHER FRONT WILL SPREAD
OVER THE BRISTOL BAY REGION LATE TONIGHT WHERE MIXED PRECIPITATION
WILL AFFECT MOST OF THAT AREA. THE KUSKOKWIM VALLEY AND DELTA WILL
HAVE A CHANCE FOR PRECIPITATION BUT MOSTLY LIKELY WILL REMAIN ON
THE DRIER SIDE. A STRONGER DISTURBANCE ALOFT WILL MOVE INTO THE
REGION WEDNESDAY NIGHT INTO THURSDAY KEEPING CLOUDS AND RAIN/SNOW
IN THE FORECAST...MAINLY FOR INTERIOR BRISTOL BAY. TEMPERATURES
WILL CONTINUE TO BE ABOVE NORMAL FOR MOST OF THE REGION.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A NORTH/SOUTH ORIENTED FRONTAL BOUNDARY WILL MOVE FROM THE
PRIBILOF ISLANDS TO THE CENTRAL ALEUTIANS THIS EVENING AND
TONIGHT WHERE SNOW WILL CONTINUE. ANOTHER FRONT AND SURFACE LOW
WILL APPROACH THE EASTERN ALEUTIANS AND ALASKA PENINSULA THIS
EVENING. RAIN SHOWERS WILL CONTINUE THROUGH THURSDAY FOR THESE
AREAS WITH SNOW SHOWERS IN THE WESTERN BERING SEA.

&&

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

MODELS ARE IN GENERAL AGREEMENT THAT THE UPPER LOW SOUTH OF THE
AKPEN WILL MOVE INTO THE EXTREME SOUTHERN GULF OF AK/NORTHERN
PACIFIC BY THE WEEKEND. AT THAT POINT THE MODELS BECOME OUT OF
PHASE AND FORECAST CONFIDENCE PLUMMETS. BUT EVEN BEFORE THE
WEEKEND THE SURFACE SOLUTION DEGRADES TO A SET OF LOWS PINWHEELING
AROUND THE MAIN LOW SOUTH OF THE EASTERN ALEUTIANS...AND ROTATING
ACROSS THE GULF AND NORTHERN PACIFIC. CONFIDENCE REMAINS MODERATE
THAT THE FIRST LOW PINWHEELING INTO THE GULF WILL AFFECT KODIAK
ISLAND THU NIGHT INTO FRI...AFTER THAT TIME CONSENSUS FAILS.
FORTUNATELY WPC GUIDANCE AGAIN UTILIZES AN ENSEMBLE BLEND THAT
RESTORES SOME REASON AND KEEPS HIGH PRESSURE OVER THE BERING
THROUGH EARLY NEXT WEEK...A SECOND PINWHEEELING LOW DISSIPATES
OVER THE NE GULF ON SAT...AND A SERIES OF LOWS REMAIN JUST SOUTH
OF THE ALEUTIANS AND MAINLAND AK AS THEY MIGRATE EAST.

THE FORECAST UTILIZES AN EC/NAM SOLUTION FOR THE LOW INTO
KODIAK...AND THEN WPC GUIDANCE THROUGH EARLY NEXT WEEK. IN THE
WEST...PRECIPITATION IN THE FORM OF RAIN WILL AFFECT THE AKPEN
AND EASTERN ALEUTIANS FRI INTO SAT...AND THEN SOME SNOW MAY AFFECT
THE ALEUTIANS SUN THROUGH TUE. IN THE EAST RAIN AND SNOW WILL
AFFECT MAINLY COASTAL ZONES THROUGH TUE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 119 120 130 131 132 137 138 139 150 155 170
	171 172 173 174 176 177 185.
	HEAVY FREEZING SPRAY WARNING...185.
FIRE WEATHER...NONE.

&&

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