Small Craft Advisory 112, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
423 PM AKST WED FEB 4 2015

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL RIDGE REMAINS CENTERED OVER THE NORTHERN BERING
SEA AND EXTENDS SOUTHEASTWARD OVER THE GULF OF ALASKA. THIS RIDGE
WILL REMAIN ENTRENCHED OVER THE BERING SEA BUT AN UPPER LEVEL
TROUGH IN THE YUKON THAT EXTENDS OUT OF AN ARCTIC LOW WILL DIG
INTO THE NORTHEAST GULF OF ALASKA LATE TONIGHT INTO TOMORROW
WHICH WILL SHIFT THE UPPER LEVEL PATTERN OVER SOUTHERN MAINLAND
ALASKA FROM WEAK FLOW ALOFT TO FAIRLY STRONG NORTHERLY FLOW
STARTING BY TOMORROW AFTERNOON AND CONTINUING INTO THE WEEKEND.
THIS WILL INCREASE THE CHANCE FOR GUSTY NORTHERLY WINDS TO MAKE IT
TO THE SURFACE IN BOTH SOUTHWEST AND SOUTHCENTRAL ALASKA. THE
SURFACE HIGH PRESSURE OVER INTERIOR ALASKA COMBINED WITH LOW
PRESSURE SOUTH OF THE GULF OF ALASKA AND ALEUTIANS WILL KEEP A
TIGHT PRESSURE GRADIENT OVER SOUTHWEST ALASKA AND THE BERING SEA.
IN FACT THE PRESSURE GRADIENT WILL INCREASE OVER THE NEXT FEW DAYS
OVER JUST ABOUT ALL OF SOUTHERN MAINLAND ALASKA WHILE REMAINING
TIGHT OVER THE BERING SEA AND ALEUTIANS.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN VERY GOOD AGREEMENT WITH EACH OTHER FROM THE 12Z
AND 18Z RUNS. THE MAIN ISSUES REVOLVE AROUND THE RESOLUTION OF THE
MODELS AND THE TIMING OF SOME WEAK SHORT WAVES AS THEY TRAVERSE
THE STRONGER PRESSURE GRADIENT BETWEEN THE UPPER LEVEL RIDGE AND
LOW. THE ONLY OTHER FEATURE TO WATCH IS THE TROUGH ALONG THE NORTH
GULF COAST. THE GFS IS MORE PRONOUNCED WITH IT WHICH MAKES SOME
SENSE AS IT IS A LEE SIDE TROUGH...BUT THAT DIFFERENCE IN MODELS
ENDS BY FRIDAY AFTERNOON AS MODELS ALL DEVELOP A LOW JUST A LITTLE
EAST OF MIDDLETON ISLAND ALONG THAT TROUGH. BY SATURDAY AFTERNOON
THAT LOW THEN IS MOVED INTO THE WESTERN GULF BY ALL THE MODELS.
HOWEVER AN ITEM TO NOTE IS THAT THE NAM IS DEVELOPING A SECONDARY
LOW SOUTHWEST OF MIDDLETON ISLAND ON SATURDAY. THIS IS INTERESTING
AS THE NAM IS A HIGHER RESOLUTION MODEL AND MAY BE DETECTING THE
DEVELOPMENT OF THE LOW DUE TO COLD AIR OUTFLOW FROM MAINLAND
ALASKA. THIS COMMONLY HAPPENS WITH THIS SORT OF A SET UP AND THAT
CERTAINLY CAN AFFECT THE FORECAST...MOSTLY IN THE GULF AND ALONG
THE GULF COAST.

&&

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

THE FIRST IN A SERIES OF DISTURBANCES IS PUSHING SOUTH ACROSS
SOUTHCENTRAL LATE THIS AFTERNOON AND WILL BEGIN THE CHANGE FROM
COLD...DRY...AND CALM CONDITIONS TO COLD...DRY...AND WINDY
CONDITIONS THAT WILL PERSIST THROUGH THE END OF THE WEEK.

THERE IS LITTLE CHANGE IN THOUGHT FROM THE PREVIOUS FORECAST
EXCEPT TO SPEED UP THE ONSET OF WINDS BY ABOUT 3 HOURS OR SO LATE
TONIGHT AS MODELS GET A BETTER HANDLE ON THE DISTURBANCES MOVING
RAPIDLY SOUTH ACROSS THE SOUTHCENTRAL REGION.

THE UPPER LEVEL JET WILL REMAIN LARGELY ANCHORED TO THE EAST AND
SOUTHEAST FLANKS OF THE UPPER LEVEL CUT-OFF HIGH THAT WILL SLOWLY
RETROGRADE FROM THE NORTHERN BERING SEA TO EASTERN RUSSIA THROUGH
FRIDAY. THIS WILL RESULT IN THE BEST UPPER LEVEL JET DYNAMICS
MOVING IN A GENERAL EAST TO WEST DIRECTION ACROSS SOUTHCENTRAL
THROUGH FRIDAY. THUS...THE EASTERN PRINCE WILLIAM SOUND REGION
WILL SEE THE EARLIEST ONSET OF STRONG WINDS LATE TONIGHT AND WILL
SEE AN EARLIER DIMINISHING OF WINDS TOWARD THE WEEKEND.

FOR ANCHORAGE AND THE MAT-SU VALLEY...WINDS WILL BEGIN TO BECOME
GUSTY DURING THE DAY ON THURSDAY AND WILL PERSIST INTO SATURDAY
BEFORE BEGINNING TO DIMINISH. THIS WILL BRING WIND CHILLS TO 15 BELOW
IN THE MORE WINDY AREAS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
AN UPPER LEVEL HIGH PRESSURE IS POSITIONED JUST WEST OF SAINT
LAWRENCE ISLAND. WITH A RIDGE EXTENDING ALONG THE SOUTHWEST ALASKA
COASTLINE ACROSS THE ALASKA PENINSULA INTO THE NORTHERN PACIFIC.
THIS WILL CONTINUE TO BRING CLEAR AND DRY CONDITIONS THROUGHOUT
SOUTHWEST ALASKA. THE COLD TEMPERATURES WILL REMAIN WITH CONTINUED
COLD AIR ADVECTION WITH AN UPSTREAM TROUGH APPROACHING THE REGION
FROM THE NORTH. THE BIGGEST CONCERN WILL BE HOW MUCH THE UPPER
LEVEL WINDS WILL MIX DOWN TO THE SURFACE...BUT WERE EXPECTING THE
NOCTURNAL INVERSION TO PREVENT ANY STRONG WINDS AT THE SURFACE.
IF THE WINDS DUE MIX DOWN MORE THAN EXPECTED THAN THE WIND CHILL
ADVISORY CRITERIA OF MINUS 40 BELOW ZERO DEGREES FAHRENHEIT WILL
MATERIALIZE FOR THE LOWER KUSKOKWIM VALLEY BY FRIDAY MORNING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A NORTH PACIFIC LOW PRESSURE SYSTEM SOUTH OF DUTCH HARBOR WILL
TRACK WESTWARD RUNNING PARALLEL TO THE CHAIN. THIS WILL BRING
LIGHT RAIN AND STRATUS TO THE CENTRAL TO WESTERN ALEUTIANS WITH
SOME OF THE MOISTURE SPILLING OVER INTO THE WESTERN BERING SEA
THROUGH FRIDAY. THE REST OF THE BERING IS DOMINATED BY HIGH
PRESSURE LOCATED WEST OF SAINT LAWRENCE ISLAND.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE MAIN FOCUS THROUGH THE MID-TERM AND INTO PART OF THE LONG TERM
REMAINS CENTERED AROUND AN OUTFLOW WIND EVENT OVER THE SOUTHERN
MAINLAND...WHICH WILL BEGIN TO SLOWLY DIMINISH INTO EARLY NEXT
WEEK. MODELS ARE IN GOOD AGREEMENT WITH THE UPPER RIDGE OVER THE
BERING CONTINUING TO TRACK WESTWARD INTO THE WEEKEND...AS A STRONG
SHORTWAVE DIVES DOWN ALONG THE EASTERN SIDE OF THE RIDGE AND
THROUGH THE SOUTHWEST MAINLAND. WITH THE REINFORCEMENT OF THIS
TROUGH OVER THE SOUTHERN MAINLAND AND COLDER DRY AIR SPILLING IN
FROM THE EASTERN INTERIOR...WINDS ALONG PARTS OF THE GULF COAST
AND SOUTHWEST MAINLAND SHOULD REMAIN GUSTY INTO EARLY NEXT WEEK.
MODELS CONTINUE TO DEVELOP A LOW OVER THE GULF SATURDAY
MORNING...WHICH COULD HELP TO ENHANCE THE OUTFLOW WINDS OVER THE
NORTHERN GULF COAST. HOWEVER...THE STRENGTH OF THESE WINDS REMAIN
DEPENDENT ON THE PLACEMENT OF THE GULF LOW...WHICH CURRENT MODELS
DO NOT HAVE A FIRM GRIP ON JUST YET. THE ECMWF SOLUTION KEEPS THE
LOW JUST SOUTH OF THE NORTHERN GULF COAST THROUGH THE
WEEKEND...WHICH WOULD CONTINUE TO ENHANCE THE OUTFLOW WINDS OVER
THE AREA. HOWEVER IF THE GFS SOLUTION VERIFIES WITH A MORE
SOUTHWESTERLY PLACEMENT OF THE LOW...WINDS WOULD SLOWLY DECREASE
BY THE END OF THE WEEKEND. EITHER WAY...THIS PATTERN WILL KEEP THE
SOUTHERN MAINLAND UNDER DRY NORTHERLY FLOW WITH SHOWERY
PRECIPITATION ACROSS THE BERING AND PARTS OF THE GULF COAST
THROUGH EARLY NEXT WEEK.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...

PUBLIC...WIND CHILL ADVISORY 131
MARINE...GALES 126 127 128 130 131 155 171 172 173 174 175 177.
FIRE WEATHER...NONE.

&&

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