Winter Weather Advisory 13, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
438 AM AKDT MON APR 4 2016

.ANALYSIS AND UPPER LEVELS...

AT THE SYNOPTIC SCALE...A DEEP TROUGH REMAINS OVER THE CENTRAL
BERING SEA SOUTHWARD THROUGH THE CENTRAL PACIFIC OCEAN WITH A
WEAKENING RIDGE OVER THE NORTHEASTERN RUSSIAN COAST AND SOUTHWARD
INTO THE WESTERN PACIFIC. THE POLAR JET IS LOCATED PRIMARILY ON
THE EASTERN SIDE OF THIS TROUGH WITH A JET MAX REMAINING NEAR
160KT. WITHIN THIS TROUGH...A 975MB VERTICALLY STACKED LOW IS
LOCATED ABOUT 300 NM SOUTH OF DUTCH HARBOR /IN THE LEFT EXIT
REGION OF THE JET/ WITH THE ASSOCIATED OCCLUDED FRONT MOVING INTO
THE ALASKA PENINSULA AND KODIAK ISLAND THIS MORNING. MULTIPLE
SHORTWAVES CONTINUE TO MOVE AROUND THE VERTICALLY STACKED LOW.

OVER THE GULF OF ALASKA AND THE NORTHEAST PACIFIC...THE PERSISTENT
HIGH AMPLITUDE RIDGE THAT HAS BEEN IN PLACE FOR SEVERAL DAYS IS
SHIFTING EASTWARD AS A SHORTWAVE TROUGH MOVES INTO SOUTHEAST
ALASKA AND THE PACIFIC NORTHWEST. OVER MAINLAND ALASKA...THE
NORTHERN EXTENSION OF THE RIDGE REMAINS IN PLACE...ALLOWING FOR
SOUTHERLY FLOW TO CONTINUE OVER THE WESTERN HALF OF THE STATE.
BERING SEA WEST OF 170W...NORTHERLY FLOW CONTINUES FOR THE BERING
SEA WEST OF 170W WITH MULTIPLE WEAK SHORTWAVES MOVING DOWN THE
WESTERN SIDE OF THE TROUGH.

&&

.MODEL DISCUSSION...

THROUGH DAY 2...GLOBAL MODELS CONTINUE TO BE IN REASONABLE
AGREEMENT WITH NO SIGNIFICANT INITIALIZATION ISSUES. IN THE DAY 2
TO DAY 3 PERIOD...THERE REMAINS SOME MINOR DIFFERENCES IN THE
STRENGTH AND LOCATION OF A LOW /CURRENTLY DEVELOPING NEAR JAPAN/
AS IT MOVES INTO THE WESTERN ALEUTIANS...ALTHOUGH THE 00Z MODELS
ARE IN BETTER AGREEMENT WITH THIS SYSTEM THAN YESTERDAY. IN THE
SHORT TERM...THE NAM WAS USED FOR RESOLUTION WITH A BLEND OF THE
GFS BY THE END OF DAY 3.

&&

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

THE MAIN FEATURES AFFECTING SOUTHCENTRAL THROUGH TUE NIGHT ARE TWO
WEATHER FRONTS MOVING NORTH ACROSS THE GULF OF ALASKA. THE THE FIRST
FRONT MOVES TO THE NORTHERN GULF TONIGHT THEN WEAKENS AS IT MOVES
INLAND TUE. A SECOND FRONT THEN MOVES TO THE NORTHERN GULF LATE
TUE. THE COASTS WILL RECEIVE THE LIONS SHARE OF THE RAIN. AREAS
NORTH AND EAST OF THE COASTAL/KENAI MOUNTAINS WILL LARGELY BE
DOWNSLOPED (CROSS BARRIER FLOW) SO PRECIPITATION SHOULD BE FAIRLY
SPOTTY IN THESE AREAS. PRESSURE GRADIENTS WILL INTENSIFY WITH THE
APPROACH OF THE FIRST FRONT WITH WINDS INCREASING TO GALES ACROSS
MANY COASTAL MARINE AREAS ALONG WITH GAP FLOWS IN FAVORED LOCALS
(TURNAGAIN ARM/PORTAGE VALLEY/MAT VALLEY) THIS AFTERNOON AND
EVENING. WINDS WILL FALL BELOW GALES ACROSS THE MARINE AREAS ON
TUE MORNING AND LIKELY WILL REMAIN THAT WAY AS THE NEXT FRONT
MOVING NORTH ON TUE DOES NOT LOOK AS INTENSE. GAP FLOWS WILL
DIMINISH SOME TUE MORNING BUT WILL INCREASE TUE AFTERNOON WITH
PRESSURE FALLS ACROSS THE INTERIOR AS THE FIRST FRONT PUSHES
INLAND. THIS WILL GIVE RISE TO BRISK AND GUSTY SOUTH/SOUTHEAST
WINDS ACROSS THE COPPER RIVER BASIN AND KNIK RIVER VALLEY TUE
AFTERNOON/EVENING.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE BULK OF ACTIVE WEATHER IS ASSOCIATED WITH A SYSTEM SPINNING
WELL TO THE SOUTH BUT THE MAINLAND COULD BE CLIPPED BY SOME
MOISTURE AND OCCASIONAL SHOWERS FOR THE NEXT COUPLE DAYS...MAINLY
IN THE GREATER BRISTOL BAY AREA. CLOUDS WILL BE HIGHLY VARIABLE
WITH CLEARER SKY TODAY OVER THE KUSKOKWIM VALLEY AND DECREASING
CLOUDS OVER THE DELTA...HOWEVER MOISTURE FROM THE SOUTHERN SYSTEM
WILL WORK ITS WAY NORTHWARD THROUGH TUESDAY RETURNING MOSTLY
CLOUDY SKY FOR MOST OF THE MAINLAND. THIS MATURE UPPER LEVEL LOW
HANGS OUT FOR THE DURATION OF THE SHORT TERM FORECAST...THOUGH
WEDNESDAY BUT WILL BE WEAKENING THE ENTIRE TIME...MEANING
GENERALLY LIGHT WINDS AND SPOTTY PRECIPITATION. TEMPERATURES WILL
REMAIN MUCH ABOVE NORMAL FOR THIS TIME OF YEAR WITH DAYTIME HIGHS
IN THE 40S...EVEN APPROACHING 50 INLAND.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE BERING FORECAST FEATURES A STUBBORN STACKED SYSTEM WITH
DECAYING FRONTAL BOUNDARY DRAPED FROM THE EASTERN ALEUTIANS INTO
THE GULF. THE PRIBILOFS LIE JUST ON THE COLD SIDE OF THE FRONT AND
WILL SEE SNOW FOR THE NEXT DAY OR SO WHILE EVERYWHERE TO THE EAST
IS ON THE WARM SIDE OF THE FRONT GETTING RAIN. THE EASTERN
ALEUTIANS WILL SEE STEADIER RAIN TODAY AND TUESDAY WHILE RAIN WILL
BECOME A BIT MORE INTERMITTENT AFTER THE FRONT PASSES THIS
AFTERNOON. THE SYSTEM WILL CONTINUE TO DECAY THROUGH WEDNESDAY
MEANING LESS AND LESS PRECIPITATION COVERAGE AND LIGHTENING WINDS.
LATE TONIGHT A SLOW MOVING GALE FORCE FRONT ENTERS THE WESTERN
ALEUTIANS AND WILL SLOWLY PROGRESS EASTWARD BY MID-WEEK

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A BROAD UPPER LEVEL LOW WILL STRETCH ACROSS THE BERING WITH ITS
MAIN CENTER IN THE SOUTHERN BERING LATE ON TUESDAY. THIS WILL
BRING PRECIPITATION TO THE BERING AND NORTH GULF COAST. EARLY
FRIDAY RIDGING WILL BUILD BACK IN OVER EASTERN ALASKA WHILE THE
TROUGH STAYS OVER THE BERING WHICH WILL BRING ANOTHER PUSH OF
WARM SOUTHERLY FLOW TO THE SOUTHERN MAINLAND. THERE IS OVERALL
DECENT AGREEMENT AMONGST THE MODELS WITH PLACEMENT OF THE MAJOR
FEATURES...ESPECIALLY WITH THE RIDGE. HOWEVER...THEY ARE STILL
STRUGGLING WITH SMALLER LOWS THAT WILL MOVE THROUGH THE BROAD
TROUGH.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 120 130 131 138 150 173 174 177 178
         HEAVY FREEZING SPRAY 412

&&

SYNOPSIS AND MODEL DISCUSSION...RLF
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
LONG TERM...DEK