Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 061240
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
440 AM AKDT FRI MAY 6 2016

.ANALYSIS AND UPPER LEVELS...

A DEEP POSITIVE TILT TROUGH IS THE DOMINANT SYNOPTIC FEATURE
ACROSS THE REGION THIS MORNING...STRETCHING FROM 30N ON THE
SOUTHERN END OF THE TROUGH TO GULF OF ALASKA ALONG THE NORTHERN
END. THE WARM FRONT HAS ALREADY MOVED INLAND AND IS MOVING NORTH
(THE LEFTOVER REMNANTS OF THE UPPER LEVEL FRONT) OF THE ALASKA
RANGE. THE REMAINDER OF THE WARM CONVEYOR BELT/SUBTROPICAL JET
STREAM CAN BE SEEN AS A REGION OF HIGH CLOUD TOPS ON SATELLITE
IMAGERY MOVING EAST INTO THE YUKON. THE PARENT UPPER LOW...NOW
STACKED AND BAROTROPIC...IS SPINNING JUST SOUTH OF KODIAK ISLAND.
OVER THE BERING...SHORTWAVE RIDGING IS BUILDING AHEAD OF A WARM
FRONT WHICH IS MOVING EAST ACROSS THE THE WESTERN BERING IN
ASSOCIATION WITH A KAMCHATKA UPPER LEVEL TROUGH.

AN INVERTED SURFACE TROUGH AXIS IS EXTENDING NORTH INTO INTERIOR
BRISTOL BAY...WHICH IS SUPPORTING SHOWERS AND RAIN FROM THE
SOUTHERN KUSKOKWIM DELTA TO BRISTOL BAY. RAIN IS MORE COASTAL
BASED ACROSS SOUTHCENTRAL WHERE DOWNSLOPE SHADOWING...WHICH HAS
DOMINATED SO FAR THIS SPRING...IS KEEPING MOST AREAS DRY WITH THE
EXCEPTION OF SPORADIC LIGHT RAIN ACROSS WEST ANCHORAGE AND PARTS
OF THE WESTERN KENAI PENINSULA.

WITH TIME...THE PACIFIC TROUGH WILL DEAMPLIFY AND MOVE
EAST...ALLOWING FOR HIGH PRESSURE ALOFT TO BUILD ACROSS
SOUTHERN ALASKA SATURDAY.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN EXCELLENT AGREEMENT WITH NO SUBSTANTIAL
DIFFERENCES IN THE SYNOPTIC FIELDS OR MESOSCALE FIELDS TO NOTE.
THE ONLY LOCAL SCALE DIFFERENCES REVOLVE AROUND PRECIPITATION
DISTRIBUTION INLAND TODAY AS THE TROUGH MOVES EAST...AND THE
STRENGTH OF TURNAGAIN WINDS (AND COPPER BASIN WINDS) WHICH ARE
EXPECTED TO DEVELOP THIS AFTERNOON. THE NAM AND HI RES MODELS WERE
LARGELY FAVORED AND INCORPORATED INTO THE FORECAST THROUGH MOST OF
THE WEEKEND.

&&

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

THE FRONT ACROSS THE NORTH GULF COAST IS BEGINNING TO DIMINISH
THIS MORNING...BRINGING AN END TO THE GUSTY WINDS THAT DEVELOPED
ACROSS CHANNELED TERRAIN ACROSS SOUTHCENTRAL AND THE INNER WATERS
AREAS. WATER VAPOR SATELLITE DEPICTS A PRONOUNCED DRY SLOT BEHIND
THE FRONT MOVING INLAND...WHICH MEANS THAT INSTABILITY WILL BE
INCREASING AS THE UPPER TROUGH REMAINS NEARLY STATIONARY OVER THE
REGION. THIS WILL MEAN SCATTERED TO NUMEROUS SHOWER ACTIVITY
DEVELOPING WITH EVEN MINIMAL DAYTIME HEATING TODAY...ESPECIALLY
OVER THE MOUNTAIN RANGES BUT WITH GOOD CHANCES AT THE LOWER
ELEVATIONS AS WELL. SATURDAY WILL BE A TRANSITION DAY AS THE UPPER
LOW SLIDES OFF TO THE EAST WITH A TRANSITORY RIDGE MOVING ACROSS
THE AREA SATURDAY NIGHT.

&&

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

THE PATTERN WILL SHIFT MULTIPLE TIMES OVER THE NEXT FEW DAYS.
TODAY WILL FEATURE THE SURFACE LOW OVER THE GULF OF AK PULLING TO
THE EAST. THIS WILL SLOWLY BRING AN END TO THE STEADY LIGHT RAIN
THROUGH THE DAY. IT WILL LEAVE SOME SHOWERS...MAINLY OVER THE
MOUNTAINS...IN ITS WAKE LATER THIS AFTERNOON. OVERNIGHT FRI INTO
SAT...A TRANSITORY SHORTWAVE RIDGE WILL MOVE THROUGH. THIS SHOULD
INCREASE STABILITY AND BRING SOME ONSHORE FLOW...ESPECIALLY TO THE
BRISTOL BAY REGION. WE EXPECT THAT EITHER SOME LOW STRATUS OR FOG
WILL FORM ALONG THE COAST TONIGHT AND COULD PUSH INLAND TO AREAS
LIKE KING SALMON. FORECAST CONFIDENCE IS LOW IN WHETHER OR NOT
PLACES WILL SEE REDUCED VISIBILITY OR JUST LOW CLOUDS.

SAT...A DISTANT LOW OVER THE WESTERN BERING WILL SLING A FRONT
THROUGH THE EASTERN BERING TOWARD THE COAST. FLOW WILL BECOME MORE
SOUTHERLY IN ADVANCE OF THE FRONT. RAIN SHOULD REACH THE COAST IN
THE LATE AFTERNOON TO EVENING TIME AND MOVE INLAND FAIRLY QUICKLY.
AS THIS SYSTEM WILL BRING BROAD SOUTHWEST FLOW...THIS WILL LIKELY
BRING A WIDESPREAD WETTING RAIN (GREATER THAN A TENTH OF AN INCH) TO
MOST OF THE AREA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...FRI AND
SAT)...

GUSTY NORTH TO NORTHWEST FLOW OVER THE ALASKA PENINSULA WILL GRADUALLY
DIMINISH BY THIS AFTERNOON AS THE LOW PULLS AWAY INTO THE GULF.
WHILE SOME SHOWERS COULD CONTINUE ON THE NORTH SIDE OF THE
PENINSULA...THE TREND SHOULD BE TOWARD DRIER CONDITIONS FOR THE
MOST PART BY SAT. MEANWHILE...THE BROAD AREA OF LOW PRESSURE NEAR
THE KAMCHATKA PENINSULA THIS MORNING WILL PUSH A MASSIVE FRONT
ACROSS THE BERING. THIS FRONT WILL PACK A SMALL CORRIDOR OF GALE-
FORCE SOUTHERLY WINDS AND PLENTY OF RAIN. IT LOOKS TO REACH THE
PRIBILOF ISLANDS LATE THIS EVENING. THEREAFTER...BROAD CYCLONIC
FLOW WILL BE LIMITED TO SMALL CRAFT FORCE BEHIND THIS LOW ON SAT.
THE BEST POTENTIAL FOR STEADY RAIN WILL CERTAINLY BE ALONG THE
FRONT...BUT THERE WILL STILL BE POTENTIAL FOR LIGHT RAIN AND SOME
SHOWERS ACROSS THE REST OF THE REGION.

&&

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

BEGINNING THE LONG TERM PERIOD FORECAST SUNDAY...A SHORTWAVE
TROUGH ACROSS SOUTHWEST ALASKA WILL SPREAD A SOUTHWESTERLY FLOW
REGIME ALOFT ACROSS ALL OF SOUTHERN ALASKA...ALLOWING FOR
WIDESPREAD LIGHT RAIN TO MOVE INTO SOUTHCENTRAL BEGINNING SUNDAY
EVENING INTO MONDAY. MEANWHILE...A LARGE TROUGH ACROSS THE FAR
WESTERN BERING SEA WILL MOVE EAST SUNDAY NIGHT THROUGH
TUESDAY BEFORE SETTING UP SHOP ACROSS THE EASTERN BERING
WEDNESDAY...THEN PERSISTING INTO THE LATE WEEK. WHAT THIS MEANS
IS ALL OF SOUTHERN ALASKA WILL BE UNDER THE THREAT FOR PROLONGED
INCREASED RAIN CHANCES AND SLIGHTLY COOLER WEATHER FOR THE FIRST
TIME THIS SPRING. BY THE WEEKEND ENSEMBLE AND DETERMINISTIC
DEPICTIONS OF THE NORTHEAST PACIFIC RIDGE AND BERING TROUGH
DIVERGE RAPIDLY...WITH SOME SOLUTIONS SHOWING THE WESTWARD
DEVELOPMENT OF A VERY STOUT EARLY SEASON BLOCKING RIDGE INTO
ALASKA. THIS YIELDS SENSIBLE WEATHER DIFFERENCES FROM CLOUDY AND
RAINY TO SUNNY AND QUITE WARM. OWING TO THE CHALLENGES MODELS HAVE
IN THIS TIME FRAME WITH BLOCKING HIGH DEVELOPMENTS...FORECAST
CONFIDENCE IS HIGH THROUGH THE WEEK THEN TANKS BEYOND FRIDAY. STAY
TUNED...

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 175-177.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...AHSENMACHER
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MSO
LONG TERM...AHSENMACHER



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