Area Forecast Discussion
Issued by NWS Anchorage, AK

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224
FXAK68 PAFC 030013
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
413 PM AKDT MON MAY 2 2016

.ANALYSIS AND UPPER LEVELS...
THERE ARE TWO MAIN LOWS OVER THE AREA WITH THE FIRST OVER THE
WESTERN ALEUTIANS. THIS LOW IS SLOWLY TRACKING EAST ALONG THE
CHAIN WITH ITS FRONT EXTENDING ACROSS THE EASTERN ALEUTIANS
HEADING TOWARDS THE ALASKA PENINSULA. THE OTHER LOW IS OVER THE
WESTERN GULF AND SLOWLY TRACKING NORTH AS IT WEAKENS. THIS LOW IS
HELPING TO KEEP SOUTHWEST ALASKA UNSTABLE WHICH AIDED IN
THUNDERSTORM DEVELOPMENT YESTERDAY AND A SIMILAR PATTERN LOOKS TO
BE DEVELOPING TODAY. EAST OF THE GULF LOW THERE IS RIDGING THAT
IS ALLOWING FOR A PUSH OF MOISTURE FROM THAT SOUTH THAT IS
BRINGING RAIN TO THE COAST WITH RAIN AND SNOW AT HIGHER
ELEVATIONS AND INTO THE COPPER RIVER BASIN.

&&

.MODEL DISCUSSION...
IN THE SHORT TERM THE MODELS ARE IN GOOD AGREEMENT SO THE HIGHER
RESOLUTION MODELS WERE PREFERRED. IN THE MID TERM THE MODELS ARE
TRENDING TOWARDS THE DEEPER SOLUTION OF THE GFS AND NAM FOR THE
LOW APPROACHING KODIAK ISLAND FRIDAY. THESE ARE THE PREFERRED
MODELS IN THE MID TERM AS THE GEM IS ALSO FASTER THAN THE OTHERS.

&&

.AVIATION...
THE BIGGEST QUESTION FOR THE ANCHORAGE TAF IS WHEN SOUTHEAST WINDS
WILL MOVE INTO OVER WEST ANCHORAGE. AS RIDGING BUILDS IN ALONG THE
COAST THROUGH THE AFTERNOON WINDS WILL PICKUP THROUGH TURNAGAIN
ARM. THAT COMBINED WITH THE UP INLET GRADIENT THAT IS ALREADY IN
EFFECT LOOKS TO PUT WINDS OVER WEST ANCHORAGE BETWEEN 00Z AND 03Z.
AS THE ORIENTATION OF THE RIDGING ROTATES...THE UP INLET GRADIENT
SLACKENS AND TEMPERATURES FALL WINDS LOOK TO FALL AGAIN AROUND
12Z.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LEVEL DISTURBANCE CROSSING THE EASTERN HALF OF SOUTH
CENTRAL TODAY WILL EXIT TO INTERIOR ALASKA THIS EVENING. COLDER
AIR ALOFT WILL MOVE IN BEHIND IT AND HELP BREAK UP SOME OF THE
CLOUDS OVER INLAND SECTIONS OF SOUTH CENTRAL WHILE LEADING TO AN
OVERALL MORE SHOWERY NATURE TO REMAINING PRECIP IN THE REGION.
MEANWHILE...A SURFACE RIDGE WILL BUILD IN ALONG THE NORTH GULF
COAST LATE THIS AFTERNOON THROUGH EVENING LEADING TO GUSTY WINDS
THROUGH THE NORMAL MOUNTAIN GAPS. OVERALL INSTABILITY WILL ALLOW
THESE WINDS TO BRIEFLY BE A LITTLE MORE WIDESPREAD OUTSIDE OF THE
GAPS.

THE BULK OF PRECIP WILL BE FOCUSED ACROSS THE NORTHERN GULF AND
PRINCE WILLIAM SOUND THE NEXT COUPLE DAYS...FIRST WITH A WEAKENING
LOW...THEN WITH THE ARRIVAL OF A WEAKENING OCCLUDED FRONT/UPPER
LEVEL SHORT-WAVE ON WEDNESDAY. DECENT AIR MASS INSTABILITY WILL
PERSISTS ACROSS THE REST OF THE REGION WHICH WILL SUPPORT
OCCASIONAL BREAKS IN THE CLOUDS ALONG WITH SCATTERED CONVECTION
DURING THE AFTERNOON AND EVENING HOURS. WITH NO REAL ORGANIZED
FORCING MECHANISM TO HONE IN ON IT WILL BE NEARLY IMPOSSIBLE TO
PINPOINT WHERE THE SHOWERS WILL FORM EACH DAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3)...
THE GENERALLY UNSTABLE PATTERN WITH DIURNALLY ENHANCED SHOWERS
AND ISOLATED AFTERNOON AND EVENING THUNDERSTORMS WILL CONTINUE
OVER SOUTHWEST ALASKA THROUGH MIDWEEK. THE THERMAL TROUGH RUNNING
FROM THE YUKON RIVER VALLEY ACROSS THE KUSKOKWIM RIVER VALLEY AND
AND INTO THE NORTHERN HALF OF THE GREATER BRISTOL BAY AREA WILL
PROVIDE A FOCUS FOR THUNDERSTORMS THROUGH THIS EVENING. WEAKENING
RIDGING ALONG THE COAST WILL BRING LOW STRATUS AND FOG TO COASTAL
PORTIONS OF THE KUSKOKWIM DELTA AGAIN TONIGHT AND PUSH IT FURTHER
INTO BRISTOL BAY AS WELL.

INSTABILITY LOOKS SOMEWHAT WEAKER TUESDAY BUT THE TROUGH LIFTING
ACROSS BRISTOL BAY AND INTO SOUTHWEST ALASKA WILL BRING NUMEROUS
SHOWERS TO THE BRISTOL BAY AREA AND SCATTERED SHOWERS FURTHER
NORTH. LINGERING INFLUENCE FROM THE THERMAL TROUGH COULD BRING AN
ISOLATED THUNDERSTORM OR TWO TO THE KUSKOKWIM VALLEY AND
SURROUNDING MOUNTAINS BUT WOULD EXPECT THEM TO BE PRETTY SPARSE IN
COVERAGE. BY WEDNESDAY INSTABILITY INCREASES AGAIN SOMEWHAT WITH
THE POTENTIAL FOR ISOLATED THUNDERSTORMS SPREAD OVER MORE OF
SOUTHWEST ALASKA. ON THURSDAY A FRONT LIFTING NORTH ACROSS THE
ALASKA PENINSULA WILL BEGIN STABILIZING CONDITIONS AS WELL AS
BRINGING SOME BREEZY EAST TO NORTHEAST WINDS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH 3)...
THE VERTICALLY STACKED LOW OVER THE WESTERN ALEUTIANS WILL
GRADUALLY WEAKEN AS IT TRACKS EAST ALONG THE CHAIN TONIGHT AND
TUESDAY THEN ELONGATES TO MORE OF A BROAD TROUGH STRETCHED OVER
THE ALASKA PENINSULA AND BRISTOL BAY TUESDAY NIGHT AND WEDNESDAY.
THE UPPER LEVEL RIDGE CURRENTLY OVER THE ALASKA PENINSULA AND
EASTERN BERING WILL SHIFT EAST AND WEAKEN THROUGH TONIGHT AHEAD OF
THE INCOMING LOW. BEHIND THE LOW A LARGE UPPER LEVEL RIDGE WILL
SHIFT EAST OVER THE WEST AND CENTRAL ALEUTIANS AND BERING
WEDNESDAY AND THURSDAY WHILE A COLD TROUGH OUT OF RUSSIA DIVES
SOUTH FROM THE ANADYR GULF ACROSS SAINT MATTHEW AND THE PRIBILOF
ISLANDS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...THU THROUGH MON)...
THE BIG PICTURE MOVING FORWARD IS THAT THE PATTERN WILL BE MORE
DYNAMIC THAN WE HAVE SEEN IT OVER THE PAST SEVERAL WEEKS. THE LOW
CURRENTLY TRACKING ALONG THE ALEUTIANS WILL SET UP SHOP NEAR
BRISTOL BAY ON THU. IT WILL STALL OUT THERE AND WEAKEN IN PLACE.
BUT IT WILL SET THE STAGE FOR ANOTHER...STRONGER LOW TO DEVELOP
OVER THE NORTHERN PACIFIC AND TRACK TOWARD KODIAK ISLAND ON FRI.
THIS SYSTEM WILL PUSH A WARM FRONT INTO THE GULF OF AK ON THU AND
INTO SOUTH CENTRAL ON FRI. THE LOW THEN QUICKLY EXITS THE AREA
OVER THE WEEKEND LEAVING SOME RIDGING IN PLACE. ANOTHER LOW
QUICKLY MOVES IN TO THE BERING SEA OVER THE WEEKEND WHILE SOME
RIDGING BUILDS FROM THE NORTH PACIFIC OVER THE MAINLAND.

MODELS HAVE ALL BEEN STRUGGLING IN HANDLING THE EVOLUTION OF THE
ENERGY FROM BRISTOL BAY INTO THE DEVELOPING SYSTEM OVER THE NORTH
PACIFIC ON THU. AS IT WEAKENS...IT DOES SEND AN UPPER LEVEL WAVE
THROUGH SOUTH CENTRAL ALASKA WED EVE INTO THU MORNING. WE HAVE
BUMPED SHOWERS UP TO SCATTERED WITH THIS FEATURE AS CROSS-BARRIER
FLOW SHOULD WEAKEN AS IT MOVES THROUGH. MODELS ARE IN MUCH BETTER
AGREEMENT IN HANDLING THE DEVELOPING NORTH PACIFIC LOW SO
CONFIDENCE HAS INCREASED THERE. IT WILL PULL UP A HEALTHY AMOUNT
OF SUB-TROPICAL MOISTURE INTO THE GULF AND BRING MODERATE RAIN TO
THE COASTLINE THROUGH FRI. WINDS WILL ALSO INCREASE TO GALE-FORCE
ACROSS PORTIONS OF THE GULF...ESPECIALLY THE BARRIER JET REGION.
HOW MUCH PRECIPITATION CAN MAKE IT INLAND IS STILL SOMEWHAT IN
QUESTION...BUT IT DOES LOOK LIKE ANOTHER DOWN-SLOPING SCENARIO
WILL KEEP MOST OF THE RAIN CONFINED TO THE COAST.

INTO THE WEEKEND...CONFIDENCE IS GROWING THAT THIS LOW WILL BE
EXITING TO THE NORTHEAST QUICKLY ON SAT. THIS SHOULD SPELL A
RAPIDLY CLEARING DAY ACROSS THE MAINLAND WITH DRY OFFSHORE FLOW.
THIS COULD RESULT IN MORE ABUNDANT SUNSHINE THAN MANY PLACES HAVE
SEEN FOR SOMETIME. BEYOND THIS...CONFIDENCE DROPS MARKEDLY. MODELS
ARE SORTING OUT HOW FAR EAST THE BERING LOW CAN TRACK VS HOW
STRONG RIDGING OVER SOUTH CENTRAL WILL BE VS IF A NORTH PACIFIC
LOW BRINGS IN MORE CLOUD COVER FROM THE SOUTH. IF RIDGING WERE TO
WIN OUT...WHICH SOME OF THE MEMBERS ARE SHOWING...WE WOULD NEED TO
DRY THE FORECAST OUT CONSIDERABLY FOR MUCH OF THE SOUTHERN HALF OF
THE STATE.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...MO



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