Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 050117
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
517 PM AKDT MON MAY 4 2015

.ANALYSIS AND UPPER LEVELS...

A BROAD UPPER LEVEL RIDGE CONTINUES ACROSS SOUTHCENTRAL ALASKA.
GENERALLY FAIR SKIES WERE OBSERVED ACROSS MUCH OF THE FORECAST
AREA WITH THE EXCEPTION OF KODIAK ISLAND WHICH HAD CLOUDS AND
ISOLATED SHOWERS ASSOCIATED WITH A UPPER LEVEL TROUGH. THE
MORNING SOUNDING AT ANCHORAGE SHOWED FAIRLY STABLE CONDITIONS.

OUT WEST...
A BROAD UPPER LOW AND SURFACE TROUGH CONTINUE ACROSS THE SOUTHWEST
MAINLAND. PRECIPITATION AS OF THE MORNING WAS GENERALLY CONFINED TO
ALONG THE SOUTHERN ALEUTIAN RANGE. SATELLITE IMAGERY THOUGH
INDICATES THAT CONVECTION IS STARTING ALONG THE NORTHERN ALEUTIAN
RANGE AND ALASKA RANGE. A STACKED AND WEAKENING LOW PRESSURE
CENTER WAS LOCATED SOUTH OF ADAK WITH ITS OCCLUDED FRONT EXTENDING
NORTH THEN SE TO OVER THE EASTERN ALEUTIANS. STORM FORCE WINDS
ASSOCIATED WITH THIS LOW HAVE DIMINISHED...THOUGH THERE ARE STILL
SOME LINGERING GALES OVER THE CENTRAL BERING SEA AND WESTERN
ALEUTIANS. BRISK TO STRONG EAST TO SOUTHEAST WINDS ARE ALSO
PRESENT IN ADVANCE OF THE FRONTAL SYSTEM.

&&

.MODEL DISCUSSION (THROUGH WED AFTERNOON)...
MODELS HANDLE THE MAIN SYNOPTIC FEATURES SIMILARLY AND REASONABLY.
A FEW DIFFERENCES HOWEVER EXIST IN THE TIMING AND EXTENT OF QPF
ASSOCIATED WITH A WEAKENING OCCLUDED FRONT AS IT MOVES ACROSS
BRISTOL BAY AND INTO THE WESTERN GULF. THE GEM REGIONAL AND
GLOBAL MODELS HAVE A LITTLE MORE QPF OVER BRISTOL BAY TONIGHT/TUE
MORNING...WHILE THE 12Z NAM IS A LITTLE ON THE LIGHT SIDE...DUE TO
STRONGER SE CROSS BARRIER FLOW. THE 18Z NAM THOUGH HAS INCREASED
THE QPF SOME. THE GEM FLATTENS THE RIDGE ACROSS THE GULF A LITTLE
FASTER THEN THE OTHER MODELS AND IN RESPONSE A LITTLE QUICKER
BRINGING IN THE PRECIPITATION ONTO THE KENAI PEN. WE WILL
PROBABLY LEAN WITH A SLOWER SOLUTION DEPICTED ON THE OTHER
MODELS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LOW OVER BRISTOL BAY WILL ELONGATE AND SEND A TROUGH
NORTHWARD UP COOK INLET AND THE SUSITNA VALLEY TODAY. THE COLDER
AIR ALOFT WILL INCREASE MID TO UPPER LEVEL LAPSE RATES...BUT SINCE
CONDITIONS ARE STARTING OUT QUITE STABLE THIS WILL ONLY CREATE
WEAK INSTABILITY. DRY AIR IS ALSO A LIMITING FACTOR. THEREFORE...
EXPECT NOTHING MORE THAN A FEW SHOWERS TO FORM...PRIMARILY OVER
THE MOUNTAINS. WEAK SOUTHERLY STEERING FLOW WILL KEEP THEM THERE.
OTHERWISE EXPECT ANOTHER MOSTLY SUNNY DAY ACROSS THE REGION WITH
SOME AFTERNOON AND EVENING SEA BREEZES ALONG THE COAST.

CLOUDS WILL BE ON THE INCREASE TONIGHT THROUGH WEDNESDAY AS THE
UPPER RIDGE SLIDES NORTH AND EAST OF SOUTHCENTRAL ALLOWING
MOISTURE FROM THE ALEUTIAN LOW TO MOVE IN. THE REMNANTS OF AN
OCCLUDED FRONT WILL MAKE SLOW NORTHWARD PROGRESS ACROSS THE GULF
WITH THE BULK OF RAIN REMAINING SOUTH OF THE KENAI PENINSULA. AS
THIS FRONT APPROACHES THE SURFACE HIGH OVER THE GULF WILL BUILD
NORTHWARD OVER SOUTHCENTRAL RESULTING IN DEVELOPMENT OF WEAK GAP
WINDS IN THE USUAL PLACES (SUCH AS TURNAGAIN AND KNIK ARMS).

AS FAR AS FIRE WEATHER CONDITIONS...THERE WILL BE VERY LITTLE
CHANGE IN RELATIVE HUMIDITIES TODAY. HOWEVER...EXPECT A GRADUAL
TREND TOWARD INCREASING MOISTURE BEGINNING TUESDAY WITH THE
ARRIVAL OF CLOUDS AND SLIGHTLY COOLER TEMPERATURES.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...TUE AND
WED)...AFTERNOON CONVECTION IS FIRING ALONG THE HIGHER TERRAIN OF
THE ALEUTIAN AND ALASKA RANGES THIS AFTERNOON. A CLOSED UPPER
LEVEL HAS BEEN SPINNING ALL DAY OVER THE SOUTHWEST AND IT IS
GETTING JUST A SLIGHT BIT OF ENHANCEMENT FROM A WEAK UPPER LEVEL
WAVE MOVING TO THE EAST FROM THE EASTERN ALEUTIANS. WITH ABUNDANT
SUNSHINE TO HEAT THINGS UP EARLIER TODAY...THE KING SALMON
SOUNDING DID COME IN WITH OVER 200 J/KG OF CAPE. OPTED TO LEAVE AN
ISOLATED CHANCE OF TS ALONG THE RANGES THROUGH THE EVENING WITH
THIS INSTABILITY IN PLACE.

AFTER THIS WE WILL SEE THE FRONT THAT IS SLOWLY CHUGGING ACROSS
THE ALEUTIANS MAKE IT TO THE COAST ON TUESDAY. THIS WILL BRING AN
INCREASE IN CLOUD COVER AND STRATIFORM PRECIPITATION TO THE ALASKA
PENINSULA AND WESTERN CAPES. EAST TO SOUTHEAST WINDS WILL ALSO BE
IN THE INCREASE TONIGHT AND TUESDAY AS THE GRADIENT TIGHTENS
ASSOCIATED WITH THE FRONT. THE PATTERN WILL BE SLOW TO CHANGE
TUESDAY NIGHT INTO WEDNESDAY AS THE FRONT DRAPES ITSELF OVER THE
AREA AND SLOWLY FALLS APART. A NEW PIECE OF ENERGY WILL MOVE
QUICKLY NORTH FROM THE NORTH PACIFIC ON WEDNESDAY. THIS WILL RE-
INVIGORATE THE FRONT WITH AROUND ROUND OF RAIN...MAINLY FOR THE
SOUTHER PORTION OF BRISTOL BAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...TUE AND
WED)...THE BROAD UPPER-LEVEL LOW COMPLEX HAS SET-UP SHOW OVER THE
CENTRAL ALEUTIANS. THIS FEATURE WILL BE SLOW TO MOVE OVER THE NEXT
SEVERAL DAYS AS A CLOSED HIGH SITS JUST TO ITS NORTH IN THE BERING
STRAIT. THESE TWO FEATURES WILL WORK TOGETHER CREATING A QUASI-
BLOCKING PATTERN FOR THE AREA. THIS WILL KEEP MUCH OF THE EASTERN
ALEUTIANS IN WARMER WEAKENING SOUTHERLY FLOW WITH THE WESTERN
ALEUTIANS IN SLIGHTLY COOLER...MORE SHOWERING NORTHWESTERLY FLOW.
HIGH PRESSURE STARTS TO BUILD INTO THE WESTERN BERING LATE
WEDNESDAY WHICH SHOULD BRING EVEN CALMER WINDS AND A DECENT
POTENTIAL FOR SOME FOG.

&&

.LONG TERM FORECAST (TUE NIGHT THROUGH SAT NIGHT)...
AFTER FAIRLY BENIGN WEATHER CONDITIONS MIDWEEK...A PACIFIC STORM
MOVES INTO THE GULF BRINGING GUSTY WINDS AND RAIN FOR THE
BEGINNING OF THE WEEKEND. STARTING THE LONG TERM WITH WEDNESDAY
NIGHT...A FRONT ALONG THE GULF PUSHES TOWARD THE COAST AND IS
QUICKLY FOLLOWED WITH ANOTHER REINFORCING FRONT AS THE MAIN UPPER
LOW IN THE NORTH PACIFIC BEGINS TO LIFT THURSDAY. BY FRIDAY THE
STORM SYSTEM BECOMES NEGATIVELY TILTED AS A RIDGE ACROSS THE ALCAN
BORDER BLOCKS EASTWARD PROGRESSION. THIS STORM SHOULD BE
MONITORED SINCE THERE IS STILL A BIT OF UNCERTAINTY BETWEEN
MODELS ON THE STRENGTH AND TRACK OF THIS LOW INTO THE WEEKEND.

OUT WEST ACROSS THE BERING AN ALEUTIANS...THE PATTERN THROUGH FRIDAY
IS DOMINATED BY A BUILDING RIDGE ACROSS THE BERING. ANOTHER LOW
MOVES UP TO THE CENTRAL ALEUTIANS FRIDAY WITH AND EASTWARD TRACK
TOWARD THE ALASKA PENINSULA INTO SUNDAY NIGHT.

&&


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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...MTL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...KH


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