Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 280030
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
430 PM AKDT MON JUL 27 2015

.ANALYSIS AND UPPER LEVELS...

EXTENSIVE MOISTURE IS DEFINITELY THE THEME OF TODAYS WEATHER
PATTERN ACROSS THE WHOLE OF SOUTHERN ALASKA. ALL OF THE 12Z
SOUNDINGS SHOW NEARLY SATURATED CONDITIONS FROM THE SURFACE UP
THROUGH AT LEAST 500 MB. THIS IS IN LARGE PART THANKS TO A NEARLY
STATIONARY UPPER LEVEL LOW CENTERED OVER THE CENTRAL GULF...WITH
UPPER LEVEL TROUGHING ACROSS ALL OF MAINLAND ALASKA. THIS PATTERN
FAVORS A CONTINUATION OF SEASONAL TEMPERATURES AND CLOUDY
CONDITIONS WITH ONLY LIMITED SUNSHINE. THE STRONGEST LIFT WILL BE
EAST OF THE TROUGH MOVING INTO SOUTHEAST ALASKA. A RIDGE IS OVER
THE FAR WESTERN BERING AND IT TOO IS VERY MOIST...WITH
PRECIPITABLE WATER VALUES OVER TWO INCHES. BETWEEN THE WESTERN
BERING RIDGE AND THE TROUGH OVER MAINLAND ALASKA...THE JET STREAM
IS IN PLACE ACROSS THE CENTRAL BERING. A MOISTURE-RICH SHORTWAVE
DISTURBANCE IN THE JET IS MOVING ACROSS THE EASTERN ALEUTIANS AND
SOUTHERN ALASKA PENINSULA...GENERATING STEADY RAINS AS IT MAKES
ITS WAY TOWARDS THE NORTH PACIFIC.

&&

.MODEL DISCUSSION...

WITH A NEARLY STATIONARY UPPER LEVEL PATTERN SET UP...THE LACK OF
BIG CHANGES IS ALLOWING THE MODELS TO ALL REMAIN IN EXCELLENT
AGREEMENT...KEEPING A TROUGH OVER MAINLAND ALASKA AND A RIDGE OVER
THE WESTERN BERING. THE GREATEST CHALLENGES PRIMARILY FOCUS ON THE
MOVEMENT AND INTERACTION OF SMALLER EMBEDDED FEATURES MOVING
THROUGH THE STAGNANT BROAD PATTERN. WITH ABUNDANT MOISTURE KEEPING
CONDITIONS CLOUDY AND COOL...THE BIGGEST FORECAST QUESTION WILL BE
WHEN AND WHERE SHOWER ACTIVITY WILL POP UP IN ASSOCIATION WITH
THOSE FEATURES. CONFIDENCE IN THAT ASPECT OF THE FORECAST IS LOWER
THAN NORMAL.

&&

.FIRE WEATHER...

FIRE WEATHER CONCERNS ARE MINIMAL ACROSS ALL OF SOUTHERN ALASKA
OWING TO A STAGNANT VERY MOIST AIR MASS IN PLACE. CLOUD COVER
WILL BE WIDESPREAD WITH SOME SHOWER ACTIVITY... AND WILL ALSO
LIMIT ANY WET THUNDERSTORMS TO MORE UNSTABLE AREAS NEAR MOUNTAIN
RANGES THIS EVENING AND TUESDAY AFTERNOON AND EVENING. RH VALUES
WILL REMAIN HIGH WITH LIGHT WINDS. A SLOW WEAKENING OF THE TROUGH
AND A BUILDING RIDGE WILL FAVOR A GRADUAL WARMING AND DRYING TREND
ON TUESDAY AND WEDNESDAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LEVEL LOW CURRENTLY CENTERED OVER THE NORTHERN GULF
WILL BE THE MAIN WEATHER FEATURE IMPACTING SOUTH CENTRAL ALASKA
THROUGH MIDWEEK. THE LOW WILL GRADUALLY WEAKEN TO A TROUGH AS IT
DRIFTS SLOWLY EAST TO BE CENTERED NOT FAR OFFSHORE OF YAKUTAT...
BEFORE EVENTUALLY DISSIPATING TUESDAY NIGHT WITH THE REMNANTS
SWINGING INLAND. A SERIES OF SMALL TROUGHS SWINGING AROUND THE
BOTTOM OF THE LOW AND INLAND THROUGH SOUTHEAST ALASKA WILL
GRADUALLY TRANSFER BITS OF THE SURFACE REFLECTION OF THE LOW INTO
THE YUKON TERRITORY AND INTERIOR ALASKA. THIS WILL ALLOW THE
THERMAL TROUGH TO SLOWLY BECOME THE DOMINANT SURFACE LOW PRESSURE
FEATURE. WEAK SURFACE RIDGING WILL BUILD INTO THE NORTHERN GULF
THROUGH MIDWEEK.

THE RESULTS WILL BE A SLOW SHIFT FROM MOIST NORTHERLY FLOW DOWN
THE SUSITNA VALLEY AND WEAK SOUTHERLY FLOW OVER THE COPPER RIVER
BASIN...TO SOUTH TO SOUTHEAST FLOW OVER THE ENTIRE AREA BY
WEDNESDAY. SHOWERS WILL CONTINUE TO BE ABUNDANT THOUGH GRADUALLY
DIMINISH OVER TIME. A FEW ISOLATED THUNDERSTORMS ARE POSSIBLE OVER
THE COPPER BASIN AND TALKEETNA MOUNTAINS THIS AFTERNOON AND
EVENING. BETTER INSTABILITY AND A BIT MORE SUNSHINE WILL MAKE THEM
MORE LIKELY OVER A BROADER AREA TUESDAY AFTERNOON AND EVENING WITH
THE BEST CHANCES OVER THE NORTHERN SUSITNA VALLEY...COPPER RIVER
BASIN AND SURROUNDING MOUNTAINS.

&&

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

AN UPPER TROUGH REMAINS THE DOMINANT UPPER PATTERN ALONG WITH A
SURFACE TROUGH OVER THE INTERIOR THROUGH WEDNESDAY. A TROUGH AXIS
EXTENDING TO BRISTOL BAY WILL BE A FOCUS FOR AFTERNOON AND EVENING
THUNDERSTORMS TO DEVELOP. STORMS WILL GENERALLY HAVE LITTLE MOTION
AS UPPER FLOW IS WEAK. HOWEVER...ON TUESDAY EVENING AN UPPER LEVEL
WAVE DIGGING FROM THE EASTERN BERING MAY PRODUCE STRONGER STORMS
DUE TO ENHANCEMENT FROM THIS FEATURE...ESPECIALLY ACROSS BRISTOL
BAY.

&&

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

A SHORT WAVE CURRENTLY MOVING ACROSS THE CENTRAL BERING CONTINUES
TO DROP SOUTH TONIGHT BRINGING RAIN TO THE SOUTHERN BERING...
EASTERN ALEUTIANS AND ALASKA PENINSULA. AN ACTIVE WAVE PATTERN
REMAINS ACROSS THE EASTERN BERING THROUGH WEDNESDAY AS AN UPPER LOW
DEVELOPING IN THE NORTHWEST FLOW INTERACTS WITH THE LOW OVER THE
GULF. OTHERWISE...NORTH TO NORTHWESTERLY FLOW WILL ENCOMPASS THE
EASTERN BERING AND ALEUTIANS. AREAS OF FOG WILL DEVELOP AS
RIDGING SHIFTS EAST FROM THE KAMCHATKA PENINSULA. A FRONT MOVING
UP FROM THE NORTHWESTERN PACIFIC WILL SKIRT THE WESTERN HALF OF
THE CHAIN TUESDAY NIGHT THROUGH WEDNESDAY...HOWEVER PRECIPITATION
AND WINDS ARE SHUNTED FROM MAKING NORTHWARD PROGRESS AS THE UPPER
RIDGE BUILDS ACROSS THE WESTERN BERING.

&&

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

THERE ARE A FEW KEY FEATURES THAT DETERMINISTIC GUIDANCE HAVE BEEN
HAVING A TOUGH TIME RESOLVING OVER THE PAST COUPLE OF MODEL RUNS.
WHILE MODELS START OFF IN DECENT SHAPE ON WEDNESDAY WITH AN
ELONGATED TROUGH ENCOMPASSING ALL OF ALASKA...THE WAY THE PATTERN
BEGINS TO SHIFT OVER THE WEEKEND BECOMES QUITE COMPLICATED. IT
APPEARS THAT THIS UPPER LEVEL TROUGH WILL BEGIN TO PUSH SOUTH OF
THE ALASKA MAINLAND AS HIGH PRESSURE OVER THE BERING SEA BEGINS TO
NUDGE INLAND AND EVENTUALLY BUILD ACROSS THE INTERIOR OF ALASKA.
THIS WILL KEEP SHOWER ACTIVITY COMMON ACROSS SOUTHCENTRAL ALASKA
WHILE THE BERING SEA AND SOUTHWEST ALASKA WILL BE LARGELY ON THE
DRY SIDE THANKS TO THE SUBSIDENCE ASSOCIATED WITH THE HIGH
PRESSURE BUILDING ACROSS THE AREA. AS THE UPPER LEVEL TROUGH DROPS
SOUTH...TWO SCENARIOS WILL EMERGE. THE FIRST BEING A CONCENTRIC
UPPER LEVEL LOW THAT PUSHES INTO THE NORTH PACIFIC WITH RIDGING
PUSHING INTO SOUTHCENTRAL ALASKA. THE OTHER SCENARIO BEING THE
CONCENTRIC LOW STAYING IN THE GULF OF ALASKA AND KEEPING RAIN
SHOWERS IN THE FORECAST THROUGH THE EXTENDED PERIOD. AFTER LOOKING
IN DEPTH AT THE PROGRESSIVENESS OF THE UPPER LEVEL PATTERN...HAVE
TRENDED A TOUCH TOWARD THE DRIER AND WARMER SOLUTION FOR THE TIME
BEING. MODELS HAVE BEEN FLIPPING BACK AND FORTH A LOT IN THE PAST
SEVERAL DAYS SO THE FORECAST CONFIDENCE IS BELOW NORMAL.

&&


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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...JR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...MC



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