Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 050021
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
421 PM AKDT FRI SEP 4 2015

.ANALYSIS AND UPPER LEVELS...

THE ALASKA DOMAIN IS UNDER THE INFLUENCE OF MOSTLY ZONAL
FLOW...WITH WEAK JET STREAKS DRIVING INDIVIDUAL FEATURES BUT NO
COHERENT LONGWAVE FEATURES AFFECTING THE AOR. THE MOST SIGNIFICANT
SURFACE FEATURE IS A DEVELOPING LOW IN THE NORTHEAST GULF OF
ALASKA THAT IS CURRENTLY PRODUCING A GALE-FORCE BARRIER JET ALONG
THE NORTH GULF COAST. THE REST OF THE MAINLAND AND
BERING/ALEUTIANS REGION EXPERIENCED GENERALLY WEAK PRESSURE
GRADIENTS AND CORRESPONDING LIGHT WINDS. MEANWHILE...A FEW
RELATIVELY WEAK UPPER LEVEL LOWS ARE SPINNING OVER THE NORTHERN
BERING AS WELL AS NORTH OF THE Y-K DELTA...REINFORCING UNSETTLED
WEATHER AND SHOWERS.

A QUICK LOOK AT UPPER AIR SOUNDINGS FROM THIS MORNING AS WELL AS
CURRENTLY SATELLITE IMAGERY REVEALS A STAGNANT AND MOIST AIRMASS
IN PLACE ACROSS THE FORECAST DOMAIN. WITH WEAK UPPER LEVEL
SHORTWAVES CONTINUING TO MOVE EAST/NORTHEAST-WARD ACROSS THE
MAINLAND IT IS NO SURPRISE THAT SHOWER ACTIVITY IS ONGOING IN MOST
PLACES. A WEAK AND TRANSIENT RIDGE OF HIGH PRESSURE OVER THE
CENTRAL AND EASTERN BERING OFFERS SOME HOPE TO AT LEAST DRY THINGS
OUT LATER TODAY/TONIGHT OVER THE MAINLAND...BUT DOES NOT APPEAR
STRONG ENOUGH TO SIGNIFICANTLY DECREASE THE THICK CLOUD-COVER
ALREADY IN PLACE.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN GOOD SYNOPTIC AGREEMENT...NOT SURPRISING GIVEN
THE SOMEWHAT STAGNANT AND WEAK PATTERN THE REGION IS CURRENTLY
UNDER. THIS TYPE OF PATTERN (HIGH ZONAL INDEX) USUALLY RESULTS IN
NUMEROUS WEAK SHORTWAVES MOVING QUICKLY THROUGH THE PATTERN...AND
SO THE NUMERICAL MODELS STRUGGLE TO AGREE ON TIMING BECAUSE THINGS
ARE MOVING SO QUICKLY. THIS CURRENT CASE IS SLIGHTLY DIFFERENT IN
THE SENSE THAT THERE IS NO SINGLE/CONTINUOUS JET STREAM MOVING
THROUGH THE AREA...AND SO INDIVIDUAL FEATURES ARE MOVING A LITTLE
SLOWER THAN THEY NORMALLY DO. AS A RESULT...WHILE THERE ARE SOME
DIFFERENCES IN TIMING AND PLACEMENT OVER THE NEXT FEW DAYS...THE
MODELS ARE ALSO IN DECENT AGREEMENT ON SOME OF THE SMALLER SCALE
FEATURES AFFECTING THE AREA. THE MOST SIGNIFICANT OF THESE WILL
BE THE WEAK UPPER LOW CURRENTLY OVER THE NORTHERN BERING THAT WILL
SLOWLY MOVE ACROSS THE AKPEN AND INTO THE GULF BY THE END OF THE
WEEKEND. MODELS ARE ALL TRENDING A BIT FURTHER SOUTH WITH THIS
LOW...WHICH PROMISES TO BRING AN INCREASE IN RAIN/SHOWER ACTIVITY
FROM BRISTOL BAY AND THE KENAI PENINSULA SOUTHWARD...BUT WHICH MAY
NOW STAY MOSTLY SOUTH OF THE ANCHORAGE AREA. THE NAM IS THE
PREFERRED MODEL DUE TO ITS HIGHER RESOLUTION...BUT NONE OF THE
MODELS SHOWED HUGE DIFFERENCES TODAY.

&&

.HYDROLOGY...

THE RELEASE OF THE SNOW GLACIER-DAMMED LAKE IN THE MOUNTAINS OF
THE KENAI PENINSULA HAS ENDED. WATER LEVELS ON KENAI LAKE AND THE
UPPER KENAI RIVER HAVE CRESTED...AND A DIMINISHING PULSE OF WATER
WILL NOW BE MOVING INTO SKILAK LAKE AND EVENTUALLY INTO THE LOWER
KENAI RIVER. ALL FLOOD WATERS ARE NOW RECEDING...AND NO ADDITIONAL
FLOODING IS EXPECTED.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A GENERALLY CLOUDY AND SHOWERY PATTERN WILL PERSIST THROUGH THE
WEEKEND BENEATH WEAK UPPER LEVEL FLOW AS THE MOST ACTIVE WEATHER
REMAINS CONFINED TO THE SOUTHERN GULF. SHOWER ACTIVITY WILL
GRADUALLY DIMINISH IN COVERAGE TONIGHT THROUGH SATURDAY AS THE LOW
OVER THE EASTERN GULF MOVES AWAY FROM THE AREA AND WEAK TRANSITORY
RIDGING BEGINS TO BUILD IN FROM THE WEST. THIS WILL ALSO PROMOTE
PATCHY FOG THROUGHOUT THE COOK INLET REGION TONIGHT AS ABUNDANT
LOW LEVEL MOISTURE REMAINS IN PLACE...BUT LINGERING CLOUD COVER
SHOULD HELP TO INHIBIT MORE WIDESPREAD FOG DEVELOPMENT. SHOWER
ACTIVITY WILL THEN BEGIN TO INCREASE AGAIN BY SUNDAY AS AN UPPER
LOW MOVES ACROSS KODIAK ISLAND AND INTO THE SOUTHERN GULF. THE
MORE SOUTHERN TRACK OF THIS SYSTEM WILL KEEP THE BULK OF THE
PRECIPITATION FOCUSED ALONG THE GULF COAST WITH MORE SPORADIC
ACTIVITY INLAND.

&&

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

RIDGING SPREADING ACROSS THE AREA WILL CAUSE SHOWER ACTIVITY TO
DIMINISH TONIGHT. HOWEVER...THE UPPER LOW DIGGING SOUTHEAST
ACROSS THE BERING WILL BRING BACK RAIN SAT AFTERNOON. THIS WILL
BECOME SHOWERY SAT NIGHT INTO SUN AS THE UPPER LOW TRANSITS INTO
THE GULF...AND PRECIPITATION WILL TAPER OFF SUN AFTERNOON AS THE
NEXT RIDGE ARRIVES.

&&

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

SHOWERS AND AREAS OF FOG WILL PERSIST OVER THE EASTERN HALF OF THE
AREA AS A SHORT WAVE MOVES FROM THE BERING INTO THE GULF. IN THE
WEST...A FRONT WILL MOVE ACROSS THE WESTERN AND CENTRAL BERING
THROUGH SUN. IT WILL BE ACCOMPANIED BY AREAS OF DENSE FOG AND
STEADY RAIN...ALONG WITH SMALL CRAFT LEVEL WINDS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AN UPPER LEVEL LOW OVER THE ALASKA PENINSULA WILL TRACK FURTHER
EASTWARD INTO THE GULF...WITH WEAK RIDGING BRIEFLY DEVELOPING OVER
THE EASTERN BERING AND SOUTHWEST COAST IN ITS WAKE. THIS
TRANSITION WILL DIMINISH SHOWERS AND KEEP NEAR NORMAL TEMPERATURES
OVER THE SOUTHERN MAINLAND THROUGH MONDAY MORNING. MODELS CONTINUE
TO STRUGGLE WITH ANOTHER UPPER LEVEL LOW QUICKLY TRACKING INTO THE
BERING SEA FROM THE WEST AND EVENTUALLY JOINING FORCES WITH AN
ARCTIC TROUGH DIGGING OVER THE EASTERN BERING BY TUESDAY...BEFORE
TRACKING FURTHER INLAND BY MIDWEEK. THE 12Z ECMWF...WHICH IS THE
PREFERRED MODEL FOR THIS FORECAST PACKAGE...DEPICTS A MUCH BROADER
TROUGH OVER THE BERING...WHICH EVENTUALLY SWINGS OVER TO THE GULF
LATER NEXT WEEK. BY THE END OF THE WEEK AND INTO THE WEEKEND...THE
ECMWF SHOWS THE UPPER LOW REMAINING STATIONARY OVER THE WESTERN
MAINLAND...AS A NORTH PACIFIC LOW TRACKS UP ALONG THE ALASKA
PENINSULA FRIDAY NIGHT AND INTO THE GULF COAST BY SATURDAY. THE
NET RESULT WILL BE AN INCREASE OF WET AND WINDY CONDITIONS OVER
PARTS OF THE SOUTHERN MAINLAND THROUGH THE END OF THE WEEK...AND A
SURGE OF COLDER AIR FILTERING IN OVER MUCH OF THE BERING AND
ALEUTIANS BEHIND THE TROUGH. HOWEVER...HOW FAR EAST INTO THE
SOUTHERN MAINLAND THIS COLDER AIR WILL PUSH INTO...AND WHEN/WHERE
THE BULK OF THE PRECIPITATION WILL END UP IS STILL IN
QUESTION...AS MODELS CONTINUE TO STRUGGLE WITH THE TIMING AND
STRENGTH OF THE ABOVE MENTIONED SYSTEMS. THUS LEAVING A LOT OF
UNCERTAINTY AND LOWER CONFIDENCE IN THE LONG RANGE FORECAST.

&&


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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...AD
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DS
LONG TERM...TP



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