Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 292156
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
156 PM AKDT MON SEP 29 2014

ANALYSIS AND UPPER LEVELS...WATER VAPOR IMAGERY SHOWS A DIGGING
TROUGH MOVING EAST ACROSS THE CENTRAL MAINLAND. SHOWERS HAVE
STARTED TO DEVELOP EAST OF THE ALASKA RANGE IN RESPONSE TO STRONG
UPPER DYNAMICS ASSOCIATED WITH THIS FEATURE. BRISK GAP FLOWS WHERE
EVIDENT ACROSS MUCH OF SOUTHCENTRAL ESPECIALLY ALONG THE NORTH
GULF COAST AND EASTERN KENAI PENINSULA.

FURTHER WEST...AN UPPER RIDGE CONTINUED OVER THE NORTHERN BERING
SEA. A BROAD UPPER LEVEL LOW AND ITS ASSOCIATED SURFACE LOW WAS
EVIDENT SOUTH OF THE ALEUTIANS. THE SURFACE LOW AND ITS
ASSOCIATED FRONTAL TROUGH PRODUCED SOME LIGHT RAIN AS WELL AS
BRISK EASTERLY GALES ACROSS THE CENTRAL ALEUTIANS. WITH THE
EXCEPTION OF RAIN AND SNOW SHOWERS ALONG THE ALEUTIAN RANGE...MUCH
OF SW ALASKA WAS DRY.

&&

MODEL DISCUSSION...THE MODEL HANDING OF UPPER LEVEL AS WELL AS
SURFACE SYNOPTIC FEATURES ARE IN FAIRLY GOOD AGREEMENT THROUGH THE
SHORT TERM. DIFFERENCES HOWEVER DO ARISE THU SOUTH OF THE GULF
WITH THE HANDLING OF THE NEXT LOW COMPLEX. THE 00Z ECMWF RAPIDLY
DEVELOPED AN OLD TROPICAL SYSTEM AND MOVED SOUTH OF THE GULF ON
THU AFTERNOON. THE 12Z ECMWF HAS COME IN LINE WITH THE OTHER
GLOBAL MODELS WHICH DEPICT A BROADER/ELONGATED AND MUCH WEAKER
LOW PRESSURE TROUGH SOUTH OF THE GULF. THE NAM WILL BE INITIALLY
USED THROUGH WED IN THE EAST TO CAPTURE OUTFLOW CONDITIONS...THEN
WILL TRANSITION INTO THE GFS. OUT WEST...THE GFS WILL BE USED FOR
THE AFTERNOON PACKAGE.

&&

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...WINDS WILL BE THE MAIN WEATHER FEATURE OVER
THE NEXT 24 TO 36 HRS. WINDS WILL PICK UP ACROSS MUCH OF THE AREA
THROUGH THIS EVENING WITH THE ONSET OF SUPPORTING NW FLOW AND
SUBSIDENCE WITH THE PASSAGE OF THE UPPER TROUGH. VERY STRONG GAP
FLOWS WILL DEVELOP TONIGHT ACROSS MUCH OF THE NORTH GULF AND
EASTERN KENAI PEN AS PRESSURE AND TEMPS GRADIENTS INCREASE ACROSS
THE AREA. WINDS WILL BE AT A MAXIMUM DURING THE LATE TONIGHT AND
TUE MORNING THEN SLOWLY WEAKEN TUE AFTERNOON AS THE SURFACE AND
UPPER SUPPORT WANES.

STRONG DYNAMICS ACCOMPANYING THE TROUGH WILL PRODUCE RAIN AND
SNOW SHOWERS. HIGHER ELEVATIONS...ESPECIALLY OF THE NORTHERN AND
EASTERN COPPER RIVER BASIN WILL SEE SNOW WITH MEASURABLE
ACCUMULATIONS TONIGHT. PRECIPITATION WILL DECREASE ACROSS THE
AREA AS COLDER AND DRIER AIR SPREAD EAST BEHIND THE TROUGH.

SOUTHWEST ALASKA...CONDITIONS WILL BE RELATIVELY DRY ACROSS SW
ALASKA OVER THE NEXT COUPLE OF DAYS AS HIGH PRESSURE BUILDS OVER
THE AREA. FOG WILL BECOME A CONCERN FOR THE DELTA AND ADJACENT
COAST. THE NORTHERLY OFFSHORE FLOW WILL LIKELY HAMPER ANY FOG
DEVELOPMENT OVER BRISTOL BAY OVER THE NEXT DAY OR SO. BRISK
EASTERLY FLOW ASSOCIATED WITH A LOW COMPLEX OVER THE NORTH PACIFIC
WILL CONTINUE ACROSS THE AK PEN THROUGH WED.

BERING SEA/ALEUTIANS...RAIN AND WIND WILL HOLD ON ALONG THE
CENTRAL ALEUTIANS UNTIL THE LOW TO THE SOUTH FINALLY DROPS FURTHER
INTO THE PACIFIC LATER TONIGHT. OTHERWISE HIGH PRESSURE WILL BUILD
OVER THE CENTRAL BERING SEA AND CONTINUE TO STRENGTHEN THROUGH MID
WEEK...SETTING UP A BLOCKING PATTERN AND PROVIDING VERY QUIET
CONDITIONS FOR MOST OF THE REGION. THE ONE EXCEPTION WILL BE THE
WESTERN ALEUTIANS ON THE UPSTREAM SIDE OF THE RIDGE WHICH WILL SEE
IMPACTS FROM A SYSTEM PASSING TO THE WEST MID WEEK.

&&

.LONG TERM FORECAST (FRI OCT 3 - MON OCT 6)...

ON FRIDAY...A HIGHLY AMPLIFIED PATTERN WILL BE DEVELOPING ACROSS
THE REGION...WITH A BLOCKING RIDGE ACROSS THE CENTRAL BERING
EXTENDING INTO SIBERIA...AND A LARGE TROUGH ACROSS THE MAINLAND.
ARCTIC AIR WILL ACCOMPANY THE TROUGH...WITH STEADILY DROPPING
TEMPERATURES HEADING INTO THE WEEKEND. THE PATTERN WILL GENERALLY
BE DRY...BUT THERE IS THE THREAT FOR SNOW AND SNOW SHOWERS ACROSS
MOST OF SOUTHCENTRAL BY THE WEEKEND...ESPECIALLY ACROSS THE COPPER
BASIN. THERE CONTINUES TO REMAIN UNCERTAINTY WITH A LOW MOVING
THROUGH THE EASTERN GULF OF ALASKA...SO A CONSERVATIVE MIDDLE
GROUND APPROACH WAS TAKEN WITH THE PRECIPITATION FORECAST. BY
MONDAY...UNCERTAINTY IN THE PATTERN GROWS IN MAGNITUDE QUICKLY AS
THE TRACK OF NORTHWEST PACIFIC CYCLONES (POSSIBLY INCLUDING
RECURVING REMNANTS OF PACIFIC TROPICAL CYCLONES) MOVING INTO THE
BERING BECOMES HIGHLY ERRATIC...THUS RESULTING IN SYNOPTIC SCALE
DISAGREEMENT AMONG THE VARIOUS GLOBAL NUMERICAL MODELS. WITH THAT
SAID...THE COLDEST TEMPS OF THE FALL CAN BE EXPECTED BY THIS
WEEKEND.

- AHSENMACHER

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING...119 120 121 126 127 129 130 131 172 174
176 351. FIRE WEATHER...NONE.

&&

$$

RMC/AHSENMACHER SEP 14


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