Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 181316
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
516 AM AKDT MON AUG 18 2014

.ANALYSIS AND UPPER LEVELS...

THE UPPER LEVELS HAVE TRANSITIONED TO A BROAD TROUGH EXTENDING
FROM THE EXTREME WESTERN BERING TO BRITISH COLUMBIA THIS MORNING.
A WAVE IN THE BROAD TROUGH IS WELL SOUTH OF ADAK...AND A NEW WAVE
IS FORMING IN THE LEE OF THE KAMCHATKA PENINSULA. THE UPPER LOW
THAT HAD RESIDED OVER SW AK FOR THE LAST SEVERAL DAYS HAS
RETREATED NORTH...ALTHOUGH A FINAL WAVE MOVING AROUND THE LOW IS
MOVING ACROSS SOUTHWEST AK...FOLLOWED BY AN EMBEDDED UPPER HIGH.
AT THE SURFACE...A WEAK TROUGH OF LOW PRESSURE REMAINS ALONG THE
NORTH GULF COAST WITH HIGH PRESSURE OVER THE ENTIRE BERING.

&&

.MODEL DISCUSSION...

MODELS ARE IN VERY GOOD AGREEMENT FOR THE NEXT THREE DAYS. THE
WAVE OVER SOUTHWEST AK WITH ASSOCIATED SHOWERS AND A FEW
THUNDERSTORMS MOVES TO THE ALASKA AND ALEUTIANS RANGES AND INTO
SOUTHCENTRAL THIS AFTERNOON AND EVENING. A WEAK THERMAL TROUGH
WILL SET UP OVER SOUTHCENTRAL THROUGH WED AND IMPULSES MOVING
THROUGH THE UPPER FLOW WILL KEEP A THREAT OF SHOWERS AND
THUNDERSTORMS DURING THAT PERIOD. MEANWHILE...THE MAIN UPPER
TROUGH CONSOLIDATES OVER THE WESTERN BERING AND ALEUTIANS ON TUE
WITH A CUT-OFF LOW THAT REMAINS OVER THE WESTERN ALEUTIANS INTO
THU. HIGH PRESSURE AT THE SURFACE WITH RIDGING ALOFT SPREADS
ACROSS THE EASTERN HALF OF THE BERING AND MAINLAND AK INTO THU.

THE GFS HAD A GOOD COMPROMISE POSITION FOR THE ATTU LOW WHEN
COMPARED WITH THE EC AND NAM AND WAS USED FOR THE ALU
FORECAST....WHILE THE NAM WITH ITS GREATER DETAIL WAS USED FOR
AER.


&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...

AFTERNOON AND EVENING SHOWERS ARE EXPECTED THROUGH WED...WITH
ISOLATED THUNDERSTORMS...ESPECIALLY NEAR MOUNTAIN RANGES.

SOUTHWEST ALASKA...

SHOWERS...WITH AFTERNOON AND EVENING THUNDERSTORMS NEAR THE ALASKA
AND ALEUTIAN RANGES ARE EXPECTED TODAY...AND THEN A FEW LINGERING
INSTABILITY SHOWERS ON TUE. DECREASING CLOUDS WILL DEVELOP ON
WED.

BERING SEA/ALEUTIANS...

THE EASTERN HALF OF THE BERING WILL EXPERIENCE LOW CLOUDS AND SOME
FOG THROUGH WED. THE WESTERN HALF WILL HAVE SMALL CRAFT LEVEL WIND
WITH RAIN DEVELOPING AS THE SURFACE LOW MOVES OVER THE AREA
THROUGH WED.

&&

.LONG TERM FORECAST...

OPERATIONAL MODEL PERFORMANCE IN THE LONG TERM FORECAST PERIOD HAS
LEFT MUCH TO BE DESIRED WITH LITTLE AGREEMENT AND BELOW AVERAGE RUN
TO RUN CONSISTENCY. WHAT CAN BE GLEANED AT THIS JUNCTURE IS THAT AN
UPPER-LVL LOW CENTERED OVER THE WESTERN BERING SEA EARLY THU LOOKS TO
DRIFT EASTWARD TO NEAR THE AK PEN BY NEXT WEEKEND. SHORTWAVE
ENERGY EJECTING OFF OF THE ASIAN MAINLAND AND ROTATING UP FROM THE
NORTH CENTRAL PACIFIC STILL LOOK TO INTERACT WITH THE LARGE
FEATURE AND HELP FORM SOME SURFACE LOW PRESSURE SYSTEMS THAT TRACK
INTO THE GULF OR TOWARDS THE SOUTHERN MAINLAND. THE COMPLEXITY OF
THE PARENT UPPER-LOW DUE OF THE NUMEROUS LOBES OF ENERGY
INTERACTING WITH IT MAKE PLACEMENT AND TIMING OF THESE SURFACE
LOWS (AND THUS THEIR ASSOCIATED WEATHER) VERY DIFFICULT TO
PROG...AND THIS IS BEING REFLECTED IN THE POOR MODEL CONSENSUS.
THE JET STREAM WHICH WILL LARGELY BE WEAK OVER THE AOR EARLY IN
THE WEEK DOES TREND STRONGER WITH TIME AS THE PARENT UPPER-LOW
NEARS THE SW MAINLAND. AVERAGE FORECAST CONFIDENCE MID WEEK TRENDS
TO LOW FRI NIGHT AND BEYOND.


&&

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

$$

DS/JAM AUG 14


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