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FXAK68 PAFC 202147
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
147 PM AKDT WED AUG 20 2014

.ANALYSIS AND UPPER LEVELS...
AN UPPER-LVL LOW IS CENTERED NEAR SHEMYA AND IS NEARLY STATIONARY.
AN ASSOCIATED OCCLUDED FRONT IS STALLING AND WEAKENING ACROSS THE
CENTRAL ALEUTIAN CHAIN THOUGH SOME LIGHT RAINS STILL FALL OUT THAT
WAY. ALSO OF NOTE IS A WAVE OF LOW PRESSURE NEAR 42N 155E DIPPING
SE AROUND THE AFOREMENTIONED UPPER-LVL LOW. UPPER-LVL RIDGING
SUPPORTS SURFACE HIGH PRESSURE IN THE FAR EASTERN BERING SEA WHICH
NOSES INTO THE SW MAINLAND. DOWNSTREAM OF THAT RIDGE...A SHORTWAVE
TROUGH IS LIFTING NORTHEAST THROUGH THE SUSITNA VALLEY AND NW
REACHES OF THE COPPER RIVER BASIN WITH A FEW PASSING SHOWERS.
MARINE FOG/STRATUS LOOMS OVER COOK INLET AND BRUSHES KODIAK ISLAND
IN WEAK LOW LVL FLOW. 

&&

.MODEL DISCUSSION...
MODELS ARE STRUGGLING WITH SOME OF THE MAIN FEATURES AND RUN TO
RUN CONSISTENCY HAS BEEN VERY POOR OF LATE. THE UPPER RIDGE IN THE
EASTERN BERING IS DEPICTED MOVING EASTWARD TOWARDS THE ALCAN
BORDER THU AFTERNOON AND DAMPENING AS BOTH SHORTWAVE AND JET
STREAM ENERGY WORK UP AGAINST IT'S WESTERN FLANK. MODELS SHOW A
1015 MB PACIFIC LOW CENTERED AROUND 320 NM S OF SITKINAK THU
EVENING WILL MOVE TO AROUND 270 NM SE OF KODIAK CITY AT 1019 MB
FRI AFTERNOON BEFORE DISSIPATING AS IT TRACKS TO THE SOUTHERN AK
PANHANDLE ON SAT. THIS SYSTEM LOOKS TO BE A NON-PLAYER FOR THE
SOUTHERN MAINLAND AND KODIAK ISLAND. THE 1002 MB LOW NEAR SHEMYA
IS SHOWN DRIFTING TO AROUND 170 MI SE OF KISKA FRI AFTERNOON AT
1010 MB. THE SURFACE WAVE NEAR 42N 155E WILL DROP TO AROUND 1000
MI SOUTH OF ADAK THU EVENING...THEN PIVOT NORTHEAST TO AROUND 350
MI S OF UNALASKA EARLY SAT. BUT THERE ARE CONSIDERABLE DIFFERENCES
WITH HOW THE RESIDUAL SHEMYA LOW WILL INTERACT WITH THIS
APPROACHING SYSTEM...AS WELL AS THE SYSTEM'S ORIENTATION AS
STRONGER JET STREAM ENERGY INTERACTS WITH IT ALONG IT'S
SOUTHEASTERN FLANK. NO OPERATIONAL MODEL LIKELY HAS A GOOD HANDLE
ON THINGS...SO HAVE TRIED TO RETAIN THE SPIRIT OF THE INHERITED
FORECAST/GRIDS WHICH LEANED ON THE 20/00Z ECMWF. DESPITE MODEL
PROBLEMS WITH MANY DETAILS...A GENERAL POSITION OF THE PARENT
UPPER-LOW LOOKS TO BE IN THE VICINITY OF NIKOLSKI SAT AFTERNOON.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...

ACROSS KODIAK ISLAND...THE MARINE LAYER HAS HUGGED THE COAST MOST
OF THE DAY. LIGHT WIND FLOW AND SOME RIDGING MOVING OVERHEAD KEEPS
THE THREAT OF IT NOSING BACK ASHORE DURING THE OVERNIGHT HOURS
THERE. THE LOW-LVL WIND FLOW DOES TREND MORE SOUTHERLY WITH
TIME...AND THIS MAY SHOVE THE LION'S SHARE OF WHAT IS LEFT IN THE
ADJACENT WATERS NORTHWARD TO COOK INLET AND NORTHERN GULF AREAS.
THUS REFORMATION IS UNLIKELY TO BE AS LONG LASTING TOMORROW AS IT
WAS TODAY SHOULD IT REFORM. ASIDE FROM A GLANCING SHOWER FROM THE
SYSTEM THAT TRACKS THROUGH THE SOUTHERN GULF THU NIGHT...THE
ISLAND LOOKS TO REMAIN LARGELY PRECIPITATION FREE UNTIL THE
WEEKEND.

FORECAST CHALLENGES THROUGH THU SURROUND THE POTENTIAL FOR RE-
DEVELOPMENT AND EXPANSION OF THE MARINE LAYER THROUGH UPPER COOK
INLET. THE BOUNDARY LAYER REMAINS RATHER MOIST AND SATELLITE
IMAGERY WOULD SUGGEST THAT THE BURNOFF/RETREAT OF THE LAYER FROM
COASTAL AREAS HAS BEEN STUBBORNLY SLOW TO NIL. THE LONGER IT WEARS
ON THROUGH THE DAY THE HIGHER THE LIKELIHOOD IT RETURNS IN
EARNEST OVERNIGHT EVEN THOUGH WIND FLOW IS LIGHT. THE UPPER-LVL
RIDGING OVER SW AK MIGRATES THROUGH THE REGION TONIGHT AS WELL AND
THIS ADDED SUBSIDENCE COULD ASSIST IN THE SPREADING/RE-
DEVELOPMENT. AREAS MOST PRONE ARE THE NW KENAI PENINSULA UP
THROUGH THE ANCHORAGE BOWL/KNIK ARM. FOR AREAS WHICH DO NOT SEE
STABLE AIR FROM THE MARINE LAYER...THERE EXISTS POTENTIAL FOR
DIURNAL SHOWERS THIS EVENING...WITH A FEW PASSING THUNDERSTORMS
ALONG THE MOUNTAINS OF THE SUSITNA VALLEY. ONCE THE UPPER-RIDGE
AXIS MOVES EAST OF SOUTHCENTRAL AK DURING THE DAY THU...UPSTREAM
SHORTWAVE ENERGY TRAVERSING THROUGH WILL BE FAIR GAME TO SUPPORT
PASSING SHOWERS OR SPRINKLES...EVEN DURING THE EVENING HOURS. THE
FOCUS HOWEVER SHOULD BE THE HIGHER TERRAIN. ORGANIZED AREAS OF
PRECIPITATION ARE NOT EXPECTED UNTIL POSSIBLY LATER THIS WEEKEND
AND AT LEAST SOME PARTIAL SUNSHINE LOOKS REASONABLE FOR THE
COMING DAYS OVER THE SOUTHERN MAINLAND.

SOUTHWEST ALASKA... UPPER-RIDGING IS SUPPRESSING MUCH OF THE
CONVECTION OVER SW AK THIS EVENING. WITH IT'S PASSAGE
TOMORROW...SHORTWAVE LIFT MAY HELP PROMOTE MORE SHOWERS ON THU.
THE ATMOSPHERE WILL BECOME MARGINALLY UNSTABLE AND BECAUSE THE
ENERGY MOVES THROUGH MORE DURING THE EVENING HOURS THU...ACTIVITY
WOULD HOLD OFF UNTIL THEN. SHOULD A FEW THUNDERSTORMS FORM...THEY
ARE MORE PRONE OVER THE ALEUTIAN/ALASKA RANGES OF BRISTOL BAY.
LIKE SOUTHCENTRAL...FOLLOW-UP SUBTLE DISTURBANCES ON THE UPSTREAM
SIDE OF THE RIDGE KEEP THE THREAT OF SOME SHOWERS AROUND TO CLOSE
OUT THE WEEK.

BERING SEA/ALEUTIANS/AKPEN... 
FRONTAL LIFT IS WANING AS THE SHEMYA LOW FILLS...SO PRECIPIATON
OVER THE CENTRAL TO WESTERN CHAIN THROUGH THU SHOULD BE ON THE
LIGHT SIDE. THE APPROACH OF THE N PACIFIC WAVES/ENERGY SHOULD
MANIFEST THEMSELVES INTO AN EXPANDING SHIELD OF RAIN BY FRI TO
ENCOMPASS THE ENTIRE CHAIN AND PERHAPS UP TO THE PRIBILOF ISLANDS
AND AKPEN. CONSIDERABLE FORECAST UNCERTAINTY WITH REGARDS TO
WINDS ACROSS THE MARINE AREAS...PENDING SURFACE LOW(S) TRACK/STRENGTH.

&&

.LONG TERM FORECAST...
GUIDANCE CONTINUES TO STRUGGLE WITH THE BERING SEA TROUGH
TRANSLATING EAST TOWARD THE WEEKEND. THE ONLY CONTINUITY BOTH
TEMPORALLY AND RUN TO RUN/MODEL TO MODEL IS THAT THE TROUGH AND
ASSOCIATED FRONT WILL PUSH ONTO THE MAINLAND LATER THIS WEEKEND
INTO EARLY NEXT WEEK. BEYOND THAT TIMEFRAME CONTINUITY BREAKS DOWN
BUT IT DOES NOT APPEAR THAT THE PATTERN FAVORS LARGE STORM
DEVELOPMENT AFTER THE CURRENT SYSTEM EXITS. THE FRONT WILL BRING
RAIN TO MOST AREAS OF THE MAINLAND ON SUNDAY WHILE THE UPPER
TROUGH PASSAGE WILL KEEP RAIN IN THE FORECAST INTO TUESDAY. FOR
THE LATTER HALF OF NEXT WEEK EXPECT SEASONABLE TEMPERATURES AND
DRIER CONDITIONS.


&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FLOOD ADVISORY...121
MARINE...NONE. 
FIRE WEATHER...NONE.

&&

$$

JAM/MTL


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