Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 281230
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
430 AM AKDT THU AUG 28 2014

.ANALYSIS AND UPPER LEVELS...
A COMPLEX YET COMPACT UPPER LOW PRESSURE IS CROSSING INTO THE
WESTERN GULF EARLY THIS MORNING. SEVERAL DISTURBANCES ARE ROTATING
AROUND THE LOW CENTER WITH ONE DOMINANT SHORTWAVE TROUGH DROPPING
INTO THE BASE OF THE TROUGH. THERMALLY SPEAKING THERE IS NOT MUCH
OF A LOW LEVEL FRONT LEFT WITH THIS FEATURE...JUST A WEAKENING
OCCLUSION. HOWEVER...PLENTY OF FORCING ALOFT FOR PRECIPITATION AS
THE SHIELD MOVES NORTHWARD INTO THE NORTHERN GULF. DEEP LAYER
SOUTHEASTERLY FLOW KEEPING THE USUAL AREAS DOWNSLOPED FROM THE
KENAI PENINSULA THROUGH THE MATANUSKA VALLEY. THIS SYSTEM KEEPS
THE MAINLAND UNDER A LONG-WAVE TROUGH THAT EXTENDS UP TO THE POLE
WHERE COLD AIR IS BEGINNING TO BUILD. OUT WEST...A LONG OCCLUSION
STRETCHES FROM A KAMCHATKA LOW THROUGH THE CENTRAL/EASTERN
ALEUTIANS WHILE EASTERN BRISTOL BAY AND THE ALASKA PENINSULA ARE
UNDER A SHORTWAVE RIDGE AS THE PREVIOUS SYSTEM DEPARTS.

&&

.MODEL DISCUSSION...
GUIDANCE IS IN GREAT AGREEMENT WITH THE EVOLUTION OF SYNOPTIC
FEATURES IN THE SHORT TERM. NOW THAT THE INCOMING GULF SYSTEM HAS
BROUGHT THE NORTHERN STREAM TO OUR SOUTH...A STRONG COLD CORE LOW
OVER THE ARCTIC OCEAN IS ANCHORING THE LONGWAVE PATTERN. THE
CLOSED OFF KAMCHATKA LOW PRESSURE WILL DRIFT EAST AND PHASE WITH
THE NORTHERN STREAM AS IT WEAKENS. THERE ARE VERY SLIGHT
POSITIONAL DIFFERENCES AS THE SYSTEM PHASES INTO AN OPEN WAVE BUT
FOR THE MOST PART GUIDANCE SEEMS TO HAVE A GOOD HANDLE ON THE
PATTERN. THE WEST DOMAIN FAVORED THE CANADIAN REGIONAL FOLLOWED
BY A GFS/ECMWF BLEND TOWARD THE END OF THE SHORT TERM. THE EASTERN
DOMAIN FAVORED THE NAM/CANADIAN REGIONAL TRANSITIONING TO THE
ECMWF.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE UPPER SYSTEM ROTATING INTO THE GULF HAS
THE CLASSIC SOUTHEASTERLY FLOW SIGNATURE ON RADAR. BANDS OF
CONVECTION AHEAD OF THE FRONT WITH MORE STRATIFORM PRECIPITATION
APPROACHING AS A NICE DOWNSLOPE HOLE IS PRESENT FROM THE KENAI
THROUGH THE MATANUSKA VALLEY. THESE CONDITIONS WILL HOLD THROUGH
MID-DAY. THROUGH THE AFTERNOON...SOUTHEASTERLY FLOW WILL BE WANING
AS UPPER LEVEL FLOW BACKS TO THE SOUTH AHEAD OF A TROUGH
APPROACHING FROM THE WEST. RAIN WILL FILL IN THE COOK INLET REGION
DURING THE EVENING AND OVERNIGHT. RAIN WILL TAPER OFF FROM WEST TO
EAST ON FRIDAY WITH RAIN LINGERING OVER THE COPPER RIVER BASIN ALL
DAY. PREDOMINATE NORTHWESTERLY FLOW SETS UP FOR THE REST OF THE
WEEK KEEPING THE COOK INLET REGION DRIER WHILE THE PREVIOUS TROUGH
WILL LINGER OVER THE COPPER RIVER BASIN THROUGH THE WEEKEND WITH
SHOWERS DIMINISHING ON SUNDAY.

SOUTHWEST ALASKA...AS ONE LOW PUSHES QUICKLY TO THE SOUTHEAST INTO
THE GULF OF AK...THE NEXT SYSTEM IS ALREADY STARTING TO MOVE INTO
THE YK DELTA. THE GULF-BOUND SYSTEM CONTINUES TO SPREAD SOME
WRAP-AROUND SHOWERS THROUGH MUCH OF THE BRISTOL BAY AREA THIS
MORNING...BUT THESE WILL TAPER OFF QUICKLY. THE NEXT SYSTEM IS
TRACKING IN FROM THE NORTHWEST AND ALREADY STARTING TO BRING
SHOWERS TO THE YK DELTA. IT WILL SPREAD STEADY RAIN TO MOST AREAS
NORTH OF KING SALMON THROUGH THE DAY. THIS SYSTEM SHOULD ALSO HAVE
ENOUGH JET SUPPORT AND COLD AIR ALOFT TO TRIGGER A FEW ISOLATED
THUNDERSTORMS ALONG THE KILBUCKS AND ALASKA RANGE DURING PEAK
HEATING TODAY. AS THIS SYSTEMS PUSHES TO THE SOUTHEAST ON
FRIDAY...WEAK RIDGING WILL MOVE IN WITH BROAD NORTHWEST FLOW. THIS
SHOULD LEAD TO SHOWERS ALONG THE HIGHER TERRAIN FRIDAY...BUT
OVERALL...IT WILL BE A MOSTLY DRY DAY. 850MB TEMPERATURES WILL
CLOSE IN THE FREEZING MARK FOR THE FIRST TIME THIS SEASON LATE
FRIDAY. THIS MEANS THAT ANY SPOTS THAT CLEAR SATURDAY MORNING
COULD SEE THEIR COLDEST TEMPERATURES IN SEVERAL WEEKS. MODELS HAVE
TRENDED FURTHER SOUTH WITH THE BERING LOW INTO THE WEEKEND. IF
THIS TRENDS HOLDS...IT LOOKS TO BE A MOSTLY DRY WEEKEND.

BERING SEA/ALEUTIANS...AN ELONGATED FRONT DRAPED ACROSS THE AREA
THIS MORNING WILL CONTINUE TO WEAKEN. THE LOW PRESSURE CENTER
ASSOCIATED WITH IT HAS STARTED TO WEAKEN AS IT APPROACHES SHEMYA.
THIS WILL MAKE FOR WIDESPREAD LIGHT RAIN AND PATCHY FOG UNDER
RELATIVELY LIGHT WINDS FOR THE ENTIRE AREA. THIS LOW WILL CONTINUE
TO RIDE A FAIRLY POTENT SUB-TROPICAL JET AND ACCELERATE AS IT
CROSSES THE BERING AND THROUGH EASTERN ALEUTIANS BY SATURDAY
MORNING. THE REST OF THE WEEKEND WILL SEE WEAK NORTHERLY FLOW WITH
LIMITED SHOWER ACTIVITY BEFORE ANOTHER PIECE OF ENERGY DROPS
THROUGH THE BERING STRAIT EARLY SUNDAY.

&&

.LONG TERM FORECAST...
THE DOMINANT FEATURE TO BEGIN THE EXTENDED TERM WILL BE A LARGE
UPPER LEVEL LOW ANCHORED OVER THE CHUKCHI SEA WITH A BROAD
LONGWAVE TROUGH EXTENDING OVER MAINLAND ALASKA AS ANOTHER IN A
SERIES OF SURFACE LOWS MOVES EASTWARD ACROSS THE GULF THIS
WEEKEND. THIS WILL KEEP A CHANCE OF RAIN IN THE FORECAST ACROSS
MUCH OF THE SOUTHERN MAINLAND INTO EARLY NEXT WEEK...PARTICULARLY
ALONG THE NORTHERN GULF COAST. THE TROUGH AXIS WILL GRADUALLY
PROGRESS EASTWARD AND GIVE WAY TO BROAD WEST TO NORTHWESTERLY
UPPER LEVEL FLOW WHICH WILL YIELD GENERALLY DRIER CONDITIONS
BY THE MIDDLE OF NEXT WEEK.

&&

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

$$
MTL
AUG 14



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