Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 051243
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
443 AM AKDT WED AUG 5 2015

.ANALYSIS AND UPPER LEVELS...
AS THE RIDGING THAT HAD PERSISTED OVER THE SOUTHERN MAINLAND
RECENTLY CONTINUES TO WEAKEN AND SHIFT TO THE WEST...CLOUDCOVER
FROM A LOW CURRENTLY JUST SOUTH OF KODIAK OF ISLAND IS MOVING OVER
THE MAINLAND. THIS LOW WILL CONTINUE ON ITS SLOW EASTERLY TRACK
TODAY...BRINGING RAINFALL MAINLY TO KODIAK ISLAND. OVER THE
NORTHWEST COAST AN ARCTIC TROUGH CAN BE SEEN TAKING A
SOUTHEASTERLY TRACK INTO THE INTERIOR...WHERE IT WILL BECOME THE
NEXT WEATHER MAKER FOR PARTS OF SOUTHERN MAINLAND THROUGH
THURSDAY. OVER THE BERING SEA...RIDGING CONTINUES TO ALLOW FOR
WIDESPREAD FOG/STRATUS TO SPREAD INTO THE SOUTHWEST COAST. FURTHER
TO THE WEST...A NORTHWEST PACIFIC LOW CAN BE SEEN APPROACHING THE
WESTERN ALEUTIANS...HOWEVER ITS EASTWARD PROGRESSION IS SLOWING AS
IT INTERACTS WITH THE BLOCKING BERING RIDGE.

&&

.MODEL DISCUSSION...
THE MODELS HAVE BEGAN TO COME INTO SLIGHTLY BETTER AGREEMENT WITH
THE PROGRESSION OF THE ARCTIC TROUGH INTO THE INTERIOR
TODAY...ESPECIALLY WHEN YOU DISREGARD THE NAM THAT CONTINUES TO BE
FURTHER SOUTH AND DEEPER THAN THE REST OF THE MODELS. THE
GFS/EC/GEM HAVE ALL TRENDED FURTHER NORTH AND SLOWER SINCE
YESTERDAY...AND ALL 3 ARE NOW IN GOOD AGREEMENT THAT A MAJORITY
OF THE RAINFALL WILL BE CONFINED TO THE NORTHERN SUSITNA VALLEY
AND COPPER RIVER BASIN. THE NAM IS THE ONLY MODEL THAT BRINGS ANY
RAINFALL NEAR THE ANCHORAGE AREA...AND AS DISCUSSED ABOVE...CONTINUES
TO BE A STRONG OUTLIER AND WAS DISREGARDED FOR THE MORNING
PACKAGE. THE NAM WAS ALSO DISREGARDED OUT WEST FOR THE NORTHWEST
PACIFIC LOW ENTERING THE WESTERN ALEUTIANS AS IT BRINGS A FRONT
INTO THE BERING MUCH FASTER THAN THE CONSISTENT GFS/EC SOLUTIONS.

&&

.FIRE WEATHER...

WEAKENING RIDGING OVER THE SOUTH MAINLAND TODAY WILL ALLOW FOR
MORE CLOUDCOVER AND SLIGHTLY COOLER CONDITIONS OVER THE NEXT TWO
DAYS. MIN RH VALUES INTO THE MID TO UPPER 20S WILL OCCUR AGAIN
TODAY ALONG THE COPPER RIVER AS A WEAK COPPER RIVER WIND
DEVELOPS...HOWEVER THIS IS NOT EXPECTED TO REACH RED FLAG
CONDITIONS. THERE IS A SLIGHT CHANCE OF A FEW LIGHTNING STRIKES
ALONG THE ALASKA RANGE AND TALKEETNA MOUNTAINS AGAIN THIS
AFTERNOON/EVENING AHEAD OF THE ARCTIC TROUGH MOVING INTO THE
INTERIOR. THIS WILL BE THE LAST CHANCE OF THUNDERSTORMS IN THE
SHORT TERM FORECAST AS THE ARCTIC TROUGH WILL CAUSE THE THERMAL
TROUGH TO DISSIPATE ON THURSDAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LOW CENTERED SOUTH OF KODIAK ISLAND WILL MOVE EAST
ACROSS THE GULF DURING THE NEXT COUPLE OF DAYS. SOME SHOWERS FROM
THIS LOW WILL WORK INTO THE COASTAL AREAS...BUT MOST OF THE
MOISTURE WILL STAY OVER THE GULF. A TROUGH OVER CENTRAL ALASKA
WILL MOVE SOUTH AND EAST ACROSS THE STATE AND EXIT INTO CANADA
LATE THURSDAY. SOME SHOWERS ARE EXPECTED OVER THE SUSITNA AND
COPPER RIVER BASINS...BUT MOST OF THE DYNAMICS AND MOISTURE WITH
THIS TROUGH WILL STAY NORTH OF THE ALASKA RANGE. BY THURSDAY NIGHT
AN UPPER LEVEL RIDGE WILL BEGIN TO BUILD INTO SOUTH CENTRAL ALASKA
FROM THE WEST.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
HIGH PRESSURE ALOFT CONTINUES TO DOMINATE MOST OF THE WEATHER
ACROSS THE SOUTHWEST MAINLAND...WITH CONTINUED WARM TEMPERATURES
AND DRY CONDITIONS. A LOW NEAR KODIAK ISLAND CONTINUES SPREAD
MOISTURE OVER THE ALASKA PENINSULA...WITH SOME OF THIS MOISTURE
AND CONVERGENCE EXPECTED TO HELP SPARK SHOWERS OVER PORTIONS OF
THE LOWER KUSKOKWIM VALLEY AND BRISTOL BAY REGIONS THROUGH
THURSDAY MORNING. A TROUGH WILL MOVE IN FROM THE NORTH ON
THURSDAY...HELPING TO SPARK OFF SHOWERS AND ISOLATED
THUNDERSTORMS ALONG AND NEAR THE ALASKA RANGE. A SLIGHT COOLING
TREND WILL FOLLOW BEHIND THIS TROUGH...HOWEVER TEMPERATURES WILL
CONTINUE TO REMAIN ON THE WARMER SIDE THROUGH THURSDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
HIGH PRESSURE WILL CONTINUE TO DOMINATE MOST OF THE BERING
THROUGH THURSDAY...KEEPING LOW STRATUS AND PATCHY FOG OVER MUCH OF
THE BERING SEA UNDER THE STABLE HIGH PRESSURE. NORTHERLY FLOW
BEHIND THE DEPARTING LOW OVER THE WESTERN GULF WILL PERSIST OVER
THE EASTERN BERING AND ALEUTIANS THROUGH THURSDAY...KEEPING
ISOLATED SHOWERS AND GUSTY GAP DRIVEN WINDS OVER THE AREA THROUGH
THURSDAY. A FRONT ASSOCIATED WITH A NORTH PACIFIC LOW SOUTH OF THE
WESTERN ALEUTIANS WILL APPROACH THE WESTERN AND CENTRAL ALEUTIANS
THURSDAY MORNING...SPREADING RAIN AND GUSTY EASTERLY WINDS OVER
THE CENTRAL AND WESTERN ALEUTIAN CHAIN.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

THE MAIN CHALLENGE IN THE LONG TERM FORECAST IS A STORM SYSTEM
THAT IS CURRENTLY MOVING TO THE WESTERN ALEUTIANS. CONDITIONS WILL
INITIALLY BE DRIER ACROSS MOST OF THE SOUTHERN MAINLAND THURSDAY
NIGHT THROUGH SATURDAY MORNING...EXCEPT FOR ISOLATED TO SCATTERED
SHOWERS THAT LINGER OVER THE COPPER RIVER AND GULF FROM AND
EXITING SHORTWAVE. TO THE WEST...THE STORM SYSTEM CENTERS NEAR
SHEMYA PUSHING A FRONT INTO THE EASTERN BERING AND ALASKA
PENINSULA ON FRIDAY. THERE IS LITTLE PROGRESSION WITH THIS SYSTEM
UNTIL SATURDAY AND THEN IT PICKS UP EASTWARD MOMENTUM.

THE FRONT IS EXPECTED TO PUSH INTO THE SOUTHWEST THIS WEEKEND
SPREADING RAIN AND GUSTY WINDS ALONG ITS BOUNDARY AS IT MOVES
THROUGH. MODELS ARE STRUGGLING WITH THE TIMING AND TRACK OF THIS
SYSTEM AS THEY ARE HANDLING DYNAMICS FROM A SECOND SYSTEM THAT
MOVES INTO THE NORTH COAST DURING THE SAME TIME FRAME. ONLY MINOR
ADJUSTMENTS WERE MADE TODAY USING THE ECMWF TO MAINTAIN
CONSISTENCY. IT IS LIKELY THAT RAIN OVERSPREADS SOUTHCENTRAL ON
SUNDAY WITH A WETTER PATTERN FOR THE SOUTHERN MAINLAND THROUGH
TUESDAY AS AN UPPER TROUGH CENTERS OVER THE STATE. A RIDGE SHIFTS
BACK OVER THE WESTERN BERING ON SUNDAY SHIFTING EAST THROUGH THE
BEGINNING OF NEXT WEEK.

&&


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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...KH


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