Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 301209
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
409 AM AKDT TUE JUN 30 2015

.ANALYSIS AND UPPER LEVELS...
THE PERSISTENT WEATHER PATTERN OF THE LAST 24 HOURS CONTINUES TO
HOLD THIS MORNING. AN UPPER LEVEL LOW CENTERED SOUTHWEST OF
KODIAK ISLAND IS SLOWLY WEAKENING SLIDES TO THE EAST AS THE OMEGA
BLOCK BEGINS TO SHIFT EASTWARD. CLOUDY SKIES AND SHOWERS REMAIN
OVER MUCH OF THE SUSITNA VALLEY AND COPPER RIVER BASIN. THE SHOWERS
THAT OCCURRED OVER THE ANCHORAGE BOWL INTO THE LATE EVENING HAVE
SINCE DISSIPATED AS THE TURNAGAIN ARM CONVERGENCE BOUNDARY
DIMINISHED OVERNIGHT. RAINFALL CONTINUES INTO THE EARLY MORNING
ALONG THE GULF COAST FROM THIS SYSTEM...WHILE ON THE NORTHWESTERN
EDGE...ELEVATED INSTABILITY HAS ALLOWED FOR CONVECTION AND A FEW
STRAY LIGHTNING STRIKES TO PERSIST INTO THE EARLY MORNING HOURS
OVER THE KUSKOKWIM VALLEY. OVER THE EASTERN BERING...RIDGING
CONTINUES TO HOLD...WITH EXTENSIVE FOG/STRATUS STRETCHING FROM THE
PRIBILOF ISLANDS INTO THE EASTERN ALEUTIANS AND ALASKA PENINSULA.
OVER THE WESTERN ALEUTIANS...A FRONT ASSOCIATED WITH A LOW
CENTERED OVER THE KAMCHATKA PENINSULA IS BRINGING RAINFALL TO THE
AREA.

&&

.MODEL DISCUSSION...
THE MODELS REMAIN IN VERY GOOD SYNOPTIC AGREEMENT THROUGH MID WEEK
WITH BOTH THE DISSIPATION OF THE SOUTHWESTERN GULF LOW...AND HAVE
COME INTO SLIGHTLY BETTER AGREEMENT IN THE TRACK OF THE NEXT LOW
INTO THE EASTERN GULF ON WEDNESDAY. THERE STILL REMAINS SMALL
DIFFERENCES IN THE EXACT PLACEMENT OF THIS LOW...BUT THERE NOW
VERY GOOD AGREEMENT THAT THIS LOW WILL REMAIN OUT OF THE
AOR...SO THESE MODEL DIFFERENCES SHOULDNT HAVE A SIGNIFICANT
IMPACT ON FORECAST CONFIDENCE. THE NAM WAS GENERALLY PREFERRED
THROUGH FRIDAY FOR ITS BETTER HANDLING OF OUTFLOW WINDS THAT WILL
DEVELOP OVER THE GULF COAST ON WEDNESDAY AND THURSDAY.

&&

.FIRE WEATHER...
SOUTHCENTRAL...WITH RELATIVELY CLOUDY AND MOIST CONDITIONS
THROUGHOUT THE AREA TODAY...THE FIRE WEATHER FOCUS TODAY REMAINS
CENTERED AROUND DIURNAL CONVECTION. ANY WET THUNDERSTORMS TODAY
WILL BE MUCH LESS WIDESPREAD THAN IN PREVIOUS DAYS...AND SHOULD
OCCUR BE LIMITED ALASKA RANGE AND TALKEETNA MOUNTAINS ON THE VERY
SOUTHERN EDGE OF THE THERMAL TROUGH. DIURNAL GAP WINDS WILL
CONTINUE IN THE USUAL AREAS...SUCH AS TURNAGAIN ARM AND THE COPPER
RIVER THIS AFTERNOON AND EVENING. THIS WILL ALSO LIKELY BE THE
LAST DAY THAT WINDS ALONG TURNAGAIN ARM AND EXPECTED TO SPREAD
INTO SOUTH AND WEST ANCHORAGE AS PRESSURE RISES ALONG THE COAST
BEGIN TO SLOWLY DIMINISH. THESE WEAKENING PRESSURE RISES WILL ALSO
CAUSE THE COPPER RIVER WIND TO BE SLIGHTLY LESS THAN THE PAST FEW
DAYS. AN UPPER LEVEL TROUGH WILL BECOME NEARLY STATIONARY OVER THE
COPPER RIVER BASIN ON WEDNESDAY...WHICH WILL HELP TO BRING AN END
TO ANY THUNDERSTORM ACTIVITY AND INSTEAD BRING A CHANCE OF
WIDESPREAD WETTING RAINS TO MANY AREAS AROUND SOUTHCENTRAL. THIS
SYSTEM WILL THEN DISSIPATE AND BE REPLACED WITH RIDGING ON
THURSDAY...ALLOWING FOR WARMER AND DRIER CONDITIONS TO DEVELOP FOR
THE END OF THE WORK WEEK.

SOUTHWEST...MOIST AND CLOUDY CONDITIONS WILL CONTINUE TODAY OVER
THE AREA...KEEPING FIRE WEATHER CONCERNS TO A MINIMUM. THE ONLY
FIRE WEATHER CONCERN WILL ONCE AGAIN BE WET THUNDERSTORM
DEVELOPMENT THIS AFTERNOON...PRIMARILY ALONG HIGHER ELEVATIONS OF
THE KUSKOKWIM VALLEY AND NORTHWESTERN BRISTOL BAY. AN UPPER LEVEL
LOW CENTERED OVER NORTON SOUND WILL THEN APPROACH THE AREA ON
WEDNESDAY...ALLOWING FOR SHOWERS AND WET THUNDERSTORMS TO CONTINUE
OVER THE KUSKOKWIM VALLEY THROUGH MID WEEK. THE RIDGING CURRENTLY
OVER THE BERING WILL THEN APPROACH THE WEST COAST ON
THURSDAY...ALLOWING FOR WARMER AND DRIER CONDITIONS TO DEVELOP
FOR THE END OF THE WORK WEEK.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (TODAY THROUGH WED
NIGHT)...

A STACKED SURFACE LOW SOUTH OF KODIAK ISLAND DRIFTS SOUTHEAST
UNDER THE UPPER CENTER AND WEAKENS THROUGH WED. ITS ASSOCIATED
FRONT APPROACHING THE GULF COAST TODAY WEAKENS TONIGHT. RAIN IS
EXPECTED ACROSS MUCH OF THE GULF COAST WITH THIS SYSTEM WITH
SHOWERS INLAND. A WEAKENING THERMAL TROUGH AND ABUNDANT CLOUD
COVER SHOULD KEEP ANY THUNDERSTORM DEVELOP TO A MINIMUM THIS
AFTERNOON AND EVENING. THE MAIN AREA FOR ISOLATED WET
THUNDERSTORMS WILL BE ALONG THE MOUNTAINS(AK RANGE/TALKEETNA) IN
THE COPPER RIVER/EASTERN SUSITNA VALLEY. PRECIPITATION WILL BECOME
MORE STRATIFORM FROM THE WESTERN COPPER RIVER BASIN WESTWARD AS AN
EASTERLY WAVE MOVES IN FROM THE NORTHEAST AND BRINGS WETTING RAINS
WED. AREAS WEST OF THE COPPER RIVER BASIN WILL SEE DRIER
CONDITIONS SPREADING IN FROM THE WEST WITH A BUILDING RIDGE LATE
WED NIGHT.

BRISK GAP WINDS ARE EXPECTED IN THE FAVORED LOCATIONS(TURNAGAIN
ARM/PORTAGE VALLEY/KNIK ARM/COPPER RIVER) THIS AFTERNOON AND
EVENING AS THE COASTAL RIDGE BUILDS WITH APPROACH OF THE
APPROACHING FRONT. GENERALLY LIGHT WINDS ARE EXPECTED ACROSS
SOUTHCENTRAL ON WED TO BE THEN FOLLOWED INCREASING WESTERLY AND
NORTHERLY GAP FLOWS ACROSS THE EASTERN KENAI PEN LATE WED NIGHT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TODAY THROUGH WED NIGHT)...

THE BIGGEST PLAYER FOR SOUTHWEST ALASKA OVER THE NEXT SEVERAL DAYS
WILL BE AN UPPER LEVEL LOW HANGING OUT SOUTH OF KODIAK ISLAND.
WHILE THE SURFACE REFLECTION IS EXPECTED TO DISSIPATE QUICKLY THIS
MORNING...THE UPPER LEVEL LOW WILL CONTINUE TO PUSH A SERIES OF
UPPER LEVEL DISTURBANCES ACROSS SOUTHWEST ALASKA OVER THE NEXT
SEVERAL DAYS. THESE DISTURBANCES WILL INTERACT WITH A CONDITIONALLY
UNSTABLE AIR MASS OVER SOUTHWEST ALASKA AND AID IN THE DEVELOPMENT
OF DIURNAL THUNDERSTORMS. THE THERMAL TROUGH OVER THE INTERIOR
APPEARS TO BE WEAKENING AS SURFACE HIGH PRESSURE IS STARTING TO
BUILD IN. THIS WILL HELP LIMIT CONVECTION IN THE COMING DAY AND
ALLOW FOR A STEADY DECREASE IN AREAL COVERAGE OF THE THUNDERSTORMS.
THE HIGHEST LIKELIHOOD OF THUNDERSTORMS FOR TODAY AND WEDNESDAY
WILL BE ALONG THE MOUNTAINOUS TERRAIN OF THE ALASKA RANGE...THE
AHKLUN MOUNTAINS AND KILBUCK MOUNTAINS. A TROUGH WILL APPROACH
SOUTHWEST ALASKA FROM THE NORTHWEST ON WEDNESDAY AND INTERACT WITH
THE UPPER LEVEL LOW SOUTH OF KODIAK ISLAND TO PRODUCE A DEFORMATION
BAND OVER THE KILBUCK AND AHKLUN MOUNTAINS. TEMPERATURES WILL BE
NEAR NORMAL TO SLIGHTLY ABOVE NORMAL THROUGH THE FORECAST PERIOD.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TODAY THROUGH WED NIGHT)...

THE OVERALL SYNOPTIC PATTERN LOOKS QUITE SIMILAR TO YESTERDAY WITH
LONGWAVE RIDGING EXTENDING ACROSS MUCH OF THE BERING SEA. THE
THEME WILL BE SIMILAR TO YESTERDAY AS THE MARINE LAYER WILL
CONTINUE TO BE PREVALENT WITH LOW STRATUS AND FOG SEEN THROUGH THE
FORECAST PERIOD. AN AREA OF LOW PRESSURE SOUTH OF SHEMYA IS STUCK
BETWEEN THE RIDGE IN THE BERING SEA AND ANOTHER IN THE NORTHWEST
PACIFIC WHICH HAS BROUGHT RAIN TO THE WESTERN ALEUTIANS AND WILL
CONTINUE TO DO SO THROUGH WEDNESDAY NIGHT.

&&

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

WEDNESDAY NIGHT ANOTHER ROUND OF CONVECTION IS EXPECTED ACROSS THE
SOUTHERN MAINLAND AS THE UPPER LOW IN THE GULF SENDS SHORTWAVES
AS IT PICKS UP NORTHEASTERLY MOMENTUM. A WEAK SURFACE TROUGH WILL
BE A FOCUS FOR THUNDERSTORMS ACROSS THE WESTERN ALASKA RANGE AND
BRISTOL BAY. TO THE WEST...RIDGING CONTINUES TO KEEP LOW STRATUS
AND FOG ACROSS THE BERING INTO THE WEEKEND. THE RIDGE FLATTENS
SLOWLY ON FRIDAY AS LOW PRESSURE WORKS ANOTHER FRONT INTO THE
WESTERN ALEUTIANS.

THE CHALLENGE HEADING INTO THE WEEKEND IS THE PATTERN SHIFT WITH
THE UPPER LEVEL SYSTEMS OVER THE MAINLAND. THERE IS POTENTIAL FOR
ANOTHER STRETCH OF WARM DAYS TO START ON FRIDAY AS AN UPPER LEVEL
RIDGE BUILDS FROM THE BERING STRAIT. THE GFS IS THE MOST
AGGRESSIVE MODEL ON THE WARM PATTERN...WHILE THE EUROPEAN MODEL
BRINGS FRONTS INTO THE NORTHERN GULF WHICH WOULD SUPPRESS THE
RIDGE DOMINANCE. WITH THIS MUCH UNCERTAINTY BETWEEN THE
MODELS...THE LONG TERM FORECAST WAS INFLUENCED BY THE CONSERVATIVE
ECMWF. COOL AND CLOUDY CONDITIONS CONTINUES ACROSS THE
ALEUTIANS/BERING THROUGH THE BEGINNING OF NEXT WEEK WITH PERIODS
OF LIGHT RAIN.

&&

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

&&

$$

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


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