Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 291231
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
431 AM AKDT MON JUN 29 2015

.ANALYSIS AND UPPER LEVELS...
A NEARLY STATIONARY UPPER LEVEL TROUGH CENTERED JUST SOUTHWEST OF
KODIAK ISLAND CONTINUES TO BRING MOISTURE AND RAINFALL TO THE GULF
COAST. THE TYPICALLY DOWNSLOPE PRONE AREAS ON THE LEE SIDE OF THE
CHUGACH MOUNTAINS AROUND SOUTHCENTRAL HAVE REMAINED MOSTLY DRY
THROUGHOUT THE NIGHT...WHILE FURTHER TO THE NORTH AND WEST RAIN
SHOWERS HAVE CONTINUED TO FALL OVERNIGHT OVER THE SUSITNA VALLEY
AND KENAI PENINSULA. JUST NORTH OF THIS LOW...THE THERMAL TROUGH
HAS REMAINED STRONG ENOUGH TO SUPPORT LIMITED CONVECTION INTO THE
EARLY MORNING FROM THE KUSKOKWIM VALLEY INTO THE WEST/CENTRAL
INTERIOR. THIS TROUGH IS EXPECTED TO STRENGTHEN OVER THIS SAME
GENERAL AREA TODAY...AND SHOULD SUPPLY ENOUGH INSTABILITY FOR
ANOTHER ROUND OF AFTERNOON/EVENING THUNDERSTORM ACTIVITY TODAY.
OVER THE CENTRAL AND EASTERN BERING SEA RIDGING CONTINUES TO BRING
FOG AND STRATUS TO MUCH OF THE AREA...ESPECIALLY NEAR SAINT PAUL
WHERE DENSE FOG HAS FORMED OVERNIGHT AND IS EXPECTED TO CONTINUE
THROUGH THE MORNING. THIS RIDGE WILL SLOWLY DRIFT EASTWARD TODAY
IN ADVANCE OF AN ALEUTIAN LOW CURRENTLY BRING RAIN AND
SOUTHEASTERLY WINDS TO THE WESTERN ALEUTIANS.

&&

.MODEL DISCUSSION...
THE MODELS HAVE ALL INITIALIZED WELL WITH THE PLACEMENT OF THE LOW
NEAR KODIAK ISLAND...AND REMAIN IN VERY GOOD SYNOPTIC AGREEMENT
INTO MID WEEK. AS A RESULT THE HIGHER RESOLUTION NAM AND GEM
REGIONAL WERE MOSTLY UTILIZED THIS MORNING TO BETTER CAPTURE GAP
WINDS ALONG THE GULF COAST...AND FOR DIURNAL CONVECTION OVER THE
INTERIOR. BY WEDNESDAY...MODEL AGREEMENT BEGINS TO BREAK DOWN
WITH THE TRACK OF A LOW OVER THE EASTERN GULF. THE NAM AND GFS
WERE MOSTLY USED FOR THIS LOW TRACK IN THE MORNING PACKAGE FOR
THEIR GOOD RUN TO RUN CONSISTENTLY. THE EC ON THE OTHER HAND HAS
BEEN TRENDING STRONGER AND FURTHER WESTWARD...HOWEVER THERE IS
GENERALLY GOOD AGREEMENT THAT THIS LOW WILL REMAIN MOSTLY EAST OF
THE AOR AND SHOULDNT HAVE A SIGNIFICANT IMPACT ON FORECAST
CONFIDENCE.

&&

FIRE WEATHER...
SOUTHCENTRAL...ISOLATED WET THUNDERSTORM ACTIVITY WILL BE THE
MAIN FIRE WEATHER CONCERN TODAY. THE PRIMARY AREA OF ACTIVITY WILL
BE ALONG THE ALASKA RANGE...AS WELL AS THE TALKEETNA AND WRANGELL
MOUNTAINS. ANY THUNDERSTORMS THAT FORM ALONG THE WRANGELL
MOUNTAINS TODAY WILL MOVE TO THE NORTHWEST...SO THERE IS A CHANCE
THAT A FEW OF THESE MAY MIGRATE INTO THE LOWER ELEVATIONS OF THE
COPPER RIVER BASIN STARTING LATE THIS AFTERNOON. THESE SHOULD BE
SHORT LIVED AND WEAKENING HOWEVER...SO THE MAJORITY OF THE
LIGHTNING ACTIVITY AND RAINFALL SHOULD REMAIN CENTERED OVER THE
HIGHER ELEVATION. GAP WINDS WILL ALSO DEVELOP THIS AFTERNOON FROM
TURNAGAIN ARM EASTWARD TO THE COPPER RIVER...WITH WINDS ALSO
STRETCHING INTO SOUTH/WEST ANCHORAGE AND THE MATANUSKA VALLEY THIS
AFTERNOON/EVENING. RH VALUES ALONG THE COPPER RIVER WILL ALSO DIP
INTO THE LOW TO MID 30S DURING THE STRONGEST WINDS THIS
AFTERNOON...HOWEVER WITH MOSTLY CLOUDY SKIES OVERHEAD CONDITIONS
SHOULD REMAIN ABOVE RED FLAG CRITERIA.

SOUTHWEST...WET THUNDERSTORMS FROM THE LOWER KUSKOKWIM VALLEY TO
NORTHERN BRISTOL BAY WILL ONCE AGAIN BE THE FIRE WEATHER FOCUS
OVER THE SOUTHWEST MAINLAND TODAY. WITH VERY LITTLE PATTERN CHANGE
SINCE YESTERDAY THESE THUNDERSTORMS ARE EXPECTED TO DEVELOP AT
VERY SIMILAR LOCATIONS AS YESTERDAY...AND SHOULD ALSO AGAIN HAVE
SOUTH-SOUTHWESTERLY STORM MOTION. ISOLATED WET THUNDERSTORMS WILL
THEN DEVELOP AGAIN OVER THE SOUTHWEST INTERIOR FOR THE
AFTERNOON/EVENING ON TUESDAY AND WEDNESDAY. OTHERWISE MINIMUM RH
VALUES ARE EXPECTED TO REMAIN WELL ABOVE RED FLAG CRITERIA THROUGH
TUESDAY WITH GENERALLY LIGHT WINDS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (TODAY AND TUE)... A
UPPER LOW NEAR KODIAK CONTINUES BROAD CYCLONIC FLOW ACROSS MUCH OF
SOUTHCENTRAL ALASKA THROUGH TUE NIGHT. A WEAKENING SURFACE LOW
UNDER THE UPPER CENTER AND A COUPLE OF WEATHER FRONTS MOVING NORTH
ACROSS THE GULF WILL CONTINUE RAIN ALONG THE COASTS WITH SHOWERS
INLAND. THE POSITIONING OF THE THERMAL TROUGH AND STABILITY
INDICES INDICATE WET THUNDERSTORM POTENTIAL OVER THE COPPER RIVER
BASIN AND SUSITNA VALLEY THIS AFTERNOON AND EVENING. THE MAIN
FOCUS AREAS WILL BE ALONG THE MOUNTAINS(WRANGELLS/TALKEETNAS/AK
RANGE) THOUGH A EASTERLY STEERING FLOW IN THE COPPER RIVER BASIN
WILL CARRY THUNDERSTORMS OVER THE VALLEY. ON TUE...THE THERMAL
TROUGH WEAKENS AND SLIDES NORTH AND THE STEERING FLOW BECOMES
LIGHT SOUTHERLY...SO WOULD EXPECT ANY THUNDERSTORM ACTIVITY WILL
BE MORE CONFINED TO ALONG THE MOUNTAINS. LOCALLY GUSTY GAP FLOWS
ARE EXPECTED ACROSS SOUTHCENTRAL IN THE AFTERNOON AND EVENING
HOURS THROUGH TUE WITH HIGHER PRESSURES ALONG THE COAST AND LOWER
PRESSURE WITH THE THERMAL TROUGH INLAND.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TODAY AND TUE)...

NOT MUCH CHANGE IN THE OVERALL PATTERN IS EXPECTED OVER THE NEXT
COUPLE OF DAYS AS AN OMEGA BLOCKING PATTERN LOOKS TO PERSIST. AN
UPPER LEVEL (AND SFC BASED) LOW SOUTH OF KODIAK ISLAND WILL PUSH A
PRETTY POTENT SHORTWAVE ACROSS THE BRISTOL BAY AREA AND ALASKA
PENINSULA EARLY THIS AFTERNOON. THIS WILL COMBINE WITH A
STRENGTHENING THERMAL TROUGH ACROSS THE INTERIOR TO HELP PRODUCE
SCATTERED THUNDERSTORMS ACROSS A GOOD PORTION OF SOUTHWEST ALASKA
THIS AFTERNOON. INSTABILITY PARAMETERS LOOK MORE FAVORABLE THIS
AFTERNOON THEN THEY DID ON SUNDAY...WHICH ALSO BODES WELL FOR
INCREASED THUNDERSTORM ACTIVITY. IT LOOKS QUITE POSSIBLE THAT
THUNDERSTORM ACTIVITY MAY PERSIST IN AN ISOLATED FASHION MONDAY
NIGHT INTO TUESDAY MORNING AS MID-LEVEL LAPSE RATES WOULD HELP
KEEP ELEVATED THUNDERSTORMS GOING. THUNDERSTORMS WILL AGAIN RE-
DEVELOP ON TUESDAY BUT WILL BE MUCH MORE ISOLATED AS THE THERMAL
TROUGH AND INSTABILITY PARAMETERS LOOK MUCH WEAKER. THE PROXIMITY
OF THE UPPER LEVEL LOW SOUTH OF KODIAK ISLAND WILL KEEP SCATTERED
TO NUMEROUS SHOWERS IN THE FORECAST THROUGH TUESDAY NIGHT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TODAY AND TUE)...

LONGWAVE RIDGING WILL PERSIST ACROSS MUCH OF THE BERING SEA
THROUGH TUESDAY WITH AND UPPER LEVEL LOW SITUATED ACROSS THE
KAMCHATKA PENINSULA. THE LOW OVER KAMCHATKA WILL ACT AS AN ANCHOR
TO THE ONGOING OMEGA BLOCK AND PREVENT IT FROM BREAKING DOWN IN
THE NEAR FUTURE. THE RIDGING WILL CREATE A VERY STABLE AIR MASS
THAT WILL ALLOW FOR LOW STRATUS AND FOG TO DEVELOP ACROSS MUCH OF
THE BERING SEA...WITH THE PRIBILOF ISLANDS FEELING THE FULL FORCE
OF THE LOW CLOUDS AND FOG. THE FOG WILL THIN OUT UNDER THE
ABUNDANT SUNLIGHT RECEIVED DURING THE SUMMER...BUT WILL NOT BE
ENOUGH TO FULLY BURN IT OFF. THIS WILL CREATE A DIURNAL TREND OF
IMPROVING AND DETERIORATING CONDITIONS. THE LOW ANCHORED OFF
KAMCHATKA WILL ALSO BRING RAIN TO SHEMYA THROUGH THE BEGINNING OF
THE WEEK AND THEN FINALLY BEGIN TO SPREAD EASTWARD COME TUESDAY
NIGHT.

&&

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

BEGINNING THE EXTENDED FORECAST TUESDAY EVENING...THE MAIN WEATHER
FEATURES OF IMPACT WILL BE A CLOSED LOW IN THE VICINITY OF KODIAK
ISLAND...A SHORTWAVE RIDGE AXIS ALOFT OVER THE CENTRAL BERING
SEA...AND A FRONTAL ZONE OVER THE FAR SOUTHWEST BERING SEA.
ANOTHER SHORTWAVE TROUGH MOVING IN ACROSS WESTERN ALASKA WILL WORK
IN TANDEM WITH THE GULF LOW...WITH THE LATTER FEATURE CONTINUING
TO ADVECT MOISTURE INTO SOUTHERN ALASKA. THIS WILL SUPPORT RATHER
WIDESPREAD AREAS OF SHOWERS ALONG THE NORTHERN GULF
COAST...INTERIOR SOUTHWEST ALASKA...AND ALONG ALL THE MOUNTAINS
AND HIGHER TERRAIN OF SOUTHCENTRAL. BY WEDNESDAY...THE GULF LOW
WILL BEGIN TO MOVE NORTHEAST TOWARD THE ALCAN...WITH AN
ASSOCIATED DEFORMATION ZONE ALOFT SUPPORTING WIDE SPREAD SHOWERS
ACROSS PORTIONS OF SOUTHCENTRAL ALASKA. CURRENTLY THERE IS SOME
DISAGREEMENT WITH THE PLACEMENT OF THAT FEATURE...BUT WITH A
GENERAL LACK OF DOWNSLOPE FLOW...ANY AREAS...INLAND OR ALONG THE
MOUNTAINS...MAY SEE PERIODS OF HEAVIER RAIN. ENOUGH INSTABILITY ALOFT
WILL ALSO SUPPORT THUNDERSTORMS ACROSS THE INTERIOR BASINS AND
ALONG THE TALKEETNA MOUNTAINS AND ALASKA RANGE. THE SYSTEM WILL
DEPART BY FRIDAY...ALLOWING FOR WARMING TEMPERATURES AND LARGELY
DRY CONDITIONS ACROSS INLAND LOCATIONS FRIDAY INTO EARLY SATURDAY.

BY THE WEEKEND...A LARGE TROUGH WILL FORM OVER THE BERING AND
NORTH PACIFIC...WITH A DEVELOPING RIDGE OVER THE NORTHEAST
PACIFIC. A WEAK FRONT WILL TRACK INTO SOUTHERN ALASKA SOMETIME
NEAR THE FOURTH...SPREADING CLOUDS AND SHOWERS OVER PARTS OF
SOUTHERN ALASKA...ALTHOUGH THIS FRONT CURRENTLY LOOKS RATHER WEAK.
BY SUNDAY INTO MONDAY...THE POTENTIAL FOR A MAJOR WARMUP IS
INCREASING AS THE GLOBAL DETERMINISTIC AND ENSEMBLE GUIDANCE
DEPICTS THE DEVELOPMENT OF A HIGH LATITUDE RIDGING/BLOCKING
PATTERN OVER THE STATE OF ALASKA. THE 12Z ECMWF/18Z GFS
DETERMINISTIC RUNS SUPPORT A 590+ DM 500 HPA HIGH OVER
ALASKA...AND LOW LEVEL 850 TEMPS NEARING 20C. WITH OFFSHORE WINDS
AS PROGGED BY THE MODELS...THIS WOULD RESULT IN REGION WIDE
MULTIPLE STANDARD DEVIATION TEMPERATURE ANOMALIES...AND WOULD
POSSIBLY MATCH IF NOT EXCEED THE MOST RECENT HEAT WAVE IN TERMS OF
HIGH TEMPS...IF THAT PATTERN PANS OUT. HOWEVER...AS
USUAL...DETAILS REMAIN SOMEWHAT UNCERTAIN...BUT THERE IS
INCREASING CONFIDENCE IN AT LEAST WELL ABOVE AVERAGE TEMPERATURES
ACROSS A LARGE PORTION OF ALASKA WITH A RETURN TO LARGELY DRY
WEATHER.

&&


.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...JA



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