Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 310025
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
425 PM AKDT THU JUL 30 2015

.ANALYSIS AND UPPER LEVELS...
VERY FEW CHANGES HAVE OCCURRED FROM YESTERDAY AS THE STAGNANT
WEATHER PATTERN HAS PERSISTED. AN UPPER LOW OVER THE SOUTHWESTERN
GULF IS NOW BEGINNING TO CUT OFF AS A RIDGE OVER THE WESTERN
BERING AND EASTERN RUSSIA SHIFTS EASTWARD DUE TO SUBSIDENCE.
BETWEEN THESE FEATURES...THE JET STREAM IS FLOWING GENERALLY ALONG
THE 170W MERIDIAN THROUGH THE BERING INTO THE NORTH PACIFIC. A
STATIONARY VERTICALLY STACKED LOW PERSISTS SOUTH OF THE WESTERN
ALEUTIANS...CUT OFF SOUTH OF THE WESTERN BERING RIDGE. THAT LOW
REMAINS THE STRONGEST SURFACE FEATURE TO AFFECT THE AOR. OVER THE
BERING...VISIBLE SATELLITE IS SHOWING LOW STRATUS COVERING NEARLY
ALL OF THE SEA AND IS EXPECTED TO PERSIST FOR THE NEXT SEVERAL
DAYS.

&&

.MODEL DISCUSSION...
THE MODELS REMAIN IN EXCELLENT AGREEMENT ON THE LARGE SCALE
PATTERN EVOLUTION GOING INTO THE WEEKEND. THE LACK OF DEFINABLE
SURFACE FEATURES NEAR MAINLAND ALASKA MEANS THAT SMALL UPPER LEVEL
DISTURBANCES INTERACTING WITH THE TERRAIN WILL REMAIN THE DRIVING
FACTORS FOR PRECIPITATION THROUGH FRIDAY. AS AN UPPER LEVEL RIDGE
BUILDS EAST INTO MAINLAND ALASKA...WARMING TEMPERATURES IN THE
UPPER LEVELS BY SATURDAY WILL DIMINISH THE INSTABILITY THAT HAS
SUPPORTED SPORADIC PERIODIC SHOWER AND THUNDERSTORM DEVELOPMENT.
AS HAS BEEN THE CASE FOR MUCH OF THE PAST WEEK...CONFIDENCE IS
HIGH ON THE OVERALL PATTERN BUT REMAINS LOWER THAN NORMAL ON THE
TIMING AND LOCATION OF ANY SHOWERS AND ISOLATED THUNDERSTORMS.

&&

.FIRE WEATHER...
A MOIST WEATHER PATTERN HAS PERSISTED FOR THE PAST WEEK AND
BROUGHT PERIODIC SHOWERS TO MUCH OF SOUTHERN ALASKA. A WARMER AND
MODESTLY DRIER PATTERN IS EXPECTED WITH LESS IN THE WAY OF CLOUD
COVER BY THE WEEKEND...THOUGH RELATIVE HUMIDITY WILL REMAIN ABOVE
CRITICAL LEVELS DESPITE DEVELOPING WEAK OFFSHORE FLOW. THE WET
THUNDERSTORM POTENTIAL REMAINS THROUGH FRIDAY...AFTER WHICH
WARMING TEMPERATURES ALOFT WILL CAP POTENTIAL CONVECTION AND
SIGNIFICANTLY REDUCE THE THREAT FOR THUNDERSTORMS. THE LACK OF ANY
STRONG SURFACE FEATURES THROUGH THE WEEKEND WILL KEEP WINDS IN
MOST AREAS LIGHT.


&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
MUCH LIKE THE LAST TWO DAYS...THE FOCUS TODAY CENTERED AROUND
DIURNAL THUNDERSTORM DEVELOPMENT. SHOWERS AND THUNDERSTORMS ARE
EXPECTED TO DEVELOP AGAIN THIS EVENING ALONG THE HIGHER ELEVATIONS
AROUND SOUTHCENTRAL AS THE THERMAL TROUGH PERSISTS UNDER A
DEVELOPING MID LEVEL RIDGE. ONE NOTABLE CHANGE WITH THE AFTERNOON
PACKAGE TODAY WAS TO BRING ISOLATED THUNDERSTORMS TO THE AREAS OF
CHUGACH MOUNTAINS NEAR THE ANCHORAGE BOWL AND MATANUSKA VALLEY AS
INCREASED DAYTIME HEATING FROM CLEARING SKIES THIS AFTERNOON
SHOULD SUPPLY ENOUGH INSTABILITY FOR A FEW STRIKES. THESE
THUNDERSTORMS AGAIN ARE EXPECTED TO HAVE LITTLE IF ANY MOTION AS
WINDS ALOFT REMAIN WEAK...SO ANY DEVELOPMENT WILL BE CONFINED TO
THE MOUNTAINS. THE ATMOSPHERE IS ALSO MOISTURE LADEN (AS WAS
INDICATED WITH PRECIPITABLE WATER VALUES OF 0.75 INCHES)...SO ANY
SHOWERS OR THUNDERSTORMS THIS EVENING HAVE THE POTENTIAL TO
PRODUCE MODERATE TO HEAVY RAINFALL AT TIMES. WITH LITTLE CHANGE IN
THE OVERALL PATTERN OR LOCATION OF THE THERMAL TROUGH ON
FRIDAY...DIURNAL CONVECTION IS EXPECTED AGAIN IN THESE SAME AREAS.
A WEAK LOW THAT WILL DEVELOP NEAR PRINCE WILLIAM SOUND WILL THEN
BRING GUSTY OUTFLOW WINDS TO THE NORTH GULF COAST FROM FRIDAY TO
SATURDAY MORNING...WITH THE STRONGEST WINDS EXPECTED NEAR WHITTIER
WITH GUSTS TO 30 MPH ON FRIDAY AFTERNOON.

A MID LEVEL RIDGE WILL THEN BUILD INTO THE AREA BY SATURDAY
MORNING...ALLOWING FOR WARMER AND DRIER CONDITIONS TO SPREAD INTO
THE AREA FOR THE WEEKEND.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...
AFTERNOON AND EVENING SHOWERS ARE EXPECTED ACROSS MUCH OF SOUTHWEST
ALASKA FROM THE KILBUCK MOUNTAINS AND EAST. THERE IS ALSO ENOUGH
INSTABILITY FOR THUNDERSTORM DEVELOPMENT ALONG THE ALASKA RANGE.
OVERNIGHT SHOWERS WILL DIE DOWN BUT WILL COME BACK FRIDAY
AFTERNOON. HOWEVER...AS THE UPPER LEVELS WARM FROM THE NORTHWEST
THE AREA WILL BECOME MORE STABLE PUSHING THE MAJORITY OF THE
SHOWERS TO THE BRISTOL BAY AND ALASKA RANGE AREAS. THESE AREAS
WILL ALSO BE THE LOCATION OF THE BEST OPPORTUNITY FOR
THUNDERSTORMS. AS THE UPPER LEVELS CONTINUE TO WARM INTO THE
WEEKEND THE THREAT OF SHOWERS AND THUNDERSTORMS WILL FADE AWAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
WITH ABUNDANT MOISTURE AND HIGH PRESSURE BUILDING IN...FOG AND
STRATUS WILL BE THE NORM FOR THE BERING AND ALEUTIANS INTO THE
WEEKEND. FOR THE CENTRAL AND WESTERN ALEUTIANS A WEAK LOW SOUTH
OF THE ISLANDS WILL BRING IN SOME LIGHT RAIN INTO THE WEEKEND IN
ADDITION TO THE FOG AND STRATUS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE 12Z DETERMINISTIC AND ENSEMBLE GUIDANCE ARE FINALLY IN GOOD
AGREEMENT WITH THE PROGRESSION OF THE SYNOPTIC PATTERN THROUGH THE
MAJORITY OF THE EXTENDED PERIOD. AN UPPER LEVEL TROUGH SOUTH OF
THE ALEUTIANS ISLANDS AND EXTENDING TO THE ALASKA PANHANDLE WILL
BEGIN PINCHING OFF FROM THE MEAN FLOW AS HIGH PRESSURE OVER THE
BERING SEA AND NORTH PACIFIC BUILD AND CUT OFF AN UPPER LEVEL LOW
SOUTH OF THE EASTERN ALEUTIANS ON SUNDAY. THIS LOW LOOKS AS IF IT
WILL STAY NEARLY STATIONARY WHILE TRACKING SLIGHTLY NORTH DURING
THE WEEK AS BUILDING HIGH PRESSURE TRAPS THE LOW IN THE NORTH
PACIFIC/BERING SEA. TWO OTHER UPPER LOWS (ONE LOCATED OVER THE
KAMCHATKA PENINSULA AND THE OTHER OVER THE ALASKA PANHANDLE) WILL
ACT AS ANCHORS IN THE LONGWAVE PATTERN AND PREVENT THE BREAKDOWN
OF THE RIDGES WHICH WOULD LEAD TO A MORE PROGRESSIVE UPPER LEVEL
PATTERN AND A PATTERN CHANGE. WHAT THIS MEANS FOR ALASKA IS THAT
SOUTHCENTRAL ALASKA WILL LIKELY REMAIN ON THE DRY SIDE WITH PLENTY
OF BREAKS IN CLOUD COVER AS HIGH PRESSURE REMAINS IN FULL CONTROL
OF THE WEATHER. HOWEVER...SOUTHWEST ALASKA AND THE BERING SEA
COULD SEE A BIT CLOUDIER AND WETTER WEATHER DEPENDING ON THE EXACT
TRACK AND EXTENT OF THE UPPER LEVEL LOW AND ITS ASSOCIATED SFC
FEATURE.

&&


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

&&

$$

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



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