Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 030051
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
451 PM AKDT TUE JUN 2 2015

.ANALYSIS AND UPPER LEVELS...
THE SHIFT IN THE OVERALL PATTERN TO A WETTER MORE MOIST FLOW OVER
THE SOUTHERN MAINLAND HAS ARRIVED. AN UPPER LEVEL TROUGH EXTENDS
FROM THE CANADIAN ARCTIC INTO THE INTERIOR WHILE THE RIDGE ALOFT
EXTENDS FROM THE EASTERN GULF OF ALASKA TO THE NORTH GULF COAST.
THE BUILDING SURFACE RIDGE INTO THE NORTH GULF COAST AND THE
TROUGH THAT WAS ACROSS THE COOK INLET TO COPPER RIVER BASIN THAT
HAS BEEN MOVING NORTH INTO THE INTERIOR RESULTED IN THE STRONG
WINDS THROUGH TURNAGAIN ARM AND ACROSS THE CHUGACH MOUNTAINS. THE
TROUGH WILL CONTINUE TO MOVE NORTH OF THE ALASKA RANGE EXTENDING
ALONG THE YUKON RIVER VALLEY BY WEDNESDAY. THE AIRMASS HAS BECOME
MUCH MORE STABLE THAN YESTERDAY OVER THE SOUTHERN MAINLAND AND
SOUTHWEST ALASKA. THE BERING SEA AND ALEUTIANS HAVE BEEN UNDER THE
INFLUENCE OF THE SURFACE AND UPPER LEVEL LOWS ALONG AND SOUTH OF
THE CHAIN. AS THE MAIN SURFACE AND UPPER LOWS TRANSITION TO THE
GULF OF ALASKA AND SOUTHERN MAINLAND HIGH PRESSURE WILL BUILD OVER
THE BERING SEA.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN GOOD AGREEMENT WITH RESPECT TO THE OVERALL LARGE
SCALE SYNOPTIC PATTERN. ALL MODELS ARE IN AGREEMENT TO THE SHIFT
TO A PROLONGED COOLER WETTER PATTERN THROUGH THE MIDDLE OF NEXT
WEEK WITH THE UPPER TROUGH ESSENTIALLY EXTENDING FROM THE ARCTIC
COAST INTO THE GULF. THE MODELS DO DIFFER SLIGHTLY WITH THE
POSITION OF THE LOW APPROACHING THE BARREN ISLAND AREA WEDNESDAY
NIGHT AND THE CONSENSUS IS TO BRING THIS LOW TO THE BARRENS AS
OPPOSED TO HOLDING IT TO THE SOUTH. THIS INTENSIFYING STORM ABOUT
500 MILES SOUTH OF THE ALASKA PENINSULA WILL BE THE BIG IMPACT
MAKER WEDNESDAY AND THURSDAY. THIS STORM IS EXPECTED TO PUSH A
STRONG FRONT TO ALONG THE NORTH GULF COAST WITH GALE AND STORM
FORCE WIND WITH HEAVY RAIN ALONG THE NORTH GULF COAST. THE MODELS
ARE ALSO IN GOOD AGREEMENT WITH RESPECT TO HEAVY PRECIPITATION
ALONG THE NORTH GULF COAST. THE NAM IS THE HEAVIEST AS IT TENDS TO
BE AND WE HAVE SETTLED ON 24 TO 36 HOUR RAINFALL AMOUNTS OF UP TO
3 INCHES IN THE WESTERN PRINCE WILLIAM SOUND AREA WEDNESDAY NIGHT
AND THURSDAY. THE NAM HAS HAD THE BEST HANDLE ON THE INSTABILITY
AND IS THE MODEL OF CHOICE FOR THIS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
TWO UPPER LEVEL TROUGHS THAT WILL PERSIST OVER THE AREA WILL KEEP ACTIVE
WEATHER THROUGHOUT THE SOUTHERN MAINLAND AND THE GULF OF ALASKA
THROUGH MID WEEK. THE FIRST TROUGH OVER THE INTERIOR WILL BRING
CONTINUED RAIN FROM ANCHORAGE INTO THE SUSITNA VALLEY THIS
EVENING. TO THE EAST OF THIS TROUGH...THERE IS ENOUGH
INSTABILITY FROM SOME PARTIAL CLEARING THAT OCCURRED THIS
AFTERNOON TO BRING SHOWERS AND THUNDERSTORMS OVER THE COPPER RIVER
BASIN THROUGH THIS EVENING. THESE SHOWERS AND THUNDERSTORMS ARE
THEN EXPECTED TO REFORM OVER THE NORTHERN COPPER RIVER BASIN ON
WEDNESDAY AFTERNOON...AHEAD OF AN APPROACHING LOW OVER THE GULF.
THIS NEXT LOW WILL BRING RAIN TO KODIAK ISLAND STARTING LATE THIS
EVENING...AND THEN SPREAD WIDESPREAD RAINS THROUGHOUT THE GULF
COAST STARTING ON WEDNESDAY. THE HEAVIEST OF THESE RAINS WILL
OCCUR OVER THE EASTERN KENAI PENINSULA...WHERE STRONG AND MOIST
UPSLOPE FLOW WILL BRING RAINFALL AMOUNTS AS HIGH AS 3 INCHES TO
SOME AREAS BY THURSDAY EVENING. A GALE FORCE FRONT ASSOCIATED WITH
THIS LOW WILL ALSO STRENGTHEN TO STORM FORCE AS IT APPROACHES THE
NORTH GULF COAST LATE WEDNESDAY EVENING...AND HAS THE POTENTIAL TO
BRING STORM FORCE GUSTS TO PRINCE WILLIAM SOUND THROUGH THURSDAY
MORNING. THIS SYSTEM WILL THEN BEGIN TO DISSIPATE BY THURSDAY
AFTERNOON WITH DIMINISHING WINDS AND WIDESPREAD RAIN BREAKING INTO
SHOWERS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE SOUTHWEST REGION IS UNDER THE INFLUENCE OF A DEFORMATION
ZONE IN THE UPPER LEVELS AND WEAK ONSHORE FLOW IN THE LOWER LEVELS.
THE WEAK ONSHORE FLOW IS BRINGING MARINE LAYER STRATUS WITH AN
ELONGATED UPPER LEVEL LOW POSITIONED OVER THE EASTERN ALEUTIANS.
ANY THUNDERSTORM ACTIVITY THROUGH THIS EVENING IN THE SOUTHWEST
REGION WILL BE ISOLATED FOR THE INLAND AREAS FOR THE BRISTOL BAY
REGION. WHILE...THE LOWER KUSKOKWIM VALLEY WILL RECEIVE ISOLATED
THUNDERSTORMS DUE TO DIURNAL HEATING WITH PARTLY CLOUDY SKIES AND
THE WEAKENING OF THE REMNANTS OF THE UPPER LEVEL THERMAL TROUGH.
THE KUSKOKWIM DELTA REGION...THERE WILL BE ISOLATED THUNDERSTORMS
THROUGH THIS EVENING AS THE THUNDERSTORMS DEVELOP OVER THE
KILBUCK MOUNTIANS AND TRACK WESTWARD THROUGH THE REGION. BY
WEDNESDAY...A NORTH PACIFIC GALE FORCE LOW TRACKS TO THE EAST
SIDE OF KODIAK ISLAND. THIS WILL BRING MOISTURE AND RAIN WHICH
WILL SPREAD OVER THE ALASKA PENINSULA INTO THE SOUTHWEST ALASKA
REGION. THIS WILL DIMINISH THE CHANCES FOR THUNDERSTORM
ACTIVITY...EXCEPT FOR THE LOWER KUSKOKWIM VALLEY. THIS IS DUE TO
AN UPPER LEVEL TROUGH DROPPING DOWN INTO THE VALLEY AND COINCIDING
WITH DIURNAL HEATING WILL KICK OFF THUNDERSTORMS FOR WEDNESDAY
AFTERNOON AND EVENING HOURS FOR THE LOWER KUSKOKWIM VALLEY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE KAMCHATKA LOW CONTINUES TO TRACK SOUTH OF THE WESTERN
ALEUTIANS WITH GALE FORCE NORTHEASTERLY WINDS ALONG THE CHAIN.
THIS SYSTEM WILL WEAKEN AS IT TRACKS WESTWARD AND WILL BE LOCATED
SOUTH OF DUTCH HARBOR BY WEDNESDAY AFTERNOON. THIS WILL RESULT IN
MARINE LAYER STRATUS WITH INTERMITTENT LIGHT RAIN BEFORE
TRANSITIONING TO MORE SCATTERED SHOWERY REGIME WITH THE NORTHERLY
FLOW OVER THE BERING SEA. THE NORTHERN BERING SEA WILL HAVE THE
STRONGER GRADIENT RESULTING IN GALE FORCE WINDS THROUGH BERING
STRAIT GOING INTO THE MIDWEEK. THE BERING SEA WILL HAVE THE USUAL
STRATUS LAYER CLOUDS WITH PATCHY FOG...EXCEPT AREAS OF FOG WILL
BE FORMING ALONG THE SOUTHWEST COASTLINE THROUGH WEEK.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE FORECAST BEGINNING THURSDAY AFTERNOON LOOKS MUCH THE SAME ON
THE LARGE SCALE. A LONGWAVE TROUGH CONSISTING OF THREE MERGING
SYSTEMS CONTINUES TO TAKE SHAPE OVER THE SOUTHWEST MAINLAND. THE
MAIN DIFFERENCE IN GUIDANCE FROM YESTERDAY IS THE EMERGENCE OF A
STRONGER UPPER LEVEL LOW DROPPING DOWN FROM THE POLE OVER
NORTHWEST ALASKA...HOWEVER A WEAKER TROUGH OVER THE
SOUTHWEST/ALASKA PENINSULA REMAINS. OVER THE WEEKEND INTO NEXT
WEEK THE JET STREAM REMAINS SOUTH OF THE ALEUTIAN CHAIN THAT WILL
SEND PERIODIC DISTURBANCES INTO THE GULF.

THE FORECAST AND SENSIBLE WEATHER IMPACT REMAIN MUCH THE SAME
DESPITE CHANGES IN GUIDANCE. A FRONT AND UPPER LEVEL WAVE WILL
PUSH FROM THE GULF INTO THE INTERIOR ON THURSDAY/FRIDAY KEEPING
THE CLOUDY AND SHOWERY PATTERN IN PLACE. BEHIND THIS
SYSTEM...LINGERING COLD AIR ALOFT ON FRI WILL KEEP SHOWERS ALONG
MOST HIGHER TERRAIN ACROSS THE SOUTHCENTRAL AND SOUTHWEST. INTO
SATURDAY...THE ACTIVE PATTERN CONTINUES AS A WEAK
DISTURBANCE/FRONT MOVE INLAND OVER THE GULF WITH THE COASTAL AREAS
TAKING MOST OF THE MOISTURE. INTO EARLY NEXT WEEK COLD AIR ALOFT
REMAINS BUT THE FLOW SLACKENS A BIT WHICH SHOULD KEEP
CLOUDS/MOISTURE OVER THE TERRAIN AND POSSIBLY SOME SNEAKY NICE
DAYS BEFORE A RETROGRADING POLAR SYSTEM RELOADS THE PATTERN BACK
INTO AN ACTIVE/PROGRESSIVE STATE.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM 119
         GALES 120 125 130 131 NONE.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SA
SOUTHCENTRAL ALASKA...DEK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...ML


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