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FXAK67 PAJK 012230
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
230 PM AKDT MON SEP 1 2014
.SHORT TERM...AN UPPER LEVEL TROUGH IS PASSING OVER THE PANHANDLE
FROM NORTHWEST TO SOUTHEAST. AT THE SURFACE, WEAK LOW PRESSURE OFF
THE CENTRAL OUTER COAST WITH A TROUGH EXTENDING WNW WILL MOVE EAST
INTO CANADA OVERNIGHT. SHOWER ACTIVITY IS STILL PRESENT OVER
SOUTHEAST ALASKA, BUT IS DIMINISHING FROM WEST TO EAST. COLD AIR
ALOFT WILL MAINTAIN THE THREAT OF ISOLATED MARINE THUNDERSTORMS
TONIGHT OVER SOUTHERN COASTAL WATERS AS WELL AS THE DIXON ENTRANCE.
HAVE ALSO INCLUDED THEM OVER THE SOUTHWESTERN OUTER COAST, WHERE
THE THREAT IS THE GREATEST. AS SHOWERS DEPART TO THE EAST, PARTIAL
CLEARING IS EXPECTED TONIGHT AND TOMORROW OVER PORTIONS OF THE
PANHANDLE. LARGE BREAKS IN THE CLOUD COVER HAVE ALREADY FORMED
OVER WESTERN PORTIONS OF THE YAKUTAT ZONE AS OF EARLY THIS
AFTERNOON. WITH THE DECREASING CLOUD COVER, OVERNIGHT TEMPS WILL
DIP A FEW DEGREES LOWER THAN IN THE PAST FEW NIGHTS WITH SOME
LOCATIONS GETTING DOWN INTO THE UPPER 30S. SIMILARLY, TOMORROW'S
HIGH SHOULD BE A BIT WARMER THAN IN RECENT DAYS WHERE PARTLY
CLOUDY SKIES LAST INTO THE AFTERNOON. WITH BREAKS IN THE CLOUDS
TONIGHT, POTENTIAL FOR FOG IS ENHANCED AND HAVE INCLUDED THIS IN
BOTH MARINE AND PUBLIC ZONE FORECASTS. CONDITIONS SHOULD IMPROVE
QUICKER THAN WHAT WAS OBSERVED TODAY, WHERE MANY LOCATIONS SAW
CEILINGS REMAIN WELL BELOW 1000 FEET FOR MOST OF THE DAY. LOOKS
LIKE IT WILL BE A MOSTLY DRY AND PARTLY SUNNY DAY...JUST IN TIME
TO GO BACK TO WORK.

USED A BLEND OF NAM AND ECMWF FOR UPDATES TO PRESSURE AND WIND.
POP AND QPF FROM GEM AND ECMWF. TEMPS PER BIAS CORRECTED NAM AND
ECMWF. FORECAST CONFIDENCE IS AVERAGE. 
.LONG TERM...MODELS REMAIN IN GENERAL AGREEMENT THROUGH THURSDAY
EVENING WITH AN UPPER LEVEL SHORTWAVE TROUGH OVER BRITISH COLUMBIA
COAST TUESDAY NIGHT MOVING EAST AWAY FROM THE AREA AND AN ANCHORED
LARGE UPPER LEVEL LOW OVER THE SOUTHERN BEAUFORT SEA STARTS
DRIFTING EAST TO BANKS ISLAND THROUGH THURSDAY NIGHT. A WEAK UPPER
LEVEL RIDGE WILL CONTINUE TO DOMINATE ACROSS THE GULF OF ALASKA
WITH NEAR ZONAL UPPER FLOW OVER SOUTHEAST ALASKA. A WEAK SURFACE
LOW PRESSURE SYSTEM OVER PRINCE WILLIAM SOUND TUESDAY NIGHT WILL
DISSIPATE BY LATE WEDNESDAY MORNING AS A SURFACE HIGH ACROSS THE
WESTERN ALASKA INTERIOR EXPENDS EAST AND A RIDGE OF HIGH PRESSURE
CONTINUES TO BUILD OVER THE EASTERN GULF TO THE PANHANDLE. BLENDED
THE INHERITED FORECAST PACKAGE WITH THE NAM AND GFS FOR THEIR GOOD
CONSENSUS AND INITIALIZATION THROUGH THURSDAY EVENING.

AT THE LOWER LEVEL...A DEVELOPING LOW SOUTH OF ALASKA PENINSULA
HAS A SUB-TROPICAL MOISTURE CONNECTION AND WILL DRIFT NORTH TO
BRISTOL BAY THROUGH THURSDAY NIGHT...PUSHING A FRONTAL PASSAGE
EAST OVER THE GULF IN BETWEEN THE HIGH PRESSURE OVER WESTERN
INTERIOR DRIFTING EAST INTO THE THE YUKON AND THE RIDGE OF HIGH
PRESSURE ACROSS THE GULF MOVING EAST OVER THE PANHANDLE. THE RIDGE
ACROSS THE PANHANDLE WEDNESDAY NIGHT WILL ERODE SOUTHEASTWARD BY
THURSDAY NIGHT...OPENING A DOOR FOR FRONTAL RAIN BANDS COMING INTO
THE OUTER WATERS AND THE CENTRAL PANHANDLE WEDNESDAY NIGHT...THEN
MOVE TO THE SOUTHERN AREAS BY THURSDAY BEFORE DISSIPATING LATE
THURSDAY EVENING. WITH PREVAILING NEAR ZONAL UPPER FLOW...EXPECT
NO SIGNIFICANT UPPER DYNAMICS SUPPORTING THE SURFACE PROGRESS BUT
THE SUB-TROPICAL ORIGIN OF THE INCOMING MOISTURE MAY POSE CERTAIN
MODERATE RAINFALL OVER THE CENTRAL AND SOUTHERN PANHANDLE COASTAL
REGIONS.

PRESSURE GRADIENT OVER SOUTHEAST ALASKA WILL REMAIN SOMEWHAT
RELAXED BETWEEN THE MAIN HIGHS AND LOWS IN DISTANCE...AND EXPECT NO
SIGNIFICANT WIND SPEEDS BUT SMALL CRAFT LEVEL SEAS OVER THE
CENTRAL OUTER WATERS WEDNESDAY NIGHT DUE TO WESTERLY SWELLS.
CONTINUED ONSHORE LOW TO MID LEVEL FLOW WILL KEEP SOUTHEAST ALASKA
UNDER MOSTLY CLOUDY TO CLOUDY SKIES WITH OVERNIGHT LOWS IN THE MID
TO UPPER 40S ACROSS THE NORTHERN AND CENTRAL PANHANDLE TO THE
LOWER 50S OVER THE SOUTHERN AREAS...AND DAYTIME HIGHS MOSTLY IN
THE MID TO UPPER 50S OVER THE NORTHERN AREAS TO THE LOWER 60S
ACROSS THE SOUTHERN PANHANDLE.

FROM FRIDAY ONWARD...MODEL DIVERTING BECOMES LARGER AS THE GFS
STAYS ON A FAST PROGRESSIVE MODE WITH THE BRISTOL BAY LOW DRIFTING
NORTHEAST ACROSS THE SOUTHERN INTERIOR AND YUKON TOWARD THE
WEEKEND...WHILE THE ECMWF SHOWS A SIGNIFICANT SLOWER MODE TO BRING
THE LOW OVER THE NORTHERN GULF BY SATURDAY MORNING. AS A
RESULT...THE GFS BUILDS A RIDGE OF HIGH PRESSURE QUICKLY ACROSS
THE GULF OVER THE WEEKEND WHILE THE ECMWF KEEPS THE INFLUENCE OF
LOW PRESSURE ACROSS THE GULF. OPTED THE NEW WPC ENSEMBLE SOLUTIONS
FOR THE REMAINING LONG TERM PERIODS. FORECAST CONFIDENCE IS ABOUT
AVERAGE THROUGH LATE THURSDAY THEN FALLS BELOW AVERAGE FOR THE REST
OF LONG TERM PERIODS.

&&
.AVIATION...MARGINAL VMC CONDITIONS WILL PREVAIL FOR MOST OF THE
NIGHT WITH SOME LINGERING POCKETS OF LOW IMC. POTENTIAL FOR
WIDESPREAD FOG LATE TONIGHT MAY BE A FACTOR FOR EARLY MORNING
AVIATION OPERATIONS. WEAK PRESSURE GRADIENT AT THE SURFACE AND
ALOFT SHOULD PREVENT ANY SIGNIFICANT TURBULENCE THROUGH TOMORROW
AFTERNOON. 

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012. 
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043. 

&&

$$

FRITSCH/AHN

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