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564
FXAK67 PAJK 251402 CCA
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE JUNEAU AK
600 AM AKDT SAT OCT 25 2014

.SHORT TERM...EARLY MORNING SATELLITE IMAGE SHOWS A WEAKENING LOW
WEST OF HAIDA GWAII WITH A WEAK TROUGH EXTENDING FROM THE LOW
NORTHWESTWARD TO THE NORTHERN GULF. SPORADIC SHOWERS SLOWLY
DIMINISH ACROSS THE OUTER WATERS AND NORTHERN PANHANDLE WITH
PATCHY FOG FORMING OVER THE CENTRAL AND SOUTHERN PANHANDLE. LIGHT
AND VARIABLE WINDS PREVAIL OVER THE LAND AREAS WITH 10 TO 20
KNOTS OFFSHORE FLOW ACROSS THE OUTER WATERS AND LESS THAN 10 KNOTS
OVER THE INNER CHANNELS. ROUGH SMALL CRAFT SEAS CONTINUE OVER THE
SOUTHERN OUTSIDE WATERS. OVERNIGHT TEMPERATURES RANGE FROM THE MID
30S ACROSS THE NORTHERN PANHANDLE TO THE MID 40S OVER THE SOUTHERN
AREAS.

MODELS REMAIN IN FAIR AGREEMENT FOR THE WEAKENING LOW WEST OF HAIDA
GWAII THIS MORNING MOVES SOUTHEASTWARD TO BRITISH COLUMBIA COAST
THROUGH LATE TONIGHT. THE WEAK INVERTED TROUGH OF LOW PRESSURE
EXTENDING NORTHWESTWARD FROM THE LOW WILL REMAIN ACROSS THE
PANHANDLE THROUGH LATE TONIGHT. REFRESHED THE INHERITED FORECAST
PACKAGE WITH THE ECMWF FOR ITS GOOD CONSISTENCY. CHANGES MADE OVER
THE INHERITED FORECAST WERE MINOR AND MOSTLY COSMETIC TOUCHES.

AS THE WEAKENING LOW WEST OF HAIDA GWAII SLOWLY DRIFTS
SOUTHEAST...THE WEAK INVERTED TROUGH ACROSS THE EASTERN GULF WILL
SLOWLY MOVE EASTWARD OVER THE PANHANDLE LATE TONIGHT. EASTERN
PERIPHERY OF THE LOW MAY BRING A LITTLE MORE SHOWERS ACROSS THE
SOUTHERN PANHANDLE THIS MORNING...BUT WITH INCREASING OFFSHORE
FLOW OVER THE PANHANDLE...SPORADIC SHOWERS WILL CONTINUE TO
DIMINISH THIS MORNING AS THE WEAK TROUGH CONTINUES EXTENDING
NORTHWESTWARD ACROSS THE EASTERN GULF.

WITH RELAXING PRESSURE GRADIENT ACROSS SOUTHEAST ALASKA...EXPECT
NO SIGNIFICANT WINDS/SEAS THROUGH TONIGHT. CLOUDS WILL CONTINUE TO
DECREASE THIS AFTERNOON INTO TONIGHT AND EXPECT PATCHY FOG RETURNS
TO THE CENTRAL AND SOUTHERN PANHANDLE TONIGHT. IN ADDITION TO THE
RADIATIONAL COOLING TONIGHT...MODERATE COLD AIR ADVECTION WILL
AFFECT THE NORTHERN PANHANDLE AND EXPECT OVERNIGHT TEMPERATURES
DROPPING TO AROUND 30 NEAR YAKUTAT AND HAINES AREAS...AND IN TO
THE LOWER 30S OVER THE NORTH CENTRAL PANHANDLE. SOUTHERN AREAS WILL
BE IN THE MID TO UPPER 30S.

.LONG TERM...ON LATE SUNDAY THE NORTHERN PANHANDLE IS CLIPPED BY A
SHORTWAVE IN THE GENERAL WESTERLY FLOW ALOFT...THIS WILL CREATE A
SHOWERY PERIOD FOR AREAS IN THE NORTHERN HALF. PRECIPITATION TYPE
WILL BE A CHALLENGE AS SNOW LEVELS WILL LIKELY BE THEIR LOWEST OF
THE SEASON SO FAR. NORTHERLY LOW LEVEL FLOW WILL INCREASE AS THE
WAVE PASSES THROUGH AND THIS WILL BRING FURTHER COOLING TO THE LOW
LEVELS AFTER THE SYSTEM PASSES. DRYING WILL ALSO BE A FACTOR IN
THIS COOL AIR...SO HOW LONG THE PRECIP PERSISTS IS ONE QUESTION.
MODELS ARE IN AGREEMENT THAT QPF AMOUNTS WILL BE LIGHT WITH THIS
SYSTEM AS THERE IS NOT A LOT OF MARINE MOISTURE TO UTILIZE AND
PRECIPITATION WILL BE OF SHORT DURATION. APPEARS THAT WITH -4 TO
-5C AT 850 THE JUNEAU AREA WILL BE SPARED ACCUMULATION ALTHOUGH
NORTH OF THERE AND OVER SLIGHTLY HIGHER ELEVATIONS ACCUMULATION
CAN BE EXPECTED. FOR NOW PUT SNOW SHOWERS IN THE FORECAST BUT
SUBSEQUENT MODEL RUNS WILL NEED TO BE EXAMINED FOR THERMODYNAMIC
DETAILS AND POSSIBLE CHANGES AS ANY SUBTLE DIGGING OF THE WAVE OR
ADDITIONAL COLD ADVECTION WOULD HAVE A DIRECT IMPACT ON THIS
SCENARIO. MODELS ALSO AGREE THAT BEHIND THIS SYSTEM NORTHERLY FLOW
WILL BECOME DEEP AND TAKU SCENARIO IS POSSIBLE FOR THE TYPICAL
AREAS FOR LATE MONDAY/TUESDAY AS 850 MB FLOW INCREASES TO 35-40
KT. TIGHTENING PRESSURE GRADIENT OF NOTE ALONG THE COAST WITH WARM
MARINE AIR PILED UP AGAINST A DRY/COOL INTERIOR AIR MASS. WORKING
AGAINST THE STRONG WIND SCENARIO WILL BE STABLE LOW LEVEL LAPSE
RATES BUT THESE COULD BE OVERCOME LOCALLY. DETAILS OF THIS WILL
NEED TO BE WORKED OUT IN SUBSEQUENT NUMERICAL GUIDANCE IN TERMS OF
STABILITY AND POSSIBLE DOWNSLOPE ENHANCEMENT. FOR NOW WE BROAD-
BRUSHED THE ZONE WITH 15 MPH WINDS. ALSO ON TUES A NEW SOUTHERN
LOW WILL MAKE ITS WAY INTO THE SOUTHERN PANHANDLE WITH SOME RAIN
AND MODEST INCREASES IN WIND THERE. WHAT REMAINS OF TROPICAL
STORM ANA SHOULD BE IMBEDDED IN THIS SYSTEM ALTHOUGH CURRENT MODEL
GUIDANCE SHOWS LITTLE APPARENT EFFECT IN INCREASING QPF VALUES.
ALSO THE GEM APPEARS WEAKER ON THIS SYSTEM THAN THE EC/GFS...NAM
APPEARED THE ODD MODEL OUT BY THIS POINT WITH ITS MLSP FIELD AWRY
BY TUES.

MODEL DIVERGECE INCREASES SIGNIFICANTLY ON WEDNESDAY BUT IN
GENERAL A TREND IN CONTINUING INCREASING WIND TO AT LEAST MODERATE
LEVELS AND RAIN MOVING IN FROM THE SOUTH APPEARS LIKELY. THE GEM
AND GFS ARE STRONGER IN FORMING AN ORGANIZED NORTHERN GULF FRONT
AND LOW WHILE THE ECMWF IS FURTHER SOUTH AND WEAKER. LATELY THE
TREND HAS BEEN SOUTHWARD AND I DON`T SEE A VALID REASON AT THIS
POINT TO DOUBT THAT....HAVE THUS LEANED TOWARDS THE EC MODEL IN THE
MIDWEEK FORECASTS. DURING THE THURS-FRI PERIOD THE LONGWAVE TROUGH
REMAINS OVER THE GULF IN GENERAL BUT IT REMAINS DIFFUSE ESPECIALLY
ON THE EC MODEL WITH THE GFS MAINTAINING STRONGER SOUTHEASTERLY
FLOW ON THE EAST SIDE OF THE TROUGH IMPACTING THE PANHANDLE. THEN
BY SAT A STRONG GULF WAVE ENTERS THE WESTERN GULF FROM THE WEST ON
THE EC. ALL OF THIS PRESENTS THE POSSIBILITY OF ANY WAVE SPINNING
UP AN EASTERN GULF LOW GIVEN THE STILL-WARM WATER AND LARGE
BAROCLINICITY IN THE SITUATION AT SEVERAL POINTS DURING THE LATTER
HALF OF THE WEEK...EG. REMEMBER THE EARLY-WEEK SPINUP WHICH WAS
POORLY HANDLED BY THE MODELS UNTIL IT WAS ALREADY ACTUALLY
DEVELOPING...HAD SEVERE WINDS AND THUNDERSTORMS FROM THAT SYSTEM.
WE HAVE LEANED HEAVILY AFTER WEDNESDAY WITH WPC GUIDANCE AS AN
ENSEMBLE APPROACH SEEMS TO BE THE MOST LIKELY SCENARIO AT THIS
POINT. FORECAST CONFIDENCE IS ABOVE AVERAGE FOR THE FIRST FOUR
DAYS DETERIORATING TO BELOW AVERAGE FOR THE FINAL THREE EVEN WITH
THE TENDENCY FOR SOUTHERN DEVELOPMENT LATELY. IMPOSSIBLE TO
DILENEATE DETAILS TO A LARGE DEGREE AFTER ABOUT WED.

&&

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

&&

$$

JWA/WESLEY

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