Area Forecast Discussion
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FXAK67 PAJK 292346
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
346 PM AKDT TUE JUL 29 2014

.SHORT TERM...AFTERNOON WV IMAGERY SHOWS AN UPPER-LEVEL
SHORTWAVE IMPULSE MOVING N OVER THE SRN/CNTRL PANHANDLE. FORCING
FOR ASCENT ASSOCIATED WITH THIS FEATURE COMBINED WITH PW VALUES
NEAR 1 INCH ARE SUPPORTING AREAS OF LIGHT TO MODERATE RAIN ACROSS
THE REGION. MIDLEVEL TEMPERATURES WILL CONTINUE TO COOL TO AROUND
-22C THROUGH THE NIGHT AND SUPPORT A TRANSITION TO A CONVECTIVE
SHOWER REGIME...WHICH IS ALREADY BECOMING EVIDENT PER IR/VIS
SATELLITE IMAGERY AND AREA WEB CAMS. AS THE UPPER-LEVEL SHORTWAVE
TROUGH ROTATES INTO THE NRN PANHANDLE TONIGHT THROUGH WED...THE
MIDLEVEL AIRMASS WILL BEGIN TO DRY OVER THE SRN PANHANDLE AND
BRING AN END TO SHOWERS BY WED AFTERNOON...WITH A GRADUAL DECLINE
IN SHOWER COVERAGE/INTENSITY EXPECTED OVER THE CNTRL PANHANDLE AS
WELL. DRYING MIDLEVEL AIRMASS WILL ALSO PRESENT AN OPPORTUNITY
FOR BREAKS IN THE CLOUD COVER TONIGHT AND AID IN FOG DEVELOPMENT.

 AT THE SURFACE...AREA OF LOW PRESSURE OVER THE GULF IS FORECAST
TO RETROGRADE WWD THROUGH WED...WHILE A RIDGE OF HIGH PRESSURE
BUILDS NWD OVER THE PANHANDLE. THIS WILL YIELD A TIGHTENING
PRESSURE GRADIENT OVER NRN LYNN CANAL TONIGHT...BUT CURRENTLY
EXPECT SLY WINDS TO FALL SHY OF SMALL CRAFT SPEEDS. USED AN
ECMWF/GEM/NAM BLEND FOR A REFRESH OF PRESSURE/WINDS. PREVIOUS POP
FORECAST APPEARED TO BE ON TRACK RESULTING IN MINIMAL CHANGES
BEING MADE. FORECAST CONFIDENCE IS AROUND AVERAGE.

 &&

.LONG TERM...SUNNY DAYS ARE AHEAD.

AS THE CUT-OFF GULF LOW SLIDES SOUTHWEST...RIDGING WILL STRENGTHEN
OVER THE PANHANDLE AND RAISE THICKNESSES IN THE LOWER ATMOSPHERE.
A STABILIZING ATMOSPHERE WILL ERODE CLOUDINESS FROM WEDNESDAY
NIGHT INTO THURSDAY MORNING GIVING WAY TO A STRING OF SUNNY DAYS
AND DRY WEATHER THROUGH SATURDAY. WE HAVE NOT EXPERIENCED SUCH A
LENGTHY DRY/SUNNY SPELL FOR AWHILE. BUT THIS ONE WILL BE LONG
ENOUGH TO ALLOW SURFACE TEMPERATURES TO PUSH INTO THE HIGH 60S FOR
MANY AREAS OF THE PANHANDLE BY THURSDAY, AND EVEN LOWER 70S FOR
PARTS OF THE INTERIOR AND SOUTHERN ZONES BY FRIDAY. WE DID NOT
WARM TEMPERATURES AS HIGH ON SATURDAY AS QUESTIONS ABOUT MARINE
LAYER DEVELOPMENT/PENETRATION AS WELL AS HOW THE RIDGING BREAKS
DOWN REMAIN. BUT SOME MODELS...NOTABLY THE GFS ARE KEEPING THESE
DRY AND RELATIVELY WARM THROUGH THE WEEKEND. IN ALL THIS YAKUTAT
AND POSSIBLY CROSS SOUND AREA LESS CONFIDENT IN AS MUCH WARMING
AND CLEAR WEATHER AND WE SHOULD WATCH FOR POSSIBLE SEA STRATUS. AS
THINGS BECOME MURKIER LATE IN THE WEEKEND...LEFT FORECAST IN TACT
FOR BETTER MORE ASSURING CLUES LATER.

THE STABLE CONDITIONS WEDNESDAY NIGHT COUPLED WITH A MOIST SURFACE
LAYER FROM RAINS OCCURRING DURING THE SHORT-TERM PERIOD WILL INCITE
FOG DEVELOPMENT ACROSS THE PANHANDLE. BUT THINK THIS SHOULD BURN
OFF RELATIVELY QUICKLY THURSDAY MORNING.

THE MAIN REASON FOR CONFINING CHANGES PRE-SATURDAY IS THE ECMWF
AND GEM ARE NOW SUGGESTING A DECENT LOW PUSHING INTO THE EASTERN
GULF LATE SUNDAY INTO MONDAY. THIS WOULD BE A BIG CHANGE AND WOULD
INCREASE LIKELIHOOD OF RAIN ESPECIALLY FOR THE SOUTH AND SPREAD
BREEZIER CONDITIONS FOR MUCH OF OUR AREA. GFS IS STILL STUBBORN
AND SINCE IT HAS LED EVEN THE ECMWF WITH BACKING AWAY THE CUT-OFF
LOW, WE CANNOT DISCOUNT IT, AS IT HAS REMAINED MOST STABLE. GEM
TAKES A MIDDLE APPROACH...FOLLOWING THE GFS THROUGH FRIDAY BUT
THEN MERGING WITH THE ECMWF INTO THE WEEKEND.

FORECAST CONFIDENCE GOOD THROUGH FRIDAY...THEN LOWERING THROUGH
THE WEEKEND. MAINLY CLOUDY SKIES WITH CHANCES OF RAIN AND COOLER
WEATHER LOOK A BETTER BET FOR EARLY NEXT WEEK. HOW WINDY AND HOW
WET THE LATTER WEEKEND IS THE MAIN QUESTION.

 &&

 .AVIATION...LIGHT TO MODERATE SHOWERS ARE FORECAST TO PERSIST
ACROSS THE REGION THROUGH TONIGHT...WITH RAIN DIMINISHING OVER
THE SRN PANHANDLE TOWARD MIDDAY WED. MIDLEVEL AIRMASS WILL
GRADUALLY DRY OVERNIGHT OVER THE CNTRL/SRN PANHANDLE...WHICH
WOULD AID IN ENHANCED RADIATIONAL COOLING AND SUBSEQUENT FOG
POTENTIAL. DROPPED MOST TAF SITES TO 4-5SM BY LATE TONIGHT...BUT
AREAS EXPERIENCING GREATER CLEARING COULD REALIZE A MORE
SUBSTANTIAL REDUCTION IN VISIBILITY.

 &&

 .MARINE...SLY LOW-LEVEL JET CENTERED OVER CLARENCE STRAIT IS
QUICKLY WEAKENING THIS AFTERNOON. AS A RESULT...WINDS IN CLARENCE
STRAIT WILL GENERALLY RESIDE AROUND 10-15 KT OVERNIGHT. OVER NRN
LYNN CANAL...MODEL GUIDANCE INDICATES THE PRESSURE GRADIENT WILL
TIGHTEN THIS EVENING AS A RIDGE OF SURFACE HIGH PRESSURE BUILDS
NWD OVER THE PANHANDLE. RECENT SURFACE OBSERVATIONS INDICATE
WINDS ARE LIGHT THIS AFTERNOON...BUT POTENTIAL EXISTS FOR SLY
WINDS TO STRENGTHEN TO 15-20 KT TONIGHT.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.


$$

GARNER/JWA









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