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558
FXAK67 PAJK 282351
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
351 PM AKDT MON JUL 28 2014

.SHORT TERM...LARGE-SCALE PATTERN HAS CHANGED VERY LITTLE DURING
THE PAST 24 HRS. UPPER TROUGH REMAINS POSITIONED OVER THE
GULF...WITH A RIDGE EXTENDING NWD INTO THE BERING SEA AND A
SECOND RIDGE LOCATED OVER WRN CANADA. TWO UPPER IMPULSES ARE
OBSERVED THIS AFTERNOON ROTATING AROUND THE LARGER-SCALE TROUGH.
ONE IS POISED TO ENTER SE AK BY THIS EVENING BRINGING THE FIRST
ROUND OF MODERATE TO LOCALLY HEAVY RAINFALL. THE SECOND IMPULSE
IS CURRENTLY ENTERING THE BASE OF THE GULF TROUGH...AND IS
FORECAST TO EJECT INTO THE CNTRL/SRN PANHANDLE DURING TUE
AFTERNOON. PW VALUES WILL REMAIN AOA 1 INCH AS THIS TAKES
PLACE...THUS EXPECT MODERATE RAINFALL RATES TO OCCUR ONCE AGAIN
AS FORCING FOR ASCENT REINVIGORATES WITH THIS SECOND DISTURBANCE.

 AT THE SURFACE...MODEST AREA OF LOW PRESSURE WILL BE CENTERED
OVER THE GULF THROUGH THE SHORT TERM. MEANWHILE...A SMALLER LOW
IS FORECAST TO LIFT NWD INTO THE SRN-CNTRL PANHANDLE TONIGHT AS
THE FIRST UPPER IMPULSE ENTERS THE REGION. IN ADDITION...30-40 KT
LOW- LEVEL SLY JET WILL STRENGTHEN OVER THE SRN PANHANDLE IN
RESPONSE TO THE UPPER DISTURBANCE. THIS MOMENTUM ALOFT IS
EXPECTED TO MIX TO THE SURFACE OVER CLARENCE STRAIT AND AID IN
SMALL CRAFT TO POSSIBLE GALE FORCE WINDS.

 DIURNAL TEMPERATURE RANGE WILL BE LIMITED THROUGH TUE AFTERNOON
DUE TO WIDESPREAD CLOUDS AND RAIN. UPDATED PRESSURE/WINDS USING A
BLEND OF THE ECMWF/GEM...WITH MANUAL INCREASE IN SPEEDS OVER
CLARENCE STRAIT IN ORDER TO TAKE INTO ACCOUNT STRENGTHENING LOW-
LEVEL SLYS. PREVIOUS POP/SKY FORECAST APPEARED TO BE ON
TRACK...THUS FEW CHANGES WERE MADE. FORECAST CONFIDENCE IS
AVERAGE.
 &&

.LONG TERM...THIS SECOND IMPULSE DISCUSSED ABOVE CURRENTLY
ROTATING AROUND THE BASE OF THE TROUGH WILL PUSH A FRONT THROUGH
THE BULK OF THE PANHANDLE AND BRING IN A LITTLE COOLER AIR
ALOFT...THUS RAIN WILL TRANSITION TO SHOWERS TUESDAY NIGHT FROM
FAIRWEATHER SOUTH. YAKUTAT WILL ACTUALLY BECOME A LITTLE WETTER AS
THE ENERGY LIFTS NORTHWESTWARD TUESDAY BEFORE EVERYONE BEGINS A
TREND TO DRIER AIR AS THE LARGESCALE LOW BEGINS RETROGRADING TO
THE SOUTHWEST. THIS TEMPORARY JOG TO THE SOUTHWEST WILL ALLOW
SKIES TO PART BEGINNING THURSDAY WITH SOME PERIODS OF SUN LIKELY
THROUGH SATURDAY FOR THE NORTHERN INTERIOR PANHANDLE. CLOUDS LOOK
TO RE-ENTER THE AREA FROM THE SOUTH SATURDAY MORNING AS THE LOW
BEGINS RESPONDING TO A GENTLE NUDGE...PERHAPS BY SOME ENERGY
DIVING DOWNSTREAM INTO MAINLAND ALASKA BY THE END OF THE WEEK.
THIS WILL ONCE AGAIN BRING IN CHANCES OF RAIN...MAINLY FOR THE
LATTER HALF OF THE WEEKEND. CONFIDENCE NOT AS GREAT AS LAST
PACKAGE BECAUSE ONLY THE ECMWF NOW GOING WET BONA FIDE. GEM
UNCHARACTERISTICALLY HAS SIDED WITH THE GFS IN KEEPING THE
LARGESCALE LOW IN THE SW GULF. THUS TRENDED DOWN THE LIKELY RAIN
WE HAD FROM LAST NIGHT TO CHANCE OVER THE INTERIOR...BUT LEFT THE
COASTAL 60 PERCENT POPS IN TACT. MODELS COME IN BETTER AGREEMENT
EARLY NEXT WEEK AS GFS FINALLY INDICATES THE GULF LOW BEING DRAWN
NORTHEASTWARD BY SHORTWAVE PROGRESSING ACROSS THE BROOKS
RANGE.

WINDS LOOK TO INCREASINGLY BECOME BENIGN THROUGH THE MID-RANGE.
DID PERHAPS GET A LITTLE EXCITED BY ADDING A SMALL CRAFT FOR LYNN
CANAL...AS THE ECMWF SHOWING GRADIENTS RISING ABOVE 2 MB THEN...HOWEVER
JET WAS NOT IMPRESSIVE AND CONTINUED CLOUD COVER SHOULD KEEP
MESOSCALE EFFECTS NEGLIGIBLE...SO THIS MAY HAVE BEEN HEAVY-HANDED.
CHANNEL BREEZES MAY BEGIN TO PREDOMINATE THURSDAY AS DIFFERENTIAL
HEATING INCREASES. WHILE CURRENTLY MAINLY LIGHT WINDS ARE
REPRESENTED FOR THURSDAY...MODELS SHOWING A LITTLE HINT OF A
THERMAL TROUGH OVER THE SOUTHERN/CENTRAL PANHANDLE PERHAPS
INCREASING WINDS OUT OF THE NORTH/WEST TO 10 OR 15 KT. SAVED FOR
LATER AS MODELS IMPROVE AGREEMENT. DID VIOLATE GRADIENT FOR CROSS
SOUND FOR THURSDAY/FRIDAY AS A WESTERLY SEA BREEZE SHOULD DEVELOP.
WHILE WE TRENDED TEMPERATURES UPWARD SLIGHTLY...GFS ACTUALLY GOING
70S FOR PARTS FRIDAY, CROSS SOUND WESTERLIES MAY NEED TO BE
INCREASED DURING THIS TIME.

FORECAST CONFIDENCE ON GOOD SIDE OF AVERAGE FOR MOST ISSUES.
RELIED ON ECMWF AS A GUIDE TUE NIGHT INTO WED...FOR LATE IN THE
WEEK PREFERRED GFS/GEM BUT GRADUALLY HEDGED BETS OF DRY WEATHER
EXTENDING INTO EARLY PART OF WEEKEND WITH A LITTLE BIT OF
STUBBORNNESS FROM THE ECMWF THAT IT WILL BE WET ONCE AGAIN.

 &&

 .AVIATION...RAIN WILL INCREASE IN INTENSITY ACROSS THE CNTRL/SRN
PANHANDLE THROUGH TONIGHT WITH CEILINGS/VISIBILITY SUBSEQUENTLY
FALLING AS A RESULT. ONE EXCEPTION WILL BE YAKUTAT...WHICH WILL
EXPERIENCE THE ONSET OF STEADY LIGHT RAIN LATE TONIGHT INTO TUE
MORNING.

 &&

 .MARINE...A 30-40 KT SLY LOW-LEVEL JET IS FORECAST TO RESIDE
OVER CLARENCE STRAIT TONIGHT...AND WILL AID IN SMALL CRAFT TO
OCCASIONAL GALE FORCE WINDS FROM 25-35 KT. ELSEWHERE...PRESSURE
GRADIENT CONTINUES TO TIGHTEN OVER CROSS SOUND RESULTING IN
SUSTAINED ELY WINDS NEAR SMALL CRAFT STRENGTH. OTHERWISE...NLY
PRESSURE GRADIENT FROM GLACIER BAY INTO LYNN CANAL AND STEPHENS
PASSAGE IS FORECAST TO FLIP TO SLY BY TUE AFTERNOON.

 &&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ036.
         SMALL CRAFT ADVISORY FOR PKZ022.


$$

GARNER/JWA








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