Area Forecast Discussion
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FXAK67 PAJK 301342
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
542 AM AKDT TUE SEP 30 2014

.SHORT TERM...THE MAIN THEME OF THE SHORT RANGE FORECAST TODAY IS
CHANGE AS WE SEE THE BEGINNINGS OF THE FIRST COOL AIR MASS OF THE
FALL START TO DESCEND OVER THE NORTHERN PANHANDLE. BUT FIRST WE
HAVE TO DEAL WITH THE UPPER TROUGH THAT IS DRAGGING THE COOL AIR
DOWN IN THE FIRST PLACE. THE TROUGH IS CURRENTLY JUST EXITING
EASTERN INTERIOR ALASKA AND HEADING INTO THE WESTERN YUKON WITH
THE SOUTHERN END OF IT EXTENDING INTO THE NORTHERN GULF. A 80 KT
JET STREAK AT 500 MB THAT IS ROUNDING THE SOUTH SIDE OF THE TROUGH
IS NOT ONLY KEEPING THE TROUGH DEEP BUT ITS LEFT EXIT REGION HAS
HELPED FORM A 1002 MB SURFACE LOW OVER THE NORTHERN GULF AND
SPARKED OFF SOME SHOWERS AND THUNDERSTORMS OVER THE NORTHERN GULF
AND GULF COAST OVERNIGHT. THE AMOUNT OF LIGHTNING DETECTED IN THAT
AREA HAS DIMINISHED IN NUMBER OVER THE LAST HOUR OR TWO AS THE JET
STREAK MOVES E. SPEAKING OF WIND THERE IS A DECENT BAND OF GALE
FORCE WINDS IN THE GULF JUST SOUTH OF THE LOW AS WELL THIS
MORNING. AS FOR THE REST OF THE PANHANDLE, LOW CLOUDS, SOME FOG,
AND SOME PASSING SHOWERS ARE THE RULE OF THE MORNING.

THE TROUGH WILL MAKE ITS WAY SOUTHEASTWARD THROUGH TODAY AND
TONIGHT SPREADING RAIN SHOWERS AS IT COMES. MORE VIGOROUS SHOWERS
WILL BE STARTING UP IN THE NORTHERN PANHANDLE THIS MORNING WITH
THE SOUTHERN PANHANDLE STARTING TO GET IT THIS AFTERNOON. THIS
TROUGH SHOULD BE IN THE SOUTHERN PANHANDLE BY LATE TONIGHT ENDING
THE RAIN FOR THE NORTH BY THEN. TEMPERATURES ALOFT WITH THIS
TROUGH ARE RATHER COLD (AROUND -30 C). THAT COMBINED WITH THE
STILL PRESENT JET STREAK AND SOME UPPER VORTICITY COULD KEEP THE
POSSIBILITY OF SOME THUNDERSTORMS POPPING VALID. AS SUCH STILL
HAVE SLIGHT CHANCE OF THUNDERSTORMS UP FOR THE NEAR OUTER COASTAL
AREAS OF THE NORTHERN PANHANDLE AND THE NEAR SHORE WATERS OF THE
GULF TODAY. DECIDED TO NOT EXTEND IT INTO TONIGHT AS THE TROUGH
WILL HAVE WEAKENED SOMEWHAT AND THE MAIN FORCING WILL NO LONGER BE
OVER THE WARM WATERS OF THE GULF.

AS THE TROUGH MOVES SE THE WINDS IN THE GULF WILL START TO
DIMINISH. WESTERLY GALES WILL STILL BE PRESENT THROUGH TODAY BUT
SHOULD START TO DIMINISH TONIGHT DROPPING BELOW SMALL CRAFT BY
LATE TONIGHT. AS FOR INNER CHANNEL WINDS MOST PLACES WILL BE
STARTING OUT WITH EITHER W OR S WIND DIRECTIONS DEPENDING ON THE
LOCATION. WITH THE PRESSURE GRADIENTS AHEAD OF THE TROUGH SOME
AREAS LIKE LYNN CANAL HAVE JUMPED UP TO A SOUTHERLY SMALL CRAFT
THIS MORNING. THESE HIGHER WINDS WILL TRANSITION SOUTHWARD THROUGH
TODAY AND MOST AREAS WILL START TO SHIFT TO N AS THE TROUGH MOVES
BY. THE NORTHERN PANHANDLE WILL SEE THIS SHIFT SOMETIME THIS
AFTERNOON WHILE AREAS FARTHER SOUTH WILL HAVE TO WAIT TILL
SOMETIME TONIGHT.

BEHIND THE TROUGH THINGS RAPIDLY DRY AND CLEAR OUT AS A COOL AIR
MASS MAKES ITS WAY OUT OF THE ALASKA INTERIOR. YAKUTAT WILL LIKELY
HAVE A PARTLY CLOUDY BUT COOL NIGHT. AREAS IN THE NORTHERN HALF OF
THE PANHANDLE WILL SEE DIMINISHING CLOUDS TONIGHT. AS SUCH
OVERNIGHT LOWS WILL DROP INTO THE 30S ACROSS MUCH OF THE NORTHERN
PANHANDLE AND MAY GET BELOW FREEZING IN YAKUTAT AND WHITE PASS
AREA. ALSO WHILE THIS AIR MASS IS COMING FROM THE ARCTIC IT IS
NOT BITTERLY COLD AS WE ARE STILL EARLY IN THE SEASON. STILL IT HAS
ENOUGH PUNCH THAT NORTHERLY OUTFLOW WINDS WILL START UP ACROSS THE
NORTHERN PANHANDLE TONIGHT DUE TO PRESSURE GRADIENT ALONE. HOWEVER
THE COOL AIR POOLING IN THE YUKON DOES NOT APPEAR TO BE DEEP
ENOUGH TO GET OVER THE MOUNTAIN PASSES YET. SO NORTHERLY
WINDS IN THE CANAL ARE ONLY EXPECTED TO REACH 30 KT TONIGHT AND
SOME GUSTS TO 35 KT ARE EXPECTED IN DISENCHANTMENT BAY. OTHERWISE
MOST OTHER AREAS WILL ONLY SEE WINDS OF 20 KT OR LESS BY LATE
TONIGHT.

SHORT RANGE MODELS WERE IN DECENT AGREEMENT BUT DID DIFFER ON THE
SURFACE LOW IN THE NORTHERN GULF. NAM AND ECMWF SEEMED TO HAVE A
GOOD HANDLE ON LOW POSITION AND STRENGTH. THE GFS WAS A BIT TOO
FAR E WITH IT AND THE GEM JUST JUST A BIT TOO WEAK COMPARED TO
SURFACE OBS. FOR WINDS GEM AND NAM SEEMED TO HAVE SPEEDS DOWN
WHILE OTHER MODELS WERE JUST A LITTLE WEAK COMPARED TO SOME OBS.
OVERALL FEW CHANGES IN THE SHORT RANGE WITH THE MOST NOTICEABLE
CHANGES BEING STRENGTHEN THE OUTFLOW WINDS A BIT TONIGHT.

.LONG TERM...REMNANTS OF FAST MOVING CLIPPER LOW WILL CROSS FROM
THE SOUTHERN PANHANDLE INTO BRITISH COLUMBIA WEDNESDAY MORNING
WITH SOME LINGERING SHOWERS NEAR HYDER. SURFACE HIGH PRESSURE THAT
IS BUILDING OVER THE YUKON UNDER AN UPPER LEVEL TROUGH WILL TRACK
SOUTHEASTWARD BRINGING DRY CONDITIONS AND MOSTLY CLEAR SKIES TO
THE PANHANDLE. OFFSHORE FLOW BETWEEN THIS AREA OF HIGH PRESSURE
AND A LOW MOVING INTO THE AK GULF WILL BEGIN TO INCREASE LATE
WEDNESDAY NIGHT INTO THURSDAY. THIS NEXT LOW HAS POTENTIAL TO BE A
SIGNIFICANT SYSTEM PRODUCING STRONG WINDS AND SUBSTANTIAL
PRECIPITATION. AS THIS ADVANCING LOW STRENGTHENS OUTFLOW WINDS
WILL INCREASE AS THE PRESSURE GRADIENT TIGHTENS. WINDS OVER THE AK
GULF WILL ALSO INCREASE UP TO GALE FORCE AS THE FRONTAL BOUNDARIES
ASSOCIATED WITH THE LOW MOVE IN. BY THURSDAY NIGHT THE FRONT WILL
MOVE OVER THE PANHANDLE FORM SOUTH TO NORTH WITH WINDS CONTINUING
TO INCREASE. STRONGEST WINDS WILL BE ALONG EAST-WEST ORIENTED
CHANNELS, OVER COASTAL AREAS AND OUT OF INTERIOR PASSES. GUSTS UP
TO 50 MPH ARE NOT OUT OF THE QUESTION.

AFTER THE DRY WEDNESDAY AND WEDNESDAY NIGHT MORE WET WEATHER
RETURNS AND WILL REMAIN THROUGH THE WEEKEND. AS THIS INCOMING
SYSTEM INCORPORATES THE REMAINS OF TROPICAL STORM KUMMARI IT WILL
PROVIDE AMPLE MOISTURE WITH POTENTIAL FOR HEAVY RAIN STARTING
THURSDAY NIGHT INTO FRIDAY. PRECIP WILL TAPER OFF BY THE END OF
THE WEEKEND AS THE LOW FILLS AND STARTS TO EXIT THE REGION. THE
UPPER LEVEL TROUGH MOVING OVER THE PANHANDLE ON WEDNESDAY MOVES
COLD AIR MASS IN FROM THE YUKON OVER PANHANDLE WITH 850 MB TEMPS
IN THE -2 TO -6 C RANGE. CLEAR SKIES MAY PROVIDE ENOUGH INSOLATION
FOR DAY TIME TEMPS TO RISE INTO THE MID 50S. OVERNIGHT LOWS WILL
BE IN TO UPPER 20 TO LOW 30S FOR THE CENTRAL AND NORTHERN
PANHANDLE AND THE UPPER 30S TO LOW 40S FOR THE SOUTH DUE TO NOT
ONLY THE COLD UPPER LEVEL AIR BUT ALSO RADIATIONAL COOLING
RESULTING FROM CLEAR SKIES. TEMPERATURES WILL RETURN TO SEASONAL
NORMALS WITH THE ADVANCING FRONT WITH MOST PRECIP FALLING AS RAIN
BUT THERE MAY BE ENOUGH COLD AIR AT HIGHER ELEVATIONS TO PRODUCE
SNOW.

MODELS HAD GOOD CONSENSUS ON SYNOPTIC PATTERN THROUGH EARLY
THURSDAY BUT WITH LARGER MODEL SPECTRUM FOR TEMPERATURES. LEFT
GRIDS THROUGH WEDNESDAY MOSTLY AS IS DUE TO SIMILARITY TO NEW
MODEL RUNS WITH SOME LOWER TEMPS WEDNESDAY NIGHT. THE ADVANCING
SYSTEM FOR LATE IN THE WEEK BECAME MORE OF AN ISSUE. PREVIOUSLY
THE GEM HAD BEEN MODEL OF CHOICE DUE TO ITS CONSISTENCY, BUT THE
NEWEST RUN SHIFTED IN POSITION AND MORE SIGNIFICANTLY STRENGTH BY
DROPPING THE LOW CENTER TO 975 MB. THE GEM/ECMWF WERE CLOSER IN
STRENGTH WITH WEAKER GFS/NAM BUT THE GEM/GFS WERE CLOSER WITH
POSITION OF THE LOW WITH ECMWF/NAM FURTHER WEST. FOR NOW BUMPED UP
WINDS IN ANTICIPATION OF A DEEPER LOW BUT HELD OFF ON CHANGING THE
LOW POSITION UNTIL MODELS COME TO A BETTER CONSENSUS. FORECAST
CONFIDENCE IS AVERAGE FOR INTO WEDNESDAY NIGHT THEN IS WELL BELOW
AVERAGE STARTING THURSDAY.


&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ043-052.
         SMALL CRAFT ADVISORY FOR PKZ012-013-022-033-036-041-042-051.

&&

$$

EAL/PRB

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