Area Forecast Discussion
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FXAK67 PAJK 261358
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
558 AM AKDT SUN APR 26 2015

.SHORT TERM...A GALE FORCE LOW HAS MOVED INTO THE SOUTH CENTRAL
GULF AND THE ASSOCIATED FRONT LIES JUST OFF THE OUTER COAST.
SATELLITE IMAGERY SHOWS EXTENSIVE CLOUD COVER WELL INLAND, BUT
SURFACE OBSERVATIONS ARE INDICATING THAT MUCH OF THIS IS SOMEWHAT
HIGH CEILINGS. RAIN BEGAN FALLING IN THE PRE-DAWN HOURS IN BOTH
SITKA AND KLAWOCK. RAIN WILL SPREAD INLAND THROUGH THE DAY BEFORE
TRANSITIONING TO SHOWERS LATE THIS AFTERNOON OR EARLY EVENING.
EVIDENCE OF COLD AIR ALOFT CAN BE SEEN PUSHING EAST OVER THE GULF
ON THE BACK SIDE OF THE FRONT. A POST FRONTAL SHORT WAVE TROUGH
SOUTH OF KODIAK IN THE SOUTHWEST QUADRANT OF THE PRIMARY LOW WILL
ROTATE AROUND THE LOW THROUGH THE DAY AND SWING A STRONG LOBE OF
MID LEVEL VORTICITY INTO THE EASTERN GULF. THIS WILL PROVIDE THE
UPPER LEVEL SUPPORT NECESSARY TO GENERATE SIGNIFICANT CONVECTIVE
ACTIVITY IN THE WAKE OF THE FRONT. THUS SLIGHT CHANCE OF
THUNDERSTORMS INTRODUCED BY YESTERDAY`S DAY SHIFT WERE RETAINED IN
THIS FORECAST ISSUANCE FOR TONIGHT.

THIS SYSTEM IS ALREADY FULLY OCCLUDED. AS SUCH, NO WARM AIR
ADVECTION OF ANY SIGNIFICANCE IS EXPECTED AND SOME LOCATIONS MAY
SEE THEIR HIGH TEMPERATURES FOR THE DAY OCCURRING THIS MORNING
BEFORE TEMPS BEGIN TO FALL AS THE COLDER AIRMASS MOVES IN. LOOK
FOR HIGHS IN THE MID TO LOWER 50S TODAY WITH OVERNIGHT LOWS
TONIGHT IN THE LOWER 40S OR UPPER 30S.

BUOY DATA OVER THE GULF IS LIMITED, BUT OBSERVATIONS ARE
INDICATING THAT MAX WINDS ASSOCIATED WITH THIS FRONT ARE 35 TO 40
KTS WITH GUSTS TO 60 KTS.STRONG WIND HEADLINE HAS BEEN MAINTAINED
THROUGH 10 AM THIS MORNING FOR ZONE 27 AND ADDED TO ZONE 23 FOR
THE SAME TIME PERIOD. THINK WIND GUSTS OVER KETCHIKAN WILL MAX OUT
AT 35 MPH, SO HAVE NOT INCLUDED ZONE 28. AS THE FRONT PUSHES
INLAND, GUSTS TO 25 MPH WILL SPREAD OVER ZONE 26 AND THEN MOVE
THROUGH THE JUNEAU AREA LATER THIS AFTERNOON AND EARLY EVENING.
MARINERS SHOULD BE MINDFUL OF THE POTENTIAL FOR GUSTY CONDITIONS ABOVE
THE STEADY STATE SMALL CRAFT WINDS OVER THE INNER CHANNELS AS THE FRONT
MOVES THROUGH.

USED A BLEND OF GEM AND ECMWF FOR UPDATES TO PRESSURE AND WIND.
POP AND QPF FROM GEM, GFS, AND ECMWF. OVERALL FORECAST CONFIDENCE
IS AVERAGE.

.LONG TERM...STILL A TRICKY FORECAST FOR MON-TUE DUE TO LOW
PRESSURE WAVE DEVELOPMENT THAT THE MODELS ARE STRUGGLING WITH. THE
MAIN ISSUE IS INTERACTION BETWEEN A SHORTWAVE DIVING INTO THE BASE
OF THE UPPER TROF OVER THE ERN PAC AND SRN STREAM SHORTWAVE
LIFTING NEWD FROM N OF HAWAII. ECMWF SHOWED MOST INTENSE
DEVELOPMENT AND WAS SLOWEST TO LIFT SYSTEM NWD...WHILE THE GEM/GFS
WERE WEAKER AND FASTER. NAM STILL DOES NOT SHOW MUCH DEVELOPMENT
WITH THIS SYSTEM. DUE TO THE DIFFERENCES...DECIDED THAT WHAT WAS IN
PREVIOUS FORECAST LOOKED REASONABLE AS FAR AS THAT FEATURE
GOES...SO ENDED UP MAKING MAINLY SMALL CHANGES TO THAT TIME FRAME.

FOR MON...BANDS OF SHOWERS AROUND THE MAIN LOW WILL CONTINUE TO
AFFECT MOST OF THE AREA...BUT AN AREA OF STEADIER RAIN IS LIKELY
TO MOVE NWD INTO THE SRN AREA AS A LOW PRESSURE WAVE MOVES NNE
TOWARD THE AREA. THE WARM ADVECTION WITH THIS FEATURE WILL ALSO
DIMINISH THREAT FOR TSTMS OVER THE ERN GULF FROM THE S...ALTHOUGH
THE NE GULF WILL REMAIN MOSTLY UNDER THE COLDER AIR ALOFT THRU MON.
GIVEN THE UNCERTAINTY WITH THE LOW PRESSURE WAVE...TIMING ERRORS
ARE POSSIBLE WITH ARRIVAL OF STEADIER PRECIP AND STABILIZATION
OVER THE SE GULF. DECIDED TO USE THE GFS IDEA ON BOTH SINCE IT HAD
SOME SUPPORT FROM THE GEM. ALSO...THE NAM LOOKED TOO UNSTABLE OVER
THE FAR SE GULF FOR TOO LONG AS IT TAKES A MUCH WEAKER LOW PRESSURE
WAVE FURTHER SE AND DOES NOT SHOW THE WARMING ALOFT OVER THE SE GULF.

FOR MON NIGHT...LOOKS LIKE STEADIER PRECIP WILL MOVE NWD THRU THE
MAIN PART OF THE PANHANDLE AS WAVE LIFTS N THRU THE SERN INNER
CHANNELS. MOST OF THE ERN GULF WILL STAY SHOWERY NEAR THE MAIN LOW
CENTER. THE NE GULF COAST LOOKS TO HAVE A BREAK IN PRECIP AS
OFFSHORE FLOW INCREASES DUE TO BOTH THE MAIN LOW AND THE WAVE TO
THE E OF IT.

FOR TUE-WED...PRECIP SHOULD BE SHOWERY AREA WIDE AS MAIN LOW
BEGINS TO DRIFT INTO THE ERN GULF AND WEAKENS...BUT KEEPS ONSHORE
FLOW GOING OVER THE MAIN PART OF THE PANHANDLE. TEMPS IN COLD POOL
ALOFT SHOULD SLOWLY WARM...AND THIS WILL DIMINISH THREAT FOR ANY
TSTM ACTIVITY. THE SHOWERS AND ONSHORE FLOW WILL KEEP TEMPS A BIT
COOLER THAN AVERAGE DURING THE DAY...BUT THE CLOUD COVER WILL KEEP
MILDER NIGHTTIME TEMPS AS WELL.

AFTER WED...ANOTHER SYSTEM MAY AFFECT THE AREA FOR WED NIGHT AND
THU BUT MODELS DIFFER ON TIMING AND TRACK OF IT. MODEL DIFFERENCES
INCREASE LATER IN THE WEEK...BUT SOME HINT OF A DRIER PATTERN MAY
BE EMERGING AS SIGNALS FOR STRONGER RIDGING OVER THE GULF ARE
DEVELOPING IN THE MODELS. ENDED UP GOING WITH WPC FOR THE MOST
PART FOR THIS PERIOD...WHICH SHOWS GENERALLY DECREASING POPS THRU
NEXT WEEKEND.

&&

.AVIATION...STRONG LOW LEVEL JET WITH 65 TO 70 KTS OF WIND AT
850MB WILL RESULT IN LOW LEVEL WIND SHEAR OF MUCH OF SOUTHEAST
ALASKA THROUGH LATE MORNING OR EARLY AFTERNOON. MOST SEVERE
CONDITIONS OCCURRING THIS MORNING AND OVER SOUTHERN LOCATIONS.
CEILINGS EXPECTED TO BE MVMC OR BETTER FOR THE MOST PART WITH
LOWEST CONDITIONS DUE TO REDUCTIONS INVISIBILITY IN HEAVY
RAIN/SHOWERS.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 10 AM AKDT THIS MORNING FOR AKZ023-027.
MARINE...GALE WARNING FOR PKZ036-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ021-022-033>035.

&&

$$

FRITSCH/RWT

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