Area Forecast Discussion
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FXAK67 PAJK 122338
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
338 PM AKDT SAT JUL 12 2014

.SHORT TERM...AN OCCLUDED FRONT OVER THE ERN GULF WILL SLOWLY
WEAKEN THERE THRU SUN. WEAK LOW PRESSURE WAVE OVER THE ERN GULF
WILL DISSIPATE OVER THE FAR NE GULF TONIGHT. ANOTHER WEAK LOW
PRESSURE WAVE MAY DEVELOP JUST S OF THE ERN GULF BY LATE
SUN...BUT MODELS DIFFER SOMEWHAT ON THIS SO LOWER CONFIDENCE ON
THIS FEATURE. USED BLEND OF THE 12Z ECMWF AND GEM THRU SUN.

 MAIN FORECAST CONCERNS WILL BE PRECIP POTENTIAL/AMOUNTS...FOG
POTENTIAL...AND WINDS. RIGHT NOW...MOST PRECIP IS FALLING ALONG
AND NW OF A PAJN-PASI LINE...ALTHOUGH PATCHY DRIZZLE OR VERY
LIGHT RAIN IS OCCURRING JUST SE OF THAT AREA. LOOKS LIKE SERN
EDGE OF THE MAIN PRECIP AREA WILL SHIFT SLIGHTLY EWD TONIGHT. AS
FRONT WEAKENS FURTHER ON SUN...AREA OF PRECIP WILL BECOME
NARROWER WITH A DIMINISHING TREND NOTED FOR THE FAR ERN AND WRN
PARTS OF THE PRECIP SHIELD. LEFT HIGHEST POPS NW OF FREDERICK
SOUND THRU SUN...WITH A RAPID DROP OFF IN POPS ALONG AND SE OF
THERE. KEPT FAR SERN AREA COMPLETELY DRY AS UPPER RIDGE TO THE E
SHOULD HOLD LEFTOVERS OF THE FRONT TO THE W. THE WEAK LOW
PRESSURE WAVE THAT MAY DEVELOP S OF THE ERN GULF SUN WOULD ALSO
HOLD THE FRONT AND ITS PRECIP TO THE W OF THE FAR SERN AREA AS
WELL. HIGHEST PRECIP AMOUNTS SHOULD BE IN THE PAEL AREA
TONIGHT...WITH A SLIGHT EWD SHIFT TO THE AXIS OF HEAVIEST PRECIP
SUN. TOTAL RAINFALL TONIGHT AND SUN SHOULD REMAIN LESS THAN AN
INCH THOUGH...EVEN ALONG THE AXIS OF HEAVIER PRECIP...AS LOW
LEVEL JET WILL WEAKEN AND LIFT ALONG THE FRONT DECREASES.

 LOW LEVEL AIRMASS IS VERY STABLE OVER THE NW HALF OF THE
AREA...AND WITH PRECIP FALLING INTO IT...SOME FOG IS HANGING
AROUND. THINK THIS WILL CONTINUE INTO SUN MORNING AT LEAST OVER
THE NW HALF OF THE AREA. FURTHER SE...ENOUGH LOW LEVEL MOISTURE
AND LIGHT ENOUGH FLOW FOR PATCHY FOG TO DEVELOP THERE BY LATE
EVENING OR EARLY OVERNIGHT TIME FRAME...BUT THIS SHOULD DISSIPATE
EARLY SUN MORNING WITH THE DAYTIME HEATING.

 AS FOR WINDS...A SMALL AREA OF 15-20 KT WINDS OVER THE N-CENTRAL
INNER CHANNELS SHOULD DIMINISH THIS EVENING AS LOWER LEVEL FLOW
WEAKENS. THE 15-20 KT WINDS AHEAD OF THE FRONT OVER THE FAR ERN
GULF SHOULD ALSO WEAKEN THRU SUN...ALTHOUGH A SLOW INCREASE MAY
OCCUR OVER THE FAR SERN GULF SUN AS POTENTIAL LOW PRESSURE WAVE
DEVELOPS JUST S OF THERE. STILL...WINDS WOULD ONLY INCREASE TO
ABOUT 15 KT AT MOST THERE SUN AFTERNOON.

 OTHERWISE...LOOKING LIKE ANOTHER VERY WARM DAY OVER THE FAR SE
SUN...ALTHOUGH THE PAPG/PAWG AND SRN OUTER COAST AREAS SHOULD NOT
BE AS WARM SUN AS THEY WERE TODAY DUE TO EXPECTED CLOUD COVER.
TEMPS FURTHER N SHOULD PEAK IN THE UPPER 50S TO MID 60S SUN.

 &&

 .HYDROLOGY...THREAT FOR ANY FLOODING ACROSS THE AREA HAS
DIMINISHED TODAY. THE GLACIAL DAM OUTBURST INTO MENDENHALL LAKE
AND RIVER IS DONE. THE RAIN IS SLOWING THE DROP OFF IN THOSE
AREAS THIS AFTERNOON...BUT WATER LEVELS SHOULD STAY WELL BELOW
ANY FLOOD CONCERNS. MONTANA CREEK IS RUNNING ON THE HIGH SIDE BUT
SHOULD STAY BELOW BANKFULL LEVELS. THE TAIYA AND CHILKAT RIVERS
MAY GET TO BANKFULL LEVELS TONIGHT AND SUN. WILL UPDATE THE
HYDROLOGIC STATEMENT FOR THESE RIVERS.

 &&

 .LONG TERM...UPPER LEVEL LOW OVER THE AK GULF RETROGRADES
WESTWARD THROUGH THE START OF THE WEEK WHILE A SURFACE HIGH
PRESSURE RIDGE BUILDS OVER THE AK GULF. SHORT WAVES REMNANTS ON
THE LEE SIDE OF THE RIDGE KEEP THE WEAKENING FRONT INTACT JUST A
BIT LONGER ON SUNDAY NIGHT, BUT AS ZONAL FLOW DEVELOPS THE
PANHANDLE TRANSITIONS INTO THE DRIER PATTERN FOR MOST OF THE
WEEK. THE HIGH PRESSURE RIDGE WILL KEEP ONSHORE FLOW OVER THE
REGION SO STILL POSSIBILITY OF MARINE LAYER FORMATION UNDER THE
STABLE ATMOSPHERE EXTENDING EASTWARD. HIGH TEMPERATURES IN THE
MID TO UPPER 60S AND LOWS IN THE LOW 50S THROUGH THE WEEK WITH
THE EXPECTED CLEARER SKIES. SOUTHERLY WINDS OVER THE FAR NORTHERN
PANHANDLE DUE TO GRADIENT BETWEEN THE AK GULF RIDGE AND A LOW
OVER THE YUKON. FOR THE CENTRAL AND SOUTHERN INNER CHANNELS FLOW
ON THE LEE SIDE OF THE RIDGE WILL SHIFT WINDS TO THE NORTHWEST.
WINDS WILL BEGIN TO INCREASE THROUGH THE WEEK DUE TO TIGHTENING
PRESSURE GRADIENT OVER THE PANHANDLE. THE RETROGRADING UPPER LOW
WILL REACH THE TIP OF THE ALEUTIANS THEN CURVE BACK EAST LATE IN
THE WEEK. THE ALEUTIAN SURFACE LOW WILL EVENTUALLY MOVE EAST
UNDER THE UPPER LEVEL LOW. THIS NEXT SYSTEM AND ASSOCIATED FRONT
WILL BRING NEXT ROUND OF PRECIP AND INCREASING WINDS TO THE GULF
AND PANHANDLE TOWARDS THE END OF THE WEEK AND INTO THE WEEKEND.
MODELS ARE IN AGREEMENT ABOUT THE SYNOPTIC PATTERN AND RELATIVE
STRENGTH OF THE SYSTEMS BUT ARE OFF BY 24 HOURS TIMING WHEN THE
LOW REACHES THE NORTHEAST GULF AND MOVES INTO THE AK INTERIOR.
THE GFS IS CURRENTLY THE FASTEST OF THE LONG RANGE MODELS WITH
THE ECMWF THE SLOWEST.

 MODELS IN FAIR AGREEMENT AT THE START OF THE LONG RANGE WITH
BEST AGREEMENT BETWEEN THE GEM/ECMWF WITH THE NAM AN EARLY
OUTLIER. USING THE 12Z ECMWF/GEM TO UPDATE GRIDS THERE WAS LITTLE
CHANGE EARLY ON FROM PREVIOUS MODEL RUNS WITH THE EXCEPTION OF
THE FRONT LINGERING A BIT LONGER. OPERATIONAL ECMWF HAS BEEN MORE
CONSISTENT THEN THE GFS BUT STILL ENOUGH VARIATION THAT THE
ENSEMBLES ARE A BETTER SELECTION, EVEN THROUGH THERE IS LESS
DEFINITION WITH THE ENSEMBLES. FORECAST CONFIDENCE IS ABOVE
AVERAGE.

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

&&

$$

RWT/PRB






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