Area Forecast Discussion - Southeastern


FXAK67 PAJK 250043
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
343 PM AKST SAT JAN 24 2015
.SHORT TERM...A LOW WILL STRENGTHEN TO STORM FORCE AS IT MOVES 
NORTH ACROSS THE SE GULF THIS EVENING. STRONGEST WINDS MEASURED SO
FAR HAVE BEEN A GUST OF 61KT OUT OF THE EAST AT CAPE DECISION.
EXPECT STRONGEST WINDS ON LAND TO BE ALONG THE SOUTHERN OUTER
COAST OF BARANOF, KUIU, POW, AND ANNETTE ISLANDS. HAVE THESE
STRONG WIND GUSTS OF 40-55 MPH HEADLINED IN THE TEXT FORECAST. THE
LOW CENTER WILL CROSS OVER BARANOF ISLAND OVERNIGHT WITH A LULL IN
THE WINDS THEN A SHARP SHIFT TO THE SW. THE W-SW WINDS WILL
INCREASE WITH STRONG GUSTS AS WELL. THE LOW WILL THEN SLOWLY
WEAKEN AS IT MOVES INTO NORTHERN CANADA WITH ZONAL W TO SW FLOW
PERSISTING ACROSS THE GULF IN ITS WAKE. THE NORTHERN PANHANDLE
WILL SEE INCREASING NORTH WINDS EARLY THIS EVENING AS THE LOW
DRAWS NEAR. THEN THOSE WINDS WILL DIE DOWN LATER THIS EVENING AS
THE LOW PASSES...FOLLOWED BY A SHIFT TO THE SOUTH THROUGH THE
INNER CHANNELS WITH BUILDING HIGH PRESSURE.

THIS LOW IS BRINGING WITH IT WARM AIR ALOFT...AS THE LAST SEVERAL
HAVE. THIS WILL KEEP TEMPERATURES MODERATE OVERNIGHT AND ALL
LIQUID PRECIP IN THE FORECAST...WITH EXCEPTION OF WHITE PASS
TONIGHT WHICH COULD SEE A COUPLE INCHES OF SNOW. TOMORROW WILL BE
A DIFFERENT STORY. TEMPERATURES ALOFT WILL FALL THROUGH THE DAY
WITH CAA FROM THE WEST. 850MB TEMPERATURES OVER JUNEAU FALL FROM
ABOUT -2C TO -6C AND AS COLD AS -10C OVER YAKUTAT BY SUNDAY
AFTERNOON. THIS WILL CAUSE A TRANSITION FROM TONIGHTS HEAVY STRATIFORM
RAIN TO CONVECTIVE SHOWERS. THE COOLING TEMPERATURES WILL ALSO
CAUSE SOME OF THOSE SHOWERS TO HAVE SNOW MIXED IN FROM ABOUT THE
MENDENHALL VALLEY NORTH. DO NOT EXPECT MUCH IN THE WAY OF
ACCUMULATION HOWEVER AS SURFACE TEMPERATURES ARE EXPECTED TO BE
ABOVE FREEZING AND ANY SNOW SHOULD MELT ON CONTACT.

THIS IS A QUICKLY MOVING SYSTEM WHICH MAKES THE DETAILS AND TIMING
DIFFICULT. DID NOT MAKE TOO MANY CHANGES TO THE GOING FORECAST AS
THE LOW CENTER PATH LOOKED TO BE ON TRACK. FORECAST CONFIDENCE
OVERALL IS ABOVE AVERAGE BUT LOWER ON THE DETAILS AND SNOW
POTENTIAL FOR TOMORROW. 
.LONG TERM...PRECIP IS IN RETREATING PHASE AND WINDS WEAKENING AS
GRADIENTS SLACKEN TOMORROW NIGHT. COLD ADVECTION ALONG WITH DRYING
LOW LEVELS WILL BE THE RULE THROUGH TUESDAY AS MODIFIED ARCTIC AIR
MAKES ITS WAY SOUTHWARD THROUGH THE PANHANDLE. A NEW WEAK LOW
SKIRTS THE SOUTH END EARLY TUES WITH ONLY SOME LIGHT RAIN...BUT
THE NEW SCENARIO AFFECTED GRADIENTS AND WINDS AND THUS HAD TO
UPDATE FROM 18Z MONDAY ONWARDS AS THE PREVIOUS RUNS KEPT THIS
MOSTLY OUT OF THE PICTURE. UTILIZED MOSTLY EC/GEM FIELDS FOR THE
DYNAMIC UPDATES AND INCORPORATED SOME GFS FOR THE THERMODYNAMIC
UPDATES. LOOKS LIKE THE COLD AIR WILL REMAIN OVER AT LEAST THE
NORTHERN HALF THROUGH AT LEAST WED. COLDEST AIR WILL OF COURSE
AFFECT THE SKAGWAY AREA THE MOST BUT ALL OF THE PANHANDLE COOLS
SIGNIFICANTLY. ON TUES NIGHT THE NEXT WEAK LOW AND FRONT MOVE INTO
THE CENTRAL GULF WITH THE CURRENT SNOW LINE OVER THE CENTRAL
PANHANDLE MOVING NORTH WITH THIS SYSTEM. THIS WILL NECESSITATE
WATCHING FOR POTENTIAL IMPACTFUL SNOW AMOUNTS AT SEA LEVEL DURING
TUES-WED. TENTATIVELY LOOKS LIKE ONLY THE NORTHERN FRINGE AND
POSSIBLY JUNEAU/GUSTAVUS/YAK WILL HAVE SNOW POTENTIAL BY LATE WED.
THURS MARKS SIGNIFICANT WARMING BUT MODELS MAY BE TOO QUICK ON
THIS FOR THE NORTHERN FRINGE. ALL 3 OF THE MAJOR EXTENDED MODELS
ADVERTISE A STRONG NEW GULF LOW BY FRIDAY.

AS FOR WINDS...THE NORTHERN LYNN GALE/SCA (BLOWING FROM THE SOUTH)
APPEARS LIKELY TO HANG ON UNTIL ABOUT 09Z MONDAY BUT ALL OTHER
AREAS WILL HAVE VERY WEAK GRADIENTS BY THEN. STARTING ABOUT 00Z
TUESDAY FLOW WILL BEGIN TO INCREASE AGAIN OVER THE SOUTHERN THIRD
WITH THE WEAK LOW/FRONT; THEN 310 COULD REACH GALE AS EARLY AS
TUESDAY AFTERNOON AS NEW LOW PRESSURE WELL TO THE SOUTH ENTERS THE
PICTURE. GALES COULD REACH THE REST OF THE OUTER WATERS BY 06Z
WED. MEANWHILE OUTFLOW WINDS BEGIN AT ABOUT 00Z TUES ON THE NORTH
END AND STEADILY INCREASE FROM THAT POINT. THROUGH AT LEAST THURS
THE STORY WILL BE TIGHTENING GRADIENTS BETWEEN THE SLOWLY
APPROACHING LOW TO THE SOUTH AND THE ENTRENCHED CONTINENTAL HIGH
PRESSURE SYSTEM OVER WESTERN BC AND THE YUKON. PREDOMINANTLY
SOUTHEASTERLY FLOW OVER WATER AND STRONG NORTHERLY/NORTHEASTERLY
OUTFLOW IN THE PREFERRED REGIONS INCLUDING THE JUNEAU AREA AS EARLY
AS WEDNESDAY. THIS IS MOSTLY WHAT THE WPC GRIDS PORTEND. 

MODEL AGREEMENT IN THE EXTENDED WAS ABOVE AVERAGE SO HAVE
CONFIDENCE IN THE LARGE SCALE FEATURES THROUGH ABOUT
WEDNESDAY...NOTWITHSTANDING THE OUTLIER NAM DYNAMIC FIELDS EARLY ON.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL MIDNIGHT AKST TONIGHT FOR AKZ026-028.
         STRONG WIND UNTIL 3 AM AKST SUNDAY FOR AKZ023-027.
MARINE...STORM WARNING FOR PKZ036-041. 
         GALE WARNING FOR PKZ012-022-031-033-035-042-043. 
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-032-034-051-052. 

&&

$$

FERRIN/WESLEY

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