Storm Warning 32, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
320 PM AKST MON FEB 22 2016

.SHORT TERM...WEAKENING FRONTAL BAND MOVING OVER THE NORTHERN
PANHANDLE TODAY AS HIGH PRESSURE RIDGE BUILDS OVER THE AREA.
SHOWER ACTIVITY HAS BEEN DIMINISHING AS 500 MB VORT MAX PUSHED
NORTHWARD. A SECOND VORT MAX CROSSES THE GULF LATE THIS AFTERNOON
AND EARLY EVENING AHEAD OF THE BUILDING RIDGE WHICH COULD
PRODUCED A FEW MORE SHOWERS AS IT MOVES OVER ELEVATED TERRAIN. AS
OF NOW NOT SEEING MUCH ACTIVITY FROM SATELLITE IMAGERY OVER THE
GULF UNDER THIS WAVE, SO DID NOT INCREASE POP. INSTABILITY UNDER
THESE WAVES PRODUCED SOME LIGHTNING ACTIVITY OVER THE NORTHERN
GULF AND AS FAR INLAND AS GLACIER BAY EARLY IN THE DAY. SUFFICIENT
CAPE LASTS INTO THE EARLY EVENING FOR CONTINUED ISOLATED
THUNDERSTORM DEVELOPMENT OVER THE NORTHEASTERN GULF COAST DUE TO
OROGRAPHIC ENHANCED ASCENT. MEANWHILE TO THE SOUTH A LOW MOVES UP
FROM THE NORTHEAST PACIFIC TRACKING ALONG THE WESTERN GULF TOWARD
THE AK PENINSULA. AS THIS LOW ADVANCES THE HIGH PRESSURE RIDGE
OVER THE PANHANDLE WILL SHIFT EAST INTO WESTERN CANADA. THE FRONT
ASSOCIATED WITH THE LOW WILL MOVE STORM FORCE WINDS OVER THE
CENTRAL GULF AND GALES ALONG THE COASTAL WATERS THROUGH TUESDAY.
OUR BREAK IN RAIN WILL END AS THE NEXT BANDS OF PRECIP MOVE IN
WITH THE FRONT LATE IN THE AFTERNOON TUESDAY. MAIN ENERGY FROM
THIS LOW AND FRONT WILL REMAIN TO THE WEST OF THE REGION.

SOUTHEASTERLY WINDS DIMINISHED THROUGH THE DAY AS THE FRONT PASSED
NORTHWARD. HIGHER GUSTS LINGERED MAINLY WITH SHOWER ACTIVITY AS
PRESSURE GRADIENT SUBSIDED. WINDS WILL BECOME LIGHT THEN SHIFT TO
THE NORTH LATER TONIGHT AS THE NEW LOW MOVES IN. WITH HIGH
PRESSURE OVER WESTERN CANADA AND THE LOW OVER THE GULF EASTERLY
OUTFLOW WINDS PICK UP BY TUESDAY AFTERNOON. FOR NOW ONLY EXPECT
INNER CHANNEL WINDS TO PICK UP TO SMALL CRAFT LEVELS WITH HIGHER
GUSTS OUT OF CHANNEL TERRAIN.

WITH CLEARING OF LOW AND MID LEVEL CLOUDS THROUGH THE NIGHT
TEMPERATURES WILL BE COOLER THAN PREVIOUS NIGHT DUE TO RADIATIONAL COOLING.
AS PRECIP WILL HAVE STOPPED BY LATE TONIGHT NO CONCERN FOR SNOW
ACCUMULATION. DROPPING TEMPS AND MOIST AIR DURING THE DAY ALSO
KEEPS POTENTIAL FOR FOG DEVELOPMENT LATE TONIGHT. WITH SOUTHERLY
MID LEVEL FLOW MOVING IN EXPECT TEMPS TO WARM THROUGH TUESDAY
WITH HIGHS RANGING FROM LOW 30S UP TO THE UPPER 40S.

MODELS VARIED SLIGHTLY WITH TIMING OF THE STRONGER WINDS MOVING
INTO THE GULF ON TUESDAY. DID DROP OFF POPS FOR THE NORTHERN
PANHANDLE AS NOT GETTING AS MUCH SHOWER DEVELOPMENT WITH THE NEXT
WAVE, BUT STILL ON TRACK FOR SHOWERS CONTINUING NEAR YAKUTAT. USED
A BLEND OF 12Z GFS/NAM BUT OVERALL CHANGES WERE MINOR. FORECAST
CONFIDENCE IS A BIT ABOVE AVERAGE,

.LONG TERM...RAINY AND WINDY EXTENDED RANGE FORECAST. VERY
AMPLIFIED UPPER LEVEL RIDGE OVER WESTERN NORTH AMERICA WITH
CORRESPONDING LARGE UPPER LEVEL TROUGH OVER THE NORTH CENTRAL
PACIFIC WILL ALLOW NUMEROUS LOW PRESSURE SYSTEMS AND THEIR FRONTS
TO ENTER THE GULF FROM THE SOUTH OR SOUTHWEST FOR THE UPCOMING
WEEK. HAVE RAIN OR RAIN LIKELY BEGINNING WEDNESDAY MORNING IN
YAKUTAT, WITH THESE HIGHER POPS SPREADING SOUTH AND EAST THROUGH
LATE WEEK. LOW LEVEL SOUTHERLY OR SOUTHWESTERLY FETCH WILL
CONTINUE TO ADVECT IN WARMER THAN NORMAL TEMPERATURES. POSSIBLE
EXCEPTION WILL BE SUNDAY NIGHT, WHEN BOTH ECMWF AND GFS ARE
SHOWING A COLDER LOW LEVEL AIRMASS ADVECTING IN FROM THE
SOUTHWEST. THIS IS AN IMPROBABLE DIRECTION TO GET AIR COLD ENOUGH
TO SUPPORT ACCUMULATING SNOW, BUT IT HAS HAPPENED AT LEAST TWICE
THIS WINTER ALREADY AND SO, THIS TIME FRAME WILL BE WATCH
CLOSELY. AS IT IS, FORECAST SURFACE TEMPS FOR SUNDAY NIGHT ARE
RIGHT IN THE ZONE WHERE EITHER RAIN OR SNOW IS POSSIBLE, DEPENDING
ON EXACTLY HOW COLD THE LOWER AND MID LEVELS OF THE ATMOSPHERE GET
SUNDAY NIGHT. FOR NOW, THE EXTENDED RANGE PRECIP FORECAST IS FOR
RAIN AT THE LOWER ELEVATIONS WITH SNOW CONFINED TO HIGHER
LOCATIONS SUCH AS EAGLECREST AND THE HIGHWAYS OUT OF HAINES AND
SKAGWAY.

THE OTHER RECURRING THEME WITH THE EXTENDED RANGE FORECAST IS
WIND. CURRENTLY NO STRONG WIND HEADLINES OR HIGH WIND WARNINGS
ANTICIPATED, BUT MARINE ZONES AND INNER CHANNELS ARE SUSTAINED AT
20 KT OR ABOVE FOR THE ENTIRE WEEK, PUNCTUATED BY PERIODS OF SMALL
CRAFT AND GALE FORCE WINDS ON THE INSIDE. OTHERWISE, SOUTHERLY
GALES EASING TO SMALL CRAFT LEVELS THURSDAY NIGHT AND FRIDAY
NIGHT. SMALL CRAFT STARTING OUT WITH SOUTHEASTERLY STORM FORCE
WINDS OVER OFFSHORE ZONE 310 TUESDAY NIGHT. SEAS RANGING FROM 12
TO 30 FEET, DEPENDING ON TIME AND LOCATION.

PREVIOUS LONG RANGE FORECAST STILL LOOKS VERY GOOD WHEN COMPARED
TO LATEST MODEL GUIDANCE WITH UPDATED LIMITED TO THURSDAY/THURSDAY
NIGHT AND NEXT SUNDAY/MONDAY. USED A BLEND OF CANADIAN NH AND
GFS22 FOR THURSDAY/THURSDAY NIGHT POP, QPF, AND WIND TO BETTER
DEPICT A DEVELOPING WAVE AND ASSOCIATE FRONTAL BOUNDARY OVER THE
EASTERN GULF FOR THURSDAY. LATEST WPC FOR THE TAIL END OF THE
FORECAST. ADJUSTED TEMPS FOR WHITE PASS AND NEAR THE BORDER ON THE
HAINES HIGHWAY TUESDAY NIGHT. DECREASED DAYTIME HIGHS FOR
WEDNESDAY BY 2 DEGREES. NO OTHER CHANGES MADE. OVERALL FORECAST
CONFIDENCE IS AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ041>043-051-052.
     SMALL CRAFT ADVISORY FOR PKZ012-013-021-022-031-033-034-036.
     SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ053.
&&

PRB/FRITSCH

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