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FXAK67 PAJK 070102 CCA
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
217 PM AKST SAT FEB 6 2016

.SHORT TERM...MAIN WEATHER MAKER OVER THE NEXT 24 HOURS WILL BE A
GALE FORCE FRONT MOVING NORTH INTO THE EASTERN GULF TONIGHT AND
OVER THE PANHANDLE SUNDAY. THE PARENT LOW ASSOCIATED WITH THIS
FRONT WILL MOVE NORTH INTO THE WEST CENTRAL GULF ON SUNDAY WHILE
GRADUALLY WEAKENING.

FOR TONIGHT, THE TROUGH THAT INCREASED SHOWER ACTIVITY OVER THE
AREA LAST NIGHT AND TODAY WILL PUSH EAST. THIS WILL RESULT IN
ISOLATED TO SCATTERED SHOWERS DIMINISHING EARLY THIS EVENING.
THERE WILL BE A LULL IN THE PRECIPITATION BEFORE THE FRONTAL BAND
MOVES INTO THE SOUTHERN PANHANDLE LATE THIS EVENING. THE FRONT
WILL WEAKEN AS IT SPREADS NORTH WITH PRECIPITATION REACHING THE
JUNEAU AREA OVERNIGHT AND THE FAR NORTHERN PANHANDLE ON SUNDAY
MORNING. DECIDED TO CANCEL THE WINTER STORM WATCH FOR HYDER DUE TO A
MARGINAL THERMAL PROFILE AND LOW LEVEL WARMING THROUGH THE DAY ON
SUNDAY. ALSO BASED UPON A LACK OF AIRMASS CHANGE FROM THE PREVIOUS
STORM A FEW DAYS AGO, SNOW RATIOS WILL BE VERY LOW AT ROUGHLY 6 OR
8:1. 4-7 INCHES IS EXPECTED BEFORE THE CHANGEOVER.
ENOUGH COLD AIR WILL REMAIN OVER PORTIONS OF THE CENTRAL AND
NORTHERN INNER CHANNELS FOR SOME SNOW AT THE ONSET OF
PRECIPITATION BUT EXPECT WARM AIR ADVECTION WILL EVENTUALLY WIN OUT
AND CHANGE THINGS OVER TO LIQUID BY MIDDAY SUNDAY. DO NOT EXPECT
MORE THAN AN INCH OF ACCUMULATION. SKAGWAY AND HAINES WILL REMAIN
SNOW THROUGHOUT THE EVENT BUT STILL DO NOT EXPECT MORE THAN 1 TO 3
INCHES. THE SYNOPTIC SETUP AND TRAJECTORY OF THE FRONT ARE NOT
CONDUCIVE TO HEAVY PRECIPITATION AMOUNTS OVER THE NORTHERN HALF OF
THE PANHANDLE.

THE OTHER BIG STORY WILL BE WIND. HAVE INCLUDED STRONG WIND
HEADLINES FOR ZONES 27 AND 28 BEGINNING LATE TONIGHT AND ENDING
SUNDAY MORNING. A 50-55 KT SOUTHEASTERLY LOW LEVEL JET WILL
OVERSPREAD THE SOUTHERN PANHANDLE RESULTING IN GUSTS TO 40-45 MPH AT
THE SURFACE. THE STRONGEST WINDS WILL STAY CONFINED TO THE OUTER
COAST HOWEVER AS THE PARENT LOW IS SEVERAL HUNDRED MILES FROM THE
PANHANDLE WITH NO WAVE DEVELOPMENT ALONG THE FRONT TO ENHANCE WINDS.
A TIGHTENING NORTHEASTERLY GRADIENT OVER THE NORTHERN PANHANDLE IN
RESPONSE TO THE APPROACHING FRONT WILL BRING A BRIEF 6-9 HOUR PERIOD
OF GUSTY WINDS OUT OF INTERIOR PASSES LATE TONIGHT. INCLUDED A
MENTION OF GUSTS TO 35 MPH IN DOWNTOWN JUNEAU AND DOUGLAS.

USED THE 12Z NAM FOR MINOR UPDATES TO THE INHERITED FORECAST.

.LONG TERM...MODEL GUIDANCE SHOWS A LARGE UPPER RIDGE POSITIONED
OVER THE W COAST OF N AMERICA SUNDAY NIGHT THROUGH TUE AFTERNOON.
DEEP-LAYER SSWLY FLOW WILL BE PRESENT W OF THE RIDGE...WITH AN
EMBEDDED DISTURBANCE MOVING N ACROSS THE GULF MON EVENING/NIGHT.
MODELS DISAGREE ON HOW THE PRESSURE PATTERN WILL EVOLVE BENEATH
THE DISTURBANCE...WITH THE GFS PRODUCING A FULLY DEVELOPED SURFACE
CYCLONE...AND THE ECMWF MAINTAINING A MOSTLY OPEN WAVE /NAM
RESIDES BETWEEN THESE TWO SOLUTIONS/. DUE TO THE LARGE SPREAD IN
MODEL SOLUTIONS...SIGNIFICANT FORECAST UNCERTAINTY EXISTS IN WINDS
AND POTENTIAL AUGMENTATION TO PRECIPITATION. BEYOND TUE...PATTERN
EVOLVES FROM PERIODIC OFFSHORE WINDS GIVING WAY TO SLYS...WITH
EACH SLY BURST USHERING IN/REINFORCING A WARM LOW-LEVEL AIRMASS.
AS A RESULT...TEMPERATURES...BOTH HIGHS AND LOWS...ARE EXPECTED TO
BE MILD DURING THE LONG TERM PERIOD.

PRESSURE GRIDS WERE NOT ALTERED SUBSTANTIALLY THROUGH TUE...THEN
TRENDED TOWARD LATEST WPC GUIDANCE THEREAFTER. REMAINDER OF THE
FORECAST WAS UPDATED WITH AN ENSEMBLE BLEND.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM MIDNIGHT AKST TONIGHT THROUGH SUNDAY MORNING
     FOR AKZ027.
     STRONG WIND FROM LATE TONIGHT THROUGH SUNDAY MORNING FOR AKZ028.
MARINE...GALE WARNING FOR PKZ022-033-036-041>043-051-052.
     SMALL CRAFT ADVISORY FOR PKZ021-031-032-034-035-053.
&&

$$

TPS/GARNER

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