Gale Warning 466, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
557 AM AKST MON DEC 14 2015

.SHORT TERM...GALE FORCE FRONT MOVING FROM THE EASTERN AK GULF
OVER THE PANHANDLE THIS MORNING. AS THE FRONT MOVES EAST TOWARD
THE COAST MOUNTAINS TONIGHT IT WILL BEGIN TO WEAKEN AND SHEAR
APART. UNSTABLE AIR BEHIND THE FRONT WILL TRANSITION STEADY PRECIP
TO SHOWERS THROUGH MONDAY AFTERNOON. AS THE FRONT MOVES IN
TEMPERATURES HAVE BEEN SLOWLY RISING OVERNIGHT. AS OF NOW TEMPS
ARE JUST BELOW OR NEAR FREEZING. TEMPS WILL CONTINUE TO RISE
THROUGH THE DAY THEN BECOME STEADY OVERNIGHT OR ONLY DROP A FEW
DEGREES.

SNOW BEGAN IN THE EARLY MORNING HOURS STARTING AT YAKUTAT AND
SPREADING EAST. CENTRAL COASTAL AREAS AND SOUTHERN PANHANDLE WILL
START OUT AS, AND CONTINUE AS RAIN. TIMING OF THE FRONT HAS BEEN
ONE OF THE ISSUES THE PAST FEW DAYS SO SNOW TOTALS VARIED BY AN
INCH OR TWO DEPENDING ON THE START TIME. SNOW FALL RATES DID NOT
PICK UP QUITE AS FAST OVERNIGHT SO A FEW LOCATIONS, SUCH AS
JUNEAU, DID NOT GET THE EARLY ADDITION TO STORM TOTAL SNOW.
HEAVIER SNOW FALL ALREADY OCCURRING AT YAKUTAT WITH THE CENTRAL
PANHANDLE RATES HITTING MAXIMUM LEVELS AROUND 7 TO 9 AM. THIS IS
WHEN HIGHEST OMEGA VALUES HIT DENDRITIC GROWTH ZONE. SNOWFALL
RATES OF 1 INCH PER HOURS ARE LIKELY DURING THIS PERIOD AND HAVE
ALREADY BEEN REPORTED AT YAKUTAT. THE TIMING OF THESE HEAVIER
RATES WILL CAUSES SOME ISSUES FOR THE MONDAY MORNING COMMUTE. AS
THE FRONT MOVES INLAND AND TEMPERATURES RISE SNOW WILL BEGIN TO
MIX WITH THEN TRANSITION TO MOSTLY RAIN FOR ALL BUT THE NORTHERN
PANHANDLE. BOTH GUSTAVUS AND HOONAH HAVE REACHED 34 F BY 4 AM, SO
EXPECT MORE RAIN THERE. FOR ZONE 17, 18, 19 AND 25 SNOW FALL
AMOUNTS IN THE 3 TO 6 INCH RANGE FOR TODAY WITH ADDITIONAL AMOUNTS
OF 1 TO 2 INCHES TONIGHT FOR 18, 19 AND 25. ELSEWHERE SNOW FALL
AMOUNTS IN THE 1 TO 3 INCH RANGE WITH MOSTLY RAIN TONIGHT.
AMOUNTS TONIGHT FOR LOCATIONS THAT ARE NOT ALL RAIN WILL BE
DEPENDENT ON VARIABLE SNOWFALL RATES AND DISTRIBUTION DUE TO
CONVECTIVE ATMOSPHERE AND TEMPERATURES HOVERING NEAR FREEZING
CAUSING MORE RAIN TO MIX IN.

GALE FORCE WINDS OVER THE AK GULF ALONG THE FRONT WILL DROP OFF
THIS MORNING AND SHIFT WEST. HIGH PRESSURE RIDGE BUILDING OVER
THE GULF WILL KEEP SMALL CRAFT WESTERLY WINDS THROUGH TONIGHT
WITH ANOTHER QUICK BURST OF GALES AS SHORT WAVE MOVES OVER THE N
GULF. INNER CHANNEL WINDS SHIFTED TO THE SOUTH OVERNIGHT AND HAVE
PICKED UP OR WILL SOON REACH SMALL CRAFT LEVELS. OVERLAND WINDS
ALSO GETTING GUSTY AS THE FRONT MOVES IN, THEN DROPPING OFF BY THE
EVENING AND SHIFTING TO THE WEST.

MODELS WERE IN GENERAL AGREEMENT AND HAD LITTLE CHANGE FROM
PREVIOUS FORECAST. NAM STILL MAIN MODEL CHOICE FOR PRESS AND
WINDS, ONLY MINOR CHANGES MADE TO THESE FIELDS. STILL SOME SPREAD
ON TIMING OF PRECIP SO KEPT WITH PREVIOUS FORECAST TIMING AND
PRECIP AMOUNTS. FORECAST CONFIDENCE IS AVERAGE.

.LONG TERM...SNOWFALL FROM TODAY'S FRONT WILL CONTINUE ON TUESDAY
AS SHOWER ACTIVITY, BUT SNOW RATES ARE NOT EXPECTED TO ADD MUCH TO
WHAT FALLS DURING THIS SHORT TERM FORECAST PERIOD. A COMBINATION
OF RISING SNOW LEVELS AND DIMINISHING POP WILL LIMIT ACCUMULATIONS
TO AROUND AN INCH OR LESS.

TURNING ATTENTION TO THE NEXT WEATHER EVENT...A FRONT WILL ENTER
THE GULF FROM THE SOUTHWEST OVERNIGHT TUESDAY AND MAKE ITS
APPROACH ON THE OUTER COAST LATE WEDNESDAY NIGHT. DEEP LAYER
SOUTHWESTERLY FLOW AND 1000-500MB THICKNESS VALUES SUGGEST THIS TO
BE PRIMARILY A RAIN EVENT. 1000-850 MB THICKNESS VALUES AND LOW
LEVEL OFFSHORE FLOW MARGINALLY SUPPORTIVE OF SNOW. SURFACE TEMPS
INDICATE SNOW. IN SUM, THERE IS STILL SOME SIGNIFICANT UNCERTAINTY
REGARDING WHETHER THIS WILL BE PRIMARILY A SNOW OR A RAIN EVENT.
FORECAST AS ISSUED THIS MORNING RETAINS CONTINUITY WITH PREVIOUS
SHIFT AND HAS SOME SIGNIFICANT SNOW ACCUMULATIONS, BUT AM NOT YET
CONVINCED. GIVEN THIS REPRESENTS DAY 4 OF THE FORECAST, THERE IS
TIME TO STUDY THE SITUATION AND LOOK AT LATER MODEL RUNS FOR MORE
CLARITY.

HAVE MUCH HIGHER CONFIDENCE IN PRE-FRONTAL WINDS THAT WILL PRECEDE
THE THURSDAY FRONT. 40 KT SOUTHEASTERLY GALES WILL SPREAD ACROSS
MOST OF THE EASTERN GULF WEDNESDAY AND WEDNESDAY NIGHT. WILL
LIKELY SEE STRONG WIND GUSTS ALONG THE OUTER COAST AS WELL. VERY
STRONG EASTERLY PRESSURE GRADIENT WILL INDUCE GALE OR NEAR GALE
FORCE WINDS WEDNESDAY NIGHT INTO THURSDAY OVER MOST OF THE INNER
CHANNELS AS WELL, AND THIS LOW LEVEL COLD AIR FROM CANADA MAY BE
THE SAVING GRACE FOR PRECIP ON THURSDAY TO FALL IN THE FORM OF
SNOW. WINDS AND PRECIP WILL WIND DOWN FRIDAY AS THE ASSOCIATED LOW
WEAKENS AND MOVE OUT OF THE GULF TO THE SOUTHEAST.

LONG RANGE MODEL GUIDANCE INDICATING THE POSSIBILITY OF ANOTHER
STRONG FRONT AFFECTING SOUTHEAST ALASKA DURING THE SECOND HALF OF
THE UPCOMING WEEKEND.

UPDATED THURSDAY AND THURSDAY NIGHT WITH A BLEND OF ECMWF AND
CANADIAN NH FOR PRESSURES. WINDS DERIVED FROM GFS22. POP AND QPF
A BLEND OF GFS22 AND CANADIAN NH. REMAINDER OF THE EXTENDED RANGE
FORECAST LARGELY UNCHANGED. OVERALL FORECAST CONFIDENCE IS
AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY UNTIL 3 PM AKST THIS AFTERNOON FOR
     AKZ018-019-025.
         WINTER WEATHER ADVISORY UNTIL 9 AM AKST THIS MORNING FOR AKZ017.
MARINE...GALE WARNING FOR PKZ041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-022-031>036-053.

&&

PRB/FRITSCH

VISIT US AT HTTP://WWW.WEATHER.GOV/JUNEAU

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
648 AM AKST MON DEC 14 2015

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0645 AM     SNOW             YAKUTAT                 59.54N 139.73W
12/14/2015  M4.5 INCH                           AK   NWS EMPLOYEE

            SNOW HAS CHANGED OVER TO A RAIN/SNOW MIX.

&&

RCL