Winter Storm in Alaska, January 21 to 22, 2016

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
323 PM AKST WED JAN 20 2016

.SHORT TERM...972 MB LOW MOVES NORTHWARD INTO THE SOUTH CENTRAL AK
GULF THIS EVENING. THE ASSOCIATED FRONT WILL MOVE OVER THE
PANHANDLE AND AK GULF THIS EVENING WITH INCREASING WINDS AND
RAIN. 925 MB LOW LEVEL JET CORE OF 60 KTS ORIENTED ALONG THE
COASTAL WATERS, BIT FURTHER OFFSHORE THAN LOWS THE LAST FEW DAYS.
STORM FORCE WINDS WILL DEVELOP THIS EVENING UNDER THE JET CORE,
BUT FOR NOW ONLY EXPECT THE STORM FORCE WINDS TO HI THE SOUTHERN
GULF. AS THE LOW MOVES NORTHWARD IT AND ITS FRONT WILL WEAKEN SO
WINDS ONLY EXPECT TO REACH MAX GALES FOR THE REST OF THE GULF. AS
THE LOW CENTER IS ALSO FURTHER OFF SHORE EXPECT STRONG WINDS FOR
THE SOUTH COASTAL PANHANDLE BUT GUSTS ONLY NEAT 40 TO 45 MPH.
INNER CHANNEL WINDS WILL PICK UP TO SOUTHERN GALES FOR LOCATIONS
SOUTH OF FREDERICK SOUND. EASTERLY TO NORTHEASTERLY SMALL CRAFT
WINDS FOR THE CENTRAL INNER CHANNELS BETWEEN HIGH PRESSURE OVER
CANADA AND THE GULF LOW. NORTHERLY SMALL CRAFT WINDS OVER THE
NORTHERN INNER CHANNELS DEVELOPING LATER TONIGHT DUE TO THE MORE
NORTHERLY GRADIENT. SKAGWAY STRONG WINDS SHOULD RESULT MORE FORM
THERMAL GRADIENT WITH SINGLE DIGIT TEMPERATURES OVER THE YUKON
AND LOW TO MID 30S OVER SKAGWAY ALLOWING COLDER AIR MASS TO
ACCELERATE AS IT MOVES DOWNSLOPE. FOR JUNEAU SET UP FOR WEAK
MOUNTAIN WAVE EVENT NEAR DOWNTOWN JUNEAU AND DOUGLAS THIS EVENING.
EXPECT GOOD CROSS BARRIER FLOW, 850MB INVERSION IS FAIR WITH ONLY
CRITICAL LEVEL NOT SHOWING THE OPTIMAL DIRECTION CHANGE BUT ONLY
SPEED CHANGE AT 500 MB. SO FOR NOW ONLY EXPECT THESE GUSTS TO HIT
40 TO 45 MPH.

WARM SOUTHERLY FLOW WILL KEEP PRECIP AS RAIN FOR MOST OF THE
REGION WITH THE EXCEPTION OF THE FAR NORTHERN PANHANDLE. HAINES
AND SKAGWAY WILL ALSO WARM UP ENOUGH THURSDAY TO HAVE MORE RAIN
MIX IN THE THE SNOW. KLONDIKE AND HAINES HIGHWAYS STILL COLD
ENOUGH FOR ALL SNOW BUT ONLY EXPECT ACCUMULATIONS UPWARDS OF 2 TO
4 INCHES AT THESE HIGHER ELEVATIONS.

THURSDAY WILL HAVE A DIMINISHING TREND FOR BOTH WIND AND PRECIP AS
THE LOW AND FRONT PULL NORTHWARD AND WEAKEN. TEMPERATURES WILL
DROP SLIGHTLY TONIGHT BUT WILL RISE LATE TONIGHT AND THEN THROUGH
THE DAY.

NAM INITIALIZED WELL COMPARING SURFACE FEATURES ON IR SATELLITE.
ECMWF WAS A SLIGHT OUTLIER COMPARED TO THE NAM/GFS/GEM FOR
DEPICTION OF THE LOW CENTER BY THURSDAY AFTERNOON. HOWEVER THE
12Z RUNS WERE STILL VERY CLOSE TO INHERITED GRIDS. USED SOME 12Z
NAM TO REFRESH WIND FIELDS OVER THE GULF BUT OVERALL CHANGES WERE
VERY MINOR. STARTING TO SEE SOME WAVE DEVELOPMENT ALONG THE FRONT
OFF THE COAST OF HAIDA GWAII NOT PICKED UP BY EARLIER MODELS BUT
FOR NOW NOT EXPECTING THIS TO CAUSE MUCH IMPACT. FORECAST
CONFIDENCE IS AVERAGE.

.LONG TERM...LONG TERM FORECAST PERIOD BEGINS WITH AN OCCLUDED LOW
OVER THE WESTERN GULF WITH ITS ASSOCIATED FRONT EXTENDING EAST
ACROSS THE NORTHERN GULF, THEN SOUTHEAST ACROSS THE PANHANDLE. BY
SATURDAY, THE LOW WILL REMAIN OVER THE WESTERN GULF BUT THE FRONT
WILL BE REPLACED BY A SHORT WAVE TROUGH. IN FACT, THE ENTIRE
EXTENDED RANGE FORECAST PERIOD IS FILLED WITH A CONTINUAL SERIES
OF LOWS OVER THE CENTRAL OR WESTERN GULF WITH THEIR FRONTS OR
TROUGHS ROTATING PRECIPITATION NORTH OVER THE EASTERN GULF AND
SOUTHEAST ALASKA.

DEEP LAYER SOUTHERLY FLOW PROMISES NO COLD LOW LEVEL AIR, SO
PRECIP FOR THE UPCOMING WEEK WILL BE PRIMARILY IN THE FORM OF RAIN
WITH SNOW CONFINED TO THE FAR NORTHERN INNER CHANNELS, THE
HIGHWAYS, AND POSSIBLY HYDER.

EACH SUCCESSIVE FRONT/TROUGH WILL BRING HIGH END SMALL CRAFT TO
GALE FORCE WINDS TO THE EASTERN GULF AND COASTAL MARINE ZONES.
HIGH SEAS 8 FEET OR GREATER FOR THE ENTIRETY OF THE UPCOMING WEEK
AS WELL. PERIODS OF SMALL CRAFT WINDS OVER THE INNER CHANNELS AS
WELL, WITH THE STRONGER WINDS COINCIDING WITH FRONTS OR TROUGHS
THAT PASS BY CLOSER TO THE OUTER COAST.

UPDATED THE EARLY PORTION OF THE EXTENDED RANGE WITH A NAM/EC
BLEND FOR WIND DIRECTIONS OVER THE GULF. RETAINED INHERITED WIND
SPEEDS. REMAINDER OF THE FORECAST REMAINS ON TRACK IN THIS FAIRLY
STABLE PATTERN, SO NO SIGNIFICANT CHANGES AFTER FRIDAY
AFTERNOON/EVENING. OVERALL FORECAST CONFIDENCE IS AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND THROUGH THURSDAY MORNING FOR AKZ027.
         STRONG WIND FROM 9 PM AKST THIS EVENING THROUGH THURSDAY MORNING
     FOR AKZ025.
         STRONG WIND FROM 9 PM AKST THIS EVENING THROUGH THURSDAY
     AFTERNOON FOR AKZ018.
MARINE...STORM WARNING FOR PKZ041-042.
         GALE WARNING FOR PKZ022-033>036-043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011>013-021-031-032-053.

&&

PRB/FRITSCH

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