Small Craft Advisory 848, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
609 AM AKST TUE DEC 20 2011

.SHORT TERM...SOME LEFT OVER SHOWER ACTIVITY FROM A LOW THAT
CAME ASHORE LAST NIGHT OVER THE SOUTHERN PANHANDLE AND IS NOW
WELL INTO BRITISH COLUMBIA. SNOW SHOWERS OVERNIGHT IN YAKUTAT
WITH A BRIEF PERIOD OF FREEZING RAIN. RAIN SHOWERS WITH SOME SNOW
MIXED IN AT TIMES IN JUNEAU. RAINS SHOWERS OVER KLAWOCK AND
KETCHIKAN. SHOWER ACTIVITY WILL DIMINISH THROUGH THE DAY AS A
RIDGE OVER THE GULF AMPLIFIES AND MOVES TO THE EAST. THIS WILL
ALSO ELIMINATE THE REMAINING WESTERLY GRADIENT OVER THE SOUTHERN
PANHANDLE AND PRODUCE A WEAK SOUTHERLY GRADIENT OVER ALL OF
SOUTHEAST ALASKA BY THIS AFTERNOON. SOME BREAKS IN THE CLOUDS ARE
EXPECTED TODAY AND SATELLITE IMAGERY IS SHOWING THE MID TO HIGH
LEVEL CLOUDS CLEARING TO THE EAST. NO MAJOR SUN BREAKS THOUGH, SO
TEMPERATURES WILL BE COMPARABLE TO YESTERDAY WITH HIGHS RANGING
FROM THE LOW TO MID 30S UP NORTH AND OVER THE INNER CHANNELS TO
THE LOW 40S ALONG THE OUTER COAST SOUTH OF CAPE FAIRWEATHER AND
OVER THE SOUTHERN ZONES.

 A FRONT WILL APPROACH THE PANHANDLE FROM THE WEST TONIGHT. FIRST
MANIFESTATION OF THIS WILL BE A STRENGTHENING OF THE SOUTHERLY
PRESSURE GRADIENT, PARTICULARLY OVER THE NORTHERN HALF OF THE
PANHANDLE. HAVE WINDS STEADILY INCREASING OVER THE INNER CHANNELS
NORTH OF FREDERICK SOUND, PRIMARILY FOR THE TONIGHT PERIOD, WITH
SMALL CRAFT CONDITIONS FOR ALL INNER CHANNELS NORTH OF FREDERICK
SOUND AND A SOUTHERLY GALE OVER NORTHERN LYNN CANAL. ALSO HAVE
WINDS INCREASING STEADILY IN HAINES AND SKAGWAY WITH A STRONG
WIND HEADLINE FOR SKAGWAY LATE TONIGHT THAT EXTENDS INTO THE LONG
RANGE PERIOD. HAVE SOUTHEAST WINDS 10 TO 20 MPH IN THE JUNEAU
ZONE, BUT WOULD NOT BE TOO SURPRISED TO SEE GUSTS TO 35 MPH
DOWNTOWN JUNEAU OVERNIGHT TONIGHT.

 SHOWER ACTIVITY WILL GIVE WAY TO RAIN AND SNOW AS THE FRONT
APPROACHES FROM THE WEST. HAVE CATEGORICAL POPS AS FAR EAST AS
YAKUTAT BY THE END OF THE TONIGHT PERIOD WITH 1 TO 3 INCHES OF
SNOW ACCUMULATION. OVERNIGHT LOWS AND SNOW LEVEL FOR ZONE 17 WERE
A PARTICULAR CHALLENGE TONIGHT. SOME OF THE MODEL GUIDANCE
SUGGESTED LOW LEVEL WARM AIR ADVECTION WITH TEMPERATURES RISING
THROUGH THE NIGHT AND NO CHANCE OF SNOW. OPTED FOR AN OVERNIGHT
LOW THAT WILL SUPPORT ACCUMULATING SNOW, BUT ONLY BARELY. BELIEVE
WHEN EASTERLY WINDS IN YAKUTAT VEER TO THE SOUTHEAST, SNOW WILL
CHANGE TO RAIN AND THAT WILL BE THE END OF IT.

 USED A BLEND OF ECMWF AND GFS FOR PRESSURE AND POPS. ADJUSTED
RESULTANT WIND FIELD WITH NAM IN ORDER TO CAPTURE SMALLER SCALE
DETAILS AND A BARRIER JET THAT WILL SET UP WEST OF ICY BAY IN
COASTAL MARINE ZONE 52 LATE TONIGHT. WINDS OVER NORTHERN INNER
CHANNELS AS WELL AS HAINES AND SKAGWAY HEAVILY MODIFIED IN ORDER
TO ACCOUNT FOR EXPECTED SOUTHERLY PRESSURE GRADIENT. FORECAST
CONFIDENCE IS AVERAGE.

.LONG TERM...A VERY TRICKY FORECAST IN THE MID-RANGE AS THE GULF
WILL REMAIN ACTIVE WITH WEATHER SYSTEMS MOVING INTO THE GULF FROM
THE SOUTHWEST THROUGH THE END OF THE WEEK. THE MODELS AGREEMENT
HAVE NOT BEEN THAT GREAT BUT THE PAST FEW RUNS THERE IS SOME
AGREEMENT THROUGH THURSDAY WITH MOST GLOBAL MODELS TRENDING
TOWARDS THE GFS. AFTER THURSDAY THERE STILL IS A LOT OF
DISAGREEMENT SO THERE IS LOW FORECASTER CONFIDENCE AFTER THURSDAY
WITH ABOUT AVERAGE FOR WED AND THURSDAY. USED A BLEND OF THE
PREVIOUS FORECAST AND THE GFS THROUGH THURSDAY THEN BLENDED IN THE
NEW HPC TO HELP WITH THE MODEL UNCERTAINTY.

AT THE START OF THE LONG RANGE PERIOD A WEATHER FRONT WILL BE DRIFTING
ACROSS THE NORTHERN GULF AND OVER THE NORTHERN HALF OF THE
PANHANDLE ON WED. THE P-TYPE WILL BE MIXED OVER THE NORTHERN GULF
BUT AS THE WINDS VEER AROUND TO THE SE IT WILL SWITCH TO RAIN.
THIS WILL NOT LAST TO LONG AS THE COLD FRONT WILL PUSH EAST OF
PAYA AND SCATTERED SNOW SHOWERS WILL MOVE OVER THE AREA. THE REST
OF THE NORTH HALF OF THE PANHANDLE WILL SEE MIXED PRECIP EARLY WED
MORNING BUT AS THE SURFACE RIDGE SHARPENS UP THE SOUTHERN WINDS
WILL INCREASE AND CHANGE EVERY THING OVER TO RAIN. THERE IS A
CHANCE THAT THE HIGHWAYS WILL HOLD ON TO THE COLD AIR AND GET
SIGNIFICANT SNOW...WILL NEED KEEP AN EYE ON THIS. THE WINDS WILL
INCREASE FROM THE SOUTH AS THE FRONT DRIFTS OVER THE AREA AND
GENERATE GALES OVER N/S CHANNELS BY WED MORNING BUT THEN DIMINISH
AS THE PRESSURE GRADIENT WEAKENS. THE LAND AREAS WILL SEE GUSTY
WINDS FROM THE SOUTH THROUGH WED AND STRONG WIND NEAR PAGY. THE
SOUTHERN AREAS WILL BE ON THE DRY SIDE WED MORNING BUT ONSHORE
FLOW WILL INCREASE THROUGH THE DAY AS A STRONG LOW BEGINS TO LIFT
OUT OF THE NORTH PACIFIC. RAIN WILL DEVELOP THROUGH THE AFTERNOON
AS THE WARM FRONT LIFTS NORTH.

THE LOW MENTIONED ABOVE WILL BE A BIG WEATHER MAKER FROM WED NIGHT
THROUGH THURSDAY NIGHT. THE LOW WILL SLOWLY LIFT NORTH TO BE OVER
THE EASTERN GULF BY THURSDAY MORNING AS THE UPPER LEVEL TROF
PHASES WITH THE NORTHERN STREAM. AS THE WARM FRONT LIFTS NORTH IT
WILL INTERACT WITH SOME COLDER AIR IN THE BOUNDARY LAYER FROM LOW
LEVEL EASTERLY FLOW. THIS MAY PRODUCE HEAVY SNOW OVER THE NORTHERN
THIRD ALONG WITH SOME AREAS OVER THE CENTRAL PORTIONS FROM WED
NIGHT THROUGH THURSDAY. THE UPPER LEVEL FLOW WILL BE FROM THE SW
AND THE SURFCE WINDS WILL BE FROM THE ENE. THE TRICKY PART IS THE
850MB WINDS...IF THEY REMAIN OUT OF THE EAST THEN THERE WILL BE
MORE SNOW OVER THE NORTHCENTRAL AREAS IF NOT THEN IT WILL CHANGE
OVER TO RAIN. THE WINDS WILL BACK AROUND TO THE NORTH WED EVENING OVER
THE NORTHERN HALF OF THE PANHANDLE AND INCREASE TO SMALL CRAFTS BY
THURSDAY WITH LOCALLY HIGHER GUSTS OVER LAND NEAR INTERIOR PASSES.
THE SOUTHERN MARINE AREAS WILL SEE THE WINDS INCREASE TO GALES
THROUGH WED NIGHT THEN AS THE LOW MOVES INTO THE EASTERN GULF
INCREASE TO STORM FORCE THURSDAY. THE SOUTHERN LAND AREAS WILL SEE
THE WINDS INCREASE FROM THE E/SE WED NIGHT AND BEGIN TO GUST TO 40
MPH. THESES GUSTS WILL INCREASE THROUGH THURSDAY AS THE PRESSURE
GRADIENT TIGHTENS ALONG WITH A VERY STRONG LLJ OF 80KT. THIS MAY
PRODUCE GUSTS TO 60 MPH AND WILL NEED TO KEEP AN EYE ON THIS ALSO.
THE WINDS WILL REMAIN OUT OF THE NE OVER ZONE 29 AND THE HYDER
AREA COULD SEE SIGNIFICANT AMOUNT OF SNOW THROUGH THIS EVENT.

THE LOW WILL TRACK RIGHT THROUGH THE CENTRAL PANHANDLE AND OVER
PAJN THURSDAY NIGHT. THIS WILL TAPPER OFF MOST OF THE STEADY
PRECIP AND THE WINDS WILL RELAX BUT BACK AROUND TO THE SOUTH LATE
THURSDAY NIGHT. THE OVERALL TREND FOR LATE WEEK AND THIS WEEKEND
IT FOR AN ACTIVE WEATHER PATTERN FOR THE GULF AND KEEP THE
PANHANDLE ABOVE AVERAGE PRECIP AND ABOUT NORMAL FOR TEMPS. BUT
THERE IS LOW FORECASTER CONFIDENCE FROM FRIDAY THROUGH NEXT TUE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND LATE TONIGHT FOR AKZ018.
MARINE...GALE WARNING FOR PKZ012-022-041-042-052.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-031>033-035-036-043-051.

&&

FRITSCH/ABJ