Small Craft Advisory 549, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
617 AM AKDT WED SEP 26 2012

.SHORT TERM...SHORT RANGE FORECAST PERIOD FEATURES THE SECOND
AND STRONGER OF TWO FRONTS TO AFFECT SOUTHEAST ALASKA IN AS MANY
DAYS. SATELLITE LOOP IMAGERY OVER NIGHT HAS SHOWN A VERY WELL
DEFINED CIRCULATION TRACKING INTO THE SOUTHWEST GULF WITH A
BAROCLINIC CLOUD SHIELD EXTENDING ALL THE WAY ACROSS THE GULF.
NORTH OF THE CLOUD SHIELD, SHOWER ACTIVITY HAS PRODUCED AT LEAST
ONE THUNDERSTORM IN THE EARLY MORNING HOURS. HAVE INCLUDED
ISOLATED THUNDERSTORMS IN THE MARINE FORECAST FOR COAST WATERS
FROM CAPE FAIRWEATHER TO CAPE SUCKLING THROUGH THE MORNING. THE
LOW WILL CONTINUE TO DEEPEN THROUGH THE DAY TODAY AS IT TRACKS
NORTH ALONG 150W. PRE-FRONTAL WINDS WILL INCREASE AND PEAK RIGHT
AROUND THE TIME THE FRONT TRACKS OVER THE COASTAL WATERS. HAVE
EASTERLY 60 KT WINDS FOR THIS EVENING IN MARINE ZONE 52 BETWEEN
ICY BAY AND CAPE SUCKLING WITH 45 KT GALES EXTENDING DOWN TO NEAR
THE DIXON ENTRANCE. ALSO HAVE INCLUDED A STORM WARNING FOR
CLARENCE STRAIT FOR TONIGHT. GALES AND SMALL CRAFT ADVISORIES
ELSEWHERE FOR THE INNER CHANNELS. LOW LEVEL JET STRENGTH RIGHT
AROUND 80 KTS, SO HAVE HIGH CONFIDENCE IN THESE MARINE WINDS. LOW
LEVEL JET ALSO INDICATING A SECOND WRAP OF SIMILAR STRENGTH BUT
THAT FEATURE NOT EXPECTED TO IMPACT THE LOCAL FORECAST AREA
BEFORE THE SYSTEM AS A WHOLE WEAKENS. AS THE FRONT COMES ASHORE,
IT WILL NOT STALL ON THE OUTER COAST AS IS OFTEN THE CASE. LOW
LEVEL JET WINDS WILL BE SUFFICIENT TO CAUSE WIDESPREAD GUSTS IN
EXCESS OF 40 MPH TONIGHT SOUTH OF ICY STRAIT, SO HAVE STRONG WIND
HEADLINES IN THE PUBLIC ZONES FORECAST.

 GRADIENT FOR THE NORTHERN INNER CHANNELS PRESENTED ONE OF THE
GREATER CHALLENGES IN PUTTING TOGETHER THE SHORT TERM FORECAST.
GRADIENT IS EXPECTED TO SHIFT REPEATEDLY, WITH WINDS IN LYNN
CANAL GOING FROM SOUTH 25 TO 30 KT THIS MORNING TO NORTH LATER
THIS AFTERNOON. LATER TONIGHT, WINDS WILL SHIFT BACK TO THE THE
SOUTH AFTER THE FRONT HAS COME ASHORE AND WIND SPEEDS WILL
INCREASE TO GALE FORCE BY THE END OF THE NIGHT.

 PRECIP ASSOCIATED WITH THE FRONT WILL BE HEAVY AT TIMES FOR
LARGE PORTIONS OF THE PANHANDLE, PARTICULARLY OVER NIGHT TONIGHT
WITH 24 HOUR TOTALS RANGING FROM 1 TO NEARLY 3 INCHES. EXPECT
RAPID RISES ON SMALLER CREEKS AND STREAMS IN RESPONSE TO HEAVY
RAIN AND BE ALERT FOR POSSIBLE MUDSLIDES.

 USED A BLEND OF NAM AND ECMWF FOR UPDATES TO PRESSURE AND WIND.
BLENDED NAM AND GEM FOR POP AND QPF FIELDS. FORECAST CONFIDENCE
IS AVERAGE.

.LONG TERM...THE FORECAST MODELS ARE IN GOOD AGREEMENT IN THE MID
RANGE WITH THE LOW MENTIONED ABOVE SLOWLY DRIFTING TO THE
NORTHEAST AND FILLING. A SURFACE RIDGE WILL REMAIN OVER SE AK
THROUGH THE END OF THE WEEK TO MODERATE WINDS FROM THE SOUTH OVER
THE INNER CHANNELS. FOR THE WEEKEND INTO EARLY NEXT WEEK THERE IS
LOW FORECASTER CONFIDENCE AS THERE IS LARGE SPREADS IN THE
ENSEMBLES MEANS ALONG WITH POOR RUN TO RUN CONSISTENCY IN THE
DETERMINISTIC MODELS. SO WITH THAT SAID THERE WAS NO CHANGE IN THE
FORECAST FROM DAY 6 THROUGH 7. IN THE MID RANGE THE NAM/EC HAVE
BEEN PERFORMING VERY WELL SO USED A BLEND OF THE TWO THROUGH DAY 4.
DID A USED A 50/50 MIX OF GFS/EC ON DAY 5 AS THE TWO MODELS HAVE
AGREED SOME ON THE TRACK OF A LOW THAT WILL LIFT OUT OF THE NORTH
PACIFIC AND OVER THE PANHANDLE OVER THE WEEKEND BUT THERE IS STILL
LOW CONFIDENCE.

AT THE START OF THE LONG TERM PERIOD THE STRONG WEATHER FRONT
EXTENDING FROM THE PARENT LOW NEAR KODIAK WILL BE STILL OVER THE
FAR SOUTHERN AREAS BUT HAVE PUSHED EAST OVER THE REST OF THE
FORECAST AREA. A SURFACE RIDGE WILL BUILD OVER THE FORECAST AREA
AND SEND A STRONG SOUTHERLY PUSH OF WINDS OVER THE INNER CHANNELS
THROUGH THURSDAY MORNING. SO WITH THAT SAID...INCREASE THE WINDS
TO GALES OVER LYNN CANAL AND SMALL CRAFTS OVER THE REST OF THE
INNER CHANNELS. OVERLAND THERE WILL STILL BE SOME GUSTY WINDS IN
THE EARLY MORNING BUT THEY WILL DECREASE THROUGH THE DAY. THE
EXCEPTION TO THIS WILL BE NEAR SKAGWAY WHERE STRONG GUSTS TO 45
MPH WILL DEVELOP AS THE RIDGE BUILDS ONCE THE FRONT DRIFTS EAST
IN THE MORNING BUT THEY WILL DIMINISH SOME THROUGH THE AFTERNOON.
THE GALES AND SMALL CRAFT WINDS WILL RELAX SOME THROUGH THURSDAY
NIGHT BUT SMALL CRAFT WINDS WILL PERSIST OVER LYNN CANAL THROUGH
THE END OF THE WEEK WITH 15 TO 20 KT FROM THE SOUTH OVER THE REST
OF THE INSIDE WATERS. SEA HEIGHT OVER THE GULF WILL REMAIN IN THE
MID 20 FEET RANGE BUT WILL SLOWLY SUBSIDE THROUGH THURSDAY NIGHT.

SHOWERS WILL CONTINUE ACROSS MOST OF THE FORECAST AREA THROUGH DAY
FOUR WITH THE UPPER LEVEL LOW OVER THE WESTERN GULF SPREADS SHORT
WAVE TROF ACROSS THE AREA ALONG WITH DEEP ONSHORE FLOW. THERE DOES
SEEM TO BE ANY BREAK IN THE PRECIP THROUGH THE WEEKEND BUT THE
TREND FOR DRIER AND BREAKS IN THE CLOUD COVER TO DEVELOP EARLY
NEXT WEEK STILL SEEMS ON TRACK BUT THE CONFIDENCE IS ON THE LOW SIDE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM THIS EVENING THROUGH THURSDAY MORNING FOR
     AKZ025-026-028.
         STRONG WIND FROM THIS EVENING THROUGH LATE TONIGHT FOR AKZ027.
         STRONG WIND FROM THIS EVENING THROUGH LATE TONIGHT FOR AKZ024.
         STRONG WIND FROM THIS EVENING THROUGH LATE TONIGHT FOR AKZ017-
     021>023.
MARINE...STORM WARNING FOR PKZ036-052.
         GALE WARNING FOR PKZ012-013-021-022-033>035-041>043-051-053.
         SMALL CRAFT ADVISORY FOR PKZ011-031-032.

&&

FRITSCH/ABJ