Small Craft Advisory 181, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
555 AM AKST TUE FEB 22 2011

.SHORT TERM...SATELLITE IMAGERY THIS MORNING SHOWING INVERTED
TROUGH JUST THE WEST OF THE AK PANHANDLE, ARCTIC HIGH BUILDING
OVER THE YUKON AND HIGH PRESSURE RIDGE MOVING INTO THE WESTERN
GULF. LINE OF SHOWERS TRACKING TO THE SOUTHEAST OVER THE COASTAL
WATERS HAS REMAINED MOSTLY OFF SHORE AS SEEN ON RADAR. A FEW
ISOLATED SHOWERS MAY REACH THE SOUTHERN OUTER COAST THIS MORNING
BUT OVERALL THE REGION WILL REMAIN DRY. NORTHERLY GALE FORCE
WINDS OVER THE AK GULF AND COASTAL WATERS WITH GALES OVER THE
NORTHERN INNER CHANNELS. AS YUKON HIGH BUILDS WILL SEE INCREASE
IN OUTFLOW WINDS THROUGH THE DAY. OUTFLOW WINDS AT HAENKE ISLAND
NEAR YAKUTAT HAVE REACHED ADVY LEVELS GUSTS ALREADY. FELT WIND
ADVY WERE NOT NECESSARY FOR OTHER LOCATIONS DUE TO LIMITED SCOPE
OF THE HIGHER GUSTS BUT REGIONS SUCH AS SKAGWAY AND INTERIOR
PASSES NEAR JUNEAU WILL NEED TO BE MONITORED. OTHERWISE NORTHERLY
WINDS OVER THE PANHANDLE WILL BE LESS THAN 20 MPH. SKIES HAVE
BEEN PARTLY CLOUDY TO CLEAR THIS MORNING WITH MOSTLY SUNNY SKIES
EXPECTED THIS AFTERNOON AND TONIGHT, WITH A FEW HIGH CIRRUS
CLOUDS. AS ARCTIC AIR CONTINUES TO MOVE OVER THE PANHANDLE OVER
EXPECTING COLD OVER NIGHT TEMPS WITH LOWS IN THE TEENS TO SINGLE
DIGITS. THE COLD TEMPS ALONG WITH THE INCREASED WINDS WILL BRING
FREEZING SPRAY TO HEAVY FREEZING SPRAY THIS AFTERNOON THROUGH
TONIGHT.

 MODELS WERE IN GOOD CONSENSUS TODAY WITH THE NAM AND WRF SHOWING
THE BEST RESOLUTION OF OUTFLOW WINDS. FEW TO ANY CHANGES WERE
MADE TO THE CURRENT GRIDS. FORECAST CONFIDENCE IS ABOVE AVERAGE.

 &&

.LONG TERM...MODELS REMAIN IN VERY GOOD AGREEMENT DEPICTING A
WEAKENING INVERTED TROUGH JUST OFF THE COAST BEING SURROUNDED
FROM THE WEST, NORTH, AND EAST BY VERY STRONG SURFACE HIGH
PRESSURE AT THE START OF THE LONG RANGE FORECAST PERIOD. AS THE
VERY LARGE SURFACE HIGH COMPLEX MOVES SOUTH, IT DIVIDES INTO TWO
DISTINCT SURFACE CIRCULATIONS IN THE PROCESS OF DISPLACING THE
REMNANTS OF THE INVERTED TROUGH WHILE AT THE SAME TIME BEING
IMPINGED UPON FROM THE NORTH BY A DEVELOPING SHORTWAVE ASSOCIATED
WITH A VERY DEEP LOW IN THE BEAUFORT SEA AND ITS ASSOCIATED
FRONTAL BOUNDARY THAT EXTENDS SOUTHWEST INTO THE NORTH CENTRAL PACIFIC.
THE MUCH LARGER SURFACE HIGH CENTERED OVER THE SOUTHWEST GULF WILL
BLOCK WARM, MOIST ZONAL FLOW FROM ENTERING THE GULF FROM THE WEST
OR SOUTHWEST. THE SMALLER SURFACE HIGH LOCATED OVER BRITISH
COLUMBIA WILL PROVIDE FOR A STRONG NORTHEASTERLY PRESSURE GRADIENT
OVER THE PANHANDLE WHICH WILL GENERATE COLD NORTHEASTERLY OUTFLOW
WINDS THROUGH THURSDAY AFTERNOON WITH THE REGION OF MAXIMUM
NORTHEAST WINDS MIGRATING FROM JUST EAST OF YAKUTAT TO MISTY
FJORDS ALONG THE COAST MOUNTAINS THROUGH THAT TIME FRAME.

VERY LITTLE POP IN THE LONG RANGE FORECAST PERIOD WITH THE MAIN
EVENT OVER THE NEXT WEEK BEING THE SHORT WAVE IMPINGING ON THE
SURFACE HIGH FROM THE NORTH. A WEAK SURFACE LOW IS FORECAST TO
DEVELOP ALONG THE FRONTAL BOUNDARY VICINITY CAPE SUCKLING IN THE
EARLY MORNING HOURS OF SATURDAY WITH FRONTAL PRECIPITATION
BEGINNING IN YAKUTAT FRIDAY NIGHT AND REACHING THE SOUTHERN ZONES
BY SATURDAY MORNING. AM EXPECTING A SNOW EVENT THAT CHANGES TO
RAIN ALONG THE OUTER COAST BY SATURDAY AFTERNOON. WILL LIKELY SEE
A RAIN-SNOW MIX OVER THE MIDDLE SECTION OF THE PANHANDLE, TO
INCLUDE ANGOON AND POINTS SOUTH OF FREDERICK SOUND. CURRENTLY, AM
EXCEPTING AN ALL SNOW EVENT FOR JUNEAU AND POINTS NORTH, TO
INCLUDE GUSTAVUS, HAINES, AND SKAGWAY.

SOME LOW LEVEL WARM AIR ADVECTION WILL BE ASSOCIATED WITH THIS
PRECIPITATION EVENT, BUT THE ARCTIC FRONT IS EXPECTED TO DROP BACK
SOUTH SOON AFTER THE FRONT CLEAR THE AREA TO THE SOUTH.

FORECAST CONFIDENCE IS SLIGHTLY ABOVE AVERAGE THROUGH THE WEEKEND.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND ADVISORY UNTIL 6 AM AKST WEDNESDAY FOR AKZ017.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ011>013-031.
         GALE WARNING FOR PKZ011>013-022-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ021-031>036.

&&

PRB/FRITSCH