Storm Warning 18, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
557 AM AKST FRI FEB 25 2011

.SHORT TERM...TODAY AND TONIGHT WILL MARK A CHANGE IN THE
WEATHER OVER SOUTHEAST ALASKA. BANDS OF LOW TO MID LEVEL CLOUDS
ARE ALREADY STREAMING OVER THE PANHANDLE FROM NORTH TO SOUTH WITH
PRE- DAWN CEILINGS DOWN TO 3000 FEET OVER SOME LOCATIONS.
OVERNIGHT TEMPERATURES ARE NOT QUITE AS COLD AS LAST NIGHT WITH
VALUES RANGING FROM 2 DEGREES IN THE MENDENHALL VALLEY TO 36 IN
SITKA. STILL NOT SEEING EVIDENCE OF CYCLOGENESIS IN THE FAR
NORTHERN GULF NOR IS IT EXPECTED UNTIL LATE THIS EVENING...BUT
THE ASSOCIATED BAROCLINIC CLOUD SHIELD EXTENDS FROM JUST WEST OF
YAKUTAT SSW ACROSS BRISTOL BAY AND OVER THE CENTRAL ALEUTIANS
WITH PRECIPITATION BEING REPORTED AT STATIONS ALONG THIS PATH.

 THE TWO MAIN ISSUES DURING THE SHORT RANGE FORECAST PERIOD HAVE
TO DO WITH THE TRACK OF THE DEVELOPING LOW AND TIMING THE ARRIVAL
OF PRECIPITATION RELATIVE TO THE ARRIVAL OF THE ASSOCIATED WARM
AIR.  THE POP FIELD IS VERY SPOTTY OWING TO THE FRAGMENTED NATURE
OF THIS FRONT...WHICH IS NOT HOLDING UP WELL AS IT MAKES ITS WAY
OVER THE TOP OF THE SURFACE HIGH LOCATED IN THE CENTRAL GULF. FOR
THOSE LOCATIONS WHERE PRECIP BEGINS BEFORE ABOUT NOON...THE EVENT
WILL BEGIN AS SNOW...THEN LIKELY CHANGE OVER TO A RAIN-SNOW MIX
OR EVEN STRAIGHT RAIN BY LATE THIS AFTERNOON IN CONJUNCTION WITH
DAYTIME HIGH TEMPS. PRECIP TYPE WILL THEN TRANSITION BACK TO
STRAIGHT SNOW FOR LOCATIONS NORTH OF SUMNER STRAIT AND EAST OF
CHATHAM STRAIT THIS EVENING. QPF VALUES ARE NOT TOO IMPRESSIVE.
THIS COMBINED WITH THE FRAGMENTED POP FIELD WILL LIMIT SNOW
ACCUMULATIONS TO 2 INCHES OR LESS.

 REGARDING THE TRACK OF THE LOW...THIS SYSTEM WILL BE FORMING IN
AN UNUSUAL LOCATION AND HAVE AN EQUALLY UNUSUAL TRACK...FORMING
VICINITY YAKUTAT BAY AND TRACKING TO THE SOUTHEAST. RESULTANT
PRESSURE CONTOURS WILL PRODUCE A FAIRLY STRONG NORTHWEST WIND
OVER THE FAR NORTHEAST GULF. HAVE ISSUED A GALE WARNING FOR CROSS
SOUND AND ICY STRAIT IN RESPONSE TO THIS. ALSO AM EXPECTING WINDY
WEST TO NORTHWEST CONDITIONS IN SITKA TONIGHT AS WELL.

 USED NAM FOR UPDATES TOT HE SHORT TERM FORECAST. CONFIDENCE ONLY
AVERAGE DUE TO THE VERY SPOTTY NATURE OF THE POP FIELD.

 &&

 .LONG TERM...A RETURN TO DRY, COLD, AND WINDY CONDITIONS ARE IN
THE CARDS FOR NEXT WEEK AS AN OMEGA BLOCK RIDGE BUILDS TO OUR
WEST. AT THE SURFACE, THE REMAINS OF THE SYSTEM THAT WILL MOVE
THROUGH THE AREA FRI NIGHT AND SAT WILL CONTINUE TO HEAD SOUTH
INTO SUNDAY BEFORE SLOWING DOWN OVER DIXON ENTRANCE AND NEARLY
STALLING OVER THE QUEEN CHARLOTTE ISLANDS MONDAY. BEHIND IT THE
NORTHERLY PRESSURE GRADIENT WILL BUILD AS A 1040 MB HIGH BUILDS
INTO THE YUKON. OUTFLOW WINDS WILL START UP AS EARLY AS SAT NIGHT
NEAR YAKUTAT AND SPREAD OVER THE REST OF THE AREA BY SUNDAY.

 THE STRONGEST WINDS AND LOWEST TEMPS WILL NOT BE UNTIL SUN NIGHT
AND MON AS THE HIGH IN THE YUKON REACHES ITS PEAK. PRESSURE
GRADIENTS ARE FORECAST TO BE AS HIGH AS 13 MB BETWEEN PAJN AND
PAGY, AND 20 MB BETWEEN CYXY AND PAYA. AS SUCH I AM EXPECTED AT
LEAST GALE FORCE WINDS IN LYNN CANAL, STEPHENS PASSAGE, AND
GLACIER BAY ON MONDAY AND WITH THE COLDER TEMPS SOME FREEZING
SPRAY IS NOT OUT OF THE QUESTIONS IN MOST OF THE INNER CHANNELS.
THE USUAL OUTFLOW AREAS MAY BE INTERESTING ON MONDAY AND THERE IS
THE POSSIBILITY OF A MOUNTAIN WAVE EVENT FOR DOWNTOWN JUNEAU AND
DOUGLAS AS WELL. THE ONLY PROBLEM IS THAT NOT ALL THE INGREDIENTS
WILL BE PRESENT FOR A TAKU EVENT. WE WILL HAVE THE INVERSION, AND
THE CROSS BARRIER FLOW WILL BE THERE AS WELL, BUT THE CRITICAL
LEVEL IS NOT THAT WELL DEVELOPED OR NON-EXISTENT. FORECAST
SOUNDINGS SHOW AN AREA OF DIMINISHING WIND INTENSITY JUST ABOVE
THE CROSS BARRIER FLOW FOLLOWED BY AN INCREASE IN SPEED AT ABOUT
500 MB BUT, THERE IS NO CHANGE IN DIRECTION. STILL THE CBF WILL
BE BLOWING AT ABOUT 50 TO 70 KT OVER THOSE RIDGES SO IT STILL
BEARS WATCHING.

 TEMPS WILL ALSO BE FALLING EARLY NEXT WEEK AS THE ARCTIC AIR
RUSHES IN. LOWS WILL BE APPROACHING SINGLE DIGITS ABOVE AND BELOW
ZERO IN MOST NORTHERN LOCATIONS WITH TEENS FOR HIGHS. LATER NEXT
WEEK BRINGS A BIT OF A WARM UP AS THE OUTFLOW WEAKENS, BUT THE
DRY AND CLEAR CONDITIONS CONTINUE.

 MODEL AGREEMENT WAS STILL VERY GOOD TONIGHT WITH ONLY MINOR
DIFFERENCES NOTED BETWEEN THEM. REFRESHED THE MID RANGE FORECAST
WITH A BIT OF THE NAM TONIGHT.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ021-022-043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ012-031>036-041-042.

&&

FRITSCH/EAL