Small Craft Advisory 108, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
2 PM AKST TUE FEB 7 2012

.SHORT TERM...SATELLITE IMAGERY THIS AFTERNOON SHOWING A 963 MB
LOW IN THE NORTH PACIFIC TRACKING NORTHWARD TOWARD THE WESTERN AK
GULF. THIS LOW WILL MOVE TOWARD THE AK PENINSULA THROUGH
WEDNESDAY. THE FRONT ASSOCIATED WITH THE LOW WILL MOVE NORTHWARD
OVER THE EASTERN AK GULF AND PUSH OVER THE PANHANDLE OVERNIGHT INTO
WEDNESDAY. THIS FRONT IS FAIRLY WEAK AND IS SHOWING SIGNS OF
SHEARING APART SO INCREASED CLOUDS WILL BE THE MAIN RESULT TONIGHT
INTO WEDNESDAY WITH SOME RAIN MOVING OVER THE SOUTHERN PANHANDLE
LATE WEDNESDAY MORNING. THE MAIN ISSUES FOR TONIGHT WILL BE WITH
THE SURFACE HIGH REMAINING OVER THE YUKON WILL SEE AN INCREASE IN
OUTFLOW WINDS WAS THE EAST-WEST PRESSURE GRADIENT INCREASES. WHILE
THE WINDS WILL NOT BE EXCEPTIONAL A WARM MID LEVEL AIR MASS IS
MOVING UP WITH THE FRONT AND THESE WARM TEMPS WILL EITHER MIX DOWN
WITH STRONGER WINDS WHICH WILL INCREASE TEMPERATURES OVER NIGHT IN
THESE WIND SPOTS. IN ADDITION ANY DOWNSLOPING EFFECTS WILL HELP TO
INCREASE TEMPERATURES. HOWEVER IN WIND SHELTERED ARES TEMPERATURES
SHOULD FOLLOW A MORE DIURNAL TREND. WEDNESDAY HIGHS TEMPS WILL
GENERALLY BE IN THE UPPER 30S TO LOWER 40S SO ANY PRECIP THAT MOVES
IN THROUGH THE DAY WILL BE RAIN. WINDS OVER THE COASTAL WATERS WILL
PICK UP TO GALE OR NEAR GALE FORCE THROUGH THE TUESDAY NIGHT INTO
WEDNESDAY BEFORE SUBSIDING IN THE AFTERNOON. N LYNN CANAL WILL
REMAIN AT GALE FORCE THROUGH THE DAY WITH THE TIGHT NORTH-SOUTH
PRESSURE GRADIENT. SKAGWAY WINDS GUSTS SHOULD REMAIN AT OR JUST
BELOW 35 KTS BUT WILL NEED TO MONITOR IN CASE THEY REACH 40 KTS.

MODELS START IN GOOD AGREEMENT FOR THE SHORT TERM FORECAST. MAIN
DIFFERENCES WERE SOME TIMING OF THE FRONT MOVING IN WITH THE ECMWF
A BIT FASTER THEN THE GFS FOR THE 12Z RUN. UPDATED GRIDS WITH A
BLEND OF 12Z NAM AND 12Z ECMWF AS THE PRESSURE FIELD OVER THE
YUKON PANHANDLE BORDER LOOKED A BIT BETTER. OVERALL CHANGES WERE
FAIRLY MINOR. FORECAST CONFIDENCE WITH THE GENERAL WEATHER PATTERN
IS ABOVE AVERAGE BUT OVERNIGHT TEMPERATURES ARE IN QUESTION IF THE
STRONGER WINDS WILL MIX DOWN THESE HIGHER MID LEVEL TEMPERATURES.
PRB
&&

.LONG TERM...
MAIN FEATURE TO BE CONSIDERED IS THE PLANETARY SCALE UPPER LOW THAT
WILL PERSIST FOR A WEEK IN THE VICINITY OF KAMCHATKA. THE WEST
COAST (US) UPR RIDGE IS LESS CONSISTENT. SUCCESSIVE MINOR WEATHER
SYSTEMS MOVING AGAINST THIS RIDGE WILL FLATTEN IT AND PERHAPS CAUSE
A RETROGRADE ON THE RIDGE AXIS DUE TO A STRENGTHENING ON THE HUDSON
BAY UPPER LOW. HAVE REASONABLE CONFIDENCE THAT THIS PATTERN WILL
GENERALLY PAN OUT SO THAT FLOW ALOFT OVER THE PANHANDLE THAT IS
SOUTH WILL EVENTUALLY SHIFT TO SW THIS WEEKEND.

IMMEDIATE PROBLEM IS A WEAK WARM FRONT MOVING INTO THE SOUTHERN
PANHANDLE WED EVENING FOLLOWED BY SOME SORT OF SURFACE WEATHER
SYSTEM WSW OF DIXON ENTRANCE ON THU. ALL 07/12Z OPS MODELS VARY IN
IMPORTANT DETAILS THROUGH DAY 3. WEIGHED THE EVIDENCE OF THE
DIFFERENT SOLUTIONS AND RELUCTANTLY ACCEPTED THE 07/12 ECMWF WHICH
WAS CLOSE TO THE GFS-ENSEMBLE AND SREF MEANS. CONFIDENCE IS LOW TO
MODERATE ON DETAILS & TIMING. JC

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 6 PM AKST THIS EVENING FOR AKZ018.
MARINE...GALE WARNING FOR PKZ012-043-051-052.
         SMALL CRAFT ADV PKZ011-013-021-022-033-035-036-041-042.

&&