Gale Warning 201, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
612 AM AKDT TUE APR 16 2013

.SHORT TERM...A LOW IN THE WEST CENTRAL GULF HAS BEGUN TO TRACK
NORTHEAST AND IS HEADED TOWARD CAPE FAIRWEATHER. VERY EXTENSIVE
BAROCLINIC CLOUD SHIELD IN ADVANCE OF THE ASSOCIATED FRONT
COMPLETELY COVERED THE PANHANDLE BEFORE DAYBREAK TODAY. PERIODS
OF SNOW HAVE OCCURRED IN YAKUTAT OVERNIGHT AND THAT PRECIPITATION
WILL BECOME MORE STEADY AS THE DAY GOES BY. NO PRECIP BEING
REPORTED ANYWHERE ELSE AS OF 5 AM, BUT IT IS COMING.

COLD LOW LEVEL AIR OVER SOUTHEAST ALASKA CONTINUES TO HAMPER A
STEADY TRANSITION TO MORE SPRING LIKE CONDITIONS AND MORE SNOW IS
IN THE SHORT TERM FORECAST PERIOD. DEPENDING ON WHEN PRECIP BEGINS
FOR LOCATIONS OTHER THAN YAKUTAT, IT MAY START OUT AS SNOW, BUT AM
EXPECTING MOST LOCATIONS TO TRANSITION TO RAIN LATER TODAY.
EXCEPTION IS THE FAR NORTHERN INNER CHANNELS AND THIS REPRESENTS
THE GREATEST UNCERTAINTY IN THE SHORT RANGE FORECAST. OPTED TO USE
HIGH RESOLUTION MODEL FIELDS FOR POP AND QPF. RESULTING SNOW
TOTALS WERE SIGNIFICANTLY HIGHER FOR HAINES HIGHWAY AND, IN
PARTICULAR, THE KLONDIKE HIGHWAY. INFREQUENT USE OF HIGH
RESOLUTION MODEL FIELDS REDUCES CONFIDENCE IN SUCH A DRAMATIC
SHIFT IN THE SHORT RANGE FORECAST, SO HAVE CAREFULLY CRAFTED SNOW
TOTALS FOR THE KLONDIKE HIGHWAY TO BE SIGNIFICANT, BUT LESS THAN
THE 4 INCHES IN 12 HOURS NECESSARY FOR A WINTER WEATHER ADVISORY.
STAY TUNED FOR UPDATES TO THIS BY THE DAY SHIFT.

USED NAM FOR UPDATES TO PRESSURE AND WIND. USED HIGH RESOLUTION
NAM FOR POP AND QPF FIELDS. UPDATED TEMPERATURES WITH A BLEND OF
NAM AND GFS. SNOW LEVEL ADJUSTED PER FORECAST WET BULB
TEMPERATURES. CONFIDENCE IS BELOW AVERAGE FOR SNOW TOTALS ALONG
THE KLONDIKE HIGHWAY BUT AVERAGE TO ABOVE AVERAGE IN OTHER ASPECTS
OF THE FORECAST.

.LONG TERM...COOLER CONDITIONS ARE TO BEGIN, AND THESE ADJUSTMENTS
ARE PROBABLY THE MOST IMPORTANT CHANGES FOR MOST OF OUR USERS.
CONFIDENCE IS AVERAGE.

THE LOW TRACKING FROM THE GULF TOWARD CAPE FAIRWEATHER IS
DISCUSSED IN THE SHORT RANGE SECTION ABOVE. ABOUT 18Z WED, THE
PRECIPITATION RATE IN THE NORTHERN PANHANDLE WILL BE RAPIDLY
DIMINISHING, AND THE MAXIMA OF PRECIP WILL BEGIN TO MOVE SE ALONG
THE COAST MOUNTAIN RANGE. ALSO, THE UPPER LEVEL SUPPORT FOR THIS
LOW WILL MOVE NE AND SUPPORT A 1012 MB LOW ABOUT 120 MI E OF
WHITEHORSE 00Z THU. THIS LOW WILL BECOME COMPLEX IN THE CANADIAN
NW BUT THE PRIMARY CENTER WILL MOVE AWAY TO THE ESE THEREAFTER.

MODEL CONSENSUS HAS IMPROVED FOR THU NIGHT AND INTO THE WEEKEND.
THE SOLUTION USED HAS COOLER CONDITIONS BEGINNING THU NIGHT, AND
ARE ASSOCIATED WITH AN OUTFLOW FROM YUKON TERRITORY. THIS COOLER
AIRMASS IS INDICATED BY 1000-500 DAM THICKNESSES OF 522 REACHING S
OF SKAGWAY AT ABOUT 00Z FRI, AND REACHING JUNEAU ABOUT 12Z FRI.
THE GFS MODEL WAS THE PRIMARY GUIDANCE FOR 00Z THU ONWARD, AND IT
PRESENTS A 1037 MB HIGH ABOUT 60 NM NE OF WHITEHORSE AT 12Z SAT,
WITH A 516 DAM ARCTIC OUTBREAK BEGINNING TO MOVE SE ON THE
CANADIAN SIDE OF THE COAST MOUNTAIN RANGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ042-043-051.
         SMALL CRAFT ADVISORY FOR PKZ011-021-022-033>036-041-052.

&&

FRITSCH/JBT