Gale Warning 152, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
319 PM AKST TUE FEB 10 2015

.SHORT TERM...A LOW HAS DEVELOPED ALONG AN OCCLUDED FRONT IN THE
GULF. THE LOW WILL TRACK NORTH THROUGH THE CENTRAL GULF TONIGHT
AND ENHANCE THE ASSOC FRONT. EXPECT SELY GALE FORCE WINDS OF 45KT IN
THE GULF TO SPREAD INTO THE COAST AND UP CLARENCE STRAIT LATE
TONIGHT. LAND AREAS WILL SEE WIND GUSTS OF 35 TO 45 MPH WITH THE
FRONT. EXCEPTION TO THIS IS SKAGWAY WHICH HAS A STRONG NORTHERLY
PRESSURE GRADIENT STILL DUE TO HIGH PRESSURE IN THE YUKON. WINDS
HAVE BEEN GUSTING 45-55MPH ALL DAY...CAUSING BLOWING SNOW AND
REDUCING VISIBILITY TO AROUND 2 MILES. FOR THIS REASON AND DUE TO
COLD WIND CHILLS AT WHITE PASS...THE WINTER STORM WARNING IN
SKAGWAY WAS STARTED THIS MORNING DESPITE THE SNOW WITH THE FRONT
NOT ARRIVING UNTIL LATE TONIGHT.

PRECIP WILL MOVE INTO THE COAST THIS EVENING AND SPREAD INLAND
OVERNIGHT. EXPECT HEAVIEST AMOUNTS TO BE AFTER MIDNIGHT THROUGH
EARLY WEDNESDAY MORNING. PRECIP WILL START OFF AS SNOW FROM NORTH
OF A YAKUTAT TO PETERSBURG/HYDER LINE THEN CHANGE OVER TO RAIN
FROM SOUTH TO NORTH THROUGH TOMORROW AFTERNOON. YAKUTAT/GUSTAVUS/JUNEAU
HAVE AN ADVISORY IN EFFECT FOR 3-7 INCHES OF SNOW EXPECTED. AS
WINDS VEER FROM NE TO SE TOMORROW THE TEMPERATURE WILL JUMP UP AND
CHANGE THE SNOW TO RAIN. TIMING OF THIS HAS BEEN A CHALLENGE AND
FORECAST CONFIDENCE IN THAT PART REMAINS BELOW NORMAL. A WINTER
STORM WARNING REMAINS IN EFFECT FOR HAINES AND SKAGWAY...EXPECT
6-12 INCHES THERE WITH PEAK AMOUNTS DURING THE SAME OVERNIGHT
TIMEFRAME.

WINDS WILL SHIFT TO THE SOUTH BEHIND THE FRONT AND DECREASE.
TEMPERATURES WILL SLOWLY WARM OVERNIGHT THEN JUMP UP WITH THE WIND
SHIFT TOMORROW. USED MAINLY THE NAM FOR UPDATES TO PRESSURE THEN
SOME HIRES MODELS FOR ADJUSTMENT TO WIND SPEEDS. AGAIN THE BIGGEST
FORECAST CHALLENGE LIES WITH TEMPERATURES AND TIMING OF THE WIND
SHIFT.

.LONG TERM...A SERIES OF UPPER-LEVEL SHORTWAVE IMPULSES ARE
FORECAST TO MOVE NWD ACROSS THE GULF DURING THE START OF THE LONG
TERM PERIOD THU MORNING/AFTERNOON. EACH IMPULSE WILL BE
ASSOCIATED WITH WEAK SURFACE LOW CENTERS...WHICH WILL AID IN
PERIODIC INCREASES IN WINDS OVER THE GULF...AND MODEST INCREASES
IN ASCENT. BURSTS OF ASCENT COMBINED WITH PW VALUES FROM 0.6-0.8
INCH AND SLY 850 MB WINDS FROM 30-50 KT ENHANCING MOISTURE FLUX
WILL FAVOR WIDESPREAD RAIN OVER THE CNTRL/SRN PANHANDLE...AND
LIGHT SNOW NEAR HAINES...SKAGWAY...AND WHITE PASS. A STRONGER/MORE
ORGANIZED UPPER DISTURBANCE IS THEN FORECAST TO MOVE FROM THE SRN
TO NRN GULF THU NIGHT THROUGH FRI AFTERNOON. THIS TROUGH AND
SURFACE CYCLONE WILL CONTINUE TO YIELD WINDS UP TO GALE STRENGTH
OVER THE GULF...WHILE INLAND A FRONTAL BOUNDARY WILL SPREAD N.
MODERATE RAINFALL RATES ARE EXPECTED WITH THIS FRONT...AS WELL AS
MODERATING TEMPERATURES OVER THE ENTIRE REGION. THE LOW WILL THEN
GRADUALLY DISSIPATE OVER THE NRN GULF BY SAT...AND POP/QPF WILL
LIKEWISE DECREASE.

MODEL GUIDANCE IS IN GOOD AGREEMENT SHOWING AN UPPER RIDGE
DEVELOPING FROM THE NERN PAC NWWD ACROSS THE ERN/CNTRL GULF INTO
INTERIOR AK ON SUN. THE ATMOSPHERE OVER THE PANHANDLE WILL LIKELY
BECOME COLDER AND DRIER IN RESPONSE TO A GREATER CONTINENTAL
INFLUENCE OCCURRING E OF THE RIDGE. POP GRIDS TRANSITION FROM AN
ECMWF/INHERITED BLEND TO WPC BY THIS POINT...WHICH YIELDS A
VIRTUALLY PRECIP FREE FORECAST DURING EARLY TO MID NEXT WEEK.
HOWEVER...ENSEMBLE MODEL SPREAD INCREASES SUBSTANTIALLY BY
WED...WITH UNCERTAINTY HINGING ON THE EVOLUTION OF RIDGE BREAK
DOWN AS WELL AS THE INFLUENCE FROM NRN STREAM TROUGHS EMANATING
FROM THE ARCTIC REGION. HOW THE RIDGE BREAKS DOWN WILL DETERMINE
HOW QUICKLY THE PANHANDLE RETURNS TO A RELATIVELY MORE MILD AND
MOIST ONSHORE FLOW REGIME.

USED AN ECWMF/GEM/INHERITED BLEND FOR PRESSURE 09Z FRI THROUGH 00Z
SUN...THEN TRANSITIONED TO 12Z WPC. AS PREVIOUSLY MENTIONED...POP
GRIDS WERE DERIVED FROM AN ECMWF/INHERITED BLEND THROUGH
SAT...THEN MAINLY WPC FOR THE REMAINDER OF THE LONG TERM. FORECAST
CONFIDENCE IS AT OR SLIGHTLY ABOVE AVERAGE THROUGH SAT...THEN
TRENDS BELOW AVERAGE BY THE MIDDLE OF NEXT WEEK.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND THROUGH LATE TONIGHT FOR AKZ027.
         WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO NOON AKST
     WEDNESDAY FOR AKZ017-020-025.
         STRONG WIND FROM 9 PM THIS EVENING TO 3 AM AKST WEDNESDAY FOR
     AKZ018-022.
         STRONG WIND UNTIL 3 AM AKST WEDNESDAY FOR AKZ023.
         STRONG WIND FROM 9 PM AKST THIS EVENING THROUGH LATE TONIGHT FOR
     AKZ028.
         WINTER STORM WARNING FROM 9 PM THIS EVENING TO 4 PM AKST
     WEDNESDAY FOR AKZ019.
         STRONG WIND UNTIL 6 PM AKST THIS EVENING FOR AKZ018.
         WINTER STORM WARNING UNTIL 4 PM AKST WEDNESDAY FOR AKZ018.
MARINE...GALE WARNING FOR PKZ012-021-022-033-035-036-041>043-051>053.
         SMALL CRAFT ADVISORY FOR PKZ011-013-031-032-034.

&&

FERRIN/GARNER

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