Wind Chill Advisory 7, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
421 PM AKST FRI FEB 6 2015

.SHORT TERM...UPPER TROUGH EXTENDING SSWWD FROM THE YUKON INTO THE
NERN GULF WILL EVOLVE INTO A CLOSED LOW AS COLD MIDLEVEL AIR IS
INJECTED SWD INTO IT/S BASE TONIGHT. MEANWHILE...UPPER IMPULSE IS
IN THE PROCESS OF MOVING NE ACROSS THE SRN PANHANDLE THIS
AFTERNOON...WITH DRY MIDLEVEL AIR SPREADING EWD IN IT/S WAKE. THE
DRIER AIR WILL SHUT DOWN HEAVY SNOWFALL RATES BY THIS EVENING FROM
PETERSBURG/WRANGELL TO HYDER...THOUGH A FEW MORE INCHES OF
ACCUMULATION WILL BE POSSIBLE IN THE MEANTIME FOR BOTH OF THESE
LOCATIONS. HIGH PRESSURE OVER NWRN CANADA AND MUCH LOWER PRESSURE
OVER THE ERN GULF WILL CONTINUE TO SUPPORT STRONG OUTFLOW WINDS
ACROSS NRN/CNTRL AREAS...THOUGH SPEEDS WILL DECREASE DURING THE
NIGHT AS THE GRADIENT SLACKENS SLIGHTLY. MOUNTAIN WAVE POTENTIAL
OVER DOWNTOWN JUNEAU WILL COME TO AN END BY EVENING AS THE
CRITICAL LEVEL LOWERS AND CROSS BARRIER FLOW WEAKENS.
ELSEWHERE...HURRICANE FORCE WINDS OVER NRN LYNN CANAL WILL
DIMINISH TO STORM FORCE TONIGHT...AND THEN GALE DURING SAT.
HOWEVER...HEAVY FREEZING SPRAY WILL REMAIN POSSIBLE THROUGHOUT THE
SHORT TERM PERIOD. STRONG WIND GUSTS UP TO 50 MPH WILL REMAIN
POSSIBLE IN SKAGWAY DUE TO CONTINUED TIGHT PRESSURE GRADIENT.
STRONG GUSTY WINDS ALONG THE KLONDIKE HIGHWAY/WHITE PASS COMBINED
WITH TEMPERATURES RANGING FROM -10 TO -15F WILL ALSO SUPPORT WIND
CHILL VALUES FROM -30 TO -40F THROUGH SAT.

BY SAT AFTERNOON...UPPER TROUGH OVER THE NRN GULF IS FORECAST TO
RETROGRADE WWD INTO THE WRN GULF. LOW-LEVEL FLOW WILL BECOME
ONSHORE OVER THE SRN PANHANDLE AS THIS TAKES PLACE...WHICH WILL
AID IN MODERATING HIGH TEMPERATURES. OVER CNTRL/NRN
AREAS...OFFSHORE DIRECTED PRESSURE GRADIENT WILL MAINTAIN A
DRIER/SUBFREEZING SURFACE AIRMASS. SWLY 925-850 MB FLOW OVER THE
SRN PANHANDLE WILL ADVECT MOISTURE INLAND DURING THE DAY...AND
STRONGEST ASCENT WILL BECOME FOCUSED ALONG A BOUNDARY EXTENDING
EWD FROM THE CNTRL GULF TOWARD WRANGELL. RAIN SHOWERS WILL BE
PROBABLE S OF THE BOUNDARY FROM SITKA TO KETCHIKAN...WHILE SNOW
SHOWERS ARE EXPECTED ALONG AND TO IT/S N. MODEST SNOW ACCUMULATION
IS FORECAST FOR PETERSBURG/WRANGELL AS A RESULT...WITH TOTALS
DURING THE AFTERNOON RANGING FROM 1-4 INCHES. LIGHTER AMOUNTS WILL
OCCUR FARTHER N TOWARD JUNEAU.

.LONG TERM...UPPER TROF/LOW OVER THE ERN GULF WILL REDEVELOP TO
THE SW GULF AS A STRONG SHORTWAVE DIVES S THRU INTERIOR AK AND
INTO THE SW GULF BY SAT EVENING. THIS WILL DEVELOP A LOW OVER THE
CENTRAL GULF WHICH WILL DEEPEN AND DRIFT WWD TO THE SW GULF SUN.
EXPECT SEVERAL TROFS/WEAK OCCLUDED FRONTAL BANDS TO MOVE NE ACROSS
THE ERN GULF AND SE AK SAT NIGHT-MON. THESE WILL BRING BANDS OF
PRECIP WITH THEM...AND AREAS TO THE N OF THE ARCTIC FRONT WILL
ALSO GET SOME OVERRUNNING AS AIRMASS OVER THE SE GULF WARMS AND
MOISTENS UP...THEN IS FORCED NWD OVER THE ARCTIC AIR. THE ARCTIC
FRONT WILL SLOWLY LIFT N THRU MON...LIKELY GETTING TO THE PAJN
AREA BY LATE SUN NIGHT. SNOWFALL COULD GET LOCALLY HEAVY AT TIMES
ESPECIALLY AS THE TROF/FRONTAL BANDS MOVE THRU THE AREA...BUT
TIMING AND TRACK OF THESE FEATURES DIFFERS SOMEWHAT AMONGST THE
MODELS. SO...WILL NOT ISSUE ANY SNOW RELATED HEADLINES FOR THE SAT
NIGHT-MON TIME FRAME AND ALLOW LATER SHIFTS TO GET BETTER HANDLE
ON THIS.

EVENTUALLY THE UPPER LOW WILL SPLIT...WITH ONE PIECE LIFTING NEWD
ACROSS THE GULF AND INTO THE YUKON BY MON AFTERNOON...WHILE
ANOTHER PIECE GETS PULLED INTO A LARGER UPPER LOW THAT WILL DRIFT
EWD ACROSS THE NPAC. THIS LARGER LOW WILL REACH ABOUT 160W AND
BECOME A FAIRLY DEEP FULL LATITUDE UPPER TROF WITH RIDGE BUILDING
DOWNSTREAM OVER WRN NOAM. THIS WILL LIKELY BRING IN A SLOW MOVING
FRONTAL SYSTEM WITH MULTIPLE LOW PRESSURE WAVES RUNNING NWD ALONG
IT. MAIN QUESTION IS HOW FAST WILL THE FRONT GET E AND SPREAD
PRECIP INTO THE AREA FOR MIDWEEK. GFS IS A BIT SLOWER THAN THE
ECMWF MOVING THE FRONT IN. OVERALL...THIS PATTERN WILL WARM THINGS
UP QUITE A BIT...AND PUT THE AREA BACK INTO THE WARM/WET PATTERN
THAT WAS IN PLACE FOR MUCH OF JANUARY. RAISED TEMPS...ESPECIALLY
THE MINS...TO REFLECT THIS PATTERN CHANGE. ONLY AREAS WITH ANY
SNOW MENTION AFTER TUE NIGHT ARE THE PAHN/PAGY AREAS. ONE
POTENTIAL THING THAT COULD SLOW THE EROSION OF THE COLD AIRMASS
OVER THE FAR N IS A NRN STREAM TROF PASSING BY THE AREA TO THE N
AND REINFORCING THE ARCTIC AIRMASS...BUT CURRENT MODELS SUGGEST
ANY TROF WOULD BE TOO FAR N TO HELP MAINTAIN THE COLD AIRMASS OVER
THE NRN AREAS.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WARNING UNTIL 6 PM AKST THIS EVENING FOR AKZ026-029.
         STRONG WIND UNTIL MIDNIGHT AKST TONIGHT FOR AKZ017-025.
         STRONG WIND UNTIL 9 PM AKST THIS EVENING FOR AKZ019.
         STRONG WIND UNTIL 3 AM AKST SATURDAY FOR AKZ018.
         STRONG WIND SATURDAY AFTERNOON FOR AKZ018.
         WIND CHILL ADVISORY UNTIL 6 PM AKST SATURDAY FOR AKZ018.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ011.
         HEAVY FREEZING SPRAY WARNING FOR PKZ012.
         STORM WARNING FOR PKZ012.
         GALE WARNING FOR PKZ011-013-021-022-031-043-051>053.
         SMALL CRAFT ADVISORY FOR PKZ032>036-041-042.

&&

GARNER/RWT

VISIT US AT HTTP://WWW.WEATHER.GOV/JUNEAU

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