Gale Warning 142, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
541 AM AKST SAT FEB 7 2015

.SHORT TERM...EARLY MORNING SATELLITE IMAGE SHOWS A 978 MB LOW
OVER THE NORTH CENTRAL GULF AND A WEAK OCCLUDED FRONT STRETCHING
SOUTHEASTWARD ACROSS DIXON ENTRANCE. HIGH PRESSURE REMAINS OVER
THE NORTHWESTERN CANADA. NORTHERLY PRESSURE GRADIENT HAS BEEN
RELAXING A LITTLE BETWEEN THE HIGH PRESSURE AND THE LOW IN THE
GULF...BUT STILL MAINTAINING GALE FORCE WINDS OVER NORTHERN LYNN
CANAL WITH GUSTS UP TO 60 KNOTS. GUSTY OUTFLOW WINDS CONTINUES
ACROSS THE INTERIOR PASSES AS WELL. A COLD UPPER LEVEL LOW NEAR
NORTHEASTERN GULF COAST CONTINUES TO KEEP SOUTHEAST ALASKA FROZEN
WITH EARLY MORNING TEMPERATURES RANGE FROM 1 TO 3 DEGREES OVER THE
NORTHERNMOST PANHANDLE TO THE TEENS ACROSS THE CENTRAL AREAS TO THE
UPPER 20 TO THE LOWER 30S OVER THE SOUTHERN ZONES. EXPECT WINDS
BECOME MORE ONSHORE OVER THE SOUTHERN AREAS WHILE OFFSHORE OUTFLOW
WINDS CONTINUE ACROSS THE NORTHERN PANHANDLE.

MODELS REMAIN IN GENERAL AGREEMENT FOR THE LOW PRESSURE OVER THE
NORTH CENTRAL GULF MOVES FURTHER WEST TO NEAR KODIAK THROUGH
SUNDAY WHILE HIGH PRESSURE PERSISTS OVER THE NORTHWESTERN CANADA.
THE ASSOCIATED OCCLUDED FRONT WILL MOVE NORTH ACROSS SOUTHEAST
ALASKA THIS AFTERNOON INTO TONIGHT. REFRESHED THE INHERITED
FORECAST WITH THE ECMWF AND NAM12 FOR PRESSURE AND WIND FIELDS.
USED ENSEMBLE APPROACH FOR POP/QPF FIELDS THROUGH SATURDAY NIGHT.
TEMPERATURES WILL SLIGHTLY WARM THIS AFTERNOON...BUT REMAIN BELOW
FREEZING EXCEPT THE SOUTHERNMOST PANHANDLE WHERE AFTERNOON HIGHS
POSSIBLY GO UP TO THE MID 30S. OVERNIGHT LOWS WILL BE SIMILAR AS
FRIDAY NIGHT WITH SOME LOCATIONS GET EVEN COLDER. EXTENDED WIND
CHILL ADVISORY FOR WHITE PASS UNTIL SUNDAY MORNING AND POSTED
ANOTHER WIND CHILL ADVISORY FOR HAINES ZONE TONIGHT. LIKELY POPS
FOR SNOW SHOWERS WILL SPREAD OVER THE PANHANDLE AND BECOME
CATEGORICAL LATE TONIGHT AS MORE STRATIFORM SNOW. LIMITED QPF
VALUES WILL PRODUCE 1 TO 2 INCHES OF SNOW ACCUMULATION THROUGH
TONIGHT.

.LONG TERM...NEW REINFORCING DYNAMIC WAVE DIVING INTO THE WESTERN
PORTION OF THE UPPER POLAR VORTEX CURRENTLY ENTRENCHED OVER THE
PANHANDLE WILL DRIVE THE CLOSED CENTER TO THE WEST AND
SOUTH...CENTERED SOUTH OF THE ALEUTIAN CHAIN...BY SUNDAY MORNING.
FRONTAL FORCING AND THE BEGINNING OF A SWITCH IN LOW/MID-LEVEL
WINDS TO ONSHORE WILL MARK THE ONSET OF STRATIFORM PRECIPITATION
ACROSS MUCH OF THE PANHANDLE BY LATE SAT PM AND SUNDAY
MORNING...AIDED BY OVERRUNNING OF THE PREEXISTING COLD AIR MASS
AND MAXIMIZED OVER THE NORTHERN PANHANDLE WHERE THE COLD AIR IS
DEEPEST. THOUGH MODEL QPF TOTALS INTO MONDAY BACKED OFF FROM SOME
RECENT RUNS...STILL SEEMS THAT A THIRD TO A HALF INCH OF LIQUID
EQUIVALENT IS A REASONABLE BET FOR THE AREAS ACROSS THE NORTH THAT
SHOULD SEE ALL SNOW UNTIL AT LEAST MONDAY MORNING. NAM VALUES MUCH
HIGHER BUT IT IS THE CURRENT OUTLIER. USING A REASONABLE SNOW
RATIO YIELDS 3-8" ACROSS THE AREA CONSERVATIVELY, WITH YAKUTAT ON
THE HIGH END. ONLY POSSIBLE MONKEY WRENCHES ARE THE MODELS NOT
HANDLING THE COLD AIR RETREAT WELL (TOO SLOW...NOT LIKELY) OR DRY
AIR AT LOW LEVELS LIMITING THE EARLY SNOWFALL. DECIDED TO HANDLE
SITUATION AT THIS POINT WITH AN SPS...ESPECIALLY WITH CURRENT WIND
PROBLEMS CONTINUING DURING THE SHORT TERM. TODAY'S MODEL RUNS
SHOULD ALLOW A DECISION ON ANY HIGHLIGHTS. SOUTHERN SECTIONS
SHOULD SEE MINIMAL IMPACT AS SNOW WILL BE RELATIVELY BRIEF
THERE...AKT IS BORDERLINE ALREADY BY SUNDAY AND ONLY THE
HAINES/SKAGWAY HAS ANY MENTION OF SNOW AFTER ABOUT LATE MONDAY. AS
FOR WINDS...STRONG OUTFLOW APPEARS LIKELY TO CONTINUE TO PLAGUE
NORTHERN LYNN, CROSS SOUND AND YAKUTAT BAY ON SUNDAY WITH THE
NORTHERN LYNN GALE GOING ALL THE WAY INTO TUESDAY.

THE CONCLUSION OF THIS COLD EVENT WILL MARK THE ONSET OF A MAJOR
CHANGE TO THE UPPER AIR PATTERN. AS THE COLD AIR RETREATS TO THE
NORTH...WARM ADVECTION AND RAIN WILL GRADUALLY TAKE OVER AS STRONG SSWLY
FLOW BUILDS OVER THE GULF...ESTABLISHED BY MIDWEEK ON THE MODELS.
BY THEN MAJOR GALES ARE ADVERTISED FOR OFFSHORE WITH THE APPROACH
OF THE NEW LOW FROM THE SOUTH AS THE UPPER RIDGE AXIS GETS TO THE
PANHANDLE ABOUT TUES AM. THIS SCENARIO WILL INCLUDE ACCELERATION
FOR THE EAST- WEST ORIENTED INNER CHANNELS ON TUES PM IF THE MODEL
TIMING IS ACCURATE. BY MIDWEEK LOW PRESSURE CONTINUES TO
STRENGTHEN OVER THE WESTERN GULF ALONG WITH A SERIES OF WAVES
EJECTING NORTHEASTWARD THROUGH THE EXTENDED PERIOD...THE TIMING OF
THESE WILL DETERMINE THE RAIN AND WIND IMPACTS ON THE PANHANDLE
WITH SOME HEAVY RAIN POTENTIAL. ONE OR MORE OF THESE WAVES HAS THE
POTENTIAL OF BEING STRONG BUT TOO EARLY TO DELINEATE TIMING AT
THIS POINT. ALL OF THE MODELS PAINT A SIMILAR PICTURE THROUGH NEXT
WEEK WITH PRIMARY DIFFERENCES IN THE TIMING DETAILS.

WENT WITH AN ENSEMBLE EC/NAM/GFS APPROACH ON THE GRIDS THROUGH
MONDAY WITH THE TYPICAL WIND AND SNOW LEVEL/QPF TWEAKS AND DID NOT
MAKE MAJOR CHANGES TO EXTENDED WHICH WAS BASED ON 12Z WPC GUIDANCE
AND NEW MODEL RUNS WERE MOSTLY CONSISTENT. HAD TO INCREASE
TEMPERATURES FOR MOST AREAS ON TUESDAY AS NEW GUIDANCE QUICKENED
THE TRANSITION AT THAT POINT.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM 3 PM AKST THIS AFTERNOON THROUGH LATE TONIGHT
     FOR AKZ018-022.
         STRONG WIND FROM THIS EVENING THROUGH LATE TONIGHT FOR AKZ019.
         WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM AKST SUNDAY
     FOR AKZ019.
         WIND CHILL ADVISORY UNTIL 6 AM AKST SUNDAY FOR AKZ018.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ011.
         HEAVY FREEZING SPRAY WARNING FOR PKZ012.
         STORM WARNING FOR PKZ012.
         GALE WARNING FOR PKZ011-013-021-022-043-051>053.
         SMALL CRAFT ADVISORY FOR PKZ031>035-042.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041.

&&

AHN/WESLEY

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