Small Craft Advisory 54, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
606 AM AKST FRI JAN 20 2012

.SHORT TERM...AN AMAZING COMBINATION OF ARCTIC AIR REMAINING
NEARLY STATIONARY FOR ALL OF SE ALASKA WHILE A WARM FRONT GOES
ALOFT IS THE MORNING SITUATION. ONE LOOK AT THE ANNETTE SOUNDING
SHOWS WIND JUST OFF THE SURFACE AND MULTIPLE FRONTAL INVERSIONS.
HURRICANE FORCE GUSTS ARE SHOWING UP IN THE OBS THIS MORNING FOR
SEVERAL LOCATIONS IN THE NORTHERN PANHANDLE WHILE SNOW HAS
STARTED IN THE SOUTH. THE ARCTIC AIR WILL MODIFY SOMEWHAT TODAY
IN THE SOUTH BUT PRECIP SHOULD REMAIN AS SNOW. HEAVY FREEZING
SPRAY AND LOW LEVEL WIND SHEAR CONTINUE TO CAUSE PROBLEMS ON
AVIATION AND MARINE. BIORKA RADAR SHOWS SUCCESSIVE SNOW BANDS
ENTERING THE AREA FROM THE SOUTH-SOUTHEAST AND SATELLITE IMAGERY
SHOWS A NICE SPIRAL WRAP AROUND THE STORM CENTER AT 53N 146W. THE
SECONDARY WAVE WHICH WILL BECOME THE MAIN LOW CENTER IS NEAR 48N
135W AT 15Z. A BLEND OF MODELS WAS USED FOR THIS MORNINGS
FORECASTS FOCUSING ON TWO LOW CENTERS IN THE COMPLEX STORM.

.LONG TERM...COMPLICATED WWA SITUATION AND MODEL ISSUES BEYOND
SUN LED ME TO ONLY MAKE TWEAKS THRU 12Z SUN PERIOD. USED A BLEND
OF THE 00Z GFS AND EC FOR THAT TIME FRAME...WITH SOME 06Z NAM
BLENDED IN FOR THE WINDS. USED HPC TO ADD IN DAY 8 PERIOD.

 MAIN CONCERNS ARE WITH SNOWFALL AND WINDS. DEEP ARCTIC AIRMASS
WILL BE OVERRUN BY A FAIRLY WARM AND JUICY AIRMASS FROM THE
SOUTH...AS EVIDENCE BY WARM SECTOR DEWPOINTS IN THE MID 40S. AS
COMPLEX LOW LIFTS NEWD INTO THE SE GULF THEN ACROSS SE AK BY SAT
NIGHT...THERE WILL BE SOME DYNAMIC SUPPORT TO THE OVERALL LIFTING
ENVIRONMENT...WHICH WILL ENHANCE SNOWFALL QUITE A BIT. SNOW
RATIOS WILL ALSO BE FAIRLY HIGH ESPECIALLY OVER THE CENTRAL AND
NRN AREAS IN THE DEEPER COLD AIRMASS. ONE CONCERN OVER THE FAR
SRN AREA IS THE WARMER AIR SHOULD GET IN AND LIKELY CAUSE SNOW TO
MIX WITH OR CHANGE TO RAIN SAT MORNING. THERE WILL ALSO BE A LULL
IN PRECIP ACROSS THE CENTRAL AND SRN AREAS AS INITIAL OCCLUDED
FRONT GOES ALOFT OVER THEM...BUT THE WEAKENING LOW WILL SPREAD
MORE PRECIP ONSHORE SAT EVENING AS IT MOVES IN SO WS WARNINGS
WERE KEPT GOING THRU LATE SAT NIGHT FOR ZONES 21..24..26..AND 29.
HAVE ISSUED WS WATCHES FOR ZONES 20 AND 22 FOR EARLY SAT INTO
LATE SAT NIGHT. DID NOT ISSUE A WS WATCH FOR ZONE 25 AT WCM
REQUEST DUE TO THE ONGOING HIGH WIND EVENT. WILL PROBABLY NEED WS
WATCHES OR WARNINGS AT SOME POINT FOR ZONES 19 AND 25...AND
POSSIBLY ZONE 18. SNOWFALL IN SOME AREAS COULD EXCEED 2 FEET BY
LATE SAT NIGHT.

 LEFT HIGH WIND WARNINGS GOING UNTIL 14Z FOR ZONES 18...19...AND
25. WINDS SHOULD DECREASE SOME AFTER THEN TO THE STRONG WIND
CATEGORY. KEPT STRONG WIND HEADLINE FOR ZONE 17 THRU 21Z SAT FOR
OUTFLOW WINDS. MAY NEED STRONG WIND HEADLINES OVER SOME OF THE
SRN ZONES ONCE THE WS WARNINGS END SAT MORNING. DID LEAVE IN THE
WIND CHILL ADVY FOR ZONE 18 NEAR WHITE PASS THRU SAT MORNING.

 THERE WILL LIKELY BE ONE OR MORE SIGNIFICANT SNOW AND WIND
EVENTS FOR SUN INTO LATE WEEK DUE TO PRESENCE OF A POLAR VORTEX
OVER THE GULF AND SEVERAL SRN STREAM SYSTEMS COMING IN...BUT
MODELS DIVERGE SOMEWHAT ON TIMING AND TRACK OF ANY INDIVIDUAL
SYSTEM SO CONFIDENCE WHEN THEY WILL OCCUR IS LOW.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WARNING UNTIL 5 AM AKST SUNDAY FOR AKZ024-026-029.
         WINTER STORM WARNING UNTIL 5 AM AKST SATURDAY FOR AKZ023-027.
         HIGH WIND WARNING UNTIL 5 AM AKST SATURDAY FOR AKZ018-019-025.
         STRONG WIND THROUGH THIS EVENING FOR AKZ020-022.
         WINTER STORM WATCH FROM LATE TONIGHT THROUGH LATE SATURDAY NIGHT
     FOR AKZ020-022.
         WINTER STORM WARNING FROM NOON TODAY TO 5 AM AKST SUNDAY FOR
     AKZ021.
         WINTER STORM WARNING UNTIL 9 AM AKST SATURDAY FOR AKZ028.
         WIND CHILL ADVISORY UNTIL NOON AKST SATURDAY FOR AKZ018.
         STRONG WIND THROUGH SATURDAY MORNING FOR AKZ017.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ011>013-021-031-032-034-053.
         HEAVY FREEZING SPRAY WARNING FOR PKZ035.
         STORM WARNING FOR PKZ011>013-022-036-043-051-053.
         GALE WARNING FOR PKZ021-031>035-041-042-052.

&&

JC/RWT