Small Craft Advisory 25, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
439 PM AKST MON JAN 9 2012

.SHORT TERM...RATHER QUIET SHORT TERM PERIOD TODAY. THE REMAINS
OF LAST NIGHTS LOW IS CURRENTLY MOVING EAST THROUGH THE NORTHERN
PANHANDLE. ACCOMPANYING IT ARE NUMEROUS SHOWERS THAT ARE FORMING
IN THE COLD AIR WRAPPING AROUND THE OLD LOW FROM PRINCE WILLIAM
SOUND. WITH 850 MB TEMPS DROPPING TO -14 C ABOVE YAKUTAT AND -6 C
OR LESS AS FAR SOUTH AS ANNETTE MOST OF THESE SHOWERS HAVE BEEN
IN THE FORM OF SNOW. SOME OF THESE SNOW SHOWERS HAVE BEEN HEAVY
AS VISIBILITIES AT SOME OBS SITES HAVE DROPPED TO LESS THEN
1 MILE AT TIMES AND A QUICK INCH OR TWO OF SNOW ACCUMULATED
BEFORE THE SHOWER MOVED OFF. WINDS HAVE ALSO BEEN SOMEWHAT OF A
PROBLEM WITH HIGHER WIND GUSTS NEAR SHOWERS UP TO 35 KT SHOWING
UP EVERY NOW AND THEN. WINDS HAVE ALSO BEEN SOMEWHAT BRISK OUT IN
THE GULF WITH WEST TO NORTHWEST WINDS 25 TO 30 KT RESULTING FROM
THE PRESSURE GRADIENT BETWEEN THE OLD LOW AND A RIDGE BUILDING UP
FROM THE SOUTH.

 FOR TONIGHT AND TOMORROW, WINDS AND SHOWERS WILL DIMINISH
THROUGH THE NIGHT AS THE BUILDING RIDGE OVER THE GULF MOVES EAST
OVER THE PANHANDLE WEAKENING PRESSURE GRADIENTS. ANY REMAINING
SHOWERS SHOULD BE SNOW WITH LIGHT ACCUMULATIONS AS 850 TEMPS
REMAIN WELL BELOW -6 C OVER MUCH OF THE AREA. THE COLDER AIR
ALOFT AND THE BREAKS IN THE CLOUD COVER TONIGHT WILL CAUSE
SURFACE LOW TEMPERATURES TO DIP INTO THE 20S AND POSSIBILITY INTO
THE TEENS IN SOME PLACES. LIGHT NORTH WINDS LATE TONIGHT IN THE
NORTHERN PANHANDLE WILL ALSO REINFORCE THE COLDER CONDITIONS AS
IT BRINGS SOME COLDER AIR FROM CANADA INTO THE AREA. THIS WILL
NOT BE VERY COLD AIR AIR MASS IN CANADA IS NOT DEEP ENOUGH TO
MAKE IT OVER THE MOUNTAINS.

 INTO TOMORROW, MOST AREAS WILL START SEEING INCREASING HIGH
LEVEL CLOUDS AS OUR NEXT FRONT APPROACHES FROM THE WEST. THE WIND
AND HEAVIER PRECIP WILL NOT QUITE MAKE IT TO THE PANHANDLE BY
TUESDAY AFTERNOON BUT ENOUGH ISENTROPIC LIFT WILL BE PRESENT FOR
LIGHT SNOW TO START FALLING OVER THE NORTHERN PANHANDLE. THE
EXCEPTION WILL BE YAKUTAT WHICH WILL START SEEING LIGHT SNOW TUES
MORNING AND HEAVIER SNOW TUES AFTERNOON. YAKUTAT MAY SEE 2 TO
5 INCHES BY TUES EVENING. OUT IN THE GULF, SEAS WILL BE
INCREASING AS PRE- FRONTAL SE WINDS INCREASE TO GALE FORCE OVER
MUCH OF THE GULF BY TUES AFTERNOON. SEAS COULD BE REACHING INTO
THE 22 FT MARK OVER THE CENTRAL GULF BY AFTERNOON.

 SHORT RANGE MODELS WERE IN DECENT AGREEMENT THROUGH TOMORROW.
DECIDED TO STAY WITH THE EC FOR UPDATES AS IT PROVIDED THE BEST
INITIALIZATION AND HAD THE DETAIL THAT I WAS LOOKING FOR OVER THE
PANHANDLE. FORECAST CONFIDENCE IS A LITTLE ABOVE AVERAGE.

&&

.LONG TERM...HEAVY SNOW IS EXPECTED TO CONTINUE ALONG THE
NORTHEAST GULF COAST TUESDAY NIGHT BUT EVENTUALLY CHANGE TO RAIN
AS THE AIR BECOMES WELL MIXED IN THE STRONG SOUTHEAST FLOW.
ALTHOUGH PRECIPITATION WILL BE HEAVY TUESDAY NIGHT IT IS STILL
UNCERTAIN WHEN THE CHANGE TO RAIN WILL TAKE PLACE SO A WATCH WAS
CONTINUED FOR THAT AREA THROUGH WED MORNING.

THE GFS AND ECMWF HAVE SIGNIFICANT DIFFERENCES BY THE
LATER HALF OF THE WEEK AS THE LONGWAVE PATTERN SLOWLY TRANSITIONS
TO BRING COLDER AND DRIER CONDITIONS INTO THE SOUTHEAST ALASKA BY
THE WEEKEND. THE GFS HAS BEEN WAFFLING FOR THE LAST FEW CYCLES SO
THE ECMWF SOLUTION WAS PREFERRED WITH MODIFICATIONS. THE ECMWF
MOVES AN UPPER LEVEL LOW FROM IN THE NORTH CENTRAL GULF OF AK
THU NIGHT SLOWLY DROPPING SOUTHEASTWARD TO BE SOUTH OF THE
PANHANDLE NEAR THE B.C. COAST BY SATURDAY NIGHT. WHILE THIS MAY BE
THE GENERAL SYNOPTIC TREND IT IS TYPICAL THAT A WEAK RESIDUAL
SURFACE LOW REMAINS IN THE NORTHEAST GULF SUPPORTED BY COLD AIR
FROM INTERIOR AK. THIS WILL TEND TO LEAVE AN INVERTED NW-SE TROUGH
AT THE SURFACE AS THE UPPER LOW MOVES SOUTH AND HIGH PRESSURE
BUILDS IN THE YUKON.

DURING THE WEEKEND AN ARCTIC FRONT IS PUSH DOWN FROM THE YUKON
BRINGING GALES NORTHERLIES AND COLDER TEMPERAUTURES. THERE IS
STILL A LARGE ENSEMBLE SPREAD IN THE LOW LEVEL SYNOPTIC PATTERN
OVER THE WEEKEND SO THE TIMING OF THIS SWITCH TO ARCTIC OUTFLOW IS
STILL UNCERTAIN.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WATCH FROM TUESDAY MORNING THROUGH WEDNESDAY
     MORNING FOR AKZ017.
MARINE...GALE WARNING FOR PKZ022-042-043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011-021-041-053.

&&

EAL/CFD