Small Craft Advisory 124, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
249 PM AKST SUN FEB 12 2012

.SHORT TERM...THE LATEST SATELLITE IMAGERY SHOWS SHOWERS MOVING
OVER THE EASTERN GULF AND SE AK THIS AFTERNOON. THERE IS A STRONG
LOW PRESSURE SYSTEM THAT IS LIFTING NE SOUTH OF THE AK PENN THAT
WILL EVENTUALLY WEAKEN TO A TROF AND BE OVER THE CENTRAL GULF BY
MON AFTERNOON. THERE IS AN ASSOCIATED WARM FRONT WITH THE LOW
THAT WILL MAINLY AFFECT THE NORTHERN GULF AREAS LATE TONIGHT INTO
MON AS THE FRONT WILL BE SLOW TO MOVE WEST TO EAST. THERE IS NOT
MUCH WIND OVER LAND AREAS THIS AFTERNOON WITH THE EXCEPTION TO
THE FAR NORTHERN INNER CHANNELS WHERE GUSTS TO 35 MPH HAVE BEEN
OCCURRING. OVER THE MARINE WATERS THERE IS SMALL CRAFT WINDS OVER
LYNN CANAL BUT THE REST OF THE FORECAST AREA IS SEEING SOUTH
WINDS GENERALLY LESS THAN 20 KT. THE WEST TO SOUTHWEST WINDS OVER
EASTERN GULF BEGIN TO BACK AROUND TO THE SE THIS EVENING AS THE
WARM FRONT BEGINS TO DRIFTS INTO THE CENTRAL GULF.

 THE SHOWERS OVER NORTHERN HALF WILL DIMINISH THIS EVENING AND
MAY BE MIXED WITH SNOW AT TIMES WITH VERY COLD AIR ALOFT. THE
SOUTHERN AREAS WILL SEE THE SCATTERED SHOWERS DISSIPATED ALSO
THIS EVENING WITH THE UPPER RIDGE MOVING OVER THE AREA AND
STABILIZE THE ATMOSPHERE. THIS WILL ALSO CREATE SOME PARTLY
CLOUDY SKIES OVER THE SOUTHERN AREAS LATE THIS EVENING BUT IT
WILL NOT LAST LONG AS THE RIDGE WILL CONTINUE INTO CANADA AND
ONSHORE FLOW WILL INCREASE. THE NORTHERN GULF COASTAL AREAS WILL
SEE THE MIX OF RAIN AND SNOW SHOWERS THIS EVENING BECOME MORE
STEADY RAIN LATE TONIGHT AS THE WARM FRONT APPROACHES FROM THE
SW. THE RAIN MAY BE HEAVY AT TIMES THROUGH MON WITH STRONG
VERTICAL MOTION. RAIN WITH SOME SNOW IN PLACES OVER THE NORTHER
HALF OF THE INNER CHANNELS WILL BE LIKELY MAINLY IN THE MORNING
ON MONDAY AS THE UPPER TROF DRIFTS INTO THE CENTRAL GULF THE
UPPER LEVEL FLOW OVER THE PANHANDLE WILL BECOME SE. THIS FLOW
PATTERN IS NOT THAT GREAT FOR PRECIP BUT FOR CLOUDS BUT THERE
WILL REMAIN A CHANCE IN TO THE AFTERNOON.

 THE WARM FRONT WILL INCREASE THE WINDS OVER THE NORTHER GULF TO
GALES LATE TONIGHT WITH A BARRIER JET DEVELOPING. THESE GALES
FORCE WINDS WILL SPREAD SE INTO THE EASTERN GULF THROUGH MON AS
THE SURFACE TROF MOVES INTO THE CENTRAL GULF. THE SMALL CRAFT AND
GUSTY WINDS OVER THE FAR NORTHERN INNER CHANNELS WILL REMAIN
THROUGH MON MORNING BUT AS THE SURFACE RIDGE BEGINS TO DRIFT INTO
CANADA THE PRESSURE GRADIENT WILL RELAX ALONG WITH THE WINDS. THE
WINDS OVER E/W CHANNELS WILL INCREASE THROUGH TONIGHT AND THROUGH
MON AS THE SURFACE TROF/WARM FRONT MOVES INTO THE CENTRAL TO
EASTERN GULF. THE WINDS WILL INCREASE TO SMALL CRAFT BY LATE
TONIGHT AND PERSIST INTO THE AFTERNOON.

 THERE IS ABOUT AVERAGE FORECAST CONFIDENCE IN THE FORECAST FOR
THE NEXT 24HRS. USED A BLEND OF THE 12Z EC AND SOME 12Z NAM FOR
THE SHORT TERM PORTION OF THE FORECAST.

&&

.LONG TERM...LONG RANGE MODELS ARE STRUGGLING WITH A TROUGH
ENTERING THE EASTERN GULF ON LATE MONDAY. DUE TO THE
UNCERTAINTY...REFRESHED THE INHERITED FORECAST WITH THE ECMWF
THROUGH LATE WEDNESDAY. THE ECMWF WAS INITIALIZED WELL AND HELD
THE INCOMING TROUGH A LITTLE SLOWER THAN THE GFS AND NAM. THE
ECMWF ALSO SHOWS SOMEWHAT WEAKER PROGRESS AND QUICKLY BRINGS THE
TROUGH AS AN OPEN WAVE DURING THE TUESDAY EVENING AS A RIDGE
BUILDS ACROSS THE EASTERN GULF AND SOUTHEAST ALASKA THROUGH
WEDNESDAY MORNING. CLOUDS WILL BECOME THICKER BY MONDAY NIGHT INTO
TUESDAY WITH CATEGORICAL POPS SPREADING FROM YAKUTAT SOUTHEAST TO
THE CENTRAL PANHANDLE COASTAL SECTIONS THROUGH TUESDAY MORNING.
PRECIPITATION WILL BE MOSTLY RAIN BUT MIXED WITH SNOW ACROSS THE
NORTHERN AREAS. LIKELY POPS WILL CONTINUE ACROSS SOUTHEAST ALASKA
THROUGH TUESDAY EVENING AND THE PRECIPITATION WILL BE MOSTLY RAIN.

 MODEL DIFFERENCES BECOME EVEN LARGER FROM WEDNESDAY NIGHT
ONWARD. STAYED WITH THE HPC OUTPUTS. THE HPC GUIDANCE APPEARED A
HEAVY BLENDING OF THE ECMWF AND ITS ENSEMBLE MEANS. WITH SUCH A
BIG MODEL DIFFERENCE...IT IS NOT PRACTICAL TO DEPICT SMALL SCALE
FEATURES...BUT THERE IS A CERTAIN LEVEL OF PREDICTABILITY FOR THE
PATTERN CHANGES IN SYNOPTIC SCALE. WHILE THE MAIN UPPER LOW
STAYING IN THE BERING AND MAINLY UPPER RIDGE MOVING EASTWARD
ACROSS THE FORECAST DOMAIN THROUGH SECOND HALF OF THE WEEK...A
MEAN UPPER TROUGH WILL EVENTUALLY MOVE OVER THE EASTERN GULF
TOWARD THE WEEKEND WITH COLDER AIR EMBEDDED. TWEAKED MAX/MIN
TEMPERATURES A BIT COOLER FOR DAYS 6...7 AND 8. POP FIELDS WERE
REMAINED WITH THE BROAD HPC OUTPUTS.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ042-043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ012-013-021-022-033-035-041-053.

&&

ABJ/AHN