Small Craft Advisory 105, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
309 PM AKST MON FEB 6 2012

.SHORT TERM...LOW PRESSURE IN THE NORTH PACIFIC WILL MOVE INTO
THE WESTERN GULF THROUGH THE SHORT TERM PERIOD. THIS ALONG WITH
HIGH PRESSURE OVER BRITISH COLUMBIA WILL CONTINUE THE OFFSHORE
FLOW ACROSS THE REGION AND LIMIT PRECIPITATION. THE N-S PRESSURE
GRADIENT WILL INCREASE LATER TONIGHT AND INTO TUESDAY AS THE LOW
MOVES NORTH. THIS WILL CAUSE WINDS TO INCREASE TO GALE FORCE FOR
NORTHERN LYNN CANAL...ELSEWHERE WINDS WILL BE LIGHTER WITH SMALL
CRAFT LEVEL GUSTS OUT OF INTERIOR PASSES.

 FORECAST CHALLENGE TODAY WAS CLOUD COVER AND TEMPERATURES. AN
UPPER LEVEL LOW DEPARTING TO THE NORTH HAS KEPT THE NORTHERN HALF
OF THE REGION CLOUDY TODAY. THESE CLOUDS LEFT THE SOUTHERN AREAS
THIS MORNING AND MADE FOR A MOSTLY SUNNY DAY. TONIGHT THE
NORTHERN AREAS WILL BECOME PARTLY CLOUDY TO MOSTLY CLEAR WHILE
CLOUDS FROM THE SYSTEM TO THE DISTANT SW WILL MOVE ACROSS THE
SOUTHERN PANHANDLE THIS EVENING...SO HAVE GONE WITH INCREASING
CLOUDS FOR DOWN THERE. AMOUNT OF CLOUD COVER WILL PLAY A ROLE IN
HOW MUCH RADIATIONAL COOLING THERE IS TONIGHT.

 SIMILAR TO WHAT HAPPENED SATURDAY NIGHT...THERE IS SIGNIFICANT
WARM AIR ADVECTION EXPECTED TO MOVE INTO THE LOWER TO MID LEVELS
TONIGHT AND TOMORROW. THIS WILL SET UP A TEMPERATURE INVERSION.
AREAS THAT HAVE SOME WINDS WILL BE ABLE TO MIX DOWN THESE MUCH
WARMER TEMPERATURES WHILE AREAS WITH LIGHTER WINDS WILL BE
SEVERAL DEGREES COOLER. IN ADDITION THERE IS A POSSIBILITY OF FOG
TO DEVELOP OVERNIGHT IN THE AREAS WITH LIGHT WINDS...THIS WILL
KEEP THOSE AREAS SLIGHTLY WARMER AS WELL.

 NUMERICAL MODELS WERE IN GOOD AGREEMENT WITH THE PRESSURE
PATTERN IN THE SHORT TERM. UPDATED THE GOING FORECAST WITH AN
ENSEMBLE APPROACH TO INCORPORATE FINER DETAILS OF EACH MODEL.
FORECASTER CONFIDENCE IS AVERAGE.

&&

 .LONG TERM...MID LEVEL HIGH PRESSURE RIDGE OVER THE WESTERN US
REMAINS IN PLACE THROUGH THE END OF THE WEEK THEN BEGINS TO BREAK
DOWN BY THE WEEKEND. QUASI STATIONARY LOWS NEAR HUDSON BAY AND
KAMCHATKA PENINSULA SHOW INCREASED MOVEMENT THROUGH THE WEEKEND
BUT OVERALL REMAIN THROUGH THE LONG TERM. MID LEVEL LOW OVER THE
YUKON TUESDAY NIGHT WILL MOVE NORTHWEST INTO THE AK INTERIOR
DIMINISHING TO AN OPEN WAVE. A SERIES OF LOWS WILL ROTATE AROUND
THE KAMCHATKA LOW MOVING UP FROM THE NORTH PACIFIC INTO THE AK
GULF THROUGH THE WEEK. BY THE WEEKEND TRANSITION TO MORE ZONAL
FLOW WITH THE NEXT MID LEVEL LOW WHICH WILL TRACK EASTWARD ACROSS
THE AK GULF. BY NEXT WEEK ANOTHER MID LEVEL HIGH PRESSURE RIDGE
WILL BUILD OVER THE AK GULF THEN TRACK EAST.

 AT THE SURFACE DETAILS GET SKETCH BY WEDNESDAY. THE 960 MB
SURFACE LOW MOVING INTO THE WESTERN GULF WILL TRACK TOWARD THE AK
PENINSULA BY WEDNESDAY EVENING. ASSOCIATED FRONT WILL MOVE
NORTHWARD OVER THE AK GULF AND PANHANDLE BRINGING PRECIP LATE
TUESDAY NIGHT INTO WEDNESDAY. PRECIP WILL BE MOSTLY RAIN WITH
WARM AIR ALREADY IN PLACE AND WARM AIR ADVECTION AT 850 MB BUT
WITH OVERNIGHT LOWS IN THE UPPER 20S TO LOW 30S MAY SEE SOME SNOW
MIXED IN. NOT EXPECTING ANY SIGNIFICANT SNOW ACCUMULATION FROM
THIS FRONT.

 THE NEXT SYSTEM MOVING UP FROM THE NORTH PACIFIC ON THURSDAY IS
STILL VERY MUCH IN QUESTION. THE GFS WHICH HAS BEEN FAIRLY
CONSISTENT RUN TO RUN KEEPS THE LOW ON A NORTHERLY TRACK IN THE
CENTRAL AK GULF. THE EC SHOWS A WEAKER LOW CENTER WHICH TRACKS
TOWARD HAIDA GWAII MOVING OVER THE SOUTHERN AK PANHANDLE BY
FRIDAY AND WEAKENING TO AN OPEN WAVE TROUGH. AS WINDS AND PRECIP
ARE SIGNIFICANTLY DIFFERENT WITH EACH SOLUTION HAVE KEPT POPS
BELOW CATEGORICAL AND WINDS IN A MID RANGE OF 15 TO 25 KTS.

 MODELS BEGAN IN GOOD AGREEMENT AT THE START OF THE LONG TERM.
USED SOME 12S NAM TO UPDATE GRIDS DUE TO A BIT BETTER DETAIL WITH
WINDS. HPC HAS CONTINUED WITH A EC/EC ENSEMBLE SOLUTION WHICH WAS
STILL CLOSE TO INHERITED GRIDS. WHILE HAVE BEEN LIKING THE GFS
RUN TO RUN CONSISTENCY DECIDED TO KEEP CONSISTENT WITH THE EC
INFLUENCED GRIDS UNTIL ANOTHER TREND BECOMES APPARENT. OVERALL
CHANGES TO THE FORECAST WERE MINOR. FORECAST CONFIDENCE IS WELL
BELOW AVERAGE DUE TO WIDE SPREAD WITH SURFACE FEATURES EVEN WITH
MODELS BEING IN FAIR AGREEMENT WITH MID LEVEL SYNOPTIC SCALE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ012.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-022-031>033-035-036-
     041>043-051>053.

&&

HANNON/PRB