Small Craft Advisory 97, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
1100 AM AST THU FEB 15 2007

.SYNOPSIS...

.SHORT RANGE...AN EAST WEST ORIENTED TROUGH IS LOCATED AROUND
57N OR 58N AND IS INCHING NORTHWARD. A COUPLE OF WEAK LOW
CENTERS ARE POSITIONED ALONG THIS TROUGH. PREFER THE NAM MODEL
FOR ITS DEVELOPMENT AND POSITION OF THESE MESOSCALE LOWS.
WIDESPREAD RAIN AND SNOW IS PRESENT ACORSS THE PANHANDLE WITH
MOIST ONSHORE FLOW. ONLY YAKUTAT IS ESCAPING THE PRECIPITATION.

PERIODS OF RAIN AND SNOW WILL CONTINUE TONIGHT. THE BIGGEST
CHALLENGE WILL BE WHERE THE RAIN SNOW LINE SETS UP. BEST BET AT
THIS POINT IS FOR A RAIN SNOW MIX ALONG THE TROUGH AXIS ACROSS
THE NORTH CENTRAL PANHANDLE...WITH SNOW NORTH OF THE TROUGH AXIS
AND RAIN SOUTH. AS THE TROUGH AXIS INCHES
NORTHWARD...PRECIPITATION WILL GRADUALLY SWITCH OVER TO PRETTY
MUCH ALL RAIN BY TOMORROW AFTERNOON WITH THE POSSIBLE EXCEPTION
OF THE FAR NORTHERN ZONES AND OF COURSE THE HIGHER TERRAIN.
PRECIPITATION WILL BECOME MORE SHOWERY TOMORROW WITH WEAK COLD
ADVECTION ALOFT. DRIER AIR WILL GRADUALLY MOVE IN FROM THE
SOUTHWEST WITH A BRIEF BREAK IN THE ACTION LATE TOMORROW
AFTERNOON OR EVENING BEFORE A STRONG OCCLUSION APPROACHES THE
AREA FROM THE SOUTH. GOING MOSTLY WITH THE GFS FOR TIMING OF THE
NEXT FRONT OVER THE NAM/WRF.

.LONG RANGE...FORCAST PACKAGE THROUGH NEXT WEDNESDAY WILL
CHANGE LITTLE...INCLUDING TEMPERATURES FROM NEAR FREEZING
TO A FEW DEGREES ABOVE WITH MOST FORECAST PERIODS IN CENTRAL
SOUTHEAST ALASKA HAVING BOTH SNOW AND RAIN THROUGH WEDNESDAY.
MODEL CONSENSUS FOR THE LONG RANGE IS GOOD AND THE GFS 40 KM
RESOLUTION WILL BE USED AS PRIMARY GUIDANCE...MODELS
DISCUSSED BELOW.

MOST IMPORTANT TREND IS WED AND THU...WITH THE DETERMINISTIC
MODELS DEPICTING A COLD OUTBREAK.  THIS OUTBREAK IS PLAUSIBLE
GIVEN A LARGE SCALE HIGH AMPLITUDE RIDGE ALOFT OVER THE
DATELINE TUE MOVING EAST OVER BRISTOL BAY...HOWEVER THE RIDGE
WOULD ONLY HAVE TO BE EITHER SLOWER OR OF ANY LESS AMPLITUDE
TO DELAY THE COLD OUTBREAK.  SOLN WILL BE TO LIMIT THE
COOLING UNTIL SUCCESSIVE RUNS COME IN THAT COULD VERIFY
THE TREND...IE...WE HAVE LEAST CONFIDENCE FURTHEST OUT IN
THE FUTURE.

MODELS...GFS 12Z RUN HAS A HIGH INTERNAL CONFIDENCE...IN
OTHER WORDS IT HAS LITTLE DIFFERENCE FROM THE ENSEMBLE MEAN
AND THE ENSEMBLE HAS LITTLE SPREAD AT 500 MB THROUGH NEXT
WEDNESDAY.  EUROPEAN HAS SYNOPTIC AGREEMENT.

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...NONE

MARINE...SMALL CRAFT ADVISORY ZONES 34 35 36 41 42 43 52 310.

TF JT