Small Craft Advisory 272, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
327 PM AKDT FRI APR 20 2012

.SHORT TERM...SATELLITE IMAGERY THIS AFTERNOON SHOWING A
WEAKENING GALE FORCE LOW IN THE SOUTHERN AK GULF 150 NM WEST OF
CAPE OMMANEY. GALE FORCE WINDS AND SEAS AROUND 20 FT WERE REPORTED
IN THE SOUTHEAST AK GULF. AS THE LOW WEAKENS THE WINDS WILL DROP
TO SMALL CRAFT AS SEAS BEGIN TO SUBSIDE. WEAK BARRIER JET WILL
FORM IN THE NORTHWESTERN GULF SATURDAY AFTERNOON WITH THE ADVANCE
LOW BRINGING WINDS TO SMALL CRAFT LEVEL NEAR CAPE SUCKLING.
FRONTAL BAND ASSOCIATED WITH THE LOW PRODUCED STRONG WINDS AND
MODERATE RAIN FALL OVER THE SOUTHERN PANHANDLE TODAY. AS THE FRONT
MOVES NORTHER WINDS HAVE DIMINISHED OVER THE SOUTH AS RAIN AND
WINDS INCREASING NORTHWARD. THE STRONGER WINDS WILL SUBSIDE
THROUGH THE EVENING AS THE FRONT PASSES. EXPECT RAIN OVER THE
ENTIRE PANHANDLE TONIGHT WITH THE EXCEPTION OF AREAS NEAR YAKUTAT.
HIGH PRESSURE RIDGE WILL BUILD OVER THE PANHANDLE AS THE LOW
ADVANCES TO THE NORTHWEST WITH INCREASING SOUTHERLY PRESSURE
GRADIENT. WIND FLOW WILL SHIFT TO THE SOUTH THROUGH THE AFTERNOON
INTO THE EARLY EVENING BUT MAY SEE SOME LAGGING NORTHERLY WINDS IN
LYNN CANAL IN THE EARLY EVENING. FLOW WILL REMAIN ONSHORE SATURDAY
KEEPING CATEGORICAL POPS IN THE MORNING BUT AS MID LEVEL DYNAMICS
WEAKEN WILL SEE POST FRONTAL SHOWER ACTIVITY BECOME SCATTERED IN
THE AFTERNOON.

 MODELS WERE IN FAIR AGREEMENT WITH SYNOPTIC PATTERN. ECMWF WAS
FASTEST TRANSITIONING THE CLOSED SURFACE LOW TO AN OPEN WAVE
TROUGH, NAM MOVE THE LOW A BIT TOO CLOSE TO THE PANHANDLE COAST
SO KEPT WITH THE 12Z GFS SOLUTION. MAIN DIFFERENCES WITH NEW
MODELS RUNS WAS TO PUT SOME HIGHER POPS ALONG THE PANHANDLE COAST
WITH THE ONSHORE FLOW BUT OTHER WISE CHANGES WERE MINIMAL.
FORECAST CONFIDENCE IS ABOUT AVERAGE.

&&

.LONG TERM...REMAINS OF THE LOW DISCUSSED IN THE SHORT RANGE WILL
LINGER IN THE NORTH CENTRAL GULF AS A HIGH PRESSURE RIDGE ATTEMPTS
TO BUILD IN FROM THE SOUTH THROUGH MONDAY. IT DOES LOOK LIKE A
BRIEF RIDGE WILL DEVELOP OVER THE OUTER COAST BUT BE DISPLACED TO
THE EAST MONDAY NIGHT IN ADVANCE OF AN APPROACHING FRONT. MOST OF
THE PRECIPITATION FROM THIS FRONT IS EXPECTED TO REMAIN SOUTH OF
THE PANHANDLE SO LIMITED LIKELY POPS TO THE SOUTHERN ZONES AND
HAVE CHANCE POPS AS FAR NORTH AS SITKA AND ANGOON THROUGH
WEDNESDAY WITH SOME SCATTERED SHOWER ACTIVITY EXTENDING FARTHER
NORTH WEDNESDAY NIGHT. THE LOW ITSELF IS FORECAST TO REMAIN SOUTH
OF THE PANHANDLE AND A RIDGE SHOULD SET UP LATE IN THE WEEK,
PRODUCING LOW LEVEL ONSHORE FLOW AND A RETURN TO OVERCAST SKIES
ACROSS ALL OF SOUTHEAST ALASKA LATE IN THE WEEK.

PARTIAL CLEARING RESULTING FROM A WEAK LOW LEVEL OFFSHORE FLOW
SHOULD ALLOW TEMPS TO GET DOWN NEAR OR BELOW FREEZING SUNDAY AND
MONDAY NIGHT. DAYTIME HIGHS GETTING UP TO THE MID 50S OVER MOST
PLACES. HIGHS AND LOWS RUNNING 3 TO 7 DEGREES BELOW NORMAL FOR
THIS TIME OF THE YEAR.

NO SIGNIFICANT WINDS IN THE EXTENDED RANGE FORECAST UNTIL TUESDAY
WHEN PRE-FRONTAL SMALL CRAFT WINDS TO 30 KTS WILL WORK ACROSS THE
GULF AND INTO THE COASTAL MARINE ZONES FROM CAPE EDGECUMBE SOUTH AND
EVENTUALLY MAKING IT INTO THE SOUTHERN INNER CHANNELS TUESDAY
NIGHT. OFFSHORE SEAS RUNNING 8 TO 10 FEET DURING THIS TIME.

USED A BLEND OF ECMWF AND HPC FOR PRESSURE AND WINDS. BLENDED
ECMWF AND OFFICIAL GRIDS FOR POP AND QPF FIELDS. ADJUSTED TEMPS
WITH BIAS CORRECTED MOS AND GFS. FORECAST CONFIDENCE IS AVERAGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ033-041-042.
         SMALL CRAFT ADVISORY FOR PKZ021-022-031-032-034>036-043-051-052.

&&

PRB/FRITSCH