Gale Warning 456, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
600 AM AKST SUN DEC 9 2012

.SHORT TERM...THE FAST-MOVING OCCLUDED FRONT MOVED ONSHORE ABOUT
09Z LAST NIGHT AND HAS ALREADY MOVED NE BEYOND OUR AREA OF
RESPONSIBILITY TO CANADA. THE WARM UP TO RAIN HAS ALREADY
OCCURRED ON THE OUTER COAST. IN THE INNER CHANNELS THE WARM UP
TRANSITION TO RAIN IS UNDERWAY. KETCHIKAN CHANGED FROM SNOW TO
RAIN BY 1353Z THIS MORNING. WITH THE FRONTAL PASSAGE, THE WINDS
IN THE BOUNDARY LAYER HAVE AN INCREASED COMPONENT FROM THE SSE
THIS HELPS MIXING OUT THE LAST OF THE COLD AIR THAT WAS BEING
OVERRUN. THE OVERRUN THAT WAS OVER COLDER AIR IS ALREADY BECOMING
AN OVERRUN OF TERRAIN AND GENERATE WHAT IS CALLED OROGRAPHIC
LIFT.

THE FRONTAL PASSAGE ALSO HAS AN 850H FLOW THAT IS FROM THE WSW
AND WILL RESULT IN CONTINUED PRECIPITATION. OROGRAPHIC LIFT IS NOW
THE MECHANISM, WITH THE LIFT OVER COLDER AIR ABOUT FINISHED. A
WEAK COLD ADVECTION WILL OCCUR TODAY FOR MOST OF THE AREA OF
RESPONSIBILITY, YET THIS POST FRONTAL ENVIRONMENT IS NOT
CONVECTIVE. THE STATIC STABILITY IS LESS, BUT THERE IS LITTLE
CONVECTIVE POTENTIAL ENERGY AVAILABLE. RELATIVE VORTICITY VALUES
ARE CLOSE TO NEUTRAL AND A BROAD LOW-AMPLITUDE RIDGE IS PROVIDING
MITIGATION OF THE WEAK POSITIVE VORTICITY FEATURES THAT ARE GIVEN
A WEAK INDICATION ON THE GOES IR LOOP.

MODEL CONSENSUS WAS USEFULLY GOOD, AND A VARIETY OF BOTH
STATISTICAL AND DETERMINISTIC VERSIONS WERE USED. CONFIDENCE IS
AVERAGE.

.LONG TERM...ALTHOUGH THE FLOW ALOFT IS ANTICYCLONIC ON
MONDAY...THERE IS MOISTURE IN IT AND A SURFACE LOW DEVELOPS
SOMEPLACE IN THE EASTERN HALF OF THE GULF. SATELLITE IMAGERY SHOWS
THAT THE DEVELOPMENT HAS BEGUN NEAR 40N 172W SORTA NEAR A STRONG
JET EXIT. ALL 09/00Z OPS MODELS AGREE ON THIS LOW BUT THE DEVIL IS
IN THE DETAILS. OPTED FOR THE AK-GFS-40 WHICH WAS IN AGREEMENT
WITH THE UKMET WHICH ALSO AGREED WITH THE PREVIOUS FORECASTS. HAVE
TO BELIEVE THAT THIS CENTER WILL DIE OUT OVER THE CENTRAL
PANHANDLE EARLY TUE AND ALL OPS MODELS BUILD A STRONGER UPPER
RIDGE ALONG 160W ALSO EARLY TUE. NO DOUBT THAT THIS PROGRESSIVE
PATTERN WILL MOVE THE UPPER RIDGE OVER THE GULF BY EARLY WED. THIS
IS ACCEPTED AND GIVES SE ALASKA A BREAK IN PRECIPITATION AND EVEN
IN THE CLOUDS TUE NIGHT INTO WED. ITS A SHORT BREAK AND BACK INTO
MOIST FLOW LATER ON WED...AGAIN DUE TO THE PROGRESSIVE PATTERN.

CONFIDENCE IS MODERATE. PRECIP TYPE IS DICEY IN THIS SET OF FORECASTS
BUT EXPECT NO SNOWSTORMS IN THE LONG TERM FORECASTS AT THIS TIME.
MOST LIKELY OUTCOME IS RAIN OR MIXED RAIN SNOW UNTIL LATER IN THE
WEEK WHEN THE TREND WILL BE TOWARD SNOW IN THE NORTHERN SECTIONS. HPC
FORECASTS RELATIVELY WEAK ARCTIC HIGH PRESSURE BUILDING INTO THE
YUKON FROM THE WEST NEXT WEEKEND BUT WOULD HAVE TO HAVE A FEW MORE
DAYS OF MODEL RUNS TO HAVE HIGHER CONFIDENCE IN THAT SCENARIO WHICH
WOULD MEAN COLDER AIR. ENSEMBLE SPREADS TOO GREAT TO HAVE HIGH
CONFIDENCE AFTER FIVE DAYS ESPECIALLY FOR THE TIMING UNDER ZONAL
FLOW.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ011>013-021-022-031>036-041>043-051-
     052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ053.

&&

JBT/JC