Small Craft Advisory 620, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
1100 AM AST MON DEC 17 2007

.SYNOPSIS...
.SHORT RANGE...FRONTAL BANDS ARE SHOWN ON GOES IR AS MOVING W
THROUGH ZONE 17 AT THIS TIME...ALL OF OUR REGION THAT IS UPSTREAM

FROM THESE BANDS IS CONVECTIVE. PAYA 12Z RAOB SHOWED DISTINCT
FRONTAL INVERSION AT 850 MB...THE PANT 12Z RAOB WAS CLOSE TO
UNSTABLE...IE...CONDITIONAL INSTABILITY THAT WILL EASILY CONVECT
DUE TO THE VORT FIELD ALOFT.      THESE SHOWERS WILL DIMINISH
FROM THE N OVERNIGHT...SEE PARAGRAPH ABOUT ESE TRACK OF
VERTICALLY STACKED LOW IN GLFALSK.  THE POLAR FRONT ZONE IS
PERSISTING BWTN 40N AND 50N.

MODEL CONSENSUS IS IMPROVING.  NAM HAS CONSISTENTLY BEEN
DETECTING THE DEFFORMATION ZONE TRACKING NNW ALONG PNHDL AT THIS
TIME...IF SLOR THAN INDICATED BY THE GOES IR LOOP.  GFS STARTED
PICKING UP ON THIS SYSTEM WITH THE 12Z MODEL RUN. SREF ON BOARD
TOO.

THE VERTICALLY STACKED LOW OVER THE CENTRAL GULF OF ALASKA HAS
BEEN THE PARENT FEATURE BUT THE UPPER LEVEL SUPPORT FOR IT WILL
BEGIN TO WEAKEN AND MOVE ESE...AND NC TO ASSOCD TREND IN CURRENT
FCST PKG WITH POPS LOWERING NORTH OF FREDERICK SOUND TONIGHT.
NE BEYOND THE PANHANDLE TUE.

.LONG RANGE...MODELS ARE A MESS THIS MORNING.  RUN TO RUN
CONSISTENCY IS POOR. THE MOST RECENT RUN OF THE OPERATIONAL
MODELS ARE IN AGREEMENT THROUGH 00Z SATURDAY AND DIVERGE
DRASTICALLY BEYOND.  ENSEMBLE MEMBERS ARE WIDELY SKEWED THROUGH
THE PERIOD AS WELL AND IT APPEARS THAT THE OPERATIONAL GFS IS AN
OUTLIER FROM THE MEAN.

THROUGH THURSDAY...A PAIR OF LOWS WEAKENING OVER THE EASTERN AND
NORTHERN GULF WILL CONTINUE TO MOVE SHOWERS ACROSS THE AREA.

MAIN CONCERN THROUGH THE PERIOD FOCUSES ON A LOW FORMING IN THE
WESTERN GULF.  A PAIR OF LOWS DUMBBELL NEAR BRISTOL BAY AND
KODIAK ISLAND WITH THE STRONGER LOW NEAR KODIAK DEEPENING TO THE
950S BY 12Z FRIDAY.  AN ASSOCIATED FRONT SPREADS EAST ACROSS THE
WESTERN GULF THURSDAY THEN INTO THE EASTERN GULF THURSDAY NIGHT.
BOTH THE ECM AND THE GFS ARE IN GOOD AGREEMENT WITH THIS
SOLUTION...HOWEVER THE FRONTAL TIMING IS NEARLY 24 HOURS FASTER
THAN THE CURRENT PACKAGE.  UPON COORDINATION WITH
ANCHORAGE...HAVE DECIDED TO SPLIT THE DIFFERENCE AND SPEED UP THE
FRONT ABOUT 12 HOURS.  ALSO HAVE TONED DOWN THE WINDS ALONG THE
FRONT FROM WHAT THE MODELS DEPICT.  WILL LIMIT WINDS TO HIGH
GALES OF 45 KT GIVEN THE UNCERTAINTY. ALSO EXPECT ADVISORY LEVEL
GUSTS ALONG THE COASTAL ZONES DURING FROPA.

ADDITIONAL CONCERN WITH THIS SYSTEM WILL BE THE POTENTIAL FOR A
GOOD OVERRUNNING SNOW EVENT.  AN ARCTIC AIRMASS WILL STILL BE IN
PLACE DURING THE ONSET OF THE EVENT.  WARMER AIR ADVECTING AHEAD
OF THE FRONT SHOULD WARM THINGS ENOUGH IN THE FAR SOUTH TO BE
MAINLY RAINFALL...HOWEVER PARTICULARLY THE NORTHERN INNER
CHANNELS AND NORTHEASTERN GULF COAST COULD SEE SIGNIFICANT
SNOWFALL. WILL WAIT FOR MORE MODEL RUNS BEFORE ISSUING ANY WATCH
PRODUCTS.

BEHIND THIS SYSTEM...LEFT FORECAST PACKAGE AS IS.  THE ECMWF
HINTS AT A SERIES OF TWO VERY STRONG 960 MB LOWS PASSING JUST
SOUTH OF THE QUEEN CHARLOTTES THROUGH EARLY NEXT WEEK.  MEANWHILE
THE GFS TAKES A WEAKER LOW FURTHER SOUTH NEAR WA/OR BORDER AND AT
A MUCH SLOWER PACE DURING THE TIME FRAME.

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

MARINE...SCA...PKZ011...021...022...031...041>043...051.