Small Craft Advisory 671, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
326 PM AKST MON NOV 12 2012

.SHORT TERM...SHOWER ACTIVITY WILL GRADUALLY BECOME MORE SCATTERED
THROUGH THE PERIOD AS THE PARENT SURFACE LOW CAUSING IT WEAKENS.
UPPER LEVEL SHORT WAVES AND VORTICITY MAXIMA WILL INCREASE SHOWERS
AS THEY PASS OVER. CURRENTLY MAJORITY OF THE PRECIP IS FALLING AS
RAIN. HOWEVER CAA IS BEGINNING OUT OF THE NORTH AS A HIGH PRESSURE
CENTER IN THE YUKON BUILDS AND INCREASES THE WINDS THROUGH HAINES
AND SKAGWAY. TEMPERATURES WILL FALL BELOW FREEZING TONIGHT FOR
AREAS NORTH OF A HOONAH TO JUNEAU LINE. THEREFORE EXPECT THOSE
LOCATIONS TO SEE RAIN CHANGING TO SNOW...HOWEVER THE DRIER NORTH
FLOW WILL HELP TO SCATTER OUT SHOWERS EVEN FURTHER. SO NOT
EXPECTING MUCH IN THE WAY OF ACCUMULATIONS. THE CENTRAL
AREAS...INCLUDING JUNEAU...WILL HAVE SLIGHTLY HIGHER QPF AMOUNTS
OVERNIGHT DUE TO ONE OF THOSE SHORTWAVES...SO HAVE GONE WITH
AROUND 2 INCHES OF ACCUMULATION WITH SNOW SHOWERS LIKELY.

 THE NORTH WIND THROUGH LYNN CANAL WILL INCREASE THROUGH THE
EVENING TO ABOUT 30KT. THERE IS A CHANCE THAT SPEEDS COULD REACH
GALE FORCE OF 35 KT...BUT HAVE OPTED TO STICK WITH MAX SMALL CRAFT
FOR NOW AS THE LOW PRESSURE CENTER WILL BE WEAKENING AND LIMIT THE
PRESSURE GRADIENT. THE PRESSURE PATTERN WEAKENS ACROSS THE CENTRAL
PANHANDLE OVERNIGHT AND TUESDAY AS THE LOW DIMINISHES AND SHIFTS
OVER THE PANHANDLE. AS A RESULT WIND SPEEDS WILL BE LIGHT AND
VARIABLE FOR MUCH OF THE DAY...THEN SHIFTING OUT OF THE SOUTH.

 OVERALL MODELS WERE IN GOOD AGREEMENT. USED AN ENSEMBLE APPROACH
WITH AN EMPHASIS ON THE NAM12 AND HIRES NMM. ONE CHALLENGE WAS
WITH THE WEAK PRESSURE PATTERN AND RESULTING VARIED WIND
DIRECTIONS. OVERALL FORECAST CONFIDENCE IS AVERAGE.

 &&

 .LONG TERM...HIGH PRESSURE RIDGE OVER THE PANHANDLE WILL CONTINUE
TO FLATTEN AS IT TRACKS TO THE EAST WHILE HIGH PRESSURE OVER THE
YUKON WILL WEAKEN AND MOVE TO THE EAST. AT THE SAME TIME A WARM
FRONT ASSOCIATED WITH 970 MB LOW IN THE BERING SEA WILL MOVE
ACROSS THE AK GULF REACHING THE PANHANDLE WEDNESDAY EVENING. THE
FRONT WILL SPREAD PRECIP OVER THE PANHANDLE FROM NORTH TO SOUTH.
TEMPERATURES WEDNESDAY NIGHT WILL REMAIN STEADY OR SLOWLY INCREASE
WITH THE PASSING FRONT. PRECIP WILL TRANSITION TO MOSTLY RAIN
OVERNIGHT DUE TO THE WARM AIR ADVECTION AND WINDS SHIFTING TO THE
SOUTH. WILL ALSO SEE AN INCREASE IN WINDS ALONG THE COAST AND
INNER CHANNELS DUE TO THE PASSING FRONT.

 BY THURSDAY THE BERING SEA LOW WILL TRACK OVER THE ALEUTIANS WITH
THE 988 LOW CENTER MOVING NEAR KODIAK. THIS LOW WILL BECOME THE
DOMINANT FEATURE IN THE GULF THROUGH SATURDAY BEFORE TRACKING TO
THE SOUTHEAST BY SUNDAY. AS THE LOW MOVES SOUTH AN ARCTIC HIGH
WILL REFORM OVER THE YUKON. THIS ARCTIC AIR ALONG WITH COLD AIR
PUSHING SOUTH WITH THE INCOMING LOW WILL DROP TEMPERATURES LATE IN
THE WEEK WITH OVERNIGHT LOWS IN THE TEENS POSSIBLE FOR THE
NORTHERN PANHANDLE. PRECIP FROM THE LOWS SECOND WARP WILL BEGIN TO
DIMINISH FROM NORTH TO SOUTH BY THE WEEKEND...BUT STILL SOME
UNCERTAINTY REGARDING THE TIMING OF THE LOWS EXIT SO HOLDING BACK
ON DRYING OUT THE CENTRAL PANHANDLE JUST YET. ON THURSDAY WINDS
WITH THE APPROACHING LOW WILL NEAR GALE FORCE ALONG THE AK GULF
COAST AND INNER CHANNELS WITH WINDY CONDITIONS OVER THE PANHANDLE
DUE TO THE TIGHTENING PRESSURE GRADIENT. MAY SEE SOME HEAVIER
PRECIP ALONG THE SOUTHERN PANHANDLE WITH THE PASSING FRONTAL
BOUNDARY.

 MODELS WERE IN GOOD AGREEMENT FOR THE START OF THE LONG TERM.
NAM/ECMWF SHOWED GOOD INITIALIZATION WITH THE GFS VERY CLOSE WITH
RESPECT TO FEATURES OVER THE AK GULF. THE GFS IS A BIT DEEPER
COMPARED TO THE ECMWF FOR THE BERING SEA LOW INITIALLY AND STAYS A
BIT DEEPER AS THE LOW MOVES NEAR KODIAK. BY 12Z FRIDAY THE GFS
BEGINS TO FILL THE LOW MUCH FASTER THAN THE ECMWF. THE 00Z ECMWF
WAS DEEPER WITH THE LOW CENTER...978 MB AT 18Z FRI COMPARED TO THE
12Z ECMWF WITH A LOW CENTER OF 985 MB...WHICH IS CLOSER TO THE 12Z
GFS. HOWEVER NEWER MODELS ARE STILL STRONGER WITH THE LOW THAN
PREVIOUS MODELS AND FORECAST. USED A BLEND OF 12Z ECMWF AND NAM
THROUGH DAY 3...MAIN CHANGES WERE TO BUMP UP SOME WINDS WITH THE
WARM FRONT PASSAGE. BY DAY 4 TRANSITIONED TO A 12Z ECMWF/GFS BLEND
THEN DID A 50/50 BLEND OF HPC WITH INHERITED GRIDS. WHILE PRESSURE
CENTER WITH NEW PACKAGE WAS DROPPED DID NOT GO AS DEEP AS THE NEW
HPC..MAINLY AS HPC WAS AN ECMWF/ECMWF ENSEMBLE BLEND AND THERE WAS
ENOUGH UNCERTAINTY WITH BETWEEN THE 00Z AND 12Z ECMWF RUNS.
FORECAST CONFIDENCE IS GOOD WITH RESPECT TO THE GENERAL SYNOPTIC
PATTERN THROUGH THE WEEKEND...BUT THERE ARE ENOUGH UNCERTAINTIES
WITH THE STRENGTH AND POSITION OF THE LOW TO KEEP CONFIDENCE JUST
BELOW AVERAGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041-042.

&&

HANNON/PRB