Snow Advisory 2, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
1100 AM AST SAT NOV 24 2007

.SYNOPSIS...
.SHORT RANGE...CONVECTIVE TROUGH MAKING LANDFALL AT THIS
TIME AND SHOULD REDEVELOP NEAR WIND ADVISORY SOUTH WINDS
FOR SKAGWAY THIS AFTERNOON.  SNOW LEVEL WITHIN 1000 FT OF SEA
LEVEL NORTH OF FREDERICK SOUND AT THIS TIME...LOWERING TO
NEAR SEA LEVEL IN THE VICINITY OF SKAGWAY OVERNIGHT.  TWO LOWS
SYNOPTICALLY TO THE WEST ARE BEING STUDIED THIS MORNING.
THEIR INTERACTION IS IMPORTANT TO OUR FORECAST AREA FOR A WIND
EVENT SUN.

LOW ONE IS 973 MB LOW ABOUT 100 NM E OF DUTCH HARBOR.  THIS
LOW HAS BEEN QUASISTATIONARY.

LOW TWO IS JUST FORMING FROM AN OPEN WV 700 NM S OF
DUTCH HARBOR...AND ACCORDING TO BOTH THE NUMERICAL MODELS
AND THE GOES LOOP IS HIGHLY CYCLOGENETIC AND TRACKING
ENE.  IT SHOULD DEEPENING TODAY AT AS RATE OF ABOUT 20 MB
IN 18 HRS.

THESE TWO LOWS ARE BEGINNING TO INTERACT CYCLONICALLY
INTERACT...OR WHAT ONE MIGHT CALL DUMBELL AROUND ONE ANOTHER.
LOW ONE IS STILL THE DEEPER FEATURE AND AT PRESENT WILL
SEND LOW TWO ON THE WIDER ARC.  HOWEVER...AS LOW
TWO DEEPENS THEY WILL CHANGE ROLLS. BY 12Z SUN LOW TWO
WILL BE DOWN TO 967 MB WITH LOW ONE LITTLE CHANGED FROM
973 MB...AND LOW TWO WILL BECOME THE PRIMARY AND SENDING
LOW ONE DISSIPATING INTO BRISTOL BAY.  THE TRACK ON
LOW ONE DOES BECOME LESS IMPORTANT FOR US TONIGHT BUT
IS HELPING TO FEED A COLD AIRMASS FROM THE BERING TO LOW
TWO AND THEREFORE HELPING TO SUSTAIN THE STRONG THERMAL
CONTRAST ASSOCIATED WITH THE RAPID CYCLOGENESIS OF LOW
TWO.

GOOD SHORT RANGE CONSENSUS BETWEEN NAM AND GFS THROUGH
00Z MON AND THE 12Z RUN OF THESE MODELS USED AS GUIDANCE.
UNUSUAL SPREAD BETWEEN UKMET AND ECMWF FOR THE SHORT RANGE
IS ASSOCIATED WITH LOW TWO.

SNOW LEVEL WITHIN 1000 FT OF SEA LEVEL NORTH OF FREDERICK
SOUND AT THIS TIME...LOWERING TO NEAR SEA LEVEL IN THE
VICINITY OF SKAGWAY OVERNIGHT.

.LONG RANGE...MODELS ARE IN PRETTY GOOD AGREEMENT SUN NIGHT
THROUGH WED WITH ONLY MINOR ADJUSTMENTS TO THE CURRENT FORECAST
ANTICIPATED. A LOW IN THE 960S WILL BE POSITIONED OVER THE
WEST-CENTRAL GULF BY SUN NIGHT. THIS LOW WILL LINGER AND WEAKEN
THERE THROUGH MON...THEN AN UPPER LEVEL RIDGE BUILDING NORTH INTO
WESTERN ALASKA WILL CAUSE THE LOW TO EJECT SOUTHEAST INTO THE
SOUTHEAST GULF THROUGH TUE WHERE IT WILL DISSIPATE.

THE OCCLUDED FRONT ASSOCIATED WITH THE LOW WILL APPROACH THE
PANHANDLE FROM THE SOUTH EARLY SUN NIGHT AND MOVE NORTH THROUGH
THE REGION THROUGH EARLY MON. A BAND OF PRECIPITATION AHEAD OF
THE FRONT WILL SPREAD RAIN INTO THE SOUTHERN HALF AND CENTRAL
COASTAL AREAS SUN NIGHT. PRECIP TYPE IS A LITTLE MORE TRICKY OVER
THE NORTHERN HALF AND WILL DEPEND ON THE POSITION OF AN ARCTIC
HIGH DROPPING SOUTH OVER THE NORTHWEST TERRITORIES. THE GFS
TRACKS THAT HIGH A BIT FURTHER WEST AND ALLOWS COLDER AIR TO WORK
ITS WAY INTO THE NORTHERN HALF AS THE EASTERLY GRADIENT INCREASES
SUN NIGHT BETWEEN THE HIGH AND THE LOW. THIS WOULD ALLOW FOR ALL
SNOW FROM JUNEAU-GUSTAVUS NORTH BUT WITH EASTERLY FLOW EXPECT QPF
AMOUNTS TO BE FAIRLY LIGHT. SHOWERS BEHIND THE FRONT THROUGH TUE
WILL BE MAINLY RAIN...EXCEPT MIXED RAIN AND SNOW AT TIMES FROM
JUNEAU-GUSTAVUS NORTH WITH ALL SNOW OVER THE NORTHERN LYNN CANAL
REGION.

OVER THE GULF...EASTERLY STORM FORCE WINDS AHEAD OF THE FRONT SUN
NIGHT STILL LOOK GOOD WITH SMALL CRAFT TO GALE FORCE WINDS BEHIND
THE FRONT DIMINISHING BY MON NIGHT. OVER THE INNER
CHANNELS...NORTHERLIES WILL INCREASE TO SMALL CRAFT TO GALES OVER
THE CENTRAL AND NORTHERN INNER CHANNELS WITH EAST TO SOUTHEAST
GALES OR STORMS OVER THE SOUTHERN INNER CHANNELS. THE POTENTIAL
IS THERE FOR HIGH WIND WARNING GUSTS (60 MPH OR HIGHER) OVER THE
SOUTHERN THIRD AND FROM SITKA SOUTH ALONG THE COAST SUN NIGHT.
WINDS AT 850 MB INCREASE TO AROUND 75 KT MON NIGHT. MAY CONSIDER
ISSUING A HIGH WIND WATCH FOR ZONES 023 AND ZONES 027-029 FROM
6 PM SUN THROUGH 4 AM MON AFTER REVIEWING THE 18Z MODEL RUNS.
WIND ADVISORY GUSTS WILL BE LIKELY FOR ZONE 026 AND POSSIBLY ZONE
025 OUT OF INTERIOR PASSES.

THE NEXT OCCLUDED FRONT MOVES EAST ACROSS THE GULF AND INTO THE
PANHANDLE TUE NIGHT THROUGH WED BRINGING GALES OVER THE
GULF...SMALL CRAFT WINDS TO THE INSIDE WATERS...AND RAIN INTO THE
PANHANDLE EXCEPT OVER THE FAR NORTHEAST WHERE ALL SNOW IS LIKELY.

BEYOND WED...NO CHANGES WILL MADE TO THE CURRENT FORECAST AS
MODEL DIFFERENCES ARE TOO LARGE IN THE LONG WAVE PATTERN
RESULTING IN LOW CONFIDENCE. THE GFS BRINGS THE PANHANDLE INTO A
COLD REGIME WITH AN ARCTIC HIGH TO THE NORTH FOR LATE WEEK INTO
NEXT WEEKEND...WHILE THE ECMWF KEEPS THE ARCTIC AIR WELL EAST OF
THE PANHANDLE AND IN A RELATIVELY MILD PATTERN. THE CURRENT
FORECAST REFLECTS THE GFS SOLUTION WITH DRY CONDITIONS DEVELOPING
BY FRI BUT DOES NOT ADVERTISE THE EXTREME COLD TEMPERATURES
DEPICTED BY THE MODEL...WHICH IS GOOD AT THIS POINT IN TIME.

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...WIND ADVY...ZONE 18 UNTIL 3 PM
MARINE...SCA...PKZ012-022-041>043-051-052

JT/TAR