Gale Warning 161, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
129 PM AKDT SAT MAR 21 2009

.SHORT TERM... A 995 MB LOW IN THE EAST-CENTRAL GULF WILL
CONTINUE TO WEAKEN AS IT SLOWLY DRIFTS NW THROUGH SUN. A 1000 MB
LOW JUST WEST OF THE QUEEN CHARLOTTES WILL DRIFT NE AND DISSIPATE
LATER THIS EVENING OVER THE SOUTHERN PANHANDLE.

 LATEST SATELLITE IMAGERY SHOWS THE NORTHERN PANHANDLE UNDER
MOSTLY SUNNY SKIES AS CLOUDS ASSOCIATED WITH A DEFORMATION BAND
LOCATED ACROSS THE SOUTHERN ZONES ARE GRADUALLY MOVING NW. SNOW
SHOWERS ASSOCIATED WITH THE DEFORMATION BAND ARE PRODUCING
REDUCED VISIBILITIES TO AS LOW AS HALF A MILE AT TIMES AS
OBSERVED IN PAKT AND PANT. WINDS ARE GENERALLY 15 MPH OR LESS
THOUGH A FEW AREAS AROUND THE PAJN AREA AND NEAR HEAVIER SNOW
SHOWERS HAVE REPORTED GUSTS TO AROUND 25 MPH.

 MAIN QUESTION IS HOW FAR WILL THE DEFORMATION BAND MOVE NORTH
BEFORE FIZZLING OUT. CURRENT THINKING IS THE BAND WILL MAKE IT TO
AKZ026 BEFORE DISSIPATING LATE THIS EVENING. NORTHEASTERLY FLOW
WILL HELP TO KEEP DRY AIR MOVING ACROSS THE PANHANDLE WHICH WILL
INHIBIT THE AMOUNT OF SNOW THAT REACHES THE SURFACE. EXPECT TO
SEE SNOW ACCUMULATIONS AROUND AN INCH ACROSS THE SOUTHERN ZONES
WITH LOCALLY HIGHER ACCUMULATIONS NEAR HEAVIER SHOWERS.
ELSEWHERE...EXPECT TO SEE LITTLE TO NO ACCUMULATION AS FLURRIES
WILL BE PRESENT ACROSS THE NORTHERN AND CENTRAL ZONES. ONLY
EXCEPTION IS PAYA WHO COULD SEE UP TO AN INCH AS A WEAK BAND OF
SHOWERS MOVES ONSHORE LATE TONIGHT/EARLY SUN MORNING.

 MODELS REMAIN IN FAIR AGREEMENT WITH ECMWF REMAINING THE
OUTLIER. NAM CONTINUES TO BE THE MODEL OF CHOICE AS IT WAS USED
TO MAKE CHANGES TO THE GRIDS. FORECASTER CONFIDENCE IS ABOVE
AVERAGE.

.LONG TERM...MODELS IN GOOD LARGE SCALE AGREEMENT THROUGH MIDWEEK.
UPPER RIDGE OVER THE BERING SEA WILL RETROGRADE W A BIT THROUGH
MIDWEEK...AND ALLOW TROF OVER THE GULF TO REFORM A BIT FURTHER W.
THIS WILL INCREASE THE DEEP LAYER ONSHORE FLOW ACROSS THE AREA
ONCE THE TRANSITION OCCURS BY EARLY NEXT WEEK. MODELS AGREE
REASONABLE ON THE EARLY AND MIDWEEK SYSTEMS NOW...WITH ONLY VERY
SMALL TRACK AND/OR INTENSITY DIFFERENCES NOTED. THAT BEING
SAID...AVOIDED MAKING ANY BIG CHANGES TO THE FORECAST ESPECIALLY
AFTER TUE.

AS FIRST LOW AND COMPLEX FRONTAL SYSTEM MOVES IN FOR SUN
NIGHT...EXPECT PRECIP TO INCREASE OVER THE ERN GULF AND ALONG THE
OUTER COAST. PRECIP SHOULD SPREAD INLAND MON AS WEAK OCCLUDED
FRONT REACHES THE COAST THEN BEGINS TO GO ALOFT. STRONGER COLD
FRONT WILL SWEEP IN MON EVENING AND INCREASE PRECIP RATES ACROSS
THE AREA. PTYPE SHOULD START AS SNOW OVER THE NRN AND ERN
CHANNELS AS WELL AS THE PAYA AREA...BUT LIKELY MIX WITH OR CHANGE
TO RAIN OVER ALL BUT THE FAR NRN AREA BY MON AFTERNOON. DO NOT
THINK THAT SNOWFALL WILL REACH WARNING LEVELS WITH THIS SYSTEM DUE
TO THE MIX/CHANGEOVER...WITH THE FAR N HAVING A LOW PROB OF 6
INCHES OF SNOW OUT OF THIS. WILL NOT BE ISSUING ANY WINTER WWA
HEADLINES WITH THIS SYSTEM ATTM. WINDS COULD BE AN ISSUE LATE SUN
NIGHT INTO MON ALONG THE OUTER COAST...AND WIND ADVYS MAY BE
NEEDED FOR THOSE AREAS. ORIENTATION OF THE WEAK OCCLUDED FRONT IS
NOT THE BEST HOWEVER WITH A LITTLE TOO MUCH OF AN E-W
ORIENTATION...SO THE STRONGER WINDS SHOULD BE MUCH MORE LOCALIZED
THAN IF THE FRONT WAS MORE N-S ORIENTED. ENDED UP BLENDING IN THE
NAM12 WITH THE PREVIOUS GRIDS TO TAKE INTO ACCOUNT SLIGHTLY FASTER
MODEL TIMING WITH THIS SYSTEM FOR SUN NIGHT INTO MON NIGHT.

AFTER COLD FRONT GOES INLAND MON NIGHT...SHOULD GO OVER TO SHOWERS
AROUND DAYBREAK TUE. LOOKS LIKE AIRMASS WILL BE COLD ENOUGH FOR AT
LEAST MIXED PRECIP ESPECIALLY DURING THE MORNING AND NIGHTTIME
PERIODS. HEATING DURING THE DAY COULD LIMIT AMOUNT OF SNOW DURING
THE AFTERNOON AND EARLY EVENING HOURS. IN HEAVIER SHOWERS THE
PRECIP MAY BE MOSTLY SNOW.

NEXT SYSTEM WILL MOVE IN FOR MIDWEEK. MODELS CLOSE ON THE TRACK
WITH GFS TAKING LOW JUST E OF KODIAK ISLAND AND ECMWF TAKING IT
JUST W OF KODIAK ISLAND. ONLY ADJUSTMENT MADE FOR THIS SYSTEM WAS
TO INCREASE STRONGEST WINDS TO MIN GALES FOR WED OVER THE N GULF.
IF SYSTEM IS AS STRONG AS CURRENTLY ADVERTISED...WINDS WILL NEED
TO BE INCREASED FURTHER...BUT ONLY WANTED TO BEGIN A TREND UPWARD
AT THIS POINT. THIS SYSTEM SHOULD BE A WARMER ONE SO MOST PRECIP
WILL BE RAIN WITH IT. MAY SEE SOME SNOW OVER THE NE INNER CHANNELS
AND THE PAYA AREA AT THE PRECIP ONSET WED. AIRMASS BEHIND THIS LOW
WILL NOT BE AS COLD AS THE AIRMASS BEHIND THE MON NIGHT COLD
FRONT...SO PRECIP TYPE WILL LIKELY REMAIN LIQUID IN THE
POST-FRONTAL ENVIRONMENT FOR LATE WEEK.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ011>013-021-022-041>043-051-052.

MAM/RWT