Small Craft Advisory 236, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
319 PM AKDT SAT MAR 31 2012

.SHORT TERM...A LOW CONTINUES TO SPIN IN THE CENTRAL GULF THIS
AFTERNOON, GENERATING ISOLATED TO SCATTERED SHOWERS OVER THE
PANHANDLE. GENERALLY, SNOW SHOWERS CHANGED OVER TO RAIN SHOWERS
BY MID MORNING, HOWEVER SNOW PELLETS AND SNOW SHOWERS WERE
OBSERVED IN THE JUNEAU AREA EARLY IN THE AFTERNOON. HAVE A
DIMINISHING POP TREND FOR TONIGHT, BUT OPEN CELL CUMULUS CLOUDS
VISIBLE IN SATELLITE IMAGERY INDICATE THAT THERE IS STILL PLENTY
OF COLD LOW LEVEL AIR OVER THE EASTERN GULF. THIS SHOULD RESULT
IN A CHANGE BACK TO SNOW SHOWERS THIS EVENING. QPF VALUES LOW
ENOUGH THAT NO ACCUMULATION IS FORECAST. AS THE SHOWER ACTIVITY
DIMINISHES, AM EXPECTING PARTIAL CLEARING OVER THE NORTHERN HALF
OF THE PANHANDLE TONIGHT.

 TOMORROW IS LOOKING BASICALLY DRY AND PARTLY CLOUDY OVER THE
NORTHERN HALF OF THE PANHANDLE TOMORROW. SITUATION NOT QUITE AS
NICE FOR THE SOUTHERN THIRD, AS A WEATHER FRONT MOVES IN FROM THE
SOUTH TOMORROW MORNING. SOUTHERN ZONES WILL LIKELY SEE SNOW AT
THE START BUT IT WILL CHANGE TO RAIN EARLY IN THE DAY.

 WINDS ARE NOT MUCH OF A CONCERN. HAVE SMALL CRAFT WINDS FOR
COASTAL MARINE ZONES 41 AND 42 OVERNIGHT TONIGHT. OTHER THAN
THAT, MARINE WINDS 20 KTS OF LESS THROUGH THE SHORT TERM FORECAST
PERIOD. SEAS OVER THE EASTERN GULF WILL KEEP SMALL CRAFT
ADVISORIES IN PLACE EAST OF ICY BAY THROUGH TONIGHT AND SOUTH OF
CAPE FAIRWEATHER FOR MOST OF TOMORROW.

 SHORT RANGE MODEL AGREEMENT WAS GOOD. EXISTING PRESSURE AND WIND
GRIDS NOT CHANGED. ADJUSTMENTS MADE TO TEMPS USING BIAS CORRECTED
NAM. USED NAM40 FOR POP FIELD WITH MODIFICATIONS. FORECAST
CONFIDENCE IS AVERAGE.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...DEEPENING LOW WILL
MOVE INTO THE SOUTHEAST GULF BRINGING GALE FORCE AND STRONG WINDS
TO THE SOUTHERN PANHANDLE AND COASTAL WATERS. RAIN WILL DEVELOP
SUNDAY NIGHT INTO MONDAY FOR THE SOUTHERN REGIONS WITH OFFSHORE
FLOW KEEPING THE NORTHERN PANHANDLE ON THE DRIER SIDE. THE LOW
WILL EXIT TO THE SOUTH MID WEEK WITH HIGH PRESSURE BUILDING OVER
THE AK GULF WITH CLEARING SKIES, LIGHT WINDS AND DRY CONDITIONS
FOR ALL OF SE AK THROUGH THE WEEK. BY THE WEEKEND SHORTWAVE WILL
MOVE ACROSS THE NORTHERN AK GULF BRINGING INCREASING CLOUDS AND
CHANGE PRECIP MAINLY FOR THE NORTHERN PANHANDLE.

MID LEVELS: SHORTWAVE WILL ROTATE AROUND BROAD ARE OF LOW PRESSURE
MOVING OVER THE SOUTHEAST GULF SUN NIGHT INTO MONDAY. MEANWHILE A
RIDGE OF HIGH PRESSURE WILL BUILD OVER THE NORTHERN PACIFIC
EXTENDING INTO THE BERING SEA WITH A LOW PRESSURE SYSTEM DEEPENING
TO THE WEST OVER THE KAMCHATKA PENINSULA. THESE FEATURES WILL BEGIN
TO SHIFT TO THE EAST AND SOUTH BY WEDNESDAY WITH THE MID LEVEL
RIDGE BECOMING THE DOMINANT FEATURE OVER THE AK GULF FOR THE REST
OF THE WEEK. BY THE WEEKEND THE TROUGH TO THE WEST OF THE RIDGE
WILL MOVE EASTWARD WITH FLOW SPLITTING WITH MAIN ENERGY PUSHING
SOUTH WITH REMAINING SHORTWAVE MOVING ACROSS THE NORTHERN AK GULF
THEN TOWARD THE PANHANDLE.

SURFACE: THE GALE FORCE SURFACE LOW WILL MOVE UP FROM THE
SOUTHWEST TOWARD HAIDA GWAII ABSORBING THE REMNANTS OF THE AK GULF
LOW. THE LOW WILL BECOME QUASI STATIONARY BEFORE WEAKENING AND
MOVING SOUTH. STILL SOME QUESTION REGARDING THE EXACT LOCATING AND
STRENGTH OF THIS LOW. THERE HAVE BEEN TWO SOLUTIONS WITH GFS/NAM
IN ONE CAMP AND ECMWF/UKMET IN THE OTHER. THE GFS SOLUTION SHOWS A
WEAKER LOW CENTER AND PUSHES THE LOW FURTHER NORTH AND EAST AT A
FASTER RATE. THE ECMWF SOLUTION SHOWS A MUCH DEEPER LOW FURTHER TO
THE WEST OF HAIDA GWAII AND KEEPS THE LOW IN PLACE LONGER AND
STRONGER. FOR PRACTICAL WEATHER THE GFS SOLUTION BRINGS STRONGER
WINDS THE THE SOUTHERN PANHANDLE WHILE THE ECMWF BRINGS STRONGER
WINDS THE THE COASTAL WATERS AND BRINGS MORE PRECIP TO THE
SOUTHERN PANHANDLE. MODELS WERE ALL INITIALIZING WELL WHEN
COMPARED TO SATELLITE IMAGERY AND WERE SHOWING GOOD RUN TO RUN
CONSISTENCY. THUS NEITHER SOLUTION WAS SHOWING ANY INDICATION OF
BEING THE BETTER CHOICE. AN ENSEMBLE SOLUTION WAS CHOSEN AGAIN AND
MATCHED UP WITH INHERITED GRIDS.

BY MIDWEEK MODELS BEGIN TO DIVERGE BUT STILL SHOW GENERAL TREND OF
HIGH PRESSURE BUILDING OVER THE AK GULF AND PANHANDLE. BY THIS
TIME THE ECMWF RUN TO RUN REMAINS FAIRLY CONSISTENT WHILE GFS
SHOWS INCREASED DISCONTINUITY. NEW HPC GUIDANCE REFLECTS THIS
TREND AND AS IT WAS VERY CLOSE TO INHERITED GRIDS OVERALL CHANGES
FOR THE REMAINDER OF THE LONG TERM WERE MINOR.

FORECAST CONFIDENCE IS HIGH WITH RESPECT TO THE GENERAL SYNOPTIC
PATTERN BUT STILL LOW CONFIDENCE IN DETAILS AT THE SURFACE THROUGH
TUESDAY. WHILE MODEL DIVERGENCE INCREASE THROUGH THE WEEK HAVE
AVERAGE TO ABOVE AVERAGE FORECAST CONFIDENCE AS PRACTICAL WEATHER
DIFFERENCES ARE SMALL THROUGH THE WEEKEND.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ041-042.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ043-051-052.

&&

FRITSCH/PRB