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FXAK67 PAJK 291345
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
545 AM AKDT SUN MAR 29 2015

.SHORT TERM...EARLY MORNING WV IMAGERY SHOWS A SHORTWAVE IMPULSE
RAPIDLY MOVING NE TOWARD THE FAR SRN PANHANDLE. THERMODYNAMIC
PROFILES SUPPORT DEEP MOIST CONVECTION AND ISOLATED
LIGHTNING...WHICH HAVE BEEN INCLUDED IN THE MORNING FORECAST
PACKAGE. THIS VORT FEATURE WILL THEN EXIT THE AREA BY MIDDAY SUN.
REGION WILL CONTINUE TO RESIDE IN DEEP-LAYER SWLY FLOW FAVORABLE
FOR SHOWERS THROUGHOUT THE DAY GIVEN THE CONTINUED PRESENCE OF
STEEP LAPSE RATES. GOING INTO SUN NIGHT...MODEL CONSENSUS EXISTS
WITH A SMALL UPPER IMPULSE MOVING N INTO THE ERN GULF. THIS WAVE
WILL HAVE A MINOR REFLECTION AT THE SURFACE RESULTING IN ENHANCED
ESELY WINDS UP TO SMALL CRAFT LEVELS OVER OUTSIDE MARINE ZONES 42
AND 43 DURING THE LATE NIGHT TIME PERIOD.

MOISTURE AND A FOCUSED ZONE OF ASCENT WILL ALSO SPREAD NWD OVER
THE SERN GULF WITH THE UPPER IMPULSE...WHICH WILL MAXIMIZE SHOWER
PROBABILITIES FROM COASTAL AREAS NEAR SITKA SWD. IN ADDITION...AXIS
OF SBCAPE VALUES FROM 100-400 J/KG WILL BE FOCUSED ALONG THIS
ZONE OF HIGHER SHOWER POTENTIAL. ALTHOUGH A STRAY LIGHTNING
STRIKE CANNOT BE RULED OUT...MODEL FORECAST SOUNDINGS INDICATE THE
BOUNDARY LAYER TEMPERATURE PROFILE WILL BE SLIGHTLY SUB-OPTIMAL
FOR THUNDERSTORM DEVELOPMENT. THUS...HAVE LEFT THUNDER OUT OF THE
SUN NIGHT PERIOD ATTM.

USED A BLEND OF THE ECMWF/NAM WITH INHERITED GRIDS FOR PRESSURE.
POP AND QPF WERE UPDATED USING AN ARW/GFS/ECMWF/INHERITED BLEND.

.LONG TERM...MODELS HAVE TRENDED TOWARD SWINGING THE UPPER LEVEL
LOW OVER THE GULF A LITTLE FARTHER EASTWARD, THUS SHUNTING THE
THE JET SOUTHEAST TOWARD THE CENTRAL BC COAST FOR MONDAY. THE
SALIENT POINT OF THIS IS THAT THE SURFACE LOW WE HAVE BEEN
UNCERTAIN OF IN BOTH INTENSITY AND TRACK, NOW LOOKS TO FOLLOW WITH
A MORE EASTERLY TRACK NORTH THROUGH HECATE STRAIT MONDAY MORNING.
THEN IT WILL WEAKEN VERY QUICKLY AS IT REACHES THE SOUTHERN
PANHANDLE MONDAY AFTERNOON, DEPRIVED OF BOTH UPPER LEVEL JET
SUPPORT AND BAROCLINICITY. THUS RAIN AMOUNTS AND WIND HAVE BEEN
CURTAILED, ALTHOUGH THAT IS NOT TO SAY IT WILL NOT RAIN OVER THE
SOUTHERN PANHANDLE MONDAY. AS THE UPPER LOW OVER THE GULF
BROADENS INTO A TROUGH, COOLER AIR ALOFT WILL SPREAD EAST INTO THE
PANHANDLE, DESTABILIZING THE ATMOSPHERE BY MONDAY NIGHT FOR ALL
BUT THE FAR NORTH, THUS CHANGING THE RAIN TO SHOWERS. SHOWERS WILL
REMAIN IN THE FORECAST THROUGH WEDNESDAY BEFORE A WARM FRONT WITH
ITS SLOW STEADY ASCENT PREPARES TO MOVE INTO THE CENTRAL GULF
MIDWEEK. STEADIER RAINS ARE LIKELY AFTERWARD.

TWO OTHER FEATURES MORE EMBEDDED IN THE COLDER AIR ROUNDING THE
BASE OF THE UPPER LOW WILL TRACK NORTHWARD, WELL TO THE WEST OF
THE PANHANDLE. THESE FEATURES WILL LACK THE BAROCLINIC FUEL OF THE
TRAVELING WAVE TO THEIR SOUTH THAT WILL BE RESPONSIBLE FOR THE
LOW PUSHING THROUGH HECATE STRAIT MONDAY. ESSENTIALLY THEY WILL,
ONE, IMPOSE SMALL CRAFT LEVEL WINDS FOR THE NORTHERN GULF MONDAY
AS THEY NEAR THE COAST, AND TWO PROVIDE A FOCUS FOR SHOWERS OVER
THE GULF AND THE SOUTHEAST COASTLINE.

ACROSS THE INSIDE CHANNELS, WINDS WILL FLIP NORTH EARLY MONDAY
MORNING AS THE HECATE STRAIT LOW NEARS. BUT EXPECT WINDS TO STAY
BELOW SMALL CRAFT LEVELS AS THE LOW WILL WEAKEN AS IT APPROACHES.
BY MONDAY NIGHT, GRADIENTS FALL FLAT IN PARTICULAR OVER THE
NORTHERN PANHANDLE. ALTHOUGH CLOUDS BEGIN TO SPREAD FROM THE
SOUTH, THERMODYNAMIC PROFILES OVER THE FAR NORTH STILL SUGGEST
ATMOSPHERIC STABILITY, THUS ADDED SOME PATCHY FOG FROM SKAGWAY TO
HOONAH/JUNEAU.

SOLUTIONS STARTING TO CONGREGATE OVER THE POSSIBILITY OF A GALE
FORCE FRONT ARRIVING IN THE CENTRAL GULF WEDNESDAY AFTERNOON,
IMPACTING THE OUTSIDE WATERS WEDNESDAY NIGHT. THUS LOOK FOR WINDS
TO BE INCREASED IN FUTURE. WHAT WE ARE SURE OF IS THAT WET
CONDITIONS WILL PREVAIL THROUGH THURSDAY NIGHT, AFTER WHICH THE
PARENT LOW WILL PASS TO OUR SOUTHEAST AND OPEN THE DOOR TO THE
POSSIBILITY OF A DRY WEEKEND. HINTS OF A COOL-DOWN INTO THE WEEKEND
APPEAR AS WELL, BUT SEASONAL TEMPERATURES LARGELY DOMINATE THROUGH
THE WEEK.

UPDATED FORECAST WITH NAM/ECMWF THROUGH MONDAY NIGHT, WHILE
RESERVING EDITS FOR LOCAL TWEAKS ON WEDNESDAY. NO WIND CHANGES
MADE AFTERWARD. FORECAST CONFIDENCE IMPROVING IN THE MID-RANGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ041>043-052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ051.

&&

$$

GARNER/JWA

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