Area Forecast Discussion
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FXAK67 PAJK 210109
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
409 PM AKST SAT DEC 20 2014

.SHORT TERM...YESTERDAYS LOW FROM THE SOUTHEAST GULF OF ALASKA HAS
WEAKENED AND MOVE NORTH-NORTHWEST PULLING BACK TOWARDS PRINCE
WILLIAM SOUND THROUGH SATURDAY WITH A SECONDARY SPINNER IN THE
CLOUD MOVING TO OFF CROSS SOUND. THE MAJORITY OF THE SHOWERS WITH
LOW HAVE EITHER MOVED WEST TOWARDS THE KENAI PENINSULA OR ARE
BEING LIFTED NORTH INTO PANHANDLE OR BRITISH COLUMBIA.

REALLY EASY TO SPOT THE JET STREAM BY THE FAST MOVING STREAM OF
CLOUDS FROM THE PACIFIC AIMED AT THE PACIFIC NORTHWEST OF THE
LOWER 48. ALONG THE NORTH SIDE OF THE JET STREAM SMALL VORTICITY
LOBES AND SHORT WAVES ARE SPREADING ENERGY AND SMALL LOWS TOWARDS
THE PANHANDLE. YET ANOTHER WILL BE USHERED INTO THE SOUTHEAST GULF
TO MOVE ACROSS THE SOUTHERN PANHANDLE ON SUNDAY MORNING. THIS
FEATURE IS NOT EXPECTED TO DEEPEN SIGNIFICANTLY BEFORE MAKING LAND
FALL SO JUST EXPECT SOME STRATIFORM RAIN TO SPREAD IN. WINDS
SHOULD STAY GENERALLY UNDER 25 KT ONCE THE WINDS DO SETTLE DOWN
THIS EVENING.

STILL HAVE AN EARLY EVENING GALE IN CROSS SOUND AND POSSIBLY
NORTHERN LYNN THIS EVENING BUT THEY SHOULD BE DIMINISHING TO SMALL
CRAFT LEVELS OR LESS BY THE MIDNIGHT TIME FRAME.

PRECIPITATION TYPE STILL THE TYPICAL FORECAST HEADACHE ACROSS THE
REGION. MOST AREAS WILL SEE RAIN WHILE THE FAR NORTH WILL LIKELY
BE SNOW EXCEPT NEAR THE MAIN CHANNELS. THE NORTH WINDS HOLDING THE
HAINES AND SKAGWAY AREAS IN THE COOL ENOUGH AIR TO LEAVE THAT IT AS
LIGHT SNOW. OVERALL THINK THE BEST DESCRIPTION FOR THE NORTH
PANHANDLE IS A HIGH POP AND LOW QPF SITUATION. AREAS ARE QUITE
LIKELY TO GET SOME RAIN OR SNOW BUT AMOUNTS WILL BE LIGHT.

CONFIDENCE IS AVERAGE WITH SHOWER PATTERN AND DIFFICULTIES OF
ALONG/SLIGHTLY OFFSHORE FLOW FOR THE NORTHERN AREAS.

.LONG TERM...POTENTIAL FOR A SIGNIFICANT LOW PRESSURE SYSTEM TO
IMPACT THE PANHANDLE EARLY NEXT WEEK THEN THE PATTERN BEGINS TO
CHANGE TOWARD THE END OF THE WEEK.

ONSHORE FLOW AND SHOWERS WILL BE ONGOING AT THE BEGINNING OF THE
EXTENDED PERIOD ON SUNDAY NIGHT. SHOWERS WILL DIMINISH DURING THE
DAY ON MONDAY AS OFFSHORE FLOW INCREASES IN ADVANCE OF A
STRENGTHENING LOW PRESSURE SYSTEM MOVING NORTHEAST INTO THE
SOUTHEAST GULF. MODELS CONTINUE TO STRUGGLE WITH THIS FEATURE BUT
THE GFS HAS HAD GOOD RUN TO RUN CONTINUITY AND THE 12Z/18Z NAM
ALSO IS IN GOOD AGREEMENT WITH THE GFS. COMPLICATING MATTERS IS
THE 12Z ECMWF AND GEM WHO SPLIT THE ENERGY AND DEVELOP TWO LOW
CENTERS INSTEAD OF ONE STRONGER SYSTEM. DUE TO BETTER CONSISTENCY,
HAVE OPTED TO GO WITH THE GFS/NAM SOLUTION FOR THIS FORECAST
PACKAGE WHICH HAS RESULTED IN THE INTRODUCTION OF GALE FORCE WINDS
ACROSS THE SOUTHEAST GULF AND SOUTHERN INNER CHANNELS MONDAY NIGHT
INTO TUESDAY. BOTH THE NAM/GFS HAVE THIS STORM SYSTEM REACHING THE
UPPER 970`S BEFORE WEAKENING TUESDAY AS IT DRIFTS INLAND NEAR
CAPE DECISION. THE STRONGER SOLUTION WILL ALSO STRENGTHEN THE
NORTHERLY PRESSURE GRADIENT OVER THE NORTHERN HALF OF THE
PANHANDLE WITH SMALL CRAFT WINDS DEVELOPING DURING THIS TIME
FRAME. PRECIPITATION MAINLY IN THE FORM OF RAIN WILL SPREAD NORTH
MONDAY NIGHT AND TUESDAY BUT STRUGGLE TO MAKE IT INTO THE NORTHERN
PANHANDLE WITH STRONG OUTFLOW WINDS IN PLACE. WHILE PORTIONS OF
THE NORTHERN PANHANDLE WILL BE COLD ENOUGH FOR SNOW, EXPECT
PRECIP TO HAVE A HARD TIME MAKING IT THERE AND ANY PRECIP THAT
DOES FALL WILL BE ON THE LIGHTER SIDE. HEAVIEST PRECIP WILL BE IN
THE FORM OF RAIN ACROSS THE SOUTHERN HALF OF THE PANHANDLE.

UPPER TROUGH WEAKENS ACROSS THE AREA BY MID WEEK WITH A FEW
SMALLER IMPULSES IMPACTING THE PANHANDLE CHRISTMAS DAY AND FRIDAY.
IT STILL APPEARS A WEAKENING FRONTAL FEATURE WILL BRING PRECIP TO
THE PANHANDLE LATER CHRISTMAS DAY AND WITH A COOLER AIRMASS IN
PLACE THE LIKELIHOOD OF SNOW IS HIGHER WITH THIS SYSTEM THAN THE
PAST FEW WEEKS. THIS WILL CONTINUE TO BE MONITORED.

PATTERN CHANGE WILL RESULT IN RIDGING BEING THE DOMINANT FEATURE
OVER THE EASTERN GULF AND PANHANDLE BY NEXT WEEKEND. AS DISCUSSED
BY THE PREVIOUS SHIFT, MODELS CONTINUE TO STRUGGLE AS USUAL WITH
THE PATTERN CHANGE AND HOW IT WILL EVOLVE SO DETAILS WILL NEED TO
BE WORKED OUT IN FUTURE SHIFTS.

USED A BLEND OF THE 18Z NAM AND 12Z GFS THROUGH 84
HOURS THEN TRANSITIONED TO THE LATEST WPC GUIDANCE FOR THE
REMAINDER OF THE LONG RANGE. CONFIDENCE IS STILL LACKING ON THE
LOW PRESSURE SYSTEM MOVING INTO THE EASTERN GULF EARLY NEXT WEEK.
HOWEVER, CONFIDENCE IS INCREASING ON A PATTERN CHANGE BY LATE NEXT
WEEK BUT MODELS CONTINUE TO STRUGGLE WITH THE DETAILS.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 6 PM AKST THIS EVENING FOR AKZ018.
MARINE...GALE WARNING FOR PKZ022-043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ012-021-035-036-041-042.

&&

$$

BEZENEK/TPS

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