Area Forecast Discussion
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FXAK67 PAJK 222245
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
245 PM AKDT TUE APR 22 2014

.SHORT TERM...UPPER LOW REMAINS OVER THE AK GULF AND PANHANDLE
THROUGH WEDNESDAY. AT THE SURFACE WEAK ARE OF HIGH PRESSURE OVER
THE AK GULF WITH AN INVERTED TROUGH OVER THE PANHANDLE PRODUCING
WEAK GRADIENT. AN SHORT WAVE MOVING IN FROM BRITISH COLUMBIA INTO
THE SOUTHEASTERN GULF THIS AFTERNOON WILL TRACK NORTHWARD WHILE
IT EXTENDS TO THE WEST BY WEDNESDAY MORNING REACHING THE
NORTHEASTERN PANHANDLE BY WEDNESDAY AFTERNOON.

 SCATTERED RAIN SHOWERS AND INCREASING CLOUD COVER WILL EXTEND
NORTHWARD WITH THE ADVANCING SHORT WAVES FOLLOWED BY SOME
CLEARING SKIES OVER THE SOUTHERN PANHANDLE LATE TONIGHT. FOG
DEVELOPMENT IS POSSIBLE OVER THE SOUTHERN REGIONS LATE TONIGHT
DUE TO THESE CLEARING SKIES. NOT MUCH IN THE WAVE OF PRECIP
ACCUMULATION FROM THIS WEAK WAVE. THERE WILL BE LESS DIURNAL
TEMPERATURE RANGE WITH THE INCREASED CLOUD COVER KEEPING
OVERNIGHT LOWS A BIT WARMER TONIGHT AND HIGHS SLIGHTLY LOWER FOR
TOMORROW.

 ISSUE FOR WINDS TODAY IS THE NORTHERLY AND WESTERLY WIND FLOW V
SEA BREEZE DEVELOPMENT FOR SOME LOCATIONS. THE JUNEAU WESTERLY
SEA BREEZE IS IN PHASE WITH THE FLOW PATTERN WHILE SKAGWAY
SOUTHERLY SEA BREEZE IS IN OPPOSITION. AT THIS TIME THE HIGH THIN
STRATUS OVER THE NORTHERN PANHANDLE WAS NOT ENOUGH TO LIMIT THE
AFTERNOON SOUTHERLY SEA BREEZE DEVELOPMENT THERE. WINDS WILL
SHIFT AS THE SHORT WAVES TRACK NORTHWARD TONIGHT INTO WEDNESDAY,
BUT OVERALL SPEEDS WILL BE LESS THAN 15 KTS. WITH INCREASED CLOUD
COVER FOR WEDNESDAY NOT EXPECTING ANY SEA BREEZE.

 MAIN MODEL DIFFERENCES WERE WITH THE TIMING OF THE BRITISH
COLUMBIA WAVE. NAM WAS THE SLOWEST AND MORE OF AN OUTLIER
COMPARED TO THE ECMWF/GFS/GEM. ECMWF WAS MAINTAINED GOOD RUN TO
RUN CONSISTENCY SO REMAINED MODEL OF CHOICE. THERE WERE ONLY
MINOR DIFFERENCES WITH THE 12Z MODEL RUNS SO CHANGES TO THE
INHERITED FORECAST PACKAGE WERE LIMITED. FORECAST CONFIDENCE IS
ABOVE AVERAGE.

&&

.LONG TERM...MODELS ARE IN GENERAL AGREEMENT THROUGH FRIDAY
EVENING WITH A WEAKENING UPPER LEVEL SHORTWAVE TROUGH MOVING
NORTHWARD ACROSS SOUTHEAST ALASKA THROUGH LATE THURSDAY...FOLLOWED
BY GENERALLY DRY AIR MASS EXPANDS FROM THE SOUTH. A WEAK INVERTED
TROUGH OF LOW PRESSURE WILL MOVE OVER THE SOUTHERN PANHANDLE LATE
LATE THURSDAY NIGHT INTO FRIDAY...BRINGING CLOUDS AND SCATTERED
SHOWERS. REFRESHED THE INHERITED FORECAST PACKAGE WITH THE 12Z RUN
ECMWF AND NAM. THE RESULTANT CHANGES ARE SMALL AND MOSTLY COSMETIC
TOUCHES OVER PRESSURE AND WIND FIELDS.

 SCATTERED SHOWERS ACROSS THE NORTHERN AREA WEDNESDAY NIGHT WILL
BECOME ISOLATED ON THURSDAY AS THE DRY WEATHER CONTINUES TO
EXPANDS NORTHWARD. DECREASING CLOUDS AND WARMING TREND WILL GRANT
THE PANHANDLE PLEASANT WEATHER ON THURSDAY. RELAXED PRESSURE
GRADIENTS WILL PROMPT NO SIGNIFICANT WINDS ACROSS SOUTHEAST
ALASKA. INCREASING CLOUDS AGAIN OVER THE SOUTHERN AREAS WITH
SCATTERED SHOWERS WILL COOL DOWN TEMPERATURES A BIT ON FRIDAY.

 MODEL SPREADS BECOME LARGER OVER THE WEEKEND INTO NEXT WEEK AS
ANOTHER UPPER LEVEL SHORTWAVE TROUGH TRIES TO MOVE NORTHEASTWARD
ACROSS THE GULF...BUT THE MAIN JET STREAM WILL REMAIN SOUTH OF THE
AREA. BLENDED THE 12Z RUN WPC SOLUTIONS OF ECMWF ENSEMBLE APPROACH
FOR THE REMAINING LONG TERM FORECAST PERIODS.

 FOR EARLY NEXT WEEK...THE 250 MB JET STREAM ASSOCIATED WITH THE
NEXT DEEP SHARP UPPER LEVEL SHORTWAVE TROUGH WILL CURVE SOUTHWARD
OVER THE WESTERN GULF AND TURN TO NORTH ACROSS THE EASTERN GULF
AND THE PANHANDLE TUESDAY AND WEDNESDAY. AS THE UPPER LEVEL
PATTERN SHIFTS FROM NEAR ZONAL FLOW TO MERIDIONAL...UPPER LEVEL
DYNAMICS WILL BRING SOUTHEAST ALASKA A SERIES OF DISTURBANCES
ORIGINATING IN SUB-TROPICS. THIS CAN BE TRANSLATED FOR A
SIGNIFICANT WARMING NEXT WEEK. DUE TO INCREASED
UNCERTAINTIES...PREDICTABLE SURFACE FEATURES ARE DIFFICULT TO PIN
POINT BUT INCREASED CLOUDS AND POPS MAINLY OVER THE SOUTHERN HALF
OF THE PANHANDLE.


&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ042.

&&

$$

PRB/AHN








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