Area Forecast Discussion
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FXAK67 PAJK 011356
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
556 AM AKDT SAT AUG 1 2015

.SHORT TERM...POSITIVELY TILTED UPPER TROUGH EXTENDS SW FROM NWRN
CANADA ACROSS THE NRN PANHANDLE AND THEN WSW TO THE CNTRL
ALEUTIANS. THIS FEATURE IS FORECAST TO EVOLVE INTO TWO SEPARATE
CLOSED UPPER LOWS BY 12Z SUN...ONE OF WHICH WILL BE SITUATED
IMMEDIATELY S OF THE ALEUTIANS...AND THE SECOND POSITIONED FROM
THE CNTRL PANHANDLE TO THE SERN GULF. ANOTHER SMALL/COMPACT UPPER
VORT LOBE IS ALSO MOVING S FROM YAKUTAT THIS MORNING...AND IS
AIDING IN A BAND OF LOCALLY VIGOROUS NON-THUNDERING CONVECTION
OVER MARINE ZONE 51. THE NRN GULF DISTURBANCE WILL GRADUALLY
BE ABSORBED BY THE SECOND/LARGER CLOSED LOW DEVELOPING TO ITS SSE.
THIS LARGER TROUGH WILL CONTINUE TO AID IN ISOLATED-SCATTERED
SHOWERS AND ABUNDANT CLOUD COVER OVER THE SRN TWO THIRDS OF THE
PANHANDLE TODAY AND TONIGHT.

AT THE SURFACE...HIGH PRESSURE BUILDING OVER THE GULF AND LOWER
PRESSURE OVER WRN CANADA WILL FAVOR NNWLY WINDS ACROSS MUCH OF THE
REGION BY THIS AFTERNOON. TWO EXCEPTIONS WILL BE 1/ LYNN
CANAL...WHERE SSWLY WINDS UP TO 15 KT ARE EXPECTED...AND 2/ SEA
BREEZE PRONE LAND AREAS. OTHERWISE ...HI-RES MODEL GUIDANCE SHOWS
POTENTIAL STRATUS DEVELOPING ALONG THE COAST TONIGHT. IF THIS
GUIDANCE PROVES CORRECT...THEN LOW CEILINGS AND POSSIBLE
VISIBILITY RESTRICTIONS CANNOT BE RULED OUT FOR LOCATIONS SUCH AS
YAKUTAT...SITKA...AND KLAWOCK.

GRID MODIFICATIONS WERE ACHIEVED THROUGH A NUDGE TO THE NAM/GFS.
THIS RESULTED IN ONLY MINOR CHANGES TO THE INHERITED
FORECAST...WITH THE LARGEST DEVIATION MADE TO WIND DIRECTIONS FOR
VARIOUS INSIDE CHANNELS.

.LONG TERM...COUPLED WITH THE RIDGE OVER THE BERING SEA AND THE
ALASKA MAINLAND...THE TWO LOWS INITIALLY DESCRIBED ABOVE WILL
FORM SOME SORT OF COMBINATION OMEGA/REX BLOCK, WHICH SUDDENLY
PLACES OUR WEATHER PATTERN IN SLOW MOTION.

AS THE UPPER LOW OVERHEAD STALLS OVER THE PANHANDLE...THE DRY
WEATHER FOR THE NORTHERN PANHANDLE IS INCREASINGLY SUSPECT AS IT
LOOKS AS IF ENOUGH MOISTURE ASSOCIATED WITH THE LOW WILL SPREAD
SHOWERS EVEN INTO THE NORTHERN PANHANDLE SUNDAY INTO TUESDAY. THIS
STIRS A FAMILIAR REFRAIN AS WE HAVE SEEN THIS BEFORE DURING A WET
JULY AS SURFACE LOWS HAVE A TENDENCY TO DEEPEN A LOBE TO THE
NORTHWEST...REFLECTING ENERGY ALOFT THAT HANGS BEHIND THE PARENT
LOW FEATURE. EVEN THOUGH GFS AND ECMWF AND TO SOME DEGREE THE NAM
SING THIS TUNE IN FORTE (LOUD)...THIS IS A CHANGE IN THE SCORE.
THUS, THIS DIRECTOR IS ONLY CONFIDENT ENOUGH TO EXPERIMENT BY
PUSHING A CHANCE OF SHOWERS...PIANOFORTE (A LITTLE SOFTER).

AS LEE SIDE TROUGHING STRENGTHENS LOW PRESSURE OVER THE CENTRAL
PANHANDLE...NORTHERLIES SHOULD STRENGTHEN THROUGH THE NORTHERN
INSIDE PASSAGES LATE SUNDAY INTO MONDAY...BUT SOUTHERN AREAS
WILL REMAIN WEAKER FROM THE SOUTH AND WEST. LYNN CANAL COULD SEE
SMALL CRAFT FROM THE NORTH. IN ADDITION...ADIABATIC WARMING ON TOP
OF A WARM AIR MASS TRANSPORTED FROM CANADA MAY HEAT HAINES AND
SKAGWAY CLOSE TO 70 DEGREES MONDAY INTO TUESDAY.

THERE WILL BE A SLIGHT RISK OF THUNDERSTORMS OVER SOUTHERN AREAS
UNDERNEATH THE COOLER AIR ALOFT AT THE CENTER OF THE STALLED LOW
DURING DAYTIME HEATING ON SUNDAY AND MONDAY AFTERNOON.
HOWEVER...THE PRECIPITATION MOVING WESTWARD MONDAY NIGHT INTO
TUESDAY MAY BE A LITTLE MORE STABLE THAN PREVIOUSLY THOUGHT AS
SOME WARM AIR ROUNDS THE LOW FROM THE WEST. BUT FOR NOW...KEPT
CONSISTENCY WITH PREIOUS FORECASTS.

BOTH THE GFS AND ECMWF ARE IN CONCERT OVER THE LOW EXITING INTO BC
TUESDAY NIGHT INTO WEDNESDAY. IT APPEARS A COLD AIR CLIPPER FROM
THE CHUKCHI SEA WILL DEGRADE THE RIDGE OVER THE ALASKA MAINLAND AND
START PUSHING THE WESTERN GULF LOW EASTWARD. THERE COULD BE A TINY
BREAK BETWEEN THE TWO LOWS AS THE WESTERN GULF FEATURE MOVES INTO
THE PLACE TO REPLACE THE EXITING ONE. IF THE ECWMF IS
CORRECT...THE BREAK COULD BE TUESDAY NIGHT INTO FRIDAY. IF THE GFS
IS CORRECT...EXPECT A MUCH SHORTER ONE.

GFS AND ECMWF USED FOR CHANGES ON TUESDAY/TUESDAY NIGHT IN WINDS
AND NUDGED TO GFS AND NAM SUNDAY INTO TUESDAY. FORECAST CONFIDENCE
AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.

&&

$$

GARNER/ADKINS

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