Area Forecast Discussion
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FXAK67 PAJK 311315
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
515 AM AKDT SUN AUG 31 2014

.SHORT TERM...WEAK SURFACE RIDGE HANGING ONTO THE PANHANDLE AND
COAST MOUNTAINS THIS MORNING AS A 1000 MB LOW MOVES ACROSS THE GULF
OF ALASKA TO THE COAST BY AFTERNOON WEAKENING SLIGHTLY. THE RIDGE
MOVES INTO BRITISH COLUMBIA. THE LOW ELONGATES INTO LONG LOW ALONG
THE COAST AS THE FRONT SPREADS INTO THE PANHANDLE. MOST MODEL
SOLUTIONS FROM SATURDAY NIGHT HAD A REASONABLE HANDLE ON WHAT WAS
GOING ON.

EXPECT SOME BRIEF PERIODS OF HEAVIER RAINFALL AMOUNTS IN THE
NORTHEAST GULF COAST AREA THROUGH THE EARLY AFTERNOON...AND SOME
LESSER AMOUNTS OVER THE SOUTHERN PANHANDLE. HOWEVER AMOUNTS ARE
NOT ANYTHING THE LOCALS STREAMS CAN NOT HANDLE. WINDS WITH THE
SYSTEM WILL BE SPREADING SOME SMALL CRAFT MARINE WINDS INTO THE
COAST AND A FEW INNER CHANNELS. GUSTS ON EXPOSED POINTS AND
CHANNELED TERRAIN OF THE LAND AREA IN THE WINDY AREAS MAY REACH UP
TO 35 MPH.

EXPECT MUCH OF THE SURFACE LOW TO PUSH INTO BRITISH COLUMBIA
LEAVING A WEAK LOW IN THE NORTHERN GULF LATE SUNDAY NIGHT AN
TROUGH ACROSS THE NORTHERN PANHANDLE AND ONSHORE FLOW PATTERN FOR
SHOWERS ACROSS THE SOUTHERN PANHANDLE.

.LONG TERM...THE START OF THE LONG TERM PERIOD /MON AFTERNOON/
WILL FEATURE A WEAK LOW AMPLITUDE UPPER WAVE EXITING EWD OUT OF
SERN AK...WHILE A SECOND MORE VIGOROUS DISTURBANCE APPROACHES THE
REGION FROM THE ERN GULF. COLD MIDLEVEL TEMPERATURES /-20 TO -25C
AT H5/ ACCOMPANYING THE TROUGH OVER THE GULF WILL AID IN THE
DEVELOPMENT OF STEEP LAPSE RATES FAVORING SHOWERS. SIX HOURLY QPF
AMOUNTS NEAR A QUARTER INCH WILL BE POSSIBLE MON AFTERNOON AND
EVENING...PARTICULARLY FOR LOCATIONS INVOF WEST FACING SLOPES WHERE
OROGRAPHIC ENHANCEMENT WILL BE MOST PROBABLE. MIDLEVEL VORT LOBE
ASSOCIATED WITH THE TROUGH IS CURRENTLY FORECAST TO PASS S OF
THE REGION. THUS...POTENTIAL FOR ISOLATED THUNDERSTORM DEVELOPMENT
DOES NOT APPEAR TO BE PARTICULARLY HIGH ATTM. MEANWHILE AT THE
SURFACE...WEAKENING LOW PRESSURE IS EXPECTED TO DRIFT INLAND OVER
THE CNTRL PANHANDLE AND THEN NWRN BC. THIS WILL INITIALLY YIELD A
TIGHT PRESSURE GRADIENT OVER CLARENCE STRAIT RESULTING IN SLY
WINDS NEAR SMALL CRAFT ADVISORY LEVELS DURING MON AFTERNOON. THE
PRESSURE GRADIENT IS THEN FORECAST TO WEAKEN TEMPORARILY DURING
MON NIGHT...ONLY TO RESTRENGTHEN OVER THE NRN HALF OF THE CWA TUE
AFTERNOON AS HIGH PRESSURE BUILDS NWD OVER THE CNTRL/ERN GULF.
AS A RESULT...FORECAST GRADIENT WILL LIKELY BE SUFFICIENT FOR SLY
SMALL CRAFT WINDS OVER NRN LYNN CANAL.

AFTER A BRIEF PERIOD OF DRIER WEATHER TUE AND POSSIBLY WED...MODEL
GUIDANCE SHOWS AN UPPER-LEVEL RIDGE AMPLIFYING OVER THE NERN PAC
AND A LARGE-SCALE TROUGH BECOMING ESTABLISHED OVER THE ALEUTIANS.
SUBTROPICAL MOISTURE IS FORECAST TO SPREAD NWD BETWEEN THESE TWO
FEATURES AND APPROACH SERN AK TOWARD THE SECOND HALF OF THE WORK
WEEK. HOWEVER...DETERMINISTIC MODEL SOLUTIONS SHOW CONSIDERABLE
SPREAD WITH REGARD TO WHEN THIS MOISTURE WILL REACH THE
REGION...WITH THE ECMWF AND GEM SHOWING AN EARLIER ARRIVAL DURING
WED NIGHT...AND THE GFS HOLDING OFF UNTIL THU. FURTHER
COMPLICATING THE FORECAST IS A HIGH DEGREE OF VARIABILITY WITH THE
EVOLUTION OF SMALLER-SCALE UPPER WAVES EMANATING FROM BOTH THE NRN
STREAM FLOW REGIME AND THE SWLY FLOW REGIME LOCATED AHEAD OF THE
ALEUTIAN LONG WAVE. THUS...THE THU THROUGH SUN TIME PERIOD IS
VIEWED WITH A HIGH DEGREE OF UNCERTAINTY AND LOW FORECAST
CONFIDENCE. HANDLED THIS UNCERTAINTY BY USING A BLEND OF THE
GFS...ECMWF...GEM...AND WPC GUIDANCE FOR POP/S...WHICH YIELDS
MAXIMUM PRECIPITATION POTENTIAL NEAR THE WARM CONVEYOR BELT
POSITIONED SSW-NNE ACROSS THE GULF INTO SERN AK. THIS RESULTED IN
WIDESPREAD RAIN CHANCES AND CLOUD COVER OVER MOST OF THE REGION.

&&

.AVIATION...MVFR CEILINGS ARE SCATTERED ABOUT THE REGIONAL
AIRPORTS THIS MORNING WITH THE INCOMING WEATHER FRONT OF THE
INCOMING AREA OF LOW PRESSURE. A LOCALIZED IFR DUE TO CEILINGS FOR
THE SOUTHERN PANHANDLE AS WELL. EXPECT CONDITIONS TO SPREAD TO
MORE OF THE AIRPORTS IN THE MORNING HOURS AND THEN LIFT BEFORE
MIDDAY WITH HEATING. RAINS EXPECTED TO CONTINUE AND LOWER SOME
VISIBILITIES INTO THE 3 TO 5 MILE RANGE. ALSO AS THE FRONT MOVES INTO
THE SOUTHERN PANHANDLE, A LOWER LEVEL SOUTHERLY WIND MAX OF 30 TO
40 KT AT THE 3 TO 5 THOUSAND FOOT LEVEL COULD CAUSE SOME MODERATE
TURBULENCE SOUTHERN THIRD THROUGH THE AFTERNOON NEAR AND
DOWNSTREAM OF THE TERRAIN.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ036-041>043.

&&

$$

BEZENEK/GARNER

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