Area Forecast Discussion
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FXAK67 PAJK 312357
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
4 PM AKDT SUN AUG 31 2014

.SHORT TERM...AN AREA OF LOW PRESSURE OFF THE OUTER COAST
CONTINUES TO PUSH SHOWERS OVER THE PANHANDLE. LARGE AREAS OF
CONVECTIVE DEVELOPMENT WITH CLOUD TOP TEMPERATURES DOWN TO -50F
RAISED THE QUESTION OF WHETHER OR NOT WE WOULD SEE ANY LOCAL
THUNDERSTORM ACTIVITY. THOSE COLD CLOUDS HAVE, FOR THE MOST PART
MOVED EAST INTO CANADA. AN AREA OF DEVELOPING CONVECTION LIES JUST
WEST OF 140W AS OF THIS AFTERNOON. MODEL CAPE AND LIFTED INDICES
SUGGEST FAIR POTENTIAL FOR MARINE THUNDERSTORMS, SO HAVE INCLUDED
ISOLATED THUNDERSTORMS IN PORTIONS OF THE COASTAL MARINE ZONES FOR
THIS EVENING. AN UPPER TROUGH WILL SWEEP EAST ACROSS THE NORTHERN
GULF AND OVER THE PANHANDLE TOMORROW, MAINTAINING COLD UPPER AIR.
WITH WEAK LOW LEVEL COLD AIR ADVECTION ASSISTING, POTENTIAL EXISTS
FOR MARINE THUNDERSTORMS ONCE AGAIN TOMORROW AND HAVE INCLUDED
THEM IN THE FORECAST.

SHOWERS WILL CONTINUE THROUGH THE NIGHT AND THEN BEGIN TO
DIMINISH FROM NORTHWEST TO SOUTHEAST THROUGH TOMORROW AFTERNOON.
HAVE MAINTAINED CATEGORICAL POPS ALONG THE COAST MOUNTAINS FROM
JUNEAU SOUTH TO MISTY FJORDS THROUGH THE AFTERNOON, BUT THE OUTER
COAST SHOULD SEE SCATTERED SHOWER ACTIVITY BY LATE IN THE DAY WITH
DRY CONDITIONS EXPECTED FOR YAKUTAT AFTER NOON. QPF TOTALS TONED
DOWN A BIT FROM THE PREVIOUS FORECAST AND NO LONGER HAVE ANY HEAVY
PRECIP IN THE FORECAST. LOOK FOR RAIN TOTALS OF ONE HALF INCH OR
LESS OVERNIGHT WITH SIMILAR AMOUNTS FOR TOMORROW.

HAVE SOME SMALL CRAFT WINDS OVER THE GULF TONIGHT THROUGH LATE
MORNING, WITH RESIDUAL SEAS 8 FT OR GREATER THROUGH THE AFTERNOON.
ON THE INSIDE, ISOLATED AREAS OF WIND INCLUDE THE SOUTH SIDE OF
DOUGLAS ISLAND, WHERE WINDS HAVE BEEN OUT OF THE EAST AT 25 KTS
OR SO THROUGH THE DAY. LOOK FOR THOSE WINDS TO LET UP TONIGHT
AFTER SUNDOWN. FATHER SOUTH, MARGINAL SMALL CRAFT SOUTHEASTERLIES
OVER CLARENCE STRAIT ARE ALSO FORECAST TO DIMINISH TO 20 KTS OR
LESS LATER THIS EVENING. EASTERLY WINDS 20 KTS OR SO AT THE OCEAN
ENTRANCE REGIONS NEAR CAPE DECISION AND CAPE SPENCER WILL ALSO
RELAX TONIGHT. AS THE LOW WEAKENS AND DRIFTS INLAND TOMORROW, INNER
CHANNELS AND PUBLIC ZONES SHOULD SEE RELATIVELY LIGHT WINDS.
EXCEPTION IS CLARENCE STRAIT, WHERE SOUTHEASTERLY WINDS AT 20 KTS
WILL HOLD ON FOR MOST OF THE DAY.

USED ECMWF FOR UPDATES TO PRESSURE AND WIND. BLENDED POP FROM NAM,
GEM, GFS, AND ECMWF. QPF FROM GFS AND ECMWF. TEMPS ADJUSTED PER
BIAS CORRECTED MOS AND NAM12. FORECAST CONFIDENCE IS AVERAGE.

.LONG TERM...LAST AREA OF INSTABILITY MON EVENING FOR SOUTH COAST SO
MENTIONED ISOLD THUNDERSTORMS. WEAK AND TRANSIENT UPPER RIDGE SURE
TO BUILD OVER THE PANHANDLE MON NIGHT THRU TUE BUT UNFORTUNATELY
WESTERLIES ALOFT ALREADY DEVELOP BEHIND THE RIDGE ON WED FOR SOME
SHOWERS. MENTIONED FOG LATE MON NITE & EARLY TUE DUE TO RADIATION
COOLING. USED 31/12Z ECMWF THROUGH WED WHICH INCLUDES A DEVELOPING
LOW OFFSHORE WED NIGHT AND THU. USED WPC DAYS 4-8 AND CONFIDENCE
MODERATE.

&&

.AVIATION...MAIN IMPACT TO AVIATION ACTIVITIES IN TERMINAL AREAS
DURING THE SHORT RANGE FORECAST PERIOD WILL BE LOW CEILING,
OCCASIONALLY DROPPING TO IMC. FARTHER ALOFT, ICING WILL BE A
CONCERN WITH FREEZING LEVELS DOWN TO ABOUT 6000 FEET. TURBULENCE
IN THE LOW FLIGHT LEVELS WILL LET UP LATER TONIGHT AS A TROUGH
ALOFT ROTATES ASHORE AND MOVES INTO CANADA. MENTIONED FOG IN
PUBLIC FORECASTS DUE TO CLEARING LATE NIGHT MON AND EARLY TUE
COULD GIVE LOCAL IFR CONDS.

.MARINE...KEPT MENTION OF THUNDERSTORMS S COAST MON EVENING.
LONGER TERM SOME WIND DUE TO GULF DEVELOPMENT. ALSO MENTIONED
FOG LATE NIGHT MON & EARLY TUE. NO GALES FORESEEN AT THE MOMENT.

.HYDRO...RAINFALL AMOUNTS NOT ENOUGH TO SIGNIFICANTLY AFFECT
RIVERS AND STREAMS. SOME SMALL RISES AT TIMES BUT NO ADVERSE IMPACTS.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ031-036-041-042.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ043.

&&

$$

FRITSCH/JC

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