Area Forecast Discussion
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000
FXAK67 PAJK 212230
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
230 PM AKDT MON JUL 21 2014

.SHORT TERM...A WEAK, VERTICALLY STACKED LOW LIES JUST TO THE
SOUTHWEST OF HAIDA GWAII AND IS SLOWLY MOVING TO THE SOUTHEAST.
SATELLITE IMAGERY IS SHOWING SEVERAL BANDS OF CLOUDS SPIRALING
ABOUT THE LOW AND PRODUCING SHOWERS. ATMOSPHERE IS CLEARLY
CONVECTIVE AND THERE ARE NUMEROUS THUNDERSTORMS OCCURRING IN
BRITISH COLUMBIA. ASSESSMENT OF THE FORECAST LIFTED INDEX AND
MODELED CAPE INDICATES THERE IS VERY LITTLE RISK OF THUNDERSTORMS
OVER SOUTHEAST ALASKA, SO HAVE NOT INCLUDED THEM IN THE AFTERNOON
FORECAST. SHOWERS WILL CONTINUE TO ROTATE OVER THE REGION FROM
CANADA THROUGH THE SHORT TERM FORECAST PERIOD WITH THE BULK IT
THEM OVER THE SOUTHERN HALF OF THE PANHANDLE. FARTHER NORTH,
OFFSHORE FLOW RESULTING FROM THE CIRCULATION ABOUT THE LOW TO THE
SOUTH, A HIGH OVER SOUTHWESTERN YUKON, AND A BUILDING RIDGE OVER
THE CENTRAL AND NORTHEAST GULF HAS CLEARED OUT SKIES NICELY.
MOSTLY CLEAR SKIES OVER THE NORTHERN HALF WILL ALLOW OVERNIGHT
LOWS TO DROP DOWN INTO THE MID TO LOWER 40S. POTENTIAL FOR
RADIATIONAL FOG FORMING IS HIGH AND HAS BEEN INCLUDED IN THE
FORECAST. MOSTLY CLEAR SKIES TOMORROW WILL PROVIDE FOR SOME NICE
SUMMER WEATHER WITH HIGHS GETTING INTO THE 70S IN SOME PLACES. TO
THE SOUTH, MOSTLY CLOUDY TO CLOUDY CONDITIONS WILL CONTINUE
TONIGHT AND FOG WILL ALSO BE AN ISSUE BUT IT WILL BE MORE OF AN
ADVECTION FOG OF VERY LOW MARINE STRATUS THAT SETTLES DOWN ON THE
SURFACE. EXPECT LOWS IN THE LOWER 50S TONIGHT WITH HIGHS IN THE
MID TO LOWER 60S TOMORROW.

 EXCELLENT MODEL AGREEMENT THROUGH THE SHORT RANGE. USED A BLEND
OF NAM, ECMWF, AND GEM FOR UPDATES TO PRESSURE AND WIND. ENSEMBLE
APPROACH FOR POP USING BOTH LOW AND HIGH RESOLUTION NAM AND
ECMWF. QPF PER RIVER FORECAST CENTER. MINOR TWEAKS TO HIGH AND
LOW TEMPS PER GFS MOS. FORECAST CONFIDENCE IS ABOVE AVERAGE.

.LONG TERM...MODELS REMAIN IN GENERAL AGREEMENT IN SYNOPTIC SCALE
THROUGH LATE THURSDAY FOR THE UPPER LOW NEAR HAIDA GWAII TUESDAY
NIGHT MOVES FARTHER SOUTHEAST TO BRITISH COLUMBIA COAST AND
ANOTHER UPPER LEVEL SHORTWAVE TROUGH MOVES INTO THE NORTHERN GULF.
IN BETWEEN THESE TWO FEATURES...UPPER RIDGE WILL BUILD QUICKLY
OVER THE GULF AND RAPIDLY DRIFTS SOUTHEAST. REFRESHED THE
INHERITED FORECAST PACKAGE WITH THE 00Z ECMWF THROUGH THURSDAY
EVENING FOR PRESSURE AND WIND FIELDS. 12Z ECMWF WAS DELAYED DUE TO
POWER OUTAGE OF THEIR FACILITY. THE ECMWF HAS BEEN THE MOST
CONSISTENT MODEL OVER THE PAST SEVERAL DAYS AND POPS/QPF FIELDS
WERE UPDATED WITH THE 00Z ECMWF AS WELL FOR ENTIRE LONG TERM
PERIODS. A WEEK LONG GLOOMY SKIES WITH WET WEATHER IS EXPECTED
THROUGH EARLY NEXT WEEK.

 SHOWERS ACROSS THE EASTERN PANHANDLE TUESDAY NIGHT WILL CONTINUE
TO DIMINISH THROUGH LATE WEDNESDAY. NEXT FRONTAL PASSAGE IS
EXPECTED TO MOVE IN THE EASTERN GULF BY WEDNESDAY MORNING...THEN
MOVE ONSHORE OVER THE PANHANDLE BY LATE WEDNESDAY NIGHT INTO
THURSDAY MORNING WITH LIKELY TO CATEGORICAL POPS SPREADING OVER
THE PANHANDLE. TIGHTENED SOUTHERLY PRESSURE GRADIENT DUE TO THE
RIDGE WEDNESDAY WILL LIKELY PRODUCE SMALL CRAFT LEVEL WINDS OVER
NORTHERN LYNN CANAL. EXPECT NO SIGNIFICANT WINDS/SEAS ELSEWHERE.

 AN OMEGA BLOCK WILL DEVELOP OVER THE LOWER 48 AND THE UPPER
LEVEL SHORTWAVE TROUGH IN THE NORTHERN GULF WILL DEEPEN AND A
CLOSED UPPER LOW WILL FORM OVER THE NORTH CENTRAL GULF BY EARLY
SATURDAY MORNING...THEN DRIFT SOUTH OVER THE WEEKEND BEFORE
STALLING IN THE SOUTHEASTERN GULF BY EARLY NEXT WEEK. MODEL
DIFFERENCES BECOME LARGER ON HANDLING THE SYNOPTIC PATTERN TOWARDS
THE WEEKEND AND USED THE NEW WPC ENSEMBLE SOLUTIONS FOR PRESSURE
AND WIND FIELDS FROM FRIDAY THROUGH EARLY NEXT WEEK.

&&

.AVIATION...IMPACTS TO AVIATION ACTIVITIES OVER NORTHERN
PORTIONS OF THE PANHANDLE LIMITED TO RADIATIONAL FOG FROM LATE
TONIGHT THROUGH MID MORNING. TO THE SOUTH, AREAS OF PANNUS (SCUD)
WITH POCKETS OF LOCALLY DENSE ADVECTION FOG TONIGHT VICINITY
PETERSBURG. OTHERWISE, MVMC OR BETTER.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ022.

&&

$$

FRITSCH/AHN








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