Area Forecast Discussion
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FXAK67 PAJK 301338
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
538 AM AKDT SAT AUG 30 2014

.SHORT TERM...EARLY MORNING SATELLITE LOOP REVEALS REMNANTS OF
DISSIPATING LOW ACROSS THE SOUTHERN PANHANDLE WITH LINGERING
SHOWERS SLOWLY PASSING THE AREA. A WEAKENING LOW OVER THE NORTHERN
GULF WRAPS SHOWER BANDS OVER THE NORTHEASTERN GULF COAST. PATCHY
FOG FORMS BEHIND THE PASSING SHOWERS. A WEAK RIDGE OF HIGH
PRESSURE SLOWLY BUILDS ACROSS SOUTHEAST ALASKA. WINDS REMAIN IN
LIGHTER SIDE...BUT ROUGH SMALL CRAFT LEVEL SEAS REMAIN ACROSS THE
SOUTHERN OUTER WATERS. OVERNIGHT TEMPERATURES MOSTLY REMAIN IN
THE LOWER 50S...EXCEPT SOME SPOTS REPORTING UPPER 40S.

MODELS REMAIN IN FAIR AGREEMENT WITH THE WEAKENING LOW IN THE
NORTHERN GULF DISSIPATING THIS AFTERNOON AS THE WEAK RIDGE OF
HIGH PRESSURE CONTINUES TO BUILD ACROSS THE EASTERN GULF AND
PANHANDLE. THE RIDGE WILL REMAIN OVER SOUTHEAST ALASKA THROUGH
LATE TONIGHT. A DEVELOPING LOW IN THE WESTERN GULF LATE SATURDAY
WILL MOVE EASTWARD ACROSS THE CENTRAL GULF THROUGH LATE TONIGHT.
REFRESHED THE INHERITED FORECAST PACKAGE WITH THE 06Z RUN NAM12
FOR ITS GOOD INITIALIZATION AND CONSISTENCY.

AS THE WEAK RIDGE OF HIGH PRESSURE BUILDS OVER SOUTHEAST
ALASKA...SOUTHERLY PRESSURE GRADIENT WILL BECOME TIGHT MOMENTARILY
TO PRODUCE SMALL CRAFT LEVEL WIND OVER NORTHERN LYNN CANAL LATE
THIS AFTERNOON. SOUTHERLY WINDS WILL CONTINUE...BUT THE PRESSURE
GRADIENT WILL RELAX SOMEWHAT BY THE EVENING AND EXPECT THE WIND
WILL DECREASE TO LESS THAN 20 KNOTS FOR TONIGHT AND CONTINUE TO
DECREASE OVERNIGHT. ROUGH SMALL CRAFT LEVEL SEAS ACROSS THE
SOUTHERN OUTER WATERS WILL CONTINUE TO SUBSIDE AS WELL THROUGH
LATE TONIGHT. AS THE RIDGE CONTINUES TO BUILD...NUMEROUS SHOWERS
ALONG THE NORTHEASTERN GULF COAST AND OVER THE SOUTHERN
PANHANDLE WILL BECOME SCATTERED LATE THIS AFTERNOON INTO THE
EVENING HOURS.

THE DEVELOPING LOW IN THE WESTERN GULF WILL DRIFT EASTWARD ACROSS
THE CENTRAL GULF AND PUSH LIKELY TO CATEGORICAL POPS ACROSS THE
SOUTHERN OFFSHORE WATERS TO THE SOUTHERN OUTER WATERS LATE
TONIGHT. DUE TO CONTINUED GLOOMY SKIES AND LINGERING
SHOWERS...DAYTIME HIGHS WILL RANGE FROM THE MID TO UPPER 50S
ACROSS THE NORTHERN AND CENTRAL PANHANDLE TO THE LOWER 60S OVER
THE SOUTHERN AREAS. EXPECT NOT MUCH DIURNAL TEMPERATURE
FLUCTUATION FOR TONIGHT AND OVERNIGHT LOWS WILL BE IN THE UPPER
40S TO THE LOWER 50S.

.LONG TERM...A SERIES OF UPPER-LEVEL SHORTWAVE TROUGHS LOCATED
OVER THE SRN BERING SEA THIS MORNING ARE FORECAST TO PROGRESS EWD
ACROSS SERN AK SUN AND MON. DUE TO MULTIPLE BOUTS OF LARGE-SCALE
ASCENT IMPACTING THE REGION...CLOUDS AND RAIN ARE EXPECTED TO
LINGER SLIGHTLY LONGER OVER THE AREA THAN PREVIOUSLY ANTICIPATED.
LATEST LONG TERM PACKAGE REFLECTS THIS MODESTLY SLOWER
PROGRESSION. STABLE STRATIFORM REGIME WILL INITIALLY BE IN PLACE
OVER THE SRN HALF OF THE PANHANDLE AND GULF SUN AFTERNOON.
HOWEVER...MIDLEVEL TEMPERATURES ARE FORECAST TO COOL AS THE SECOND
UPPER WAVE ENTERS THE AREA MON...WHICH WILL RESULT IN A TRANSITION
TO A CONVECTIVE/SHOWERY REGIME. IN ADDITION...STEEPENING LAPSE
RATES ASSOCIATED WITH THE COLD AIR ALOFT COMBINED WITH ENHANCED
DESTABILIZATION DOWNSTREAM OF A POTENT UPPER VORT LOBE MAY BE
SUFFICIENT FOR ISOLATED THUNDERSTORM DEVELOPMENT OVER THE SERN
GULF AND CNTRL/SRN PANHANDLE MON AFTERNOON/NIGHT. THIS POSSIBILITY
WILL CONTINUE TO BE EVALUATED IN FUTURE OUTLOOKS.

MODEL GUIDANCE INDICATES THE SURFACE PRESSURE GRADIENT WILL
TIGHTEN OVER THE CNTRL/SRN PANHANDLE SUN-MON IN RESPONSE TO THE
PASSING UPPER WAVES. LATEST FORECAST CALLS FOR SMALL CRAFT SLY
WINDS OVER CLARENCE STRAIT...WITH ELY SMALL CRAFT WINDS NOT OUT OF
THE QUESTION FOR CROSS SOUND. IN ADDITION...SEAS OVER THE SRN
OUTSIDE WATERS ARE CURRENTLY EXPECTED TO RESIDE BETWEEN 6-8 FEET.
DETERMINISTIC GUIDANCE SHOWS MODERATE SPREAD WITH RESPECT TO THE
SURFACE PRESSURE EVOLUTION THROUGH EARLY NEXT WEEK...WHICH RESULTS
IN ELEVATED UNCERTAINTY FOR MARINE WINDS/SEAS.

BEYOND MON...MIDLEVEL SHORTWAVE RIDGING IS FORECAST TO OCCUR OVER
SERN AK TUE AND WED. THIS WILL FAVOR A DRIER AIRMASS...DECREASING
RAIN CHANCES...AND CLEARING SKIES/MODERATING HIGH TEMPERATURES.
THE ONLY CAVEAT WILL BE A SERIES OF NRN STREAM IMPULSES MOVING
FROM INTERIOR AK INTO NWRN CANADA...WHICH MAY YIELD
ISOLATED/SCATTERED SHOWERS AND GREATER CLOUD COVERAGE FOR THE NRN
HALF OF THE CWA. MODEL OUTPUT THEN SHOWS INCREASING DEEP-LAYER
MOISTURE SPREADING NWD OVER THE WRN GULF...WEDGED BETWEEN AN
ANTICYCLONE OVER THE NERN PAC AND A DEVELOPING LOW OVER THE
ALEUTIANS. THIS MOISTURE MAY ENTER THE PANHANDLE BY NEXT WEEKEND.
HOWEVER...MULTI-MODEL GUIDANCE SHOWS SUBSTANTIAL SPREAD WITH
REGARD TO TIMING. THUS...THE FRI-SUN TIME PERIOD IS CHARACTERIZED
BY DECREASING FORECAST CONFIDENCE.

OVERALL...THE INHERITED FORECAST GRIDS WERE IN GOOD SHAPE. ONLY
MAJOR CHANGE WAS TO PROLONG THE PERIOD OF HIGH POP/S SUN-MON DUE
TO THE MULTIPLE UPPER WAVES PROGNOSED TO TRAVERSE THE CWA.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041-042.

&&

$$

AHN/GARNER

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