Gale Warning 179, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
439 PM AKDT TUE APR 8 2014

.SHORT TERM...AFTERNOON SATELLITE IMAGE SHOWS A WEAKENING LOW
NEAR PRINCE WILLIAM SOUND AND A WEAK RIDGE SLOWLY BUILDS ACROSS
SOUTHEAST ALASKA. RAIN SHOWERS CONTINUE OVER THE FORECAST AREA
AND COLDER AIR MASS APPROACHES FROM THE WEST. WITH DECREASING QPF
VALUES...LOCAL RIVERS AND STREAMS HAVE SHOWN RECEDING TREND.
SEVERAL SHIPS ACROSS THE OFFSHORE WATERS REPORT SNOW SHOWERS AND
YAKUTAT STARTS TO SEE MIXED SHOWERS AS OF 1 PM. WITH THE COLD AIR
ALOFT MOVING IN FROM THE WEST...INSTABILITY INCREASES OVER THE
NORTHERN OUTER WATERS AND EXTENDS SOUTHEAST TO THE CENTRAL
PANHANDLE AREAS. BETWEEN THE RIDGE AND LOW PRESSURE AREA IN THE
YUKON...SOUTHERLY PRESSURE GRADIENT HAS BEEN TIGHTENING AND
PRODUCING SMALL CRAFT LEVEL WINDS OVER THE NORTHERN INNER
CHANNELS.

MODELS ARE IN FAIR AGREEMENT FOR THE RIDGE OF HIGH PRESSURE
ACROSS SOUTHEAST ALASKA TONIGHT WEAKENS AS IT DRIFTS EASTWARD INTO
BRITISH COLUMBIA THROUGH LATE WEDNESDAY WITH A 998 MB LOW
APPROACHES THE PANHANDLE FROM THE WEST. REFRESHED THE INHERITED
FORECAST PACKAGE WITH THE ECMWF FOR ITS BEST CONSISTENT
PERFORMANCE OVER THE PAST SEVERAL DAYS.

LIKELY TO CATEGORICAL POPS WILL CONTINUE ACROSS SOUTHEAST ALASKA.
COLD AIR ADVECTION WILL CONTINUE TONIGHT WITH SLIGHTLY MODIFIED
AIR MASS AS IT CROSSES THE OPEN WATER BODY AND ARRIVES THE
PANHANDLE COASTAL AREAS. MIXED SHOWERS WILL CONTINUE ACROSS THE
WESTERN HALF OF THE OFFSHORE WATERS. WITH THIS APPROACHING COLD
AIR MASS...OVERNIGHT TEMPERATURES ACROSS THE NORTHERN PANHANDLE
WILL BECOME COLD ENOUGH FOR SNOW SHOWERS. EXPECT UP TO AN INCH OF
SNOW ACCUMULATION OVERNIGHT. REST OF THE PANHANDLE WILL ALSO SEE A
COOLING TREND...BUT STAY ABOVE FREEZING FOR MOSTLY RAIN SHOWERS.

CONTINUED CONVECTIVE PRECIPITATION IS EXPECTED TONIGHT WITH
INCREASED INSTABILITY. ADDED ISOLATED THUNDERSTORM FOR THE
NORTHERN OUTSIDE WATERS FOR TONIGHT. PRECIPITATION WILL BECOME
STRATI FORM FOR WEDNESDAY. ACROSS THE NORTHERN AREAS...SNOW WILL
CONTINUE EARLY IN THE MORNING PRIOR TO CHANGING OVER RAIN. DAYTIME
HIGHS ARE EXPECTED TO SORE UP TO THE UPPER 30S TO THE MID 40S.

WITH THE INCOMING LOW...SOUTHERLY PRESSURE GRADIENT WILL RELAX
EARLY THIS EVENING BUT LONG PERIODS SOUTH TO SOUTHWEST SWELLS WILL
CONTINUE PRODUCING ROUGH SMALL CRAFT SEAS OVER THE OUTSIDE WATERS.
AS THE LOW APPROACHES THE PANHANDLE COAST LATE TONIGHT INTO EARLY
WEDNESDAY MORNING...SMALL CRAFT SOUTHEASTERLY WINDS WILL BEGIN
AFFECTING SOUTHERN OUTER WATERS...THEN SPREAD TO INCLUDE SOUTHERN
INNER CHANNELS AND EXPAND NORTH UP TO CROSS SOUND BY WEDNESDAY
AFTERNOON.

&&

.LONG TERM /WED NIGHT THROUGH TUE/...WED NIGHT AN UPPER LEVEL
LOW/TROUGH TRACKING EAST OVER THE SOUTHERN YUKON AND NORTHERN
PANHANDLE WITH ZONAL ONSHORE FLOW OVER THE SOUTHERN 2/3 OF THE
REGION. THE SURFACE LOW ASSOC WITH THIS WILL BE MOVING INTO THE
CENTRAL PANHANDLE AT THE START OF THE EXTENDED FORECAST WITH
WIDESPREAD RAIN STARTING TO DIMINISH BEHIND IT FROM NW TO SE. THE
WEAKENING UPPER LEVEL TROUGH IS SLOW TO DEPART ON THURS..CAUSING A
SURFACE TROUGH TO REMAIN OVER THE NORTHERN PANHANDLE AND NORTHERN
GULF COAST EXTENDING FROM THE DEPARTING LOW TO THE EAST. ALSO AN
UPPER LEVEL VORT MOVES NE ACROSS THE GULF AND PHASES WITH THE
UPPER LEVEL TROUGH...THIS IN TURN CAUSES A SURFACE LOW TO DEVELOP
OVER THE SOUTHERN GULF AND MOVE INTO THE SOUTHERN PANHANDLE THUR
NIGHT. THEREFOR THE SOUTHERN PANHANDLE WILL SEE RAIN CONTINUING
AND NOT GET AS LONG OF A BREAK BETWEEN THE LOWS.

A BUILDING RIDGE OF HIGH PRESSURE OVER THE GULF FINALLY KICKS THE
UPPER LEVEL TROUGH OUT BY FRIDAY MORNING. THIS WILL ALLOW FOR DECREASING
CLOUDS THROUGH FRIDAY WITH STRONG NWLY FLOW ALOFT. HIGH PRESSURE
RIDGE HOLDS OVER THE GULF THROUGH FRIDAY NIGHT THEN STARTS TO MOVE
OVER THE PANHANDLE SATURDAY MORNING AS AN UPPER LEVEL TROUGH/LOW
DIGS SOUTH OVER THE WESTERN GULF. THIS WILL TURN FLOW BACK SWLY
AND ONSHORE SATURDAY NIGHT. A FRONT ASSOC WITH THIS SYSTEM WILL
TRACK ACROSS THE GULF AND INTO THE PANHANDLE SUNDAY NIGHT.

MODELS START TO WEAKEN THE UPPER LEVEL TROUGH AS IT APPROACHES
THROUGH THE DAY SUNDAY...BUT WITH SOME DIFFERENCES. SOME MODELS
HAVE MOST OF THE ENERGY SOUTH OF THE AREA WHICH WOULD KEEP MOST OF
THE PRECIP OVER THE SOUTHERN AREAS WHILE OTHERS HAVE MULTIPLE
SHORT WAVES PASSING OVER INTO THE START OF NEXT WEEK. 12Z MODELS
CAME INTO BETTER AGREEMENT WITH THE LOW MOVING INTO THE PANHANDLE
WED EVENING AND REMAINED IN GOOD AGREEMENT THROUGH THE MID RANGE
SO A BLEND OF THE AVAILABLE MODELS WERE USED FOR MOST FIELDS.
MODELS DIVERGED MORE GOING INTO THE WEEKEND AND THE START OF NEXT
WEEK SO RELIED MORE ON NATIONAL WPC GUIDANCE FOR PRESSURE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 4 PM AKDT THIS AFTERNOON FOR AKZ018.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-013-021-022-033>036-041>043.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ051-052.

&&

AHN/FERRIN