Gale Warning 256, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
337 PM AKDT SUN AUG 16 2015

.SHORT TERM...WEAK FRONT MOVES OVER THE PANHANDLE TONIGHT MOVING A
HIGH PRESSURE RIDGE OVER THE PANHANDLE TO THE EAST. THE RIDGE WILL
REBUILD TOMORROW AHEAD OF A STRONG FRONT MOVING ACROSS THE GULF.
THIS FRONT IS ASSOCIATED WITH A LOW THAT HAS MOVED INTO THE
BERING SEA AND WILL THEN TRACK EAST ACROSS THE AK INTERIOR.

CURRENT WEAKENING FRONT TRACKING OVER THE PANHANDLE THROUGH
TONIGHT PRODUCING PERIODS OF LIGHT RAIN OVER MOST OF THE NORTHERN
AND CENTRAL PANHANDLE. SO FAR STEADIEST RAIN HAS BEEN OVER
YAKUTAT WHICH IS CLOSEST TO THE TROUGH AXIS. MODELS, AS THEY WERE
LAST NIGHT, STILL SHOWING BIT OF SPREAD ON EXTENT OF PRECIP AND
NOT LINING UP WITH RADAR OR SATELLITE. HOWEVER THESE DIFFERENCES
DON'T LAST AS THE NEXT FRONT MOVES IN TONIGHT INTO TUESDAY.
ATMOSPHERIC RIVER DEVELOPMENT PUSHING LONG FETCH OF TROPICAL
MOISTURE INTO THE PANHANDLE ALONG THE FRONT WITH HEAVY RAIN
STARTING AT YAKUTAT MONDAY THEN ADVANCING EASTWARD. MAJORITY OF
RAIN WILL FALL IN THE START OF THE LONG RANGE. TEMPERATURES WILL
HAVE LIMITED DIURNAL SPREAD, ESPECIALLY FOR LOCATIONS WITH
STEADIER RAINFALL TONIGHT.

BARRIER JET ALONG THE NORTHERN AK GULF THIS EVENING ALONG CURRENT
FRONT PRODUCING BRIEF PERIOD OF SMALL CRAFT WINDS OVER AKZ052.
HIGH PRESSURE RIDGE OVER THE PANHANDLE WILL SHIFT TO THE EAST THIS
EVENING AS THE FRONT MOVES OVERLAND. SMALL CRAFT WINDS OVER N
LYNN CANAL WILL DIMINISH TONIGHT WITH THE WEAKENING GRADIENT. THE
RIDGE WILL REBUILD TOMORROW AHEAD OF THE NEXT FRONT WITH SOUTHERLY
WINDS PICK UP AGAIN. OVER THE AK GULF WINDS WILL PICK UP TO MAX
SMALL CRAFT WITH THE ADVANCING FRONT BY TOMORROW AFTERNOON.

NEW MODEL RUNS WERE IN LINE FOR PRESSURE AND WINDS AND STILL
CLOSE TO PREVIOUS FORECAST. USED A BLEND OF NEW ECMWF/NAM TO
REFRESH INHERITED GRIDS, OVERALL CHANGES WERE MINOR WITH SOME
INCREASE TO WINDS OVER LYNN CANAL. FORECAST CONFIDENCE IS ABOVE
AVERAGE.

.LONG TERM...HEAVY RAIN AND WINDY CONDITIONS FOR THE NORTHEAST
GULF COAST INTO THE NORTHERN PANHANDLE MONDAY NIGHT INTO TUESDAY.
THEN A BREAK IN THE ACTIVE WEATHER FOR THE MIDDLE OF THE WEEK.
WEATHER PATTERN LOOKS FAIRLY ACTIVE FOR THE END OF THE WEEK.

 FOR THE START OF THE LONG TERM FORECAST PERIOD ON MONDAY
EVENING...THE NORTHEAST GULF COAST WILL START TO EXPERIENCE HEAVY
RAIN MOVING IN FROM THE WEST. A LOW OVER INTERIOR ALASKA AND A
HIGH OVER NORTH PACIFIC IS GOING TO PRODUCE STRONG SOUTHWEST
FLOW..AND THIS WILL ALLOW AN ATMOSPHERIC RIVER TO BRING IN
ANOMALOUSLY HIGH PRECIPITABLE WATER TO YAKUTAT AREA MONDAY
EVENING. THIS ATMOSPHERIC RIVER IS GOING TO GRADUALLY SAG SOUTH
OVERNIGHT, AND THE AXIS OF HEAVY RAIN WILL BE AIMING TOWARDS THE
COASTAL AREA WEST OF GLACIER BAY. THE HEAVY RAIN WILL SPREAD INTO
NORTHERN AND CENTRAL PANHANDLE EARLY TUESDAY MORNING, AND CONTINUE
THROUGH TUESDAY AFTERNOON. BY TUESDAY EVENING, PRECIPITATION RATE
IS EXPECTED TO DIMINISH. FOR THIS HEAVY RAIN EVENT, DO EXPECT 2 TO
3 INCHES OF RAINFALL OVER CENTRAL AND NORTHERN PANHANDLE.
NORTHEAST GULF COAST CAN SEE 4 TO 6 INCHES OF RAINFALL.

 BESIDES HEAVY RAIN...STRONG WIND IS ALSO A CONCERN. HAVE POCKETS
OF GALE FORCE WIND IN THE COASTAL WATERS MONDAY NIGHT. A LOW
PRESSURE SYSTEM IS EXPECTED TO TRACK FROM WESTERN GULF COAST INTO
PRINCE WILLIAM SOUND AND INLAND BY MONDAY NIGHT. THIS LOW WILL
COMBINED WITH THE INTERIOR LOW AND CAUSE THE PRESSURE OVER YUKON
TO LOWER TO SUB-1000 MB. MEANWHILE, THE NORTH PACIFIC RIDGE IS
REMAINED TO HOLD STRONG. THE COMBINED PRESSURE GRADIENT BETWEEN
THE TWO SYSTEMS IS GOING TO CREATE STRONG SOUTHERLY WIND OVER THE
NORTHERN AND CENTRAL PANHANDLE. THE NORTH-SOUTH PRESSURE GRADIENT
BETWEEN JUNEAU AND SKAGWAY IS FORECASTED TO BE AROUND 7 MB...WHICH
IS SUFFICIENT TO WARRANT GALE FORCE WINDS IN THE AREA. RIGHT
NOW...HAVE GALE FORCE WIND OF 40 KT FORECASTED FOR NORTHERN LYNN
CANAL FOR EARLY TUESDAY MORNING THROUGH TUESDAY NIGHT. GALE FORCE
WIND IS ALSO FORECASTED FOR STEPHENS PASSAGE AND CROSS SOUND.
STRONG WIND GUSTS OF 40 TO 45 MPH IS EXPECTED OVER SKAGWAY,
HAINES, JUNEAU, AND SITKA AREAS ON TUESDAY. WINDS WILL DIMINISH ON
WEDNESDAY BACK TO SEASONABLE LEVEL.

 WITH CLOUD COVER AND PRECIPITATION, DO EXPECT TEMPERATURES TO BE
ABOUT SEASONABLE. HIGHS WILL BE AROUND 60 DEGREES, AND LOWS WILL
BE IN THE LOWER 50S.

 AFTER THE HEAVY RAIN AND STRONG WIND EVENT, WEATHER PATTERN
EXPECTED TO STAY PROGRESSIVE. MODELS ARE HAVING A TOUGH TIME IN
PINPOINTING INDIVIDUAL SYSTEMS. HOWEVER, MODELS ARE HINTING ON
POTENTIAL DEVELOPMENT OF STORMIER WEATHER PATTERN BY THE END OF
THE WORK WEEK.

 UTILIZE ECMWF/WPC GUIDANCE IN REFRESHING THE INHERITED FORECAST
PACKAGE. FORECAST CONFIDENT IS SLIGHTLY ABOVE AVERAGE FOR THE
HEAVY RAIN AND STRONG WIND EVENT. FORECAST CONFIDENCE LOWERS TO
BELOW AVERAGE IN THE MID TO LONG RANGE AS NUMERICAL WEATHER MODELS
START TO DIVERGE. THE GENERAL TREND IS ACTIVE WEATHER PATTERN WILL
RETURN BY THE NEXT WEEKEND.

.HYDROLOGY...WITH HEAVY RAINFALL, WATER LEVELS ARE EXPECTED TO
INCREASE SEVERAL FEET FOR STREAMS AND RIVERS IN THE AREA. AT THIS
TIME...THE NATIONAL WEATHER SERVICE IS FOCUSING RIVERS AND STREAMS
ACROSS THE NORTHERN AND CENTRAL PANHANDLE. CHILKAT RIVER NEAR
HAINES AND JORDAN CREEK IN JUNEAU ARE FORECASTED TO REACH BANKFULL
CONDITIONS BY TUESDAY MORNING. TAIYA RIVER NEAR SKAGWAY...MENDENHALL
LAKE AND MONTANA CREEK IN JUNEAU ARE PREDICTED TO REACH MINOR
FLOOD STAGE BY TUESDAY MORNING.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-022-043-051-052.

&&

PRB/RCL

VISIT US AT HTTP://WWW.WEATHER.GOV/JUNEAU

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