Area Forecast Discussion
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000
FXAK67 PAJK 011344
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
544 AM AKDT SUN MAY 1 2016

.SHORT TERM...MORE RAIN TO AFFLICT THE PANHANDLE THROUGH THE NEXT
30 HOURS. BREEZY CONDITIONS TO CONTINUE AS WELL.

AN IMPRESSIVE JET AT 300 MB APPROACHING 150 KT CONTINUES TO AIM AN
ATMOSPHERIC RIVER INTO SOUTHEAST ALASKA. NAEFS MEAN PRECIPITABLE
WATER PREDICTIONS OF AROUND 1 INCH FALLS AROUND 4 STANDARD
DEVIATIONS ABOVE NORMAL FOR EARLY MAY. THE ANNETTE ISLAND 12Z
SOUNDING`S MEASUREMENT OF 1.02 INCHES CONFIRMS THESE VALUES AND
PLACES OUR ATMOSPHERE ABOVE THE 99TH PERCENTILE AGAINST
CLIMATOLOGY. WHAT HAS THIS MEANT AND WHAT DOES THIS PORTEND? LOTS
OF RAIN. 24 HOUR TOTALS HAVE RANGED BETWEEN 1 AND 3 INCHES FOR THE
SOUTHERN PANHANDLE. AMOUNTS FOR THE NORTHERN PANHANDLE MEASURED
FAR LESS AT LESS THAN AN INCH, OWING TO THE SPEED OF THE FRONT`S
PROGRESS. BUT FOR THE NORTH, THE RAIN WILL BE MOVING BACK IN, THIS
TIME MUCH HEAVIER. A WAVE FORMING IN THE 45 N 145 W VICINITY WILL
HELP STEER THIS RIVER NORTHWESTWARD OVER THE NEXT 24 HOURS. THUS
READERS OF THE FORECAST WILL FIND THE WORDS...RAIN HEAVY AT
TIMES...MIGRATING NORTHWARD INTO TONIGHT. THE SOUTHERLY DIRECTION
OF THE LOW-LEVEL JET SHOULD EVEN HELP THE RAINFALL THREAD THE
NEEDLE OF LYNN CANAL BETWEEN THE COAST MOUNTAINS AND THE CHILKAT
RANGE. THUS, TYPICALLY DRIER HAINES AND SKAGWAY SHOULD SEE MUCH
HIGHER RAIN RATES THAN IS CUSTOMARY. RAIN WILL ONLY INCREASE INTO
TONIGHT FOR MUCH OF THE NORTH, WHILE THE SOUTHERN PANHANDLE BEGINS
TO RELENT A LITTLE AS THE JET ENERGY MIGRATES NORTHWESTWARD.

RIVER RISES HAVE BEEN RECORDED OVER THE SOUTHERN PANHANDLE IN
PARTICULAR. AS THE WAVE APPROACHES FROM THE SOUTH, SOME OF THESE
RIVERS WILL SEE MORE RISES TODAY INTO THE EVENING BEFORE BEGINNING
TO FALL AS RATES RELAX. LOW WATER LEVELS OVER THE NORTH WILL BEGIN
TO RISE LATE TONIGHT AS RAINS INCREASE OVERNIGHT. NO FLOODING IS
EXPECTED THOUGH.

OVERALL THE WIND FORECAST WORKED WELL YESTERDAY. MORE EXPOSED
AREAS SUCH AS HYDABURG AND SITKA GUSTED BETWEEN 45 AND 55 MPH. AND
YAKUTAT, WHERE THE FRONT WAS STRONGEST, GUSTED TO 48 MPH YESTERDAY
AFTERNOON. INLAND IT WAS WINDY WITH SEVERAL PEAK GUSTS AROUND 40
MPH. THE WIND FORECAST TODAY IS MORE OF A CHALLENGE. THE FRONT
STILL LIES DRAPED ACROSS THE CENTRAL PANHANDLE WITH BREEZY
SOUTHERLIES EAST OF THE FRONT AND LIGHTER SOUTHERLIES TO THE WEST.
AS A SURFACE LOW DEVELOPS UNDERNEATH THE WAVE WELL TO THE SOUTH,
THERE WILL BE A TENDENCY FOR SOME WINDS ACROSS THE NORTH TO WANT
TO BACK NORTHERLY. BUT AN EXPANDING LOW LEVEL 925 MB JET WILL
OPPOSE THIS ALOFT, AT FIRST FROM THE SOUTH AND THEN EXTENDING
NORTH THROUGH TONIGHT. WITH GENERALLY STABLE CONDITIONS ACROSS
SOUTHEAST, WE THINK THIS MOMENTUM TRANSFER WILL TAKE SOME TIME,
BUT TONIGHT, THESE SOUTHERLIES WILL SPREAD THROUGH MUCH OF THE
NORTHERN PANHANDLE. IN FACT, THE LOW-LEVEL JET WAS SO STRONG OVER
THE SOUTH, THAT WE RAISED WINDS OVER WESTERN PRINCE OF WALES THIS
AFTERNOON AND OVER CHANNELS SUCH AS SUMNER AND FREDERICK TONIGHT.
CONFIDENCE IS SUSPECT OVER TIMING OF THE DIRECTIONAL SWITCH AS
WELL AS ANY ACCELERATION TONIGHT OVER THE FAR NORTH. THIS WILL
ALL DEPEND ON HOW QUICKLY THE LOW MOVES ASHORE NEAR CAPE
FAIRWEATHER OR CAPE SPENCER. READ THE FORECAST FOR SOME STARK
TRANSITIONS BETWEEN TONIGHT AND MONDAY WHEN THE RIDGE BEGINS TO
BUILD BEHIND THE LOW AND UNDERSTAND THEY COULD HAPPEN EARLIER THAN
INDICATED. THE NEXT SHIFT WILL STUDY THE TRANSITION AS WELL.

USED A GFS22/NAM12 BLEND FOR WINDS WITH GUIDANCE FROM 925 MB
MODELED JETS. CONFIDENCE IS THROUGH THE ROOF ON RAIN. CONFIDENCE
IS CLOSER TO AVERAGE ON THE DIFFICULT WIND PATTERN.

.LONG TERM...GENERAL THINKING FOR THE LONG RANGE REMAINS ON TRACK
FROM THE PAST FEW DAYS. THE WEAK WAVE OF LOW PRESSURE MENTIONED
ABOVE WILL QUICKLY BE MOVING INLAND INTO THE YUKON ON MONDAY
MORNING. A RIDGE OF HIGH PRESSURE WILL BUILD IN BEHIND THE
DEPARTING WAVE WHICH WILL RESULT IN INCREASED SOUTHERLY WINDS.
EXPECT A PERIOD OF SMALL CRAFT WINDS IN THE NORTHERN INNER CHANNELS
MONDAY MORNING AND GUSTS OF 30 TO 35 MPH OVER THE CENTRAL AND
NORTHERN AREAS. AS THE RIDGE CONTINUES TO BUILD OVER THE PANHANDLE
LATER MONDAY INTO TUESDAY EXPECT DECREASING WINDS AS THE PRESSURE
GRADIENT RELAXES. ALONG WITH THE WEAKENING WINDS, PRECIPITATION
CHANCES WILL BE ON THE DECREASE AS WELL ON TUESDAY AND WEDNESDAY.
HOWEVER THIS DRIER PERIOD OF WEATHER WILL BE SHORTLIVED AS ANOTHER
POTENT UPPER LOW MOVES INTO THE CENTRAL GULF BY THE THURSDAY-FRIDAY
TIMEFRAME. IT WILL BE ACCOMPANIED BY A 120-130 KT SOUTHWESTERLY
UPPER JET AIMED RIGHT AT THE PANHANDLE MEANING A RETURN TO WET AND
POTENTIALLY WINDY WEATHER IS LIKELY IN STORE FOR THE LATTER HALF OF
THE WEEK AND INTO THE WEEKEND.

USED THE 06Z NAM/00Z GFS FOR MINOR UPDATES TO THE INHERITED
FORECAST.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM 1 PM AKDT THIS AFTERNOON THROUGH THIS EVENING
     FOR AKZ027.
MARINE...GALE WARNING FOR PKZ036-041.
     SMALL CRAFT ADVISORY FOR PKZ012-031>035-042-043-051-052.
     SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ022-053.
&&

$$

JWA/TPS

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