Area Forecast Discussion - Southeastern
FXAK67 PAJK 291351
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
551 AM AKDT FRI APR 29 2016
.SHORT TERM...AN ELONGATED SW-NE ORIENTED UPPER LOW WAS CENTERED
OVER THE ERN ALEUTIANS/WRN AK PENINSULA FRI MORNING. E OF THE
LOW...A BROAD UPPER TROUGH WAS POSITIONED OVER THE GULF AND AK
PANHANDLE...WHILE S OF THE LOW...AN IMPRESSIVE
DISTURBANCE...CHARACTERIZED BY A DEEP STRATOSPHERIC INTRUSION /DRY
SLOT/ AND 130 KT 300 MB JET...WAS EJECTING NE ACROSS THE NCNTRL
PAC. AS THE DISTURBANCE OVER THE NCNTRL PAC APPROACHES THE SWRN
GULF THIS AFTERNOON/TONIGHT...AN UPPER RIDGE WILL QUICKLY BUILD
FROM THE NERN PAC NWD ACROSS THE PANHANDLE AND BC. AT THE
SURFACE...A RIDGE OF HIGH PRESSURE WILL PERSIST OVER THE PANHANDLE
TODAY AND TONIGHT. THIS WILL AID IN GUSTY CONDITIONS OVER LYNN
CANAL AND SKAGWAY THROUGH FRI AFTERNOON...WITH WEAKENING TAKING
PLACE BY TONIGHT AS THE RIDGE SHIFTS E.

IN THE MEANTIME...SHOWERS ARE FORECAST TO PERSIST THROUGH THIS
EVENING. RAINFALL WITH THESE SHOWERS HAS BEEN LOCALLY HEAVY IN
INTENSITY EARLY FRI MORNING...AND HEAVY SHOWER POTENTIAL WILL
CONTINUE INTO THIS AFTERNOON/EARLY EVENING AS A SECOND WAVE MOVES
ONSHORE. BY MIDNIGHT...A BREAK IN PRECIPITATION WILL BE POSSIBLE
OVER THE CNTRL/SRN PANHANDLE DUE TO SUBSIDENCE OCCURRING BENEATH
THE BUILDING RIDGE AND IMMEDIATELY AHEAD OF THE APPROACHING GULF
STORM SYSTEM. HOWEVER...MARINE WINDS OVER THE GULF WILL
PROGRESSIVELY INCREASE IN STRENGTH DURING THE NIGHT AS A FRONTAL
BOUNDARY ENTERS THE SRN GULF. E-SELY GALES FROM 35-40 KT ARE
CURRENTLY FORECAST TO DEVELOP OVER MARINE ZONE 310 BY 06Z...AND
ZONE 52 BY 12Z.

INHERITED GRIDS WERE IN GOOD SHAPE. WIND EDITS WERE LIMITED TO
LOCAL EFFECTS OVER THE INSIDE WATERS...AND A NUDGE TO HI-RES
SURFACE SPEEDS/DIRECTIONS OVER THE GULF.
.LONG TERM...THE IMPRESSIVE DISTURBANCE NOTED ABOVE HAS SUPPORTED
MODERATE TO HEAVY RAIN BANDS ACCORDING TO NASA SPORT PASSIVE
MICROWAVE RAIN RATE IMAGERY. IN ADDITION, ITS ASSOCIATED FRONT
WILL IMPACT SOUTHEAST ALASKA WITH WINDY CONDITIONS SATURDAY,
POTENTIALLY INTO SATURDAY EVENING. THE FRONT THEN WILL STALL ITS
EASTWARD PROGRESS ACROSS THE CENTRAL PANHANDLE SATURDAY NIGHT AS
JET SUPPORT ALOFT ORIENTS NORTH-SOUTH. BUT IT WILL LIKELY BUCKLE
NORTHWARD ON SUNDAY AS A WAVE DEVELOPS ALONG ITS LENGTH FAR TO THE
SOUTH. THIS WAVE WILL THEN DEVELOP INTO A LOW, POTENTIALLY OF GALE
FORCE STRENGTH, WHICH WILL LIKELY PASS NORTHWEST OFFSHORE OF THE
PANHANDLE LATE SUNDAY INTO MONDAY.

THE SURFACE FRONT LIFTS INTO THE GULF ON SATURDAY, AND AS IT
APPROACHES SHORE, WINDS WILL ACCELERATE TO STORM FORCE ACROSS THE
NORTHERN GULF. THE FRONT WILL IMPACT THE COASTLINE AS WELL WITH 40
TO 50 MPH WIND GUSTS FROM YAKUTAT SOUTHEAST TO SITKA, HYDABURG,
AND KETCHIKAN. LIKEWISE AS IT SPREADS INLAND WE EXPECT SIGNIFICANT
GUSTS EVEN INTO JUNEAU AND WRANGELL. GRADIENTS WILL RELAX INTO
SATURDAY NIGHT ALLOWING WINDS TO FALL INTO SUNDAY. HOWEVER, A
DEVELOPING WAVE IS SET TO APPROACH OUR SOUTHERN OUTSIDE WATERS
SUNDAY NIGHT INTO MONDAY AND POTENTIALLY WILL GIVE THE COAST
A SECOND ROUND OF WIND.

THE OTHER CONCERN IS RAIN. THE LATITUDINAL DEPTH OF THE STORM
CHURNING SOUTH OF THE ALEUTIANS HAS PROVIDED A ROBUST CONNECTION OF
SUBTROPICAL MOISTURE. THE NAEFS HAS RAISED THE STAKES FOR
PRECIPITABLE WATER TO 4 STANDARD DEVIATIONS ABOVE THE MEAN, ABOVE
THE 3-PLUS FROM YESTERDAY. THE FIRST ROUND OF MODERATE TO HEAVY
RAIN BANDS WILL REACH THE CENTRAL AND SOUTHERN PANHANDLE ON
SATURDAY. THE FRONT THEN PUSHES THE HEAVIEST RAINFALL EASTWARD
INTO THE SOUTHERN PANHANDLE BY SATURDAY NIGHT. MEANWHILE
INSTABILITY ACROSS THE NORTH WILL SUPPLANT THE STEADY RAINS WITH
WIDESPREAD SHOWER ACTIVITY. THEN A WAVE BUCKLES THE FRONT TO THE
SOUTH WHICH PROVIDES YET ANOTHER FOCUS MECHANISM FOR RAINFALL.
WHILE THERE ARE SOME DIFFERENCES IN THE TRACK, SPEED, AND STRENGTH
OF THE WAVE DEVELOPING LATE SUNDAY AND TRACKING NORTH, IT DOES
APPEAR THAT MORE HEAVY RAIN WILL FOLLOW IT ON ITS WAY NORTHBOUND.
THUS RAINFALL, POTENTIALLY HEAVY AT TIMES, WILL SPREAD INTO THE
NORTHERN PANHANDLE SUNDAY NIGHT AND POTENTIALLY LAST INTO MONDAY.
CURRENT GUESSES SUGGEST 2 TO 4 INCHES OF RAIN FOR MOST LOCATIONS
IN THE PANHANDLE DURING THIS 2.5 DAY EVENT. BUT LOCALLY HIGHER
AMOUNTS ARE CERTAINLY POSSIBLE. A REGION-WIDE SPECIAL WEATHER
STATEMENT WAS SENT THIS MORNING UPDATING OUR THINKING TO THE
PUBLIC. COORDINATION TODAY WITH THE AKPAC RFC WILL PROVIDE A
BETTER GAUGE OF RIVER AND STREAM RESPONSE TO THE SYSTEM, BUT AS OF
NOW, WE THINK THERE WILL BE NO FLOODING.

SHOWERS WILL FOLLOW MONDAY'S LOW ONSHORE AND PERSIST INTO MID-
WEEK. THEN TOWARD THE END OF THE NEXT WEEK, ANOTHER SYSTEM PULLS
INTO THE GULF AS IT THREATENS SOUTHEAST WITH ANOTHER SHOT OF RAIN.

CONFIDENCE IN FORECAST IS GOOD SATURDAY INTO SATURDAY NIGHT AND
SOMEWHAT HIGH SUNDAY NIGHT AND MONDAY THAT A LOW PASSES OFFSHORE
ACROSS THE GULF ON ITS WAY NORTHWEST. HOWEVER, THE DETAILS DESERVE
MORE LOOKS AS MODEL DISPARITY WITH THIS SYSTEM IS STILL AN ISSUE.
EDITS WERE GENERALLY RESERVED FOR SATURDAY AND SATURDAY NIGHT
WHERE CONFIDENCE WAS GREATEST. FOR SUNDAY AND BEYOND WE LET THE
PREVIOUS FORECAST CONTINUE AS IT AS IT STILL INDICATES A BROAD,
YET FEASIBLE CONSENSUS WITH THE DEVELOPING WAVE.





&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ052. 
     SMALL CRAFT ADVISORY FOR PKZ012-036-041>043-051. 
     SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ022-053. 
&&

$$

GARNER/JWA

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