Area Forecast Discussion
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FXAK67 PAJK 012334
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
334 PM AKDT TUE SEP 1 2015

.SHORT TERM...UPPER LOW POSITIONED NEAR HAIDA GWAII THIS AFTERNOON
IS FORECAST TO MOVE SE AWAY FROM THE REGION THROUGH WED
AFTERNOON. SECOND DISTURBANCE WILL SUBSEQUENTLY PIVOT SW ACROSS
NWRN CANADA AND APPROACH THE PANHANDLE TOWARD 00Z THU. SHOWERS
SPREADING NNW FROM THE HAIDA GWAII DISTURBANCE WILL DISSIPATE
GOING INTO TONIGHT. FARTHER N...MID/HIGH LEVEL CLOUDS WILL
CONTINUE TO SPREAD TOWARD SKAGWAY/HAINES...AS WELL AS AREAS E OF
YAKUTAT TO NEAR JUNEAU. HOWEVER...DRY OFFSHORE REGIME IS EXPECTED
TO PRECLUDE PRECIPITATION.

PRESSURE GRADIENT BETWEEN A HIGH OVER THE YUKON AND LOW PRESSURE
POSITIONED INVOF HAIDA GWAII WILL YIELD MODERATE NLY WINDS OVER
MOST OF THE INSIDE WATERS...WITH LOCALLY TIGHTER GRADIENT OVER THE
NRN INSIDE CHANNELS RESULTING IN 25-35 KT WINDS FOR LYNN CANAL AND
STEPHENS PASSAGE. IN ADDITION...PROLONGED PERIOD OF 25-35 KT NLYS
OVER THE LENGTH OF LYNN CANAL WILL SUPPORT SEA HEIGHTS TO 8 FT.

STRONG RADIATIONAL COOLING IS EXPECTED TONIGHT...WITH LOWS FALLING
INTO THE MID-UPPER 30S FOR WIND SHELTERED AREAS. ATTM...BOUNDARY
LAYER WILL LIKELY BE TOO DRY FOR FOG OVER THE NRN HALF OF THE
PANHANDLE /THOUGH THIS WILL NEED TO BE CONTINUALLY MONITORED
TONIGHT/...BUT PATCHY FOG WILL BE POSSIBLE OVER THE SRN PANHANDLE
TONIGHT DUE TO TUE AFTERNOON CLOUDS PRECLUDING STRONG DAYTIME
HEATING/DRYING.

INHERITED PRESSURE GRIDS WERE NUDGED TO THE NAM. NO SIGNIFICANT
CHANGES WERE NECESSARY FOR POP/QPF.

.LONG TERM...AMPLIFIED UPPER PATTERN AT THE START OF THE LONG
RANGE WILL GIVE WAY TO A MORE ZONAL FLOW BY FRIDAY AND INTO THE
WEEKEND. AN UPPER RIDGE OVER THE CENTRAL GULF ON THURSDAY WILL
BEGIN TO BREAK DOWN ON FRIDAY AS THE FIRST IN A SERIES OF
SHORTWAVE TROUGHS MOVES FROM THE BERING SEA INTO THE WESTERN GULF.
AT THE SURFACE...THE HIGH PRESSURE SYSTEM OVER THE YUKON
RESPONSIBLE FOR THE STRONGER OUTFLOW WINDS OVER THE NORTHERN
PANHANDLE WILL BEGIN TO WEAKEN AND SHIFT EASTWARD BY LATE ON
THURSDAY. MEANWHILE RIDGING OFF SHORE WILL GIVE WAY TO SURFACE LOW
DEVELOPMENT OVER THE NORTHERN GULF ON THURSDAY NIGHT IN RESPONSE
TO THE APPROACHING SHORTWAVE. MODELS HAVE BEEN CONSISTENT IN
SPEEDING UP THE BREAK DOWN OF THE RIDGE AND IN THE QUICKER
MOVEMENT OF THE SURFACE LOW WITH THE NAM BEING THE FASTEST AND THE
GFS THE SLOWEST. 12Z EURO WAS A GOOD COMPROMISE SO USED IT TO
UPDATE THE FORECAST THROUGH SATURDAY. AFTER SATURDAY...MODEL
AGREEMENT BREAKS DOWN AND SO LEANED HEAVILY ON WPC GUIDANCE.

MADE MINIMAL CHANGES THROUGH THURSDAY NIGHT AS OFFSHORE FLOW AND
NORTHWEST FLOW ALOFT WILL CONTINUE TO PROVIDE ONE LAST GASP OF
SUMMER FOR THE PANHANDLE. GRADUALLY BROUGHT THE STRONGER NLY WINDS
OVER THE NORTH SOUTH CHANNELS DOWN AS THE PRESSURE GRADIENT
RELAXES ON THURSDAY AND RETURNING SOUTH WINDS A LITTLE QUICKER ON
FRIDAY AFTERNOON WITH THE FASTER MOVEMENT OF THE SURFACE
FEATURES. ONLY OTHER CHANGES WERE TO INCREASE POP AND QPF VALUES
THROUGH DAY 4 IN KEEPING WITH THE NAM AND EURO TREND OF ADVANCING
A SURFACE FRONT TOWARDS THE COASTAL AREAS ON FRIDAY EVENING. WENT
WITH CATEGORICAL POPS ON FRIDAY NIGHT AND SATURDAY WITH THIS IN
MIND.

FOR SATURDAY NIGHT THOUGH TUESDAY...ALTHOUGH THERE ARE MODEL
DISAGREEMENTS ON THE TIMING AND PLACEMENT OF INDIVIDUAL SHORTWAVES
AND THEIR ASSOCIATED SURFACE FEATURES...GENERALLY EXPECT ONSHORE
MOIST FLOW WITH SMALLER DIURNAL TEMPERATURE RANGES AND CONTINUED
HIGHER RAIN CHANCES.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ012.
         SMALL CRAFT ADVISORY FOR PKZ013-022-031-041-042-051.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ043.

&&

$$

GARNER/LEVIN

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