Area Forecast Discussion - Southeastern
FXAK67 PAJK 231330
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
530 AM AKDT TUE SEP 23 2014
.SHORT TERM...VIGOROUS CYCLONE CENTERED AT 45.1N/140.6W IS IN THE
PROCESS OF OCCLUDING OVER THE NERN PAC THIS MORNING. AS THIS
FEATURE BECOMES VERTICALLY STACKED...IT IS FORECAST TO DRIFT NWD
TOWARD HAIDA GWAII THROUGH WED. MEANWHILE...PROGRESSIVE NRN STREAM
WILL BE LOCATED FROM INTERIOR AK INTO NWRN CANADA. EMBEDDED TROUGH
WITHIN THIS FLOW REGIME WILL MOVE FROM W-E DURING TUE
NIGHT...STAYING WELL N OF THE CWA. 

THE PASSAGE OF THE NRN STREAM WAVE WILL LEAD TO STRENGTHENING
SURFACE HIGH PRESSURE OVER ERN INTERIOR AK AND THE YUKON...WHICH
WHEN COMBINED WITH LOW PRESSURE APPROACHING HAIDA GWAII...WILL
YIELD A TIGHTENING GRADIENT OVER MUCH OF SERN AK. GRADIENT WILL BE
STRONGEST FROM YAKUTAT EWD TO SKAGWAY/NRN LYNN CANAL. AS A
RESULT...SMALL CRAFT WINDS ARE FORECAST TO DEVELOP OVER NRN LYNN
THIS EVENING...AND POSSIBLY SPREAD SWD INTO SRN LYNN BY LATE
TONIGHT. ELSEWHERE...NNELY BOUNDARY LAYER WINDS WILL LIKELY
STRENGTHEN TO 25 KT FROM SRN PORTIONS OF MARINE ZONE 310 INTO 41
LATE THIS AFTERNOON AND PERSIST THROUGH THE NIGHT. SEAS WILL
SUBSEQUENTLY INCREASE IN RESPONSE TO THE INCREASING WINDS...AND A
S SWELL WILL SPREAD N FROM THE PAC LOW INTO THE SRN OUTSIDE
WATERS.

THE STRENGTHENING PRESSURE GRADIENT INVOF YAKUTAT INTRODUCES
UNCERTAINTY REGARDING LOW TEMPERATURES TUE NIGHT. MOS GUIDANCE
INDICATES WINDS WILL BECOME CALM AT YAKUTAT TONIGHT...AND IF THIS
HAPPENS...THEN TEMPERATURES WILL LIKELY FALL INTO THE LOW 30S
GIVEN THE PRESENCE OF A DEEP-LAYER OF DRY AIR/CLEAR SKIES.
HOWEVER...MODELS MAY NOT BE HANDLING DOWNSLOPE WINDS
SUFFICIENTLY...IN WHICH CASE...WINDS COULD STAY UP OVERNIGHT
PROMOTING BOUNDARY LAYER MIXING AND WARMER LOW TEMPERATURES /MID
TO UPPER 30S/. ATTM...LEFT LOWS FOR YAKUTAT IN THE MID 30S...AND
ALSO MENTIONED PATCHY FROST GIVEN A KILLING FREEZE HAS NOT YET
BEEN EXPERIENCED.

FARTHER S...MOISTURE WILL GRADUALLY SPREAD NWD FROM THE NERN PAC
LOW TUE AFTERNOON AND NIGHT. HOWEVER...EXAMINATION OF FORECAST
SOUNDINGS SHOWS THE BOUNDARY LAYER WILL BE SLOW TO
MOISTEN...LIKELY AS A RESULT OF NLY-ELY BOUNDARY LAYER WINDS
EMANATING FROM THE COAST MOUNTAINS. THIS...IN ADDITION TO WEAK
SYNOPTIC/MESOSCALE FORCING FOR ASCENT SUGGESTS THAT RAINFALL WILL
BE LIGHT...AND BE CONFINED TO THE SRN PANHANDLE THROUGH TONIGHT.
.LONG TERM...THE VERTICALLY STACKED LOW OVER THE EASTERN PACIFIC
LIFTS SLOWLY TO ABOUT 300 NM SOUTH OF HAIDA GWAII AND FALLS APART
BY FRIDAY AFTERNOON. A WEAK OFF SHORE FLOW PATTERN FROM HIGH
PRESSURE OVER NORTHWEST CANADA PERSISTS. WHILE THE LOW WEAKENS AND
MOVES TO SOUTH OF HAIDA GWAII MOISTURE WILL BE PUSHING NORTH INTO
THE SOUTHERN HALF OF THE PANHANDLE THROUGH HE END OF THE WEEK. DO
NOT EXPECT LARGE RAINFALL AMOUNTS FROM THE ASSOCIATED TROUGH
FEATURE. 

MEANWHILE FURTHER WEST A LOW MOVES ACROSS THE ALEUTIANS SPREADING
FRONT INTO THE WESTERN GULF OF ALASKA LATE THURSDAY AND TO NEARLY
THE PANHANDLE BY LATE FRIDAY...BRINGING WITH IT THE NEXT SET OF
RAIN. WITH THIS SYSTEM THE JET STREAM WILL START MOVING BACK INTO
THE GULF OF ALASKA RATHER THAN FLOW SOUTH IT. THUS A MORE ACTIVE
PATTERN BACK BY THE END OF THE MONTH AND INTO EARLY OCTOBER. 

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-013-041-042. 

&&

$$

GARNER/BEZENEK

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