Freeze Warning 2, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
217 PM AKDT SUN OCT 11 2009

.SHORT TERM...THE LATEST SATELLITE IMAGERY SHOWS THE PANHANDLE
UNDER MOSTLY CLOUDY SKIES WITH NO PRECIPITATION BEING REPORTED AT
ANY WEATHER STATIONS. WINDS ACROSS THE REGION THIS MORNING ARE
FAIRLY LIGHT WITH A WEAK PRESSURE GRADIENT BUT THE WINDS ARE
BEGINNING TO INCREASE OVER THE FAR NORTHERN AREAS.

THE MID-LEVEL FLOW IS VEERING TO THE EAST AND IS INCREASING THE
OFFSHORE FLOW. THIS IS EVIDENT FROM SATELLITE IMAGERY AS CLOUDS ARE
DECREASING AS DRIER AIR IS BEING ADVECTED OVER THE PANHANDLE. THE
CLOUDS WILL SLOWLY BREAK UP AND SKIES WILL BECOME PARTLY CLOUDY
THROUGH THE EVENING AND BE MOSTLY SUNNY ON MON. WITH THE SKIES
CLEARING OUT...TEMPS TONIGHT WILL FALL INTO THE LOWER 30S AND
AREAS OF FROST WILL OCCUR OVER MOST OF THE PANHANDLE. FROST ADVY
WILL BE ISSUED FOR THE SOUTHERN HALF OF THE PANHANDLE AND THE
HAINES AREA. THE COASTAL AREAS WILL NOT BE THAT COLD AND THE REST
OF THE PANHANDLE HAS ALREADY HAD A KILLING FROST BUT WILL MENTION
AREA OF FROST FOR TONIGHT AND MON MORNING.

THE SURFACE HIGH PRESSURE OVER CANADA WILL BUILD WESTWARD AND
INCREASE THE PRESSURE GRADIENT. THIS WILL INCREASE WINDS FROM
INTERIOR GAPS OVER MARINE AREAS ADJACENT TO THE COAST MOUNTAINS.
WINDS OVER EAST/WEST CHANNELS WILL INCREASE THROUGH TONIGHT TO
20KT AND CONTINUE TO REACH MIN SMALL CRAFT THROUGH MON. ALSO WINDS
IN LYNN CANAL WILL INCREASE TO SMALL CRAFT TONIGHT AND PERSIST
THROUGH MON AFTERNOON. PAGY WILL BECOME BREEZY TONIGHT WITH THE
INCREASE PRESSURE GRADIENT AND GUSTS TO 35 MPH WILL DEVELOP NEAR
THERE THROUGH MON.

&&

.LONG TERM...VERY GOOD UPPER LEVEL AGREEMENT THROUGH THE WEEK IN
SPITE OF AN UNUSUAL PATTERN INVOLVING STRONG...RETROGRADING UPPER
LOW THAT IS PROJECTED TO MOVE SOUTHWEST OUT OF ALBERTA ON MONDAY
AND THEN INTENSIFY AFTER MOVING OFFSHORE OVER THE DIXON ENTRANCE ON
TUESDAY. SIGNIFICANT DIFFERENCES WRT THE DISPOSITION OF THIS
FEATURE DO NOT ARISE UNTIL NEXT WEEKEND. SOME GFS ENSEMBLE SPREAD
DOES EXIST...BUT CURRENT OPERATIONAL GFS AND ECMWF RUNS IN BETTER
AGREEMENT THAN EITHER ARE WITH THE GFS ENSEMBLE MEAN. FARTHER
WEST...A MUCH WEAKER UPPER LOW NEAR 50N/160W WITH SURFACE
REFLECTION IS FORECAST TO TRACK RAPIDLY TO THE EAST AND MERGE
WITH THE ALBERTA LOW SW OF THE QUEEN CHARLOTTES. AT THAT
TIME...THE MERGED COMPLEX WILL BEGIN TO INTENSIFY AND AS OF THIS
MORNING...SEA LEVEL PRESSURE IS FORECAST TO BOTTOM OUT IN THE
UPPER 960S OR LOW 970S BY MID WEEK. AFTER MAX INTENSITY...ECMWF KEEPS
THIS FEATURE SLIGHTLY DEEPER AND SLIGHTLY FARTHER NORTH THAN
GFS...GENERALLY ALONG 140W...BUT THEN VERY ABRUPTLY FILLS IT NEAR
DRY BAY EARLY IN THE WEEKEND.

MAIN FORECAST ISSUE IN THE EXTENDED RANGE WILL BE WIND INTENSITY
AND DURATION. THE BEGINNING OF A WIND EVENT WILL ALREADY BE IN
PROGRESS IN THE SOUTHERN ZONES UNDER A STRONG NORTHEASTERLY
PRESSURE GRADIENT AND A SIGNIFICANT AMOUNT OF LOW AND MID LEVEL
COLD AIR ADVECTION INTO THE PANHANDLE FROM CANADA. THIS WILL ALSO
RESULT IN PARTLY CLOUDY TO MOSTLY CLEAR SKIES FOR THE FIRST HALF
OF THE WEEK WHICH WILL RESULT IN MID 20S TO LOW 30S THROUGH
TUESDAY NIGHT. OVERNIGHT TEMPS WILL SLOWLY REBOUND TO MORE
SEASONAL VALUES IN THE SECOND HALF OF THE WEEK.

BY TUESDAY MORNING...STRONG OFFSHORE WINDS WILL HAVE SPREAD AS FAR
NORTH AS TRACEY ARM OR SO WITH GALE FORCE GUSTS OUT OF INTERIOR
PASSES OVER THE INNER CHANNELS. NORTHEASTERLY GALES IN THE
SOUTHERN COASTAL MARINE ZONES AS WELL. BY TUESDAY AFTERNOON PEAK
WINDS WILL HAVE REACHED THE NORTHERN INNER CHANNELS AND CROSS
BARRIER FLOW WILL BE MAXED OUT OVER THE JUNEAU AREA...BUT STILL
NOT SEEING A SIGNIFICANT CRITICAL LAYER OR INVERSION SET UP UNTIL
LATE TUESDAY NIGHT WHICH IS ALSO ABOUT THE TIME THAT A RELATIVE
MAXIMA IN THE MID LEVEL VORTICITY FIELD WILL BISECT THE PANHANDLE.

OFFSHORE WINDS OVER THE INNER CHANNELS SLOWLY RELAX OVER THE NEXT
TWO DAYS HOWEVER A SECOND ROUND OF GALE FORCE WINDS ARE EXPECTED
OVER THE SOUTHERN COASTAL MARINE ZONES IN THE SECOND HALF OF THE
WEEK AS THE SURFACE LOW TRACKS TO THE NORTH ALONG 140W.

NOT A LOT OF POP IN THE EXTENDED RANGE FORECAST BUT THE SNOW LEVEL
WILL BE COMING DOWN QUITE LOW. NOT EXPECTING ANY SNOW NEAR SEA
LEVEL...BUT THERE WILL BE SOME FRESH SNOW LOWER ON THE MOUNTAINS
THAN WE HAVE SEEN SO FAR THIS AUTUMN.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FROST ADVISORY FROM 1 AM TO 7 AM AKDT MONDAY FOR
	 AKZ019-024-26>029.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-013-021-022-031-035-041.
	 SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ042-043-051-052.

&&

ABJ/FRITSCH