Gale Warning 256, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
326 PM AKDT TUE SEP 22 2009

.SHORT TERM...WINDS AND RAIN CONTINUE TO IMPROVE ACROSS THE
PANHANDLE AS REMNANTS OF LAST LOW PRESSURE SYSTEM CONTINUE TO
MOVE NORTH OUT OF THE PANHANDLE. CIGS CONTINUE TO IMPROVE TODAY
FROM SOUTH TO NORTH. TWO DAY QPF TOTALS OVER FOUR INCHES IN PAKT
ALONG WITH MODERATE RAIN THIS MORNING PROMPTED SMALL STREAM FLOOD
ADVISORY WITH REPORTS OF FULL DITCHES AND PONDING OF WATER ON
ROADWAYS. BRIEF BREAK TONIGHT BEFORE NEXT SIGNIFICANT SYSTEM
MOVES INTO THE EASTER GULF. SATURATED GROUND AND MOIST BOUNDARY
LAYER WITH BKN SKIES IN THE SOUTHERN ZONES WILL LEAD TO PATCHY
FOG IN TYPICAL FOG HOLES TONIGHT.

 999MB LOW PRESSURE SYSTEM CURRENTLY NEAR 48N 140W TO DEEPEN TO
994MB AND MOVE NORTHEAST THROUGH THE NIGHT AND BE JUST WEST OF PKZ
41 BY TUESDAY MORNING. WINDS AND POPS ACROSS THE PANHANDLE WILL
INCREASE LATE TONIGHT AND TUESDAY MORNING. BOTH 12Z GFS AND 12Z
NAM12 INDICATE 50 TO 60 KTS AT 850 MB OVER ZONES 27 AND 28 BY
NOON TOMORROW. WIND ADVISORIES WITH WINDS GUSTS TO 45 MPH POSTED
FOR THESE ZONES. GALES POSTED FOR PKZ41 AND CLARENCE STRAIT.

 GLOBAL MODELS ALL HAVE A GOOD HANDLE ON THE DEVELOPING SYSTEM
POSITION TRACK AND STRENGTH. NAM12 CONTINUITY IN THE INHERITED
GRIDS WAS CONTINUED TODAY WITH 12Z NAM. MODELS SPREAD REMAINS LOW
THROUGH THE SHORT TERM LEADING TO ABOVE AVERAGE FORECAST
CONFIDENCE.

&&

.LONG TERM...MEDIUM RANGE MODELS HAVE AN UNUSUAL LARGE AMOUNT OF
SPREAD AMONG THE SOLUTIONS ESPECIALLY WITH THE GFS BEYOND SUNDAY
TIME FRAME. CONSIDERABLE DISAGREEMENT IS NOTED ON THE POSITION OF
MAJOR FEATURES OVER THE EASTERN GULF AND SOUTHEAST ALASKA OVER THE
WEEKEND INTO EARLY NEXT WEEK. FOR THE EARLIER PORTIONS OF THE LONG
RANGE FORECAST...THE GFS IS SLIGHTLY FASTER THAN THE NAM WITH THE
PROGRESSION OF THE WEAKENING MID LEVEL SHORTWAVE AND REBUILDING
SURFACE RIDGE BEHIND. THE GFS ENSEMBLE MEAN SHOWS A GOOD TRENDING
THROUGH EARLY THURSDAY THEN STARTS DIVERGING WITH SMALLER SCALE
SHORTWAVE MOVING INTO THE CENTRAL GULF THROUGH FRIDAY. THE GFS HAD
SHOWN A REASONABLY GOOD CONTINUITY WITH TIMING FROM THE PREVIOUS
DAYS. HOWEVER...AS LONG AS THE PROGRESSIVE FLOW UPSTREAM IS
CONSIDERED TO A SOLUTION IN THE MEANTIME...MODEL CONSISTENCY WITH
THE ECMWF AND HPC GUIDANCE ARE MUCH MORE PREFERRED AT THIS TIME.

 THE MOST SIGNIFICANT DIFFERENCE DURING THE EARLIER PORTIONS OF
THE LONG RANGE IS THE GFS SLIGHTLY MORE WESTWARD TRENDS THAN THE
NAM. ALSO FOR LATE THURSDAY...THE GFS IS SOMEWHAT WEAKER THAN THE
NAM WITH THE CORE OF THE UPPER LOW SOUTH OF KODIAK. THEN DURING
THE DAY OF FRIDAY...THE GFS TRACKS THE UPPER LOW A LITTLE MORE
NORTHWARD THAN THE NAM. FOR THE EARLIER PARTS OF THE
FORECAST...THE NAM OUTPUT IS GOOD ENOUGH AT LEAST THROUGH FRIDAY.
THUS...PREFER TO GO WITH THE NAM AND ECMWF COMBO BLENDING INTO THE
INHERITED GRIDS THROUGH FRIDAY AFTERNOON. BEYOND FRIDAY TIME
FRAME...IT BECOMES SOMEWHAT MORE CHALLENGEABLE AS UPSTREAM FLOW
BEGINS TO WEAKEN AND THE NEXT SHORTWAVE TROUGH DIGGING DOWN ACROSS
THE ALEUTIANS INTO THE WESTERN GULF TOWARDS THE WEEKEND. WILL LEAN
OVER THE CONSENSUS FROM THE ECMWF AND HPC BLEND AS NEW GRIDS
THROUGH THE END OF THE PERIOD.

 THE SURFACE LOW ENTERING THE SOUTHERN OUTSIDE WATERS ON
WEDNESDAY AFTERNOON WILL QUICKLY MOVE ONSHORE THEN DISSIPATE EARLY
WEDNESDAY NIGHT WITH 25 TO 30 KTS WINDS AND ROUGH SEAS ACROSS THE
SOUTHERN HALF OF THE OUTSIDE WATERS AND OCEAN ENTRANCES. WITH A
RAPID BUILDING OF RIDGE...A SHORT BREAK OF LOWER POPS IS EXPECTED
ACROSS THE SOUTHEAST ALASKA. THIS WEAK RIDGE WILL QUICKLY MOVE
EAST AND DISSIPATE BY EARLY THURSDAY EVENING AS THE NEXT LOW
ACROSS THE WESTERN GULF PUSHES A FRONTAL BOUNDARY NORTHEASTWARD
ACROSS THE EASTERN GULF AND SOUTHEAST ALASKA. THE LOW IN THE
WESTERN GULF CONTAINS ABUNDANT TROPICAL ORIGINATED MOISTURE. THIS
WILL GENERATE ANOTHER ROUND OF GALE FORCE WINDS AND ROUGH SEAS
ACROSS THE COASTAL WATERS THROUGH SATURDAY AS WELL AS BREEZY TO
WINDY CONDITIONS OVER INLAND COASTAL AREAS. ALONG WITH THE FRONTAL
PATH...LOCALLY HEAVY RAIN IS EXPECTED THURSDAY NIGHT AND FRIDAY. A
LITTLE MORE ZONAL FLOW IS EXPECTED AS THE LOW IN THE WESTERN GULF
MOVES TO NORTHEAST BEFORE WEAKENING OVER THE ALASKA PENINSULA
THROUGH SATURDAY. ANOTHER WEAK RIDGE WILL BUILD ACROSS THE LOCAL
REGION THROUGH EARLY NEXT WEEK WITH SIGNIFICANTLY LOWER POPS.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...SMALL STREAM FLOOD ADVISORY UNTIL 1045 PM AKDT FOR AKZ028.
         WIND ADVISORY FROM NOON TO 6 PM AKDT WEDNESDAY FOR
         AKZ027-028.
MARINE...GALE WARNING FOR PKZ036-041.
         SMALL CRAFT ADVISORY FOR PKZ033>035-042-043.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ051-052.

&&

CCC/AHN