Winter Storm Watch 5, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
154 PM AKST SUN JAN 29 2012

.SHORT TERM...LOW PRESSURE OVER THE FAR SE GULF WILL MOVE NE
ACROSS CENTRAL SE AK THIS EVENING...AND REACH NW BC LATE TONIGHT.
AN OCCLUDED FRONT WILL MOVE NE INTO THE ERN GULF MON...WITH A LOW
PRESSURE WAVE ON THE FRONT MOVING INTO THE ERN GULF AS WELL. USED
A BLEND OF THE UKMET AND GEM FOR THEIR GOOD HANDLING OF THE
CURRENT LOW IN THE SE GULF AND THE LOW PRESSURE WAVE ON MON.

 MAIN FORECAST CONCERN WILL BE HOW MUCH MORE SNOW FALLS OVER THE
N-CENTRAL AREA BEFORE TAPERING OFF TONIGHT. BASED ON QPF
CONSENSUS OF GEM/ECMWF/UKMET...LOOKS LIKE ANOTHER 2+ INCHES OF
SNOW SHOULD FALL IN THE PAJN/PAOH/PAGN AREAS THIS EVENING BEFORE
IT TAPERS OFF LATER TONIGHT. WILL KEEP THE WW ADVYS FOR THOSE
ZONES GOING AS IS. PAGS HAS ALSO BEEN SNOWING DECENTLY BUT THEY
WILL DIMINISH EARLIER...SO AM NOT PLANNING ON ANY ADVYS FOR THEM
ATTM. FURTHER N SOME SNOW MAY REACH THE PAHN/PAGY AREAS THIS
EVENING BUT AMOUNTS SHOULD BE LIGHT. AREAS S OF FREDERICK SOUND
SHOULD BE MOSTLY RAIN ALTHOUGH PAFE HAS BEEN SNOW OR A MIX SO FAR
TODAY BUT TEMPS ARE NOW ABOVE FREEZING AND PRECIP SHOULD BE
MAINLY RAIN BY LATE AFTERNOON HYDER IS ONLY SNOWING LIGHTLY WITH
TEMPS NOW ABOVE FREEZING SO THEY SHOULD TRANSITION TO RAIN THIS
AFTERNOON ESPECIALLY ONCE SOME WIND GETS IN THERE. MORE PRECIP
WILL COME IN MON WITH NEXT FRONT WITH MAINLY SNOW OVER THE NRN
THIRD AND RAIN OR A MIX OVER SRN AREA. NOT ISSUING ANY WW
HEADLINES FOR THAT SYSTEM RIGHT NOW DUE TO CURRENT HEADLINES AND
SOME UNCERTAINTY ON QPF WITH MON SYSTEM.

 OTHERWISE...WINDS OVER THE NRN AREA WILL BE DECREASING THIS
AFTERNOON AND EVENING. WILL ALLOW STRONG WIND HEADLINE TO END AS
IS FOR PAGY AREA. WILL HAVE MIN GALE TO START FOR NRN LYNN CANAL
AND SCA FOR SRN LYNN CANAL BUT THEY BOTH SHOULD DROP BELOW SCA BY
LATE EVENING. MORE SCA WINDS SHOULD MOVE IN FOR MON WITH THE NEXT
FRONT AND LOW PRESSURE WAVE OVER THE ERN GULF. IF THE LOW IS A
BIT STRONGER THAN CURRENTLY FORECAST MAY NEED GALES FOR THE
E-CENTRAL AND NE GULF LATER MON.

&&

.LONG TERM...MID AND EXTENDED RANGE FORECAST IS SOMEWHAT
CONVOLUTED DUE TO INCONSISTENCIES BETWEEN MODEL RUNS AND MODEL
AGREEMENT, MOSTLY AT THE SURFACE. ALOFT MODEL AGREEMENT IS MUCH
BETTER AS THE OVERALL PICTURE IS WELL REPRESENTED. 500 MB TROUGH
WILL BE DIGGING SE OVER THE WESTERN GULF AND NE PACIFIC MID WEEK.
THE HEIGHT PATTER WILL REBOUND BY THE WEEKEND INTO A RIDGE OVER SE
ALASKA WITH ANOTHER TROUGH DIGGING OUT OVER THE ALEUTIANS.

AT THE SURFACE, MODEL INCONSISTENCIES SHOWS UP AS EARLY AS WED
WITH THE NEXT FRONT MOVING EAST ACROSS THE GULF. THE NAM IS MUCH
FASTER THEN THE OTHER MODELS. 12Z GFS WAS ALSO FASTER THEN THE
12Z EC BUT HAS SINCE SLOWED UP TO NEARLY MATCH THE EC. THE NEW 18Z
GFS HAS ALSO DONE AWAY WITH A SECOND LOW THAT WOULD HAVE FORMED
ALONG THE FRONT AND MOVED NORTHWARD THROUGH THE CENTRAL GULF WED
NIGHT THAT MOST OF THE OTHER MODELS DID NOT HAVE. THIS SEEMS TO
REMAIN THE THEME THROUGH THE EXTENDED RANGE AS MODELS ARE KEEPING
SOME FEATURES THE SAME WHILE OTHER FEATURES ARE DROPPING IN AND
OUT WITH SUCCESSIVE RUNS. OVERALL THE CONSENSUS SEEMS TO BE FOR A
FRONT TO COME THROUGH LATE WED NIGHT INTO THURS THEN HAVE
SOMETHING COME NORTHWARD INTO THE GULF FRI NIGHT ACCOMPANYING A
WARMING TREND INTO THE WEEKEND. THE GFS WANTS THAT SOMETHING TO BE A
RIDGE WITH A WEAK TROUGH EMBEDDED IN IT, WHILE THE EC IS HEADING
TOWARD A 988 MB LOW.

DECIDED TO STICK WITH THE EC FOR MID RANGE UPDATES THROUGH WED
NIGHT AS IT HAD THE BEST MODEL AGREEMENT AND CONSISTENCY. FOR
THURS AND BEYOND, HEADED TOWARD THE HPC DATA THAT INCORPORATES
MORE ENSEMBLE DATA INTO ITS CONSTRUCTION TO SMOOTH OUT THE
INCONSISTENCIES PRESENT BETWEEN THE OPERATIONAL MODELS. FORECAST
CONFIDENCE IS ABOUT AVERAGE OUT TO THURS THEN DROPS TO BELOW
AVERAGE AFTER THAT.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY UNTIL 9 PM AKST THIS EVENING FOR AKZ021-
     024.
         WINTER WEATHER ADVISORY UNTIL MIDNIGHT AKST TONIGHT FOR AKZ025.
         STRONG WIND UNTIL 3 PM AKST THIS AFTERNOON FOR AKZ018-019.
MARINE...GALE WARNING FOR PKZ012.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-022-033>036-041>043-052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ051.

&&

RWT/EAL