Winter Storm in Alaska, January 5 to 6, 2012

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
606 AM AKST THU JAN 5 2012

.SHORT TERM...SCATTERED SHOWERS WILL CONTINUE THROUGH THE EARLY
MORNING AS A FRONTAL TROUGH FROM YESTERDAY DEPARTS THE REGION TO
THE EAST. CURRENT TEMPERATURES ARE AT THEIR MAX FOR THE DAY AND
WARM ENOUGH FOR THESE TO BE RAIN EVERYWHERE BUT HAINES AND
YAKUTAT. TEMPERATURES ARE EXPECTED TO FALL THROUGH THE DAY BEHIND
THIS SYSTEM. THIS HAS ALREADY STARTED IN YAKUTAT WHERE
TEMPERATURES ARE JUST ABOVE FREEZING. SATELLITE IMAGERY CLEARLY
SHOWS THE BACK EDGE OF THE DEPARTING FRONT WITH CLEAR SKIES
BEHIND IT UNDER A RIDGE OF HIGH PRESSURE BUILDING OVER THE
EASTERN GULF. THEREFORE EXPECT SHOWERS TO DIMINISH THIS MORNING
WITH DECREASING CLOUDS THROUGH THE AFTERNOON. MOSTLY CLEAR SKIES
AT SUNSET WILL ALLOW FOR RADIATIONAL COOLING AND TEMPERATURES TO
CONTINUE THEIR DOWNWARD TREND...FALLING INTO THE MID 20S TO
AROUND 30F.

 CLOUD COVER IS EXPECTED TO INCREASE THROUGH THE EVENING AS THE
NEXT SYSTEM APPROACHES FROM THE SOUTHWEST. TEMPERATURES WILL BE
COLD ENOUGH OVERNIGHT FOR ANY SHOWERS ASSOC WITH THIS SYSTEM TO
BE ALL SNOW BUT NOT EXPECTED TO REACH THE COAST UNTIL EARLY
FRIDAY MORNING.

 YAKUTAT WILL SEE A DIFFERENT LOW PRESSURE SYSTEM AFFECT IT
TODAY. THEY WILL STILL HAVE THE BREAKS IN CLOUD COVER TODAY
HOWEVER IT WILL BE FOCUSED TO MAINLY THIS MORNING AND FOR A
SHORTER TIME FRAME. A LOW TO THE WEST OF ANCHORAGE WILL PROGRESS
NEWRD THROUGH THE DAY WITH ITS ASSOC COLD FRONT REACHING THE
YAKUTAT AREA THIS AFTERNOON. HEAVIEST SNOWFALL LOOKS TO BE IN THE
EVENING HOURS WITH REDUCED VISIBILITIES. HAVE ISSUED A WINTER
STORM WARNING FOR YAKUTAT FROM 3PM THIS AFTERNOON TO 9AM FRIDAY
MORNING. 4 TO 8 INCHES OF SNOW IS EXPECTED TONIGHT WITH UP TO AN
ADDITIONAL 3 INCHES FRIDAY MORNING.

 MODELS WERE IN GOOD AGREEMENT IN THE SHORT TERM. USED MAINLY THE
NAM FOR ITS FINER DETAILS. FORECAST CHALLENGES WERE QPF/SNOWFALL
AMOUNTS FOR THE YAKUTAT AREA AND HOW COLD THE REST OF THE AREA
WILL GET TONIGHT. FORECASTER CONFIDENCE IS ABOUT AVERAGE.

 &&

 .LONG TERM...THE LONG TERM PERIOD WILL CONTINUE TO BE AN ACTIVE
PATTERN WITH A SERIES OF LOW PRESSURE SYSTEMS MOVING IN TO GULF
AND ASSOCIATED WEATHER FRONTS MOVING OVER THE AK PANHANDLE. ZONAL
FLOW AT 500 MB WILL KEEP THESE SYSTEMS ON A PROGRESSIVE TRACK
THROUGH NEXT WEEK. MODELS ARE SHOWING IMPROVED CONSENSUS SO THERE
SI HIGHER CONFIDENCE IN TIMING AND LOCATION OF THE SYSTEMS AND
STRENGTH OF WINDS. THE MAIN ISSUE BEING PRECIPITATION TYPE DUE TO
VARIATION IN TEMPERATURES OF THE INCOMING AIR MASSES.

 FOR FRIDAY GALE FORCE LOW IN THE AK GULF WILL CONTINUE TO MOVE
NORTH TOWARD YAKUTAT...WEAKENING AS IT MOVES INLAND THEN
REFORMING THE YUKON. THE ASSOCIATED OCCLUDED FRONT WILL EXIT THE
REGION WITH RAIN AND SNOW SHOWERS DIMINISHING FRIDAY NIGHT...JUST
IN TIME FOR THE NEXT SYSTEM TO ENTER THE AK GULF. EASTERLY WINDS
ALONG THE OUTSIDE WATERS ON FRIDAY WILL BE NEAR MAX GALES IN THE
MORNING AND THEN DIMINISH AND SHIFT TO THE WEST WITH FRONTAL
PASSAGE. EXPECTING STRONG WINDS ALONG THE COASTAL ZONES AND GALE
FORCE WINDS NEAR EAST WEST CHANNELS AND NEAR OCEAN ENTRANCES.

 A WEAK RIDGE WILL BUILD OVER THE PANHANDLE FRI NIGHT THEN MOVE
TO THE EAST WITH COLDER AIR MOVING IN BEHIND THE FRONT. THE NEXT
FRONT ASSOCIATED WITH A 964 MB LOW 400MN SOUTH OF THE ALEUTIANS
MOVES INTO THE AK GULF SATURDAY WITH WARM AIR RIDGE AHEAD OF THE
FRONT. THIS LOW WILL CONTINUE A NORTHEASTERLY TRACK INTO THE GULF
WEAKENING TO AROUND 970 MB AS IT MOVES TOWARD THE PRINCE WILLIAM
SOUND AREA BY SUNDAY. THIS WILL KEEP PRECIP OVER THE PANHANDLE
THROUGH THE WEEKEND AND PRECIP WILL BE A WINTRY MIX AS OVER NIGHT
LOWS DROP BELOW FREEZING BUT TRANSITION TO RAIN DURING THE DAY
WITH TEMPS IN THE MID TO UPPER 30S. EVEN WITH SOME FAIRLY HIGH
QPF VALUES DUE TO GOOD MOISTURE FEED NOT EXPECTING ANY
SIGNIFICANT SNOW FALL DUE TO THE WARMER MID LEVEL TEMPS.

 THE START OF THE WEEK WILL SEE A BRIEF BREAK IN PRECIP WITH THE
EXITING LOW AND FRONT AND SOME COLDER TEMPERATURES. THE DRY BREAK
WILL BE SHORT LIVED AS THE NEXT SYSTEM WILL TRACK NORTHEAST ALONG
THE SOUTHERN COAST OF THE ALEUTIANS WEDNESDAY. STARTING TO SEE
MORE MODEL SPREAD BY THIS TIME SO SOME UNCERTAINTY IN THE FINAL
TRACK OF THIS LOW.

 MODELS FELL MORE IN LINE FOR THE START OF THE LONG TERM. HAD
GOOD AGREEMENT BETWEEN THE 00Z NAM, SREF, GFS AND UKMET WITH
POSITION OF THE LOW IN THE SOUTH WESTERN GULF ON FRIDAY. EC WAS
NOT TOO FAR OFF BUT DID SEEM A BIT MORE OF AN OUTLIER EARLY
FRIDAY AS IT WAS FURTHER EAST BUT SOON MATCHED UP WITH THE OTHER
MODELS. EC AND GFS INITIALIZED WELL COMPARING SATELLITE FEATURES
WITH THE NAM NOT MATCHING UP TO WATER VAPOR SATELLITE IMAGERY AS
WELL. GFS WAS A BIT WEAKER THAN OTHER MODELS FOR THE WEEKEND LOW
BUT CAME IN STRONGER FOR THE TUE TO WED SYSTEM. USED A BLEND OF
00Z GFS AND EC THROUGH DAY 4 THEN CONTINUED WITH HPC GUIDANCE TO
DAY 8. HPC AND GFS WERE SHOWING A BIT BETTER AGREEMENT THAN THE
EC. WHILE THE MODELS ARE IN BETTER AGREEMENT FORECAST CONFIDENCE
IS NOT THAT HIGH AS RUN TO RUN CONSISTENCY HAS BEEN FAIRLY POOR.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WARNING FROM 3 PM THIS AFTERNOON TO 9 AM AKST
     FRIDAY FOR AKZ017.
MARINE...GALE WARNING FOR PKZ041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ012-013-021-022-031>036-053.

&&

HANNON/PRB