Winter Storm in Alaska, February 17 to 18, 2013

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
607 AM AKST SUN FEB 17 2013

.SHORT TERM...SOMEWHAT COMPLEX FORECAST IN THE WORKS FOR TODAY
AND TONIGHT. CURRENT SATELLITE PICTURES SHOW A WEATHER FRONT
SPREAD N TO S ACROSS THE CENTRAL AND EASTERN GULF WITH THE MAIN
LOW JUST SOUTH OF THE KENAI PENINSULA. IN ADDITION THERE IS A
WEAK WAVE FORMING ALONG THE FRONT POSITIONED AROUND 54N 142W. THE
PRECIP ACCOMPANYING THIS FRONT HAS ALREADY REACHED YAKUTAT AND IS
STARTING TO SHOW UP ON THE BIORKA ISLAND RADAR.

FOR TODAY THE PRECIP WILL SPREAD OVER THE REST OF THE PANHANDLE
AND CONTINUE THROUGH THE NIGHT. THE TRICKY PART IS FIGURING OUT
WHAT PRECIP TYPE IT WILL BE. YAKUTAT IS CURRENTLY SNOW WITH A
LIGHT EAST WIND. THAT WIND DIRECTION IS NOT EXPECTED TO CHANGE
MUCH SO YAKUTAT WILL MOST LIKELY REMAIN SNOW THROUGH TONIGHT,
THROUGH SOME RAIN MAY MIX IN AT TIMES THIS AFTERNOON. FOR THE
REST OF THE PANHANDLE, CURRENT TEMPERATURES ARE AT OR ABOVE
FREEZING AT THE MOMENT BUT WITH DUE POINTS IN THE UPPER 20S TO LOW
30S PRECIP WILL BE A SNOW AND RAIN MIX TO START OUT FOR PETERSBURG
TO ANGOON TO PELICAN AND POINTS NORTHWARD. EVAPORATIONAL COOLING
WILL LIKELY CAUSE SOME PLACES TO GO TO ALL SNOW SOON AFTER THE
PRECIP STARTS UP. HOWEVER, SOUTHERLY FLOW WILL STILL BE IN AFFECT
SO MANY PLACES WILL HAVE RAIN BEGINNING TO MIX BACK IN THIS
AFTERNOON AND REMAIN A RAIN SNOW MIX TONIGHT AS TEMPERATURES
REMAIN STEADY OR SLOWLY WARM. HAINES AND SKAGWAY HAVE THE OPPOSITE
PROBLEM. THEY CURRENTLY HAVE STRONG SOUTH WINDS THAT ARE KEEPING
TEMPERATURES WARM SO THEY WILL LIKELY BE A SNOW AND RAIN MIX MOST
OF THE DAY IF THE WINDS ALLOW PRECIP TO FALL AT ALL. THEN BY THIS
EVENING THEIR WINDS SWITCH TO THE NORTH AND NORTHWEST.
TEMPERATURES THEN LOWER AS A RESULT AND HAINES AND SKAGWAY WILL
SEE ALL SNOW TONIGHT. SOUTHERN PANHANDLE WILL SEE MOSTLY RAIN OUT
OF THIS SYSTEM.

AS FOR SNOW ACCUMULATIONS, YAKUTAT LOOKS LIKE IT WILL BE THE
WINNER AS IT STAYS THE COLDEST THE LONGEST WITH ITS EAST WIND. HAVE
ISSUED A WINTER WEATHER ADVISORY THROUGH 9PM IN YAKUTAT FOR 4-6
INCHES THROUGH TODAY AND ANOTHER 2-4 INCHES TONIGHT. OTHER AREAS
WILL SEE LESSER AMOUNTS DUE TO WARMER SURFACE TEMPERATURES.
HOWEVER GIVEN THAT THIS SYSTEM DOES NOT HAVE THAT GREAT OF A
MOISTURE PLUME ASSOCIATED WITH IT ACCUMULATIONS ARE ON THE LOW
SIDE...ON THE ORDER OF 1 TO 5 INCHES THROUGH TONIGHT.

WINDS WILL ALSO BE INCREASING AS THE FRONT APPROACHES, BUT IT
LOOKS LIKE THERE IS NOT ENOUGH STRENGTH WITH THE FRONT TO PRODUCE
ANY STRONG WIND HEADLINES IN THE PANHANDLE. HOWEVER, SOME GUSTS UP
TO 35 MPH ARE NOT OUT OF THE QUESTION FOR THE OUTER COAST AND
SOUTHERN PANHANDLE THIS AFTERNOON AND EVENING. THE HIGHEST WINDS
WILL BE IN THE NORTHERN GULF WHERE A BARRIER JET WILL PRODUCE GALE
FORCE WINDS BUT THE REST OF THE GULF AND INNER CHANNEL AREAS WILL
MAINLY SEE SMALL CRAFT WINDS.

SHORT RANGE MODELS WERE IN DECENT AGREEMENT BUT HAD SOME
DIFFERENCES IN VARIOUS DETAILS. NAM AND THE UKMET HAD A MORE
DEFINED LOW DEVELOPING FROM THE WEAK WAVE ALONG THE FRONT WHILE
THE GFS AND ECMWF TENDED TO SMOOTH OVER THE FEATURE. DECIDED ON A
MORE NAM WITH SOME UKMET AND GFS MIXED IN FOR UPDATES TODAY.
FORECAST CONFIDENCE IS ABOUT AVERAGE.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...ACTIVE WEATHER PATTERN
CONTINUES THROUGH THE EXTENDED FORECAST PERIOD. MULTIPLE LOWS AND
FRONTS WILL PASS THIS WEEK...ABOUT EVERY DAY AND A HALF...WITH
BRIEF BREAKS IN BETWEEN. MAJORITY OF THE WEEK THE MID LEVEL
TEMPERATURES WILL BE COLD ENOUGH FOR TO BE SNOW...HOWEVER WINDS
ALONG EACH OF THE FRONTS WILL BRING IN WARMER SURFACE MARITIME AIR
FROM THE SOUTH CAUSING A CHANGE OVER BACK TO RAIN. WHEN THE BREAKS
OCCUR THERE WILL BE ENOUGH RADIATIONAL COOLING FOR THE TEMPERATURE
TO DROP BACK BELOW FREEZING...CAUSING PATCHY FOG TO DEVELOP AND
ROAD SURFACES TO FREEZE UP ONCE AGAIN.

AN UPPER LEVEL TROUGH WILL DIG SOUTH OVER THE EASTERN GULF ON
MONDAY. THIS WILL CAUSE A SURFACE LOW...CAUSING TODAYS WEATHER...IN
THE NORTH CENTRAL GULF TO ELONGATE AND WEAKEN AS IT IS PUSHED SE.
AS THE ENERGY MOVES SOUTH SO WILL THE BULK OF THE
PRECIP...BECOMING MORE SCATTERED THROUGH THE DAY FROM NORTH TO
SOUTH. SNOWFALL ACCUMULATION MONDAY MORNING WILL BE AROUND 2
INCHES OVER THE NORTHERN HALF OF THE REGION. WINDS OVER THE NORTHERN
HALF OF THE PANHANDLE WILL HAVE A NORTHERLY COMPONENT WITH THE LOW
TO THE SOUTH. A BIT OF A BREAK IN THE WEATHER IS EXPECTED FOR
MONDAY NIGHT INTO TUESDAY AS A BUILDING UPPER LEVEL RIDGE MOVES
OVER THE GULF BEHIND THE TROUGH. SCATTERED SHOWERS WILL REMAIN IN
THE AREA HOWEVER AND BREAKS IN THE CLOUD COVER WILL ALLOW
TEMPERATURES TO BE COLD ENOUGH FOR SNOW...BUT LITTLE ACCUMULATION
IS EXPECTED. THE UPPER LEVEL RIDGE WILL MOVE SE TUESDAY AND ALLOW
ANOTHER LOW TO MOVE EAST OVER THE GULF. THE ASSOC FRONT WILL REACH
THE PANHANDLE TUESDAY NIGHT WITH PRECIP CONTINUING WEDNESDAY. A
FEW INCHES OF SNOW IS EXPECTED OVER THE NORTHERN HALF OF THE
PANHANDLE WITH THIS FRONT. THE LOW CENTER WILL BE IN THE NORTH
CENTRAL GULF WEDNESDAY..THEN WEAKEN IN PLACE THROUGH THURSDAY
BEFORE SHIFTING TO THE SE. A LOW CENTER WILL RE-DEVELOP OVER THE
SE GULF OFF OF DIXON ENTRANCE FRIDAY. THIS WILL ENHANCE RAIN FOR
THE SOUTHERN AREAS AND CAUSE A COOLER AND DRYER FLOW OVER THE
NORTH. THE LOW WILL THEN PROGRESS EAST INTO CANADA. SATURDAY SEES
A BRIEF RIDGE AND BREAK IN THE WEATHER BEFORE THE NEXT LOW MOVES
INTO THE GULF SATURDAY NIGHT.

MODELS WERE IN GOOD AGREEMENT UNTIL LATER IN THE WEEK WITH THE
LOW SHIFTING SE FRIDAY. USED AN ENSEMBLE APPROACH FOR MOST FIELDS
DUE TO THEIR SIMILARITIES THEN TRENDED MORE TOWARD HPC GUIDANCE
FOR THE END OF THE FORECAST PERIOD. FORECAST CONFIDENCE IS
AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY UNTIL 9 PM AKST THIS EVENING FOR AKZ017.
MARINE...GALE WARNING FOR PKZ051-052.
         SMALL CRAFT ADVISORY FOR PKZ011-012-021-022-031>036-041>043.

&&

EAL/HANNON