Storm Warning 10, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
355 PM AKDT THU MAR 14 2013

.SHORT TERM...SATELLITE IMAGERY THIS AFTERNOON SHOWING A WEAK
SHORT WAVE MOVING OVER THE SOUTHERN AK PANHANDLE, ARCTIC HIGH
PRESSURE OVER THE YUKON AND A DEVELOPING LOW PRESSURE SYSTEM IN
THE NORTHEAST PACIFIC. THE DEVELOPING 1000 MB LOW WILL TRACK
NORTH INTO THE SOUTHERN AK GULF TONIGHT THEN TRACK INTO THE
NORTHERN GULF THROUGH FRIDAY. WEATHER FRONT ASSOCIATED WITH THIS
LOW WILL TRACK NORTHWARD BRINGING INCREASED MOISTURE AND WARM MID
LEVEL AIR. INITIALLY SCATTERED SHOWERS OVER THE SOUTHERN
PANHANDLE WILL DIMINISH BEFORE STEADY PRECIP MOVES IN LATER
TONIGHT. FOR THE SOUTHERN PANHANDLE THE WARM MID LEVEL AIR WILL
MIX IN EARLY SO EXPECTING AREAS SOUTH OF SUMNER STRAIT TO RECEIVE
MOSTLY RAIN. COLD AIR THAT HAS BECOME ENTRENCHED OVER THE CENTRAL
AND NORTHERN PANHANDLE FROM THE YUKON ARCTIC AIR MASS AND
NORTHERLY WINDS ALONG WITH THE WARM AIR MASS MOVING OVER THE
REGION IS SETTING UP FOR A OVERRUNNING SNOW EVENT. HEAVIEST SNOW
FALL SHOULD BE IN THE ELFIN COVE TO JUNEAU CORRIDOR WITH HEAVIEST
SNOWFALL TO THE NORTH NEAR HAINES AND GUSTAVUS. HEAVIEST SNOW
WILL START LATE TONIGHT INTO THE EARLY MORNING. SNOW TOTALS OF
3 TO 10 INCHES LOOK GOOD WITH THE QPF VALUES AND COLD SURFACE AIR
WITH WARM MOIST MID LEVEL AIR MASS SETTING UP FOR AN OVERRUNNING
EVENT ALONG WITH HIGH OMEGA VALUES IN THE DENDRITIC GROWTH ZONE.
HOWEVER THE LOW IS NOT SHOWING AS WELL DEFINED CIRRUS SHIELD AS
HOPED FOR THIS AFTERNOON WHICH COULD INDICATE A WEAKER SYSTEM AND
WITH THE STRONG OUTFLOW WINDS SNOW CRYSTALS COULD FORM MORE AS
NEEDLES THAT WILL REDUCE TOTAL SNOW ACCUMULATIONS DUE TO SMALL
SNOW GRAIN SIZE.

STRONG NORTHERLY AND OUTFLOW WINDS WILL CONTINUE THROUGH FRIDAY
AFTERNOON WITH THE TIGHT PRESSURE GRADIENT BETWEEN THE YUKON
ARCTIC HIGH AND THE DEVELOPING SE GULF LOW. THE YUKON HIGH WILL
BEGIN TO SHIFT TO THE EAST THROUGH FRIDAY AFTERNOON AS THE LOW
MOVES INTO THE NORTHERN AK GULF THUS WEAKENING THE PRESSURE
GRADIENT AND DIMINISHING THE WINDS. AS THE ARCTIC FRONT PUSHES
NORTHWARD WITH THE MOVING HIGH AND INCOMING LOW WILL BEGIN TO SEE
TEMPERATURES RETURN TO SEASONAL NORMALS.

WHILE MODELS WERE IN GENERAL AGREEMENT WITH SYNOPTIC PATTERN
THERE WERE ENOUGH DIFFERENCES IN THE EXACT LOCATION OF THE LOW
CENTER ON FRIDAY TO LOWER CONFIDENCE. THE SPEED OF THE FRONT AND
RESULTING POP FIELDS WERE ALSO VARIED WITH THE ECMWF PUSHING
HIGHEST POPS TO THE NORTH, GFS TO THE SOUTH WHILE THE NAM PUSHED
THE FRONT ACROSS THE REGION THE FASTEST. DECIDED TO LIMIT CHANGES
TO THE FORECAST PACKAGE DUE TO THE VARIABILITY WITH THE NEW MODEL
RUNS.

&&

.LONG TERM...THE LOW OVER THE EASTERN GULF WEAKENS AND A SECONDARY
LOW FORMS NEAR KODIAK ISLAND LATE SATURDAY AND THEN MOVING
SOUTHEAST ACROSS HAIDA GWAII LATE SUNDAY. A WEAK INVERTED THROUGH
REMAINS LYING TOWARDS PRINCE WILLIAM SOUND INTO EARLY PART OF NEXT
WEEK. HIGH PRESSURE OVER THE INTERIOR PART OF THE START AND ALONG
THE WEST PART OF THE STATE. FOR THE LONGER RANGE PORTIONS MODELS
ARE SHOWING A NON AGREEMENT OF PLACEMENT OF LOWS AND RIDGES WITH A
VARIETY OF STRENGTHS. HAVE HAD A PREFERENCE FOR THE WPC SOLUTION
FOR THE LATER TIME FRAMES.

EXPECT SOME SHOWERS PERSISTING FROM THE ONSHORE FLOW ABOUT THE
RESIDUAL LOW ALTHOUGH THERE WILL BE CHANGE IN THE PRECIP PATTERN
LATE SUNDAY TO EARLY MONDAY ... MAINLY AFFECTING THE SOUTHERN
PANHANDLE.

IN THE FORECAST FOR NEXT WEEK IS WITH OFF SHORE FLOW THE HINT OF
PARTLY CLOUDY SKIES MAY BE SHOWING UP IN THE LONGER RANGE PORTION
OF THE FORECAST.

FORECAST CONFIDENCE IS A LITTLE ABOVE AVERAGE FALLING TO AVERAGE
AT BEST FOR THE LONG RANGE PORTIONS OF THE FORECAST.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY FROM 1 AM TO 4 PM AKDT FRIDAY FOR AKZ022-
     024.
         STRONG WIND UNTIL 7 PM AKDT THIS EVENING FOR AKZ019-025.
         WINTER WEATHER ADVISORY FROM 4 AM TO 7 PM AKDT FRIDAY FOR AKZ025.
         WINTER STORM WARNING FROM 1 AM TO 4 PM AKDT FRIDAY FOR AKZ020-
     021.
         WINTER STORM WARNING FROM 4 AM TO 7 PM AKDT FRIDAY FOR AKZ019.
         STRONG WIND THROUGH FRIDAY AFTERNOON FOR AKZ018.
         STRONG WIND THROUGH FRIDAY AFTERNOON FOR AKZ017.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ012.
         STORM WARNING FOR PKZ012.
         GALE WARNING FOR PKZ011-013-021-022-031-043-051>053.
         SMALL CRAFT ADVISORY FOR PKZ032>036-042.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041.

&&

PRB/BEZENEK