Winter Storm Watch 6, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
607 AM AKST TUE JAN 31 2012

.SHORT TERM...TRANSITION FROM COLD AND SNOWY TO WARM AND WET
WEATHER HAS BEGUN.

SATELLITE IMAGERY THIS MORNING SHOWS A 9854 MB LOW IN THE WESTERN
AK GULF THAT WILL CONTINUE TO WEAKEN AS IT TRACKS NORTHEAST MOVING
JUST NORTH OF YAKUTAT BAY BY EARLY TUESDAY EVENING. THE ASSOCIATED
OCCLUDED FRONT CURRENTLY MOVING OVER THE AK PANHANDLE AND EXITING
THE REGION THROUGH THE DAY. AS TEMPERATURES WARMED OVER NIGHT
PRECIPITATION BEGAN TO TRANSITION FROM SNOW TO RAIN OVER THE
CENTRAL PANHANDLE. EXPECT NORTHERN REGIONS TO SWITCH TO RAIN
THROUGH THE DAY AS WINDS SHIFT TO THE SOUTH AND SOUTHEAST. THE
PROBLEM AREAS ARE YAKUTAT AND HAINES. HAINES REMAINS IN COLD AIR
AS WINDS ARE NORTHWESTERLY, BUT THESE SHOULD WITH TO THE SOUTHEAST
THIS MORNING MOVING WARM AIR INTO THE REGION WITH RAIN DEVELOPING.
HAVE ALREADY SEEN THIS OCCUR IN SKAGWAY AS TEMPERATURES INCREASE 7
DEGREES OVER 2 HOURS AS WINDS SHIFTED TO THE SOUTH AND INCREASED
TO 20 KT. PRESSURE GRADIENT SHOULD WEAKEN THIS MORNING SO DO NOT
EXPECT THE STRONG WINDS OVER SKAGWAY AND NORTHERN LYNN CANAL TO
LAST. FOR YAKUTAT TEMPERATURES HAVE ALREADY NEARED FREEZING AND
ARE EXPECTED TO RISE AS WINDS SHIFT FROM THE EAST TO SOUTHEAST.

A SECOND LOW IN THE SOUTHEAST GULF HAS DEEPENED TO 995 MB AS
ROTATION DEVELOPS ALONG ITS NORTHEAST TRACK. EXPECT THE LOW TO
MOVE OVER THE SOUTHERN PANHANDLE THROUGH THE DAY BECOMING AN OPEN
WAVE AS IT MOVES OVER BRITISH COLUMBIA. PRECIP FROM THE ASSOCIATED
FRONT AS ALREADY BEGUN OVER THE SOUTHERN PANHANDLE AN SHOULD
PROGRESS NORTHWARD TO ABOUT FREDERICK SOUND. DO HAVE SOME CONCERNS
ABOUT HYDER AS THIS LOW COULD PRODUCE SOME FAIR SNOW FALL IF COLD
AIR REMAINS IN PLACE. RIGHT NOW WESTERLY FLOW WOULD KEEP COLD AIR
IN PLACE BUT EXPECTING WINDS TO SHIFT TO THE SOUTH WITH WARM AIR
ADVECTION THIS MORNING CAUSING PRECIP TO TRANSITION TO RAIN OR A
RAIN SNOW MIX BEFORE ANY SIGNIFICANT SNOW CAN ACCUMULATE. IN
ADDITION THE LOW IS FAIRLY FAST MOVING WITH PRECIP TIMING LIMITED.
PRECIPITATION WILL DIMINISH OVERNIGHT FOR THE CENTRAL AND NORTHERN
PANHANDLE ALONG THE BACKSIDE OF THE FRONT BUT THE BREAK WILL BE
SHORT LIVED BEFORE THE NEXT STRONG FRONT MOVES IN. TEMPERATES
RETURN TO A MORE DIURNAL TREND AND MAY SEE SOME SNOW MIXING WITH
RAIN AS TEMPS FOR THE CENTRAL AND NORTHERN AREAS DROP TO NEAR
FREEZING.

MODELS WERE IN GOOD AGREEMENT WITH THE DEPICTION OF THE NORTHERN
GULF LOW. FOR THE SOUTHERN SYSTEM ECMWF AND NAM WERE SHOWING MORE
DEVELOPMENT COMPARED TO THE GFS, BUT NOT SURE IF EVEN THOSE WERE
SHOWING A DEEP ENOUGH LOW. UPDATED FORECAST GRIDS WITH A BLEND OF
06Z NAM12 FOR SOME DETAILS IN THE GULF WINDS. THE AK WAVE MODEL
HAS BEEN RUNNING A BIT HIGH WITH SEA HEIGHTS SO TONED DOWN WAVES
BY A FEW FEET. FORECAST CONFIDENCE IS A BIT BELOW AVERAGE DUE TO
PRECIP TYPE BEING VERY DEPENDENT ON WIND DIRECTION AND QUESTIONS
REGARDING THE LOW IN THE SOUTHEAST GULF.

.LONG TERM...A SHARP RIDGE BUILDS NORTH ACROSS SOUTHEAST ALASKA
AHEAD OF DEEPENING SYSTEM IN WESTERN GULF WEDNESDAY MORNING THAT
SHIFTS EAST INTO CANADA BY WEDNESDAY EVENING.

A POWERFUL 944 MB LOW MOVES INTO THE SOUTHWEST GULF WEDNESDAY AND
DRIFTS NORTH TO THE KENAI PEN THURSDAY. THIS SYSTEM HAS ACCESS TO
VERY COLD AIR MASS OVER BERING AND THE REMAINS OF A TROPICAL
SYSTEM HEADING NE FROM CENTRAL PACIFIC. THIS COMBINED WITH A
160-180 KT JET MAX ROUNDING THE BASE OF THE UPPER TROUGH LEADS TO
EXPLOSIVE DEEPENING OF THE LOW. JET STREAM TURNS SLY ON WEST SIDE
OF UPPER RIDGE AND BECOMES PERPENDICULAR TO TERRAIN ACROSS NE GULF
AND SUPPORTS A STRONG 70 KT LOW LEVEL BARRIER JET OVER COASTAL
WATERS. THE ASSOCIATED OCCLUSION IS WELL AHEAD OF THE LOW CENTER
AND WILL SPREAD STORM FORCE WINDS TO COASTAL WATERS AS EARLY AS
WEDNESDAY AFTERNOON AND CONTINUING INTO THURSDAY NIGHT. WITH LOW
STAYING IN WESTERN GULF WIND WILL DIMINISH TO GALES ACROSS THE
INNER CHANNELS EXCEPT FOR CLARENCE STRAIT WHICH HAS FAVORABLE
GRADIENT ORIENTATION. CURRENT GRIDS CARRYING 55 MPH WIND GUSTS FOR
SOUTHERN AND COASTAL AND STRONG WINDS FOR ALL OTHER ZONES.

SINCE SYSTEM HAS TROPICAL CONNECTION AND HIGH P-WATER VALUES RAIN
SHOULD BE HEAVY AT TIMES ALONG FAVORABLE TERRAIN OF COASTAL AND
SOUTHERN ZONES. THE SYSTEM DOES MOVE THROUGH RELATIVELY FAST WHICH
WILL HELP TO LIMIT DURATION OF HEAVIEST RAIN. WITH A DEEP SNOW
PACK ON THE GROUND AND STORM DRAINS AND DITCHES FULL OF SNOW WILL
LIKELY HAVE SOME POUNDING OF WATER ON ROADWAYS AND LOW LYING AREAS
AND HAVE SP'S CONTINUING. ALSO WITH A WARMER AIR MASS SPREADING OVER
THE AREA SNOW LEVELS CLIMB AND WILL SEE INCREASED AVALANCHE DANGER.

A TIGHTLY WOUND LOW IS FORECAST TO DEVELOP ALONG THE FRONT AND
NEARLY BOMBS BY DROPPING 20 MB IN 24 HOURS AS IT MOVES INTO THE
SOUTHEAST GULF THURSDAY EVENING AND THEN SLOWLY WEAKENS AS IT
MOVES NORTH THROUGH THE COASTAL WATERS. MODELS STILL HAVE
DIFFERENCES WITH THIS FEATURE CONFIDENCE IN DETAILS IS STILL LOW
BUT AM CONCERNED THIS LOW COULD BE HIGH WIND MAKER FOR SE AK.

ON FRIDAY NEXT LOW TRACKS SOUTH OF THE PANHANDLE WITH ASSOCIATED
OCCLUSION WRAPPING NORTH. AT SAME TIME A HIGH STARTS TO BUILD
ACROSS YUKON AND WE END UP WITH AN EASTERLY WIND PATTERN ACROSS
PANHANDLE SO POPS BEGIN TO DROP OFF AND COULD SEE A BIT COOLER
AIR MASS OVER THE WEEKEND.

.AJK WATCHES/WARNINGS/ADVISORIES... PUBLIC...WINTER
STORM WARNING UNTIL 9 AM AKST THIS MORNING FOR AKZ019.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-036. SMALL CRAFT ADVISORY
DUE TO SEAS FOR PKZ041>043-051-052.

&&

PRB/MM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
1026 AM AKST TUE JAN 31 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1007 AM     SNOW             7 S HAINES              59.14N 135.44W
01/31/2012  E10.0 INCH                          AK   TRAINED SPOTTER

            10 INCHES OF SNOW FELL YESTERDAY IN MUD BAY.

1007 AM     SNOW             11 WSW MOSQUITO LAKE    59.45N 136.36W
01/31/2012  M8.0 INCH                           AK   CO-OP OBSERVER

            8 INCHES OF SNOW FELL YESTERDAY AT HAINES CUSTOMS.

1007 AM     SNOW             HAINES                  59.24N 135.44W
01/31/2012  M8.1 INCH                           AK   CO-OP OBSERVER

            8.1 INCHES OF SNOW FELL YESTERDAY IN DOWNTOWN HAINES.

&&

TPS

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE JUNEAU AK
243 PM AKST TUE JAN 31 2012

AKZ017>029-011400-
CAPE FAIRWEATHER TO CAPE SUCKLING COASTAL AREA-
TAIYA INLET AND KLONDIKE HIGHWAY-HAINES BOROUGH AND LYNN CANAL-
GLACIER BAY-EASTERN CHICHAGOF ISLAND-
SALISBURY SOUND TO CAPE FAIRWEATHER COASTAL AREA-
CAPE DECISION TO SALISBURY SOUND COASTAL AREA-
EASTERN BARANOF ISLAND AND SOUTHERN ADMIRALTY ISLAND-
JUNEAU BOROUGH AND NORTHERN ADMIRALTY ISLAND-
INNER CHANNELS FROM KUPREANOF ISLAND TO ETOLIN ISLAND-
DIXON ENTRANCE TO CAPE DECISION COASTAL AREA-
SOUTHERN INNER CHANNELS-MISTY FJORDS-
INCLUDING THE CITIES OF...YAKUTAT...SKAGWAY...HAINES...GUSTAVUS...
HOONAH...ELFIN COVE...PELICAN...SITKA...PORT ALEXANDER...ANGOON...
JUNEAU...PETERSBURG...WRANGELL...KAKE...CRAIG...KLAWOCK...
KETCHIKAN...METLAKATLA...HYDER
243 PM AKST TUE JAN 31 2012

...WARM AND WET ACROSS THE PANHANDLE THROUGH THE WEEK...

A WEATHER PATTERN CHANGE IS ONGOING ACROSS SOUTHEAST ALASKA WITH
WARMER CONDITIONS ALONG WITH SOME STRONG WINDS DEVELOPING LATE
WEDNESDAY AFTERNOON INTO THURSDAY. FREEZING LEVEL WILL RISE AND
RANGE FROM AROUND 1200 FEET OVER THE NORTH CENTRAL AREAS TO 2200
FEET OVER THE SOUTHERN AREAS BY WEDNESDAY. THESE FREEZING LEVELS
WILL HOVER AROUND THERE THROUGH MOST OF THE WEEK. A SERIES OF
WEATHER FRONTS WILL MOVE ACROSS THE REGION WITH RAIN BEING DOMINANT
AND POSSIBLY HEAVY AT TIMES WEDNESDAY NIGHT.

THE RAIN ON SNOW/ICE COVERED ROADS WILL MAKE TRAVEL VERY HAZARDOUS
THROUGH THE WEEK. ALSO WITH MOST AREAS ACROSS THE REGION WITH
ABOVE NORMAL SNOW ON THE GROUND THERE MAYBE AREAS OF PONDING WATER
DUE TO POOR DRAINAGE BY THURSDAY MORNING. A STRONG WEATHER FRONT
WILL MOVE OVER THE AREA PRODUCING HEAVY PRECIPITATION WEDNESDAY
NIGHT INTO THURSDAY. THE RAIN WILL MAKE SNOW VERY HARD TO MANAGE
DUE TO THE INCREASE OF WATER CONTENT AND ALSO INCREASE SNOW LOADS
ON ROOFS. PEOPLE ARE URGED TO CLEAR STORM DRAINS OF SNOW TO HELP
ALLEVIATE THE FLOODING POTENTIAL AND CLEAR OFF ROOFS TO ALLEVIATE
THE LOAD ON THE STRUCTURES.

AS THE FREEZING LEVELS RISE IT WILL INCREASE THE POTENTIAL FOR
LARGE AVALANCHES DUE TO HIGH DENSITY OF SNOW OVER LESS DENSE SNOW.
THE POTENTIAL FOR STRONG WINDS ON WEDNESDAY NIGHT WILL ALSO
INCREASE THE AVALANCHE DANGER WITH WIND GUSTS FROM 40 TO 55 MPH AT
THE SURFACE...WINDS WILL BE MUCH HIGHER IN THE MOUNTAINS. PEOPLE
WHO VENTURE INTO THE BACK-COUNTRY SHOULD REMAIN CAUTIOUS IN STEEP
TERRAIN AND IN AVALANCHE PRONE AREAS.