C. This northern high build on 12/8 as a copious amount of moisture moved up from the south associated with a storm south of Dutch Harbor.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS AJK wrote it up.
On 12/7 the arctic front was over Northern Lynn Canal with high pressure over the northern Yukon into eastern B.C. This northern high build on 12/8 as a copious amount of moisture moved up from the south associated with a storm south of Dutch Harbor. The air masses collided on the afternoon of 12/8 bring heavy snowfall to the northern Panhandle. The heavier snowfall amounts were from 5 to 9 inches during the early morning hours on 12/9. Most areas had rain later that day making snow management difficult.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Juneau, AK wrote its last area forecast discussion before the first event at Dec 8, 6:00 AM AKST, 6 hours earlier.
SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
6 AM AKST SAT DEC 8 2012
.SHORT TERM...THE SNOW EVENT BEGINNING THIS AFTERNOON AND EVENING
WILL BE ALMOST AREA WIDE. THE EXCEPTIONS ARE IN THE SOUTHERN
PANHANDLE WHERE THE ARCTIC AIR MASS HAS ALREADY BEEN MODIFIED AWAY
AND THE PRECIPITATION WILL BE PRIMARILY RAIN. WINTER STORM WARNINGS
ARE IN EFFECT THAT INCLUDE MOST OF THE PUBLIC FORECAST ZONES. PLEASE
SEE THE LISTING AT THE BOTTOM. CONFIDENCE IS AVERAGE.
AT 12Z SUN THE PARENT LOW OF ABOUT 966 MB WILL BE TRACKING INTO
BRISTOL BAY. THE ONSHORE FLOW OF MARITIME AIR, AS DISCUSSED IN THE
FOLLOWING PARAGRAPH, IS ASSOCIATED WITH THE FRONTAL SYSTEM AND
LARGE SCALE CYCLONE EVOLUTION.
THE OCCLUDED FRONT IS TO MOVE ONSHORE THE EAST GULF COAST ABOUT
12Z SUNDAY. THE SNOWFALL AMOUNTS WILL VARY MORE DUE TO IF AND WHEN
A CHANGE TO RAIN OCCURS, AND THIS CHANGE IN TURN WILL BE BASED ON
HOW THE MARITIME AIR MASS BEING MOVED ONSHORE IS TO OVERRUN THE
PRE-EXISTING MODIFIED ARCTIC AIR MASS. THE ARCTIC FRONTAL BOUNDARY
DOES NOT MOVE N, BUT WILL BE MODIFIED AWAY PROGRESSIVELY INLAND,
RESULTING A SEQUENCE OF SNOW CHANGING TO RAIN IN A S TO N
SEQUENCE. THERE IS LITTLE LEFT TO ANY OF THIS UNDERLYING COLDER
AIR MASS IN THE SOUTHERN PANHANDLE, EXCEPT TUCKED AWAY IN MISTY
FJORDS. THE DEEPEST ARCTIC AIR MASS IS IN THE NORTHERN INNER
CHANNELS, AND THE PRECIPITATION SHOULD REMAIN ALL UNMIXED SNOW
THROUGH TONIGHT.
THE MODEL CONSENSUS FOR THIS TIMING IS GOOD, WITH THE GFS, ECMWF,
AND UKMET TOGETHER AND THE NAM SLIGHTLY FASTER. THE NAM, HOWEVER
WAS STILL TO BE CONSIDERED AS THE RELATED MODEL SOUNDINGS WERE
USEFULLY CLOSE TO THE THERMAL PROFILE DATA FROM AIRCRAFT ENTERING
JUNEAU AS WELL AS SITKA.
THE PERSISTENCE OF SNOWFALL IS ASSOCIATED WITH HOW THE MARITIME
AIR MASS THAT IS BEING MOVED ONSHORE IS TO OVERRUN THE PRE-
EXISTING MODIFIED ARCTIC AIR MASS. THE ARCTIC FRONTAL BOUNDARY
DOES NOT MOVE N, BUT IS MODIFIED AWAY PROGRESSIVELY INLAND.
PARTIAL THICKNESS VALUES FOR 1000-850 MB HAVE BEEN GENERALLY
FOLLOWED FROM MODEL GUIDANCE, BUT BOUNDARY LAYER CONDITIONS ARE A
TOUGH TOPIC FOR THE MODELS. A SUBJECTIVE ADJUSTMENT FOR THE COLDER
AND LOWER LEVEL AIR MASS WAS USED AND DOES DELAY THE CHANGEOVER TO
MIXED PRECIPITATION BY ABOUT 6 HOURS.
ONE FINAL NOTE: ORIENTATION OF THE OCCLUDED FRONT AND THE WINDS
FAVOR NORTH TO EAST WINDS IN THE DEEP BOUNDARY LAYER, AND NOT THE S
TO SE WINDS THAT TEND TO MODIFY AWAY THE ARCTIC AIR MASS AND SPEED
THE RAIN MIX.
&&
.LONG TERM...
DIFFICULT DECISION AS TO SWITCHOVER FROM SNOW TO RAIN ON SUNDAY. WARM
ADVECTION WITH THE FRONT IS STRONG BUT WILL ANY LOW LEVEL WIND OR
LACK OF IT COULD KEEP COLD AIR LONG ENOUGH TO START AS SNOW? HEDGED
ON TIMING TO INCLUDE RAIN IN THE SUNDAY MORNING FORECASTS FOR
SOUTHERN AND COASTAL ZONES BUT KEPT MENTION OF MORNING SNOW MOST
INLAND AND NORTH LOCATIONS. ERROR COULD BE MORE RAPID WARMING FOR
THESE LATTER ZONES. USED TEMPERATURE FORECASTS IN LATER PERIODS TO
DETERMINE SNOW VERSUS RAIN. PATTERN IS DEFINITELY WARMER WITH ONLY
BRIEF COLDER OUTFLOW MENTIONED TUE.
EXPECT WEST TO SW LOW LEVEL WIND IN OUTSIDE MARINE AREAS. ACCEPTED
AKWAVE WAVE HEIGHTS TO 20 FT DUE TO A VERY LONG FETCH BEHIND THE
FRONT. COORDINATED WITH ANCHORAGE ON MODEL SPREAD AND USED AK-GFS-40
TO LOCATE LOW CENTER 00Z TUE BUT NOT AS STRONG. WAS STILL ABLE TO
FORECAST SOME GALES IN THE LATER PERIODS DUE TO FAIRLY STRONG WIND
ALOFT THOUGH ANTICYCLONIC. UPPER RIDGE BUILDING TO THE WEST MON
EVENING TO ALLOW FOR THE OLD LOW CENTER TO MOVE SE FOR THE BRIEF LOW
LEVEL OFFSHORE FLOW MENTIONED ABOVE.
USED DAY SHIFTS FORECASTS FOR MOST OF WEATHER ELEMENTS TUE AND
BEYOND. CONFIDENCE MODERATE TO LOW THROUGH MON ON THE DETAILS.
CONFIDENCE LOW TUE THROUGH FRI DUE TO LARGE MODEL SPREAD.
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WARNING 6 PM SAT TO 6 AM SUN
AKZ019-021-024>026.
STRONG WIND THIS EVENING FOR AKZ023-027.
WINTER WEATHER ADVISORY NOON SAT TO 6 AM SUN AKZ022.
WINTER STORM WARNING NOON SAT TO 6 AM SUN AKZ017-020.
WINTER WEATHER ADVISORY 6 PM SAT EVE TO 6 AM SUN
AKZ018-029.
MARINE...STORM WARNING PKZ052.
GALE WARNING PKZ022-033-036-041>043-051.
SMALL CRAFT ADVISORY PKZ021-031-032-034-035.
SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ053.
&&
JBT/JC5 winter storm. Local standard time, as filed.
Yakutat measured 7 inches of new snow at midnight on 12/9 most of which fell during the evening. During the night visibility lowered to 1/2 mile in snow. Snow turned to rain with gusts to 30 MPH around 2 AM on the 12/9.
Gustavus got 5.5 inches of new snow early on the morning of 12/9 which was rapidly compacted due to mixing with rain. Visibility got as low as one mile in the snow, and the heavy snow was difficult to remove and manage.
Downtown Haines got 6.2 inches of new snow during the early morning of 12/9. Visibility got as low as 1/2 mile at the airport during the snowfall.
Snowfall amounts during the storm on the early morning of Dec 9th were highly variable. Amounts ranged from 2 inches to 9 inches during the early morning hours. Visibility was as low as 3/4 miles at the airport during the morning. Snow changed to rain during the early afternoon for a very heavy snowpack at sea level.
Petersburg got 5.9 inches of new snow early on the morning of Dec 9th. Visibility was as low as 1/2 mile at the airport. Snow changed to rain later in the morning making snow management quite difficult due to the weight of the snow.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Alaska in 2012Every state in 2012This day in weather historyWarnings in Alaska, December 2012
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 426070, 426088, 426082, 426104, 426161.