A steady stream of deep Pacific moisture produced a prolonged period of very heavy snowfall in parts of the northern and central mountains. 4 inches of snowfall over a 60-hr period.
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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 BOU wrote it up.
A steady stream of deep Pacific moisture produced a prolonged period of very heavy snowfall in parts of the northern and central mountains. Storm totals generally ranged between 1 and 3 feet, however a SNOTEL site northeast of Cameron Pass measured an estimated 43.4 inches of snowfall over a 60-hr period. Moderate snowfall was also observed in the eastern part of Grand County below 9,000 feet with storm totals from 8 to 11 inches. Gusty winds up to 60 mph caused areas of blowing and drifting snow over the mountain passes. The eastbound lanes of I-70 were closed from Silverthorne to the Eisenhower Tunnel due to multiple spun out vehicles and crashes late in the afternoon on the 13th.
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 Denver/Boulder, CO wrote its last area forecast discussion before the first event at Dec 12, 4:46 AM MST, 14 minutes earlier.
Area Forecast Discussion National Weather Service Denver/Boulder CO 446 AM MST Thu Dec 12 2019 .SHORT TERM...(Today and tonight) Issued at 405 AM MST Thu Dec 12 2019 The problem of the day this time around is the developing winter storm that is expected to move into the mountains by tonight which will then continue for several periods. Ahead of that, today should be a mild day as downsloping westerly flow continues. Moisture aloft will be increasing through the day, leading to mountain wave clouds over the plains and generally increasing clouds in the mountains. Snowfall is expected to begin in the mountains during the afternoon, but accumulation rates are not expected to increase until later tonight. When the storm arrives, abundant Pacific moisture is going to be moving over the state, being driven by a 130+ knot jet stream aloft. Strong orographic effects should produce light to moderate snowfall over west-facing exposures through tonight and Friday morning. Gusty winds are also expected due to the fast flow at mid and upper levels. Blowing and drifting snow could be a problem over the higher elevations through the duration of the storm. Will be upgrading the Winter Storm Watch to a Winter Storm Warning for tonight and Friday. The rest of the Winter Storm Watch will be left as is because of the uncertainty over how long the storm may continue. (See below) Snow accumulations with the initial surge of moisture are expected to be 12 to 18 inches by Friday afternoon. Continuing strong downslope effects in the lee of the mountains will keep the plains dry. .LONG TERM...(Friday through Wednesday) Issued at 430 AM MST Thu Dec 12 2019 Water vapor imagery shows a strong jet stream moving ashore over Oregon this morning with a plume of moisture that extends as far west as Hawaii's longitude. This jet and associated moisture plume will be responsible for the prolonged snow event across Colorado's mountains that lasts through this weekend. Global models predict this jet will enter Colorado Friday morning with maximum 300-200 mb winds of up to 180 knots. During this time, our CWA's mountains will be under the left exit region of the jet which will provide lift along with a quick moving shortwave trough. This will enhance snowfall rates to between one to two inches per hour Friday morning and create hazardous travel conditions. By Friday afternoon, the jet will move directly overhead with slight ridging building in behind the departing shortwave trough. This will decrease snowfall rates to around a half inch an hour. It is important to note that while snow rates will decrease Friday afternoon, the strong winds, gusting up to 60 mph at times, will create blowing snow and poor travel conditions. It is for this reason that the Winter Storm Warning goes through Friday evening with a Winter Storm Watch continuing immediately after the warning ends. A secondary plume of moisture will arrive ahead of a shortwave trough Friday night. Snowfall rates will increase to one to two inches in the mountains with hazardous travel conditions. These snowfall rates will continue through the day Saturday and into Saturday evening before tapering off. The jet stream moves farther south to southern Colorado Saturday night which leads to the lull in snowfall. Models still show considerable differences for Sunday across our CWA but it appears a trough will deepen over the Four Corners region during the day. As this system moves eastward-northeastward, it will produce a swath of moderate snowfall. This swath will likely be farther south than the previous two systems and will hit the central and southern mountains harder than the northern mountains. By the time the snow ends Sunday night, we expect significant snowfall amounts especially on west facing mountain slopes. There was extensive discussion on the timing of warnings and watches for this storm as it will come in three waves. We determined that highlighting the first wave would be ideal at this time while signaling there is some uncertainty with the second and third waves. From Monday through Wednesday, a ridge will build over the western US keeping Colorado dry. As for the plains and urban corridor, the westerly, downslope flow will keep conditions dry on Friday and Friday night. Strong gusts will be the biggest issue as they could reach up to 45 mph during the day. We may even see some loosely attached Christmas decorations taken for a ride if a gust gets a hold of them. The second system will have better QG ascent aloft over the urban corridor and plains which will lead to a chance of snow. The ECMWF is the most bullish about snow amounts in the Denver area while other models keep the snow farther north along the Cheyenne Ridge. Since systems tend to come in slightly farther south and deeper than models predict, I trended the forecast toward the ECMWF and increased PoPs over much of the urban corridor and plains on Saturday. The third system will have the best QG and frontogenesis aloft out of the three. This system appears it will hit southeastern Colorado the hardest but areas from Denver southward may still see light to moderate snow amounts. Confidence in the track and intensity of this system is still rather low but it will need to be watched closely for those traveling on Sunday. Monday through Wednesday will see dry conditions with moderating temperatures. && .AVIATION...(For the 12Z TAFS through 12Z Friday morning) Issued at 405 AM MST Thu Dec 12 2019 Westerly winds at times will be about the only aviation impact through the next 24 hours, and most of the winds should be west of the I-25 corridor. Gusts up to 30 knots will be possible at times at KBJC. Winds at KDEN should be out of the southwest to west at speeds less than 15 knots. Mid and upper clouds will be increasing through today and tonight, but ceilings should remain above 6000 feet AGL. Mountains to the west will become obscured in clouds and snowfall. from this afternoon through tonight. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning from 5 PM this afternoon to 5 PM MST Friday for COZ031-033-034. Winter Storm Watch from Friday afternoon through late Saturday night for COZ031-033-034. && SHORT TERM...Dankers LONG TERM...Danielson AVIATION...Dankers
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 1102 AM MST Wed Dec 11 2019 COZ030>051-121815- Jackson County Below 9000 Feet- West Jackson and West Grand Counties Above 9000 Feet- Grand and Summit Counties Below 9000 Feet- South and East Jackson/Larimer/North and Northeast Grand/ Northwest Boulder Counties Above 9000 Feet- South and Southeast Grand/West Central and Southwest Boulder/ Gilpin/Clear Creek/Summit/North and West Park Counties Above 9000 Feet-Larimer and Boulder Counties Between 6000 and 9000 Feet- Jefferson and West Douglas Counties Above 6000 Feet/Gilpin/Clear Creek/Northeast Park Counties Below 9000 Feet- Central and Southeast Park County- Larimer County Below 6000 Feet/Northwest Weld County- Boulder And Jefferson Counties Below 6000 Feet/West Broomfield County- North Douglas County Below 6000 Feet/Denver/West Adams and Arapahoe Counties/East Broomfield County- Elbert/Central and East Douglas Counties Above 6000 Feet- Northeast Weld County-Central and South Weld County-Morgan County- Central and East Adams and Arapahoe Counties- North and Northeast Elbert County Below 6000 Feet/North Lincoln County- Southeast Elbert County Below 6000 Feet/South Lincoln County- Logan County-Washington County-Sedgwick County-Phillips County- 1102 AM MST Wed Dec 11 2019 This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...Today and Tonight There will be a chance of light snow in the mountains tonight with accumulations of an inch or two in some areas. Winds will increase over the mountain ridges and higher east slopes of the Front Range. Gusts up to 60 mph will produce localized blowing and drifting snow. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday The next storm system is expected to move into the mountains Thursday night and continue through much of the weekend with snow and winds causing blowing snow issues. Abundant moisture from the eastern Pacific will be brought into Colorado by a strong jet stream which will produce nearly continuous snowfall through most of the weekend. It is difficult at this time to determine snowfall amounts, however significant snow accumulations are possible in the high country as the snow stacks up over a three day period. The plains will have a slight chance of snow from Friday night through Saturday and then an increased chance of snow Saturday night and Sunday with a frontal passage. At this time the snowfall looks light, though there is a bit of uncertainty. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today or tonight. Gimmestad/Schlatter
The national radar mosaic for the moment the first event began.
3 winter storm, 1 winter weather. Local standard time, as filed.
Storm totals included: 43.4 inches, 1 mile north-northeast of Rabbit Ears Pass; 31 inches, 4 miles southeast of Mount Zirkel; 26.5 inches, 11 miles south of Rabbit Ears Pass.
Storm totals included: 26.5 inches, 7 miles south-southeast of Cameron Pass and 9 miles south-southeast of Spicer; 19.5 inches, 1 mile north-northwest of Cameron Pass; 12.5 inches, 3 miles west-northwest of Pingree Park.
Storm totals included: 33.5 inches near Climax; 32 inches, 5 miles south-southwest of Blue River; 31 inches at Berthoud Pass; 26.5 inches at Loveland Pass; 26 inches near Silverthorne; 25 inches at Copper Mountain; 23 inches at Breckenridge; 22.5 inches in Frisco and 5 miles southwest of Berthoud Falls; 21 inches at Winter Park and 5 miles west of Green Mountain Reservoir; 19.5 inches near Alma and Eldora; 17 inches, 6 miles west of Arapahoe Peak and near Brainard Lake; 14 inches near Keystone and Ward.
Storm totals primarily on the east side of Grand County included 11 inches near Grand Lake and Tabernash, with 10 inches at Fraser.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2019Every state in 2019This day in weather historyWarnings in Colorado, December 2019
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: 868320, 868321, 868322, 868345.