The first significant snowfall of the season finally made its mark, impacting the mountains, high valleys, foothills, and much of the plains with much needed moisture. In the mountains and foothills, storm totals ranged from 8 to 18 inches.
Every event with a place to put it; 13 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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.
The first significant snowfall of the season finally made its mark, impacting the mountains, high valleys, foothills, and much of the plains with much needed moisture. In the mountains and foothills, storm totals ranged from 8 to 18 inches. In the high mountain valleys of Grand, Jackson, and Summit counties anywhere from 6 to 12 inches was observed. Elsewhere 5 to 10 inches of snow fell west of I-25, 3 to 7 inches east of I-25, with 2 to 5 inches over the far eastern plains.
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 30, 3:44 AM MST, 1 hour 16 minutes earlier.
Area Forecast Discussion National Weather Service Denver/Boulder CO 344 AM MST Thu Dec 30 2021 .SHORT TERM...(Today and tonight) Issued at 302 AM MST Thu Dec 30 2021 Nearly zonal flow aloft will be over the area today through tonight as sfc low pres intensifies from sern WY into ern CO. For the mtns, cross-sections show moisture depth rather limited today but does increase by tonight. Orographics certainly are favorable along with lapse rates in the 6-7 c/km. Overall, it appears most mtn areas will see periods of light snow through the day with heavier snowfall developing late this evening and overnight. Also with strong winds expected a lot of blowing snow and poor visibility will occur over the higher passes. Thus no changes have been made to warnings. However, Middle and North Park will need an advisory for snow/blowing snow for tonight which will continue through Friday. Meanwhile, biggest headache tonight has been trying to figure out high wind potential, in and near the foothills, later this morning through the aftn hours. Hi res data has been showing stronger winds, eventually mixing down to the base of the foothills, and possibly affecting the western areas of the I-25 Corridor from Denver north to the Wyoming border. Analysis of cross-sections still don't show much mtn top stability for a mtn wave to develop. However, some of the higher resolution data does show some amplification late this morning thru mid aftn. Cross- barrier flow is in the 55-70 kt range, so if this does mix down, I certainly can't rule out strong winds at lower elevations near the base of the foothills for a few hours. HRRR shows gusts up to 90 mph and has these winds spreading further east than some of the other Hi-Res data. Confidence in all of this isn't high, however, I can't ignore what I'm seeing so will issue a High Wind Warning for zones 36,38 and 39. Overall appears high wind threat will decrease by 23z. Finally, as far as highs today, will keep readings mainly in the upper 40s to lower 50s across the plains. .LONG TERM...(Friday through Wednesday) Issued at 302 AM MST Thu Dec 30 2021 A large trough will move from the Pacific Northwest towards the Four Corners region on friday as a small shortwave trough moves from Baja California towards El Paso. At the surface, there will be strong lee cyclogenesis across southeastern Colorado while a strong high pressure system slides eastward in Montana. A weak cold front will push across northeast Colorado early on during the day on Friday creating northeasterly winds behind it. Across the higher terrain, there will be ongoing snow showers mainly across the western slopes. As the trough nears, a jet stream aloft will strengthen and low to mid level frontogenesis will create a couple bands of moderate to heavy snowfall. Snowfall rates could approach 2 inches per hour in the heavier bands while snowfall rates around a half inch per hour are expected outside of the heavier bands. A couple of these bands may produce snowfall across the foothills and adjacent plains but snowfall should be rather light since the low to mid level flow will be westerly. During the afternoon, 700 mb flow begins to turn easterly across the northeastern plains creating upslope flow and strong frontogenesis which leads to the development of a few bands of snow showers on the plains. Models aren't in full agreement yet on the placement of the heaviest bands with the ECMWF keeping these bands farther north than most other models. One thing to keep in mind is that these systems tend to arrive slower and depart much slower than models suggest a couple days before the storm. Therefore, PoPs and snow amounts were kept towards the lower side of guidance on the plains through Friday afternoon. The system will really ramp up Friday night as the depth of the easterly flow across the plains and foothills increases. PVA ahead of the trough will create strong QG ascent and there will be warm air advection from the surface to around 500 mb. As a result, there will be widespread moderate snowfall for the majority of our forecast area Friday night and PoPS in the 80s and 90s reflect that. Soundings show a deep dendritic growth zone during this time with strong vertical motion within that layer. Therefore, snow ratios will be on the higher side with ratios of between 14 to 17-1. Snowfall rates up to an inch per hour are possible from the mountains to the foothills and I-25 corridor. This will create slick and snow-covered roads leading to difficult travel conditions. This is less than ideal with it being New Year's Eve and our office will message the travel concerns heavily leading up to the event. Another impactful aspect of the forecast will be the chilly temperatures. A cold airmass from the northern plains will make it into our forecast area with temperatures falling into the single digits across the plains and below zero across the mountains. While cloud cover and snowfall will keep temperatures from bottoming out, the moderate winds speeds will create wind chills in the negative single digits across the plains and negative teens in the mountains. As mentioned before, these systems tend to move across the area slower than expected and it appears the model trend has already picked up on that. The latest guidance keeps light snowfall across most of the forecast area Saturday morning with it eventually tapers off to flurries by Saturday afternoon. This makes sense as the low level easterly, upslope flow turns northerly and then northwesterly throughout the day. There will be QG ascent in the mid to upper levels allowing snow showers to linger but that will change to QG descent by late Saturday afternoon. Highlights have been extended until 18Z/11AM Saturday. Overall, snowfall amounts will be aided by the good snow ratios and relatively slow moving nature of the system. The mountains will see the heaviest amounts with totals up to 2 feet. The foothills and adjacent plains will see values in the 5 to 12 inch range. Those values are close enough to Winter Storm Warning thresholds that a Winter Storm Watch was issued. From Denver eastward, the amounts are more uncertain but generally fall in the 3 to 6 inch range. Highlights will be needed in Denver and across the plains but none were issued at the moment due to the uncertainty in the amounts. The through moves east of our forecast area Saturday night with ridging building in over Colorado. With a fresh snowpack and clearing skies, there will be optimal radiational cooling which will allow for some very cold temperature readings. In the usual cold spots in the valleys like Greeley, Limon, and Kremmling, there is a good chance lows will reach the negative teens. Light drainage winds will keep the foothills and I-25 corridor from seeing values that cold but the low could reach below zero at DIA and other locations before the winds pickup overnight. Forecast low temperatures were brought closer to the NBM 25 percentile. There may need to be wind chill highlights as well. A large ridge will be over Colorado from Sunday through Tuesday leading to increasing temperatures and dry conditions. Depending on how fast the snow melts, high temperatures could reach the 50s across the plains as soon as Monday. By Wednesday and Thursday, a westerly jet stream will move over Colorado with snow possible in the mountains mainly. && .AVIATION...(For the 12Z TAFS through 12Z Friday morning) Issued at 302 AM MST Thu Dec 30 2021 Gusty west to southwest winds will develop by mid morning and then turn more westerly by mid aftn. Can't rule out a few gusts in the 40s later this morning thru early aftn. By mid aftn wind speeds should gradually decrease. For this evening light westerly winds should switch back to a more south southwest direction and maintain that direction overnight. Otherwise VFR conditions today through tonight. && .FIRE WEATHER... Issued at 302 AM MST Thu Dec 30 2021 Elevated fire conditions will be in place across the plains this afternoon due to gusty west southwest winds and continued dry conditions. The fire danger will quickly subside early this evening as winds decrease. && .BOU WATCHES/WARNINGS/ADVISORIES... High Wind Warning until 11 PM MST this evening for COZ033-035. Winter Storm Watch from late tonight through Saturday morning for COZ035-036-038-039. High Wind Warning from 8 AM this morning to 5 PM MST this afternoon for COZ036-038-039. Winter Storm Warning until 11 AM MST Saturday for COZ031-033-034. Winter Weather Advisory from 5 PM this afternoon to 11 AM MST Saturday for COZ030-032. && SHORT TERM...RPK LONG TERM...Danielson AVIATION...RPK FIRE WEATHER...RPK
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 356 AM MST Thu Dec 30 2021 COZ030>051-311100- 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- 356 AM MST Thu Dec 30 2021 ...Winter Storm Warning today through Saturday morning in the mountains... ...Winter Storm Watch in and near the Foothills Friday through Saturday morning... ...High Wind Warning for the northern Foothills and northern Mountains today through this evening... ...High Wind Warning for the southern Foothills and at lower elevations near the base of the Foothills this morning through this afternoon... This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...Today and Tonight Strong winds will be possible in and near the Foothills and across the northern Mountains today. Wind gusts up to 80 mph will be possible. The winds will decrease by early this evening. In the mountains, periods of light snow and blowing snow will continue today with snow becoming heavier tonight. Gusty winds will continue to produce blowing snow with near zero visibility over the higher passes with difficult travel. Snow and blowing snow will also affect Middle and North Park by tonight as well. .DAYS TWO THROUGH SEVEN...Friday through Wednesday Snow showers will continue in the mountains Friday through Saturday morning with amounts up to 2 feet across Rocky Mountain National Park and the Park Range. Across the plains and foothills, snow showers will be possible Friday morning with the coverage of snow showers increasing Friday afternoon. By Friday night, widespread moderate snow is likely which will lead to difficult to hazardous travel conditions. The snow will become lighter Saturday morning and will end saturday afternoon. There will be frigid temperatures with wind chills reaching below zero Friday night and Saturday night. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today or tonight, however, reports of wind and snow will be appreciated.
The national radar mosaic for the moment the first event began.
8 winter storm, 5 winter weather. Local standard time, as filed.
Storm totals included: 15.6 inches near Mount Zirkel, 13 inches, 9 miles south-southeast of Gould and 11 inches near Gould.
Storm totals included: 15.6 inches near Bear Lake and Trail Ridge, 13 inches, 7 miles north-northwest of Kinikinik, with 11.7 inches near Cameron Pass.
Storm totals included: 18 inches near Green Mountain Reservoir, 14.3 inches near Mount Audubon, 9 inches near Winter Park, 8 inches near Berthoud Pass.
Walden picked up 7.1 inches of snowfall.
Storm totals ranged from 5 to 12.5 inches of snowfall, heaviest in Summit County.
Storm totals ranged from 5 to 8 inches in the Fort Collins, Loveland and Wellington.
Storm totals ranged from 6 to 10 inches, including the western Denver suburbs extending north into Broomfield, Boulder and Longmont.
Storm totals ranged from 6 to 11.5 inches, with the heaviest amounts in the foothills of Boulder and southern Larimer counties.
Storm totals ranged from 6 to 15 inches of snowfall, with the heaviest amounts in northwest Jefferson and Clear Creek counties.
Storm totals around Denver ranged from 4 to 6 inches of snowfall. The official snowfall measurement at Denver International Airport was 4.5 inches.
Storm totals ranged from 4 to 7 inches of snowfall.
Storm totals ranged from 2.5 to 7.5 inches of snowfall.
Storm totals ranged from 3.5 to 5.5 inches of snowfall.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2021Every state in 2021This day in weather historyWarnings in Colorado, December 2021
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: 991136, 991138, 991139, 991140, 991143, 991144, 991145, 991146, 991147, 991148, 991149, 991150, 991151.