Moderate to heavy snow occurred in and near the Front Range Foothills, with the heaviest amounts in and near the foothills of Boulder and northern Jefferson counties. Storm totals ranged from 8 to 16 inches in those areas, with amounts from 2 to 7 inches across the |rest of the I-25 corridor.
Every event with a place to put it; 8 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.
Moderate to heavy snow occurred in and near the Front Range Foothills, with the heaviest amounts in and near the foothills of Boulder and northern Jefferson counties. Storm totals ranged from 8 to 16 inches in those areas, with amounts from 2 to 7 inches across the |rest of the I-25 corridor.
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 Apr 19, 10:09 AM MST, 51 minutes earlier.
Area Forecast Discussion National Weather Service Denver/Boulder CO 1109 AM MDT Mon Apr 19 2021 .UPDATE... Issued at 1109 AM MDT Mon Apr 19 2021 Expanded the Winter Weather Advisory across the eastern plains for late this afternooon and tonight. With the cold air already in place and slightly colder tempertures expected during the snowfall, there will be a better chance that roads will become slush and snow covered. Also, confidence a little higher there will be a couple snow bands that will spread across the eastern plains and locally drop up to 6 inches of snow. UPDATE Issued at 839 AM MDT Mon Apr 19 2021 Strong cold front has push south through northeast Colorado this morning. Low clouds, fog, and drizzle moved in right behind the front. Lowered temperatures for today. Current temperatures in southeast Wyoming and western Nebraska are in the mid to upper 20s. Overcast skies and cold air advection will limit heating today with temperatures only warming a few degrees at most. Removed the mention of rain along the Front Range because of the colder temperatures. Will see drizzle this morning. Expect this drizzle and fog to end by noon as the cold airmass deepens and a little mixing occurs. Still expect the low clouds to persist through today. Quick shot of heavy snow still on track for late this afternoon and evening. Not much change in the models with good synoptic and orographic lift. This combined with some instability will result in a period of intense snowfall. Due to the cold temperatures and heavy snowfall rates, roads are expected to quickly become snow and slush covered. && .SHORT TERM...(Today and tonight) Issued at 424 AM MDT Mon Apr 19 2021 ...EVENING COMMUTE TO BE AFFECTED BY STRONG WINTER SYSTEM... An upper trough extending from the Great Lakes west into MT will be diving down the northern Rockies and across CO tonight. That means we'll be in the region of synoptic lift during the day today. A strong cold front is charging south down the lee of the Rockies, though there will be two surges associated with it. The first surge has already pushed out of Nebraska and is heading southwest into northeastern Colorado. The GOES Nighttime Microphysics RGB curve and observations show the low stratus surging south. This will continue into the forecast area this morning with a few showers near the northern state border possible. As the first surge hits into the higher terrain, the airmass will deepen, but forecast soundings showing the saturated airmass will be warmer than -10 degrees C, which may allow for patchy drizzle across the plains and into the foothills. With the addition of this low cloud deck, ended up decreasing max temps over most of the plains north of I-70. Late this morning and into the early afternoon, a second surge, associated with 700mb frontogenesis will charge south to deepen the saturated layer and cool it off, allowing for snow production. Areas near the northern state border will likely see this begin around noon to 2pm, with snow surging into the Denver area in the 3pm to 5pm time frame. Temperatures will be rapidly cooling into the 20s. This along with the synoptic and frontogenetical lift, upslope flow and some weak CAPE, should be able to produce some moderate to heavy snowfall heading into the evening. Several models still showing upwards of an inch of liquid for the mountains and higher foothills of Boulder and Larimer counties, while down lower into the western suburbs should see .5 to .8 inches of liquid. The speed of the system will be quick, with the snow event only lasting about 12 hours. Therefore, should see some inch to inch and a half an hour at times for snowfall rates. With the expected amounts happening fairly quickly, will upgrade the Front Range mountains and foothills, as well as the western urban areas such as Boulder down into Golden to a Winter Storm Warning. Expecting hazardous driving conditions to likely develop this evening with heavy snow, rapid cooling and gusty northeasterly winds, with possible snow squall conditions. This has a high potential to impact the evening commute, so travelers are urged to alter plans in the aforementioned areas. The snow will rapidly taper off north to south after about 10pm, with flurries occurring after midnight, though areas near the Palmer Divide and southern foothills could still see some better snow production. Temperatures overnight are expected to be in the teens across the plains and single digits over the mountains. .LONG TERM...(Tuesday through Sunday) Issued at 424 AM MDT Mon Apr 19 2021 Snow should be just about done Tuesday morning, though cold temperatures will remain with lots of teens. Subsidence should provide decent clearing in the morning, but a combination of a secondary wind surge and shallow instability should cause some clouds to redevelop in the afternoon. If there are any little showers out of shallow convection, it should only be trace amounts. By Tuesday night, warm advection aloft will be setting in with clouds increasing as a deformation zone develops across northern Colorado. This should produce slow saturation from the mid levels downward Tuesday night and Wednesday, with the band either stationary or lifting very slowly north later Wednesday ahead of a weak frontal wave. Models vary a bit on the placement and amount of any snow from this, but they're all pretty light except for the main period of lift moving from the central mountains late Wednesday onto the plains of east central or northeast Colorado by Wednesday evening. Even then, this will still likely be light but with the prolonged effort some accumulation is eventually possible later Wednesday. The cloud cover and persistent easterly winds will help keep temperatures down, so we dropped Wednesday's highs a couple of degrees. Thursday looks like a break between the shortwaves, though some of the models develop weak diurnal convection over the mountains and drift it toward Denver at the end of the day. Another weak wave comes through Friday or Friday night for another chance of light showers, again potentially coupled with weak diurnal mountain showers. By Saturday we're getting under the upstream ridge with subsidence and drying. There's disagreement on just how much warming depending on how strong the upstream ridge is. Our model blend is splitting the difference with mid 60s on Saturday and then leaning toward the warmer solutions with Sunday about 10 degrees warmer. && .AVIATION...(For the 12Z TAFS through 12Z Tuesday morning) Issued at 839 AM MDT Mon Apr 19 2021 Fog, drizzle, and low clouds accompanied the cold front this morning with visibility less than a quarter mile. Visibility will slowly improve through the morning. However, low clouds will persist through the day with ceiling remaining under 2000 feet. Snow still on track for this afternoon and evening. Snow is expected to form around 21Z with heavy snow by 23Z. Snowfall rates of an inch per hour or slightly more are expected between 23Z- 03Z. Total snowfall amounts of 3-6 inches are expected at the Denver airports, possibly a little more on the west side of the Denver Metro area. Snow ends around 06-09Z with clearing skies towards 12Z Tuesday. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 3 PM this afternoon to 3 AM MDT Tuesday for COZ038-040>046-048>051. Winter Storm Warning until 3 AM MDT Tuesday for COZ033-035. Winter Weather Advisory until 3 AM MDT Tuesday for COZ034-036. Winter Storm Warning from 3 PM this afternoon to 3 AM MDT Tuesday for COZ039. && UPDATE...Meier SHORT TERM...Kriederman LONG TERM...Gimmestad AVIATION...Meier
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 1118 AM MDT Mon Apr 19 2021 COZ030>051-201730- 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- 1118 AM MDT Mon Apr 19 2021 ...POTENT BUT QUICK STORM TO BRING SNOW AND COLD TEMPERATURES THIS EVENING... This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...This Afternoon and Tonight Snow will spread south across the Front Range mountains and foothills, Urban Corridor, and eastern plains this afternoon and evening. Heavy snowfall rates, cold temperatures, and gusty winds to 30 mph will create hazardous driving conditions. These hazardous conditions will begin around 3pm in the northern mountains and I-25 corridor north of Fort Collins. Snow rapidly spreads south into the Denver Metro area by 5pm. Snowfall amounts of 8 to 14 inches are expected in the higher mountains north of I-70, with 4 to 8 inches along the urban corridor, and 2 to 5 inches across the eastern plains. Skies will clear overnight with snow decreasing by midnight and diminishing towards sunrise. Overnight lows will be cold and approach record lows in places. Most locations will fall into the teens by sunrise Tuesday morning. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday Snow will end early Tuesday morning, but there could still be icy roads in spots. Temperatures will also be very cold, falling to the teens to start the day. There will be another chance of light snow Wednesday and Wednesday night. Thursday will be warmer with a slight chance of afternoon showers. Another weak system could bring light precipitation to the region Friday. Warmer weather will finally return to the region by the weekend. .SPOTTER INFORMATION STATEMENT... Snowfall reports from spotters will be appreciated.
The national radar mosaic for the moment the first event began.
5 winter weather, 3 winter storm. Local standard time, as filed.
Storm totals included 12 inches near Meeker Park and Mt Audubon, and 11 inches near Brainard Lake.
Storm totals included: 16.2 inches near Allenspark, 15.4 inches near Sunshine, 15.3 inches near Jamestown, 14.5 inches in Aspen Springs, 13.1 inches in Meeker Park, 12.5 inches near Nederland, and 10 inches in Rollinsville.
Storm totals included: 9.1 inches near Pinecliffe, 9 inches near Kittredge, 8.6 inches just west of Golden, 8.5 inches near Floyd Hill, 7.8 inches near Aspen Park, with 7 inches near Tiny Town.
Storm totals included 8 inches, 5 miles north of Blue River, with 5 inches Breckenridge.
Storm totals included: 10 inches in west Boulder, 8.9 inches at the National Weather Service in Boulder, 8.1 inches in Niwot, 7.9 inches near Louisville, 7.1 inches in Longmont, 6.5 inches near Lafayette, 5.5 inches in northwest Arvada.
Storm totals ranged from 2 to 5 inches and included 3.1 inches at Denver International Airport.
Storm totals ranged from 2 to 5 inches.
Storm totals ranged from 2 to 5 inches.
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, April 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: 953339, 953340, 953347, 953348, 953345, 953349, 953606, 953607.