Convection/thunderstorm on Sunday afternoon (3/24) caused temperatures to rapidly drop with a quick change over to snow. From 60 degrees to snow in less than 3 hours.
Every event with a place to put it; 15 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.
Convection/thunderstorm on Sunday afternoon (3/24) caused temperatures to rapidly drop with a quick change over to snow. From 60 degrees to snow in less than 3 hours.
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 Mar 23, 7:52 PM MST, 3 hours 8 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Denver/Boulder CO 852 PM MDT Sat Mar 23 2024 .KEY MESSAGES... - A weather system will affect the area Sunday through early Monday morning. This system may bring heavier snowfall to portions of the mountains, southern foothills and Palmer Divide Sunday night. However, confidence in exact details still remain low at this time. - Blowing snow impacts possible across the Palmer Divide Sunday night through early Monday. - Snow shower activity will continue in the mountains Tuesday and Wednesday with mainly dry conditions over the plains. && .UPDATE... Issued at 833 PM MDT Sat Mar 23 2024 No significant changes have been made to the grids through the overnight period, as the previous forecast was largely in good shape. We should see a gradual increase in snow showers across the high country over the next several hours as better moisture works into the region. Have made some minor tweaks to the forecast up there to better reflect timing of the more widespread snow overnight. Meanwhile, all eyes remain on the upper trough that is expected to bring impactful weather to most of the state tomorrow. There have been a couple of noteworthy signals from the early 00z guidance this evening - with a stronger closed 500mb low developing further southwest compared to previous runs... with the surface low also reflecting this shift. This has led to a slightly more favorable NNE upslope flow across the foothills and I-25 corridor. If (and that's a big *if*) this trend continues overnight, we may need to make some adjustments to our headlines... but that will come overnight tonight or during the day Sunday. Stay tuned! && .SHORT TERM...(This evening through Sunday) Issued at 327 PM MDT Sat Mar 23 2024 Water vapor imagery reveals there is a shortwave trough moving onshore over California. There is weak QG ascent across Colorado under diffluent flow aloft ahead of the shortwave. At the surface, there is weak lee cyclogenesis across eastern Colorado. A boundary has formed along I-70 east of Denver and this boundary appears it will be the genesis point for showers and storms to form later this afternoon. These showers and storms will move northeastward along the I-76 corridor through the evening. After midnight, the plains will remain mostly dry as a pocket of drier air aloft moves in. In the mountains, radar is beginning to pick up on light showers this afternoon. These showers will stay light throughout the afternoon and evening before more low level moisture arrives after midnight. In contrast to the plains, snow showers will increase in the overnight hours with a couple inches of snow along the western slopes possible. The aforementioned shortwave trough will move northeastward tomorrow eventually ending up in eastern Colorado. Strong lee cyclogenesis will rapidly deepen a surface low pressure system that will position itself in the Arkansas River Valley. The combination of these features will create strong QG ascent and precipitation will form across the majority of our forecast area in the afternoon after many dry hours in the morning. There will be a few focus areas for heavier precipitation. The first will be the higher Front Range mountains and foothills as strong lapse rates, healthy moisture, and QG ascent will lead to moderate to briefly heavy snowfall. Another focus area for precipitation will be the base of the foothills onto the adjacent plains and I-25 corridor. There will be widespread thunderstorms in this area with briefly heavy rainfall. Some of the CAMs have rainfall up to an inch with these storms but most of the area will pick up about a quarter of an inch of rain. The final focus area for precipitation will be along I-70 in Elbert and Lincoln Counties. A boundary will setup there in the afternoon with most unstable CAPE above 500 j/kg to the north of it. Thunderstorms will form along this boundary with brief heavy rain and hail likely. Soundings indicate steep lapse rates around 9 C/km with strong forcing in the hail growth zone. While it appears instability will be a bit too weak for severe hail, hailstones up to three-quarters of an inch will be possible. By the late afternoon, a cold front/modified outflow boundary will form over the northern plains and will begin to rapidly move southward. This front will decrease temperatures to the mid 30s by 6pm and some snow will begin mixing in with the rain across the plains. No snow accumulation is expected across the plains before 6pm. .LONG TERM...(Sunday night through Saturday) Issued at 327 PM MDT Sat Mar 23 2024 ...Late weekend system to bring snow to the mountains, foothills, and portions of the plains... Sun night into Mon, an open wave trough moves across the region. It will contain a more pronounced southerly branch with an upper jet that will provide sufficient synoptic ascent. There is a general consensus among model guidance that this trough moves east across Colorado into Sun PM with a closed low developing along the CO-KS border before it lifts northeast across KS. Above normal moisture will accompany this system, further supporting precipitation. There is still notable uncertainty in the placement of this low which will have impacts on amounts. This will be discussed in more detail later on in this discussion. By Sun evening, a cold front will have settled across the region with enhanced northerly upslope flow filling in behind it across the lower elevations. Lapse rates will still hold rather unstable across the mountains, although not as unstable as the afternoon. This will keep snow going in the mountains. However, the real change will be the changeover to snow across the Palmer Divide then lower elevations as well as an uptick in snow for the southern foothills. This is reinforced by the arrival of colder air and enhanced upslope flow favoring the south foothills. Right now, seeing a changeover in the early evening timeframe (23-01Z) across the Palmer Divide, then across the adjacent plains as it continues to cool. Most model guidance is highlighting the potential for a favorable window for accumulating snowfall Sunday evening, mainly across the southern foothills and into the Palmer Divide areas. Model soundings reflect this quite well with deeply saturated profiles with notable lift/instability in the dendritic growth zone. After midnight, lapse rates weaken and moisture decreases as the larger scale forcing moves out. Snow gradually decreases in coverage and intensity toward sunrise. Monday, temperatures will be below normal in the 30s across the lower elevations and 20s/30s for the high country. Residual moisture and rebounding lapse rates in the toward the afternoon support some mountain snow showers. As tracking of the system remains lower confidence, the snow totals will be as well. Some models have been more consistent than others. The GFS (deterministic & ens) has been generally wetter than the ECMWF suite. GFS ens mean QPF puts around .7-.95" for the south foothills, front range and .5-.7 for the adjacent plains. The 12z ECMWF, although trended wetter than its previous run, but still remains the drier of the models. Higher-res models have also been on the wetter side, similar to the GFS. The GFS and higher-res guidance have unfortunately been less consistent from run to run, so although a good chunk of guidance is trending upward in amounts, there is still not a whole lot of consistency on where the higher amounts may be and exactly how much. For now, leaning on the more conservative end of guidance with snow totals. Front Range and central mountains in that 8-12 inch range with localized higher amounts. More uncertainty in store for the southern Foothills, Palmer Divide, and plains. Palmer Divide around 2-8" for now. Southern foothills 4-10". Despite this being below Winter Storm Warning criteria, there is the lower probability scenario it being closer to a foot. Given the potential, but low confidence at this time, went with Winter Storm Watches for these areas Sun eve through Mon AM. Denver metro currently has no highlights, but will be evaluated for advisories for the evening package since it may impact the Mon AM commute. And now the last concern we need to discuss...wind. This system will be accompanied by a well developed low with a sufficiently tined pressure gradient wrapped around it. This will provide plenty of wind across the plains as the low exits Colorado Sunday night into Monday. Gusty northerly winds 40-50 mph will become consistent across the east plains and Palmer Divide Sunday night. There are also areas that will be favored for higher gusts such as the east plains along WY border, Washington County, and Lincoln County. These areas have potential for gusts to peak 55-65 mph at times. As a result, a High Wind Watch has been issued. Wind and snow are a hazardous combination (blowing snow) and have potential to impact the Palmer Divide since they have a much higher likelihood for blowable snow than east. A Winter Storm Watch for blizzard conditions was issued for zone 41 (Palmer Divide) Sun eve through Mon morning. Early next week, the mountains will see periodic chance for orographic snow while the plains remain mostly dry. A ridge builds in midweek decreasing moisture in the mountains and warming temperatures. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 534 PM MDT Sat Mar 23 2024 VFR tonight with generally quiet conditions. Denver cyclone has lifted northward with a few SHRA well to the north and east of the terminals. Haven't seen any strong outflow from these showers, and winds should gradually decrease in speed over the next few hours, turning from northwest to southwest. Weak drainage flow is expected overnight. Tomorrow's forecast gets more complicated as a strong storm system brings impactful weather to the region during the afternoon and evening hours. The first question is the wind, with guidance showing a variety of different directions during the afternoon. Eventually this should switch to a northerly component as a strong cold front pushes through the terminals. With moisture increasing through the day, scattered showers and thunderstorms are forecast by the mid-afternoon hours, becoming more widespread into the evening. Rain should begin to mix with and change over to snow after 00z tomorrow evening. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from midnight tonight to 6 AM MDT Monday for COZ031-033-034. Winter Storm Watch from Sunday evening through Monday morning for COZ036-041. High Wind Watch from Sunday evening through Monday morning for COZ038-042-048. High Wind Watch from Sunday evening through Monday morning for COZ046-047-049. && UPDATE...Hiris SHORT TERM...Danielson LONG TERM...Mensch AVIATION...Hiris
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 1102 AM MDT Sat Mar 23 2024 COZ030>051-241715- 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 MDT Sat Mar 23 2024 This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...This Afternoon and Tonight Scattered light snow showers will develop over the mountains this afternoon, with minimal accumulations expected. Light to moderate snow will develop over the mountains this evening and tonight. .DAYS TWO THROUGH SEVEN...Sunday through Friday The next storm will move across the area Sunday through Sunday night. This system will bring a period of heavier snowfall to the mountains, southern foothills, and Palmer Divide Sunday and Sunday night with travel impacts into early Monday morning. Across the Denver metro and the rest of the plains, rain will switch to snow by early Sunday evening. Snowfall amounts around Denver will be in the 2 to 4 inch range with locally up to 6 inches in the far western and southern suburbs. Across the plains snowfall amounts will be in the 1 to 2 inch range. Gusty north winds may cause poor visibility in blowing snow across portions of the plains as well and across the Palmer Divide. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today or tonight.
The national radar mosaic for the moment the first event began.
15 winter weather. Local standard time, as filed.
Rabbit Ears Pass snow covered Sunday morning and again Sunday night/Monday morning.
Slick mountain roads from 4-10 inches of snowfall.
Slick mountain roads from 4-10 inches of snowfall.
Slick mountain roads from 3-7 inches of snowfall. Some wind gusts to 40 mph over eastern parts of Zone 41 produce blowing snow. Blizzard conditions weren't observed.
LSR and CoCoRaHS reports showed 5-12 inches of snowfall across the zone.
LSR and CoCoRaHS reports showed 5-12 inches of snowfall across the zone.
LSR and CoCoRaHS reports showed 1-4 inches of snowfall across the zone.
LSR and CoCoRaHS reports showed 4-7 inches of snowfall across the zone.
LSR and CoCoRaHS reports showed 2-6 inches of snowfall across the zone.
LSR and CoCoRaHS reports showed 2-7 inches of snowfall across the zone. A trained spotter NW of Strasburg reported 7 inches of snow. Radar returns and satellite the next day showed a near swath of heavier snow slightly west of Strasburg.
Snowfall less than 2 inches. No impacts reported of observed.
Snowfall of 1 to 3 inches observed.
Snowfall amounts of up to 2 inches were observed.
Snowfall amounts of up to 2 inches were observed.
Snowfall amounts of up to 2 inches were observed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2024Every state in 2024This day in weather historyWarnings in Colorado, March 2024
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 2026-10-01. Each event’s entry at NCEI: 1161098, 1161099, 1161100, 1161101, 1161102, 1161103, 1161104, 1161105, 1161106, 1161107, 1161108, 1161109, 1161110, 1161111, 1161112.