A slow moving storm system produced flooding and flash flooding across the urban corridor and northeast plains, with heavy snowfall in the higher mountains of the Front Range. Storm total rainfall during the 3-day event ranged from 4 to 7 inches across the urban corridor and Palmer Divide, with 2 to 5 inches across the plains.
Every event with a place to put it; 5 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.
A slow moving storm system produced flooding and flash flooding across the urban corridor and northeast plains, with heavy snowfall in the higher mountains of the Front Range. Storm total rainfall during the 3-day event ranged from 4 to 7 inches across the urban corridor and Palmer Divide, with 2 to 5 inches across the plains. Additionally, from 1 to 2 feet of heavy wet snow occurred above 10 thousand feet. The heaviest rainfall occurred over Arapahoe, Denver, Douglas, Elbert and southern Jefferson counties. Consequently, swollen creeks and streams produced flooding and flash flooding. Numerous roadways were damaged or completely washed out including access roads to Cherry Creek State Park and National Wildlife Refuge at the Rocky Mountain Arsenal. Numerous hiking trails in Castlewood Canyon State Park were closed as they were underwater and impassable. Dozens of roads in Adams and Weld counties were hit by flooding and were closed due to damage. In Denver, a 24-hr daily record of 2.92 inches occurred on the 11th, with a 3-day total of 4.40 inches from the 10th-12th. Three men in the foothills of Douglas County had to be rescued when their vehicle got stuck in snow along Rampart Range Road in Pike National Forest. The heavy snow toppled trees which blocked the road. Rescuers had to use chainsaws to cut through the downed trees to reach the stranded men; the rescue took nearly 21 hours to complete.
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 May 10, 11:00 AM MST, 0 minutes earlier.
Area Forecast Discussion National Weather Service Denver/Boulder CO 1200 PM MDT Wed May 10 2023 .UPDATE... Issued at 1109 AM MDT Wed May 10 2023 Current satellite imagery shows the low stratus breaking up and eroding across the plains and Palmer Divide this morning. Recent observations at the Denver airport show visibility gradually improve as the fog lifts. This is on track with what most models expressed this morning with a gradual improvement in the 17 to 19z timeframe (late morning through early afternoon). RAP model soundings show ample elevated instability already built up above this moist layer which will be an important ingredient in considering the severe potential later. There are plenty of indicators that point this to an environment that is plenty supportive for severe storms capable of large hail and a few tornadoes. However, given the cooler start from this morning's stratus, there is a possibility that some areas may struggle to reach the convective temperature thus breaking the cap/ initiating. Even then, the classic boundary that develops over the Palmer Divide should help fire off convection. CAMs are still in general agreement with storms initiating in the 20-22z timeframe this afternoon. Although there is still notable range in solutions with the evolution and location of the convection. With all that being said...the cloud cover this morning is no reason to let your guard down regarding this severe potential. Be weather ready and aware, have multiple ways to receive warnings. Any reports, if they can be safely taken, are appreciated. UPDATE Issued at 918 AM MDT Wed May 10 2023 Quick update to the grids to account for the incredibly persistent low stratus deck this morning. Day Cloud Phase satellite imagery shows a blanket of low stratus across the plains and I-25 corridor. There are signs of this eroding up in Logan County, but expect this to stay socked into the urban corridor for at least another hour or two before it gradually scatters. Remainder of forecast still on track for today's severe threat. Next forecast update expected by 11 AM MDT. && .SHORT TERM...(Today and Thursday Night) Issued at 401 AM MDT Wed May 10 2023 ...Key Messages - Today is the day with more widespread severe convection expected, mainly after 20Z - Flood potential creeps upwards late tonight through Friday across the northern I-25 corridor and the burn scars...configuration of watch could change - Higher elevation heavier snows expected tonight through Thursday... As of 9Z this morning we're socked in with stratus across a large portion of the region. That big ole MCS that produced baseballs around the Erie, Frederick, Firestone area, continues to move off into WY/NE. Surface dewpoints are still hovering in the upper-40s to low-50s in a lot of spots and given the cloud cover in place, don't see that mixing out anytime soon. So we're setting the stage for another round of severe convection this afternoon and evening with all severe hazards on the table. The convective parameter space we saw yesterday, for today's event, remains relatively unchanged. - Ample MLCAPE, 1500-2000 J/kg (whoa) - Shortwave tough still digging and going negative - Surface moisture is here, and there, and bountiful - And yes, the shear still remains robust for deeper organized convection - Some backing winds across the eastern plains could lead to better, more curved hodographs (the tor risk increases...) There has been a lot of talk of the inversion and how quickly we scour out the stratus today. The longer we keep the stratus the more build up we can get before the lid pops, for sure, but then again a slight warming in the 700mb layer could pose an issue for realizing all our convective potential. It will be interesting to say the least how today's threat develops, but with surface flow almost directly upslope, getting into the juicy air across the Foothills at the same time mid-level heights start to fall as the shortwave advances eastward, it's hard not to think of a few supercells rolling across the metro and adjacent plains before growing upscale into a bigger blob, MCS, as it all moves north and east across the plains. Put it this way, be prepared today. Thursday...Once we get through Wednesday we come to Thursday...duh right? While not expected to be as severe with thunderstorms we are concerned with a higher potential for flooding with a longer duration heavy rain event with embedded thunderstorms on Thursday. Already having received over an inch in spots from Tuesday night's storms, and more on the way today, the flood threat creeps up on Thursday. At this time we're mainly focused on the northern I-25 corridor, adjacent plains, and our two big burn scars, Cameron Peak and East Troublesome. The aforementioned shortwave trough, you know the one that is going negatively tilted today, well that hangs out with us across the NE corner of the state maybe a bit too long and keeps pumping moisture back towards the west. The tap it's using is the Gulf of Mexico and there is a lot of moisture down there...trust me I've lived there. PWATs surge upwards of 0.8" which for early May is pushing above maximums. All-in-all Thursday looks wet, maybe floody in spots, and we could see the watch expanded farther south...if needed. .LONG TERM...(Friday through Tuesday) Issued at 401 AM MDT Wed May 10 2023 An upper level will remain on track to bring ample amounts of moisture to the region through Friday. 500mb northwesterly flow continues through this weekend. Ensembles favor multiple rounds of afternoon thunderstorms from the mountains to the plains Saturday and Sunday. Snow levels began to drop near 10k ft thus expecting the western peaks to receive light snowfall overnight Saturday into Sunday morning. Some uncertainty lingers for Monday into late next week as our upper level pattern shifts with a high pressure system moves south into the Central Plains. Not much agreement in beyond Monday afternoon as ECMWF becomes the solution with higher amounts of moisture for our mountains through Tuesday. 500-700mb temperatures slightly increase by Tuesday which should keep all precipitation rain for the high elevations but will lean on NBM PoPs of scattered thunderstorms for now. && .AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon) Issued at 1158 AM MDT Wed May 10 2023 Satellite imagery shows the low stratus deck continuing to break up and erode across the terminals this morning. Latest observations show visibility gradually improving and ceilings slowly rising. Within the next hour or so, expecting terminals to improve into the MVFR category. With that concern diminishing, establishes a new one...thunderstorms. Still see potential for storms to initiate in the 20-22z timeframe this afternoon. VRB winds and gusts will accompany any passing or nearby storms. The environment also supports strong to severe storms with hail and gusty winds being the main threat. This activity continues through the early evening hours with rain showers behind it overnight. && .HYDROLOGY... Issued at 401 AM MDT Wed May 10 2023 Flood Watch in effect Thursday morning through Friday morning. Confidence is increasing in flooding issues on Thursday across portions of the region. As it stands right now, the northern I-25 corridor, adjacent plains and our burn scars are the most susceptible to flooding issues. PWATs are forecasted to climb above daily maximums for early May, and a longer duration upslope moderate to heavy rain event is expected. && .BOU WATCHES/WARNINGS/ADVISORIES... Flood Watch from Thursday morning through Friday morning for COZ033-035-038-042>044. && UPDATE...Mensch SHORT TERM...Heavener LONG TERM...AD AVIATION...Mensch HYDROLOGY...Heavener
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 423 AM MDT Wed May 10 2023 COZ030>051-111030- 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- 423 AM MDT Wed May 10 2023 Severe thunderstorms, heavy rainfall, and moderate snowfall possible today through Friday. This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...Today and Tonight More widespread severe convection expected, mainly after 20Z, with all severe hazards possible. Large hail and a few tornadoes looks to be the initial threat before developing into a wind threat late this evening. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday Flood potential creeps upwards Thursday morning through Friday morning across the northern I-25 corridor and the burn scars. Heavy snowfall is expected for higher elevations above 9k ft mainly Thursday into Friday morning. A cool and wet pattern continues this weekend. .SPOTTER INFORMATION STATEMENT... Spotter reports of hail, strong wind gusts and rainfall would be appreciated. Stay weather aware.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DENVER CO
905 AM MDT WED MAY 10 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1110 PM HAIL 2 NNE ERIE 40.05N 105.03W
05/09/2023 M1.50 INCH WELD CO TRAINED SPOTTER
FRONT WINDSHIELD SMASHED, REAR WINDOW GONE,
TREES STRIPPED, ROOF DAMAGE.
&&
ASPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DENVER CO
1013 AM MDT WED MAY 10 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1045 PM HEAVY RAIN 1 ESE BERTHOUD 40.30N 105.07W
05/09/2023 M1.46 INCH LARIMER CO PUBLIC
0.5 INCH DIAMETER HAIL FELL IN 15 MIN.
&&
ASThe national radar mosaic for the moment the first event began.
4 winter weather, 4 flood, 1 winter storm. Local standard time, as filed.
Storm totals included 10 inches, 7 miles east of Blue River and 9 inches, 5 miles north of Alma.
Storm totals included 27 inches at Berthoud Pass, 21 inches near Winter Park, 18 inches near Echo Lake, 17 inches near Loveland Pass, 14 inches, 8 miles south-southwest of Copper Mountain; 11 inches near Guanella Pass, with 10 inches near Green Mountain Reservoir.
Storm totals included: 16 inches near Trail Ridge, 10 inches near Brainard Lake, with 8 inches near Eldora and Ward.
Weld County closed 23 sections of county roads due to flooding. Roads that were closed or damaged included: Weld County Road 4 from County Roads 15-17, Weld County Road 6 from County Road 23-U.S. 85, Weld County Road 8 from County Road 23-U.S. 85, Weld County Road 10 from CO 79 - County Road 71, Weld County Road 10, from County Road 81-83, Weld County Road 14 from County Road 85-87, Weld County Road 15, from County Road 2-4, Weld County Road 16 from County Road 71-73, Weld County Road 16 from County Road 73-77, Weld County Road 17 from County Road 34-38, Weld County Road 42 from County Road 45-47, Weld County Road 48 from County Road 43-45, Weld County Road 50 from County Road 59-61, Weld County Road 57 from County Road 76-78, Weld County Road 61, from U.S. 34-County Road 50, Weld County Road 63 from U.S. 34-County Road 52, Weld County Road 72 from County Road 33-35, and Weld County Road 74 from CO 392-County Road 79.
Storm totals included 9 inches, 9 miles south-southeast of Gould.
Three men in the foothills of Douglas County had to be rescued when their vehicle got stuck in snow along Rampart Range Road in Pike National Forest. The heavy snow toppled trees which blocked the road. Rescuers had to use chainsaws to cut through the downed trees to reach the stranded men; the rescue took nearly 21 hours to complete.
Dozens of roads in Adams County were hit by flooding and were closed due to damage. Authorities believe the damage and impact to the county was severe. The following streets were closed due to flooding: 26th Ave. between Yulle Road and Wolf Creek Road, 64th Ave. between Piggott Road and Wolf Creek Road, Piggott Road from 80th Ave. to 88th Ave., Old Victory Road from US 36 to SH 79, 72nd Ave. from Bradbury-Krebs Road to Xmore Road, Road 15 from Bradbury-Krebs Road to Xmore Road, 26th Ave. from Strasburg Road to Comanche Drive, 26th Ave. from Piggott Road to Yulle Road, 48th Ave. from Strasburg Road to Piggott Road, 112th Ave. from Headlight Road to Nordbye Road, 112th Ave. from Behrens Road to Horrogate Road, 72nd Ave. from Converse Road to SH 79, 80th Ave. from Schumaker Road to SH 79, Cameron Drive from Guy Court to O Brien, Converse Road from 128th Ave. to 144th Ave., Converse Road, from 88th Ave. to 112th Ave., East 112th Ave. from SH 79 to Converse Road, 104th Ave. at Manilla Road and at Tumbleweed Court, 64th Ave. from Converse Road to Schumaker Road, Converse Road from 88th Ave. to 64th Ave., 72nd Ave. at Converse Road and SH 79, 80th Ave. from SH 79 to Schumaker Road, 112th Ave. from Himalaya Road to Picadilly. All Adams County trails were also closed, which included the South Platte River Trail.|.
The heavy rainfall has caused road damage in Cherry Creek State Park, along East Lake View Road. This resulted in the closure of the east and west boat ramps at Cherry Creek Reservoir.
Several trails in Castlewood Canyon State Park were closed as they were underwater and impassable.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2023Every state in 2023This day in weather historyWarnings in Colorado, May 2023
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: 1100919, 1100918, 1100926, 1103233, 1100921, 1100930, 1103230, 1103216, 1103227.