An isolated severe thunderstorm produced quarter size hail in northwest Morgan County. A weak tornado touched down briefly in Elbert County.
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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.
An isolated severe thunderstorm produced quarter size hail in northwest Morgan County. A weak tornado touched down briefly in Elbert County. No damage was observed.
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 21, 2:14 PM MST, 2 hours 1 minute earlier.
Area Forecast Discussion National Weather Service Denver/Boulder CO 314 PM MDT Mon May 21 2018 .SHORT TERM...(This evening through Tuesday) Issued at 314 PM MDT Mon May 21 2018 Isolated to scattered afternoon thunderstorm activity over the mountains is expected to come to an end through the evening with the loss of daytime heating. Clearing skies will then occur overnight. Tomorrow should be a repeat of today as the moist southwest flow aloft continues. An embedded short wave should be enough to produce another round of thunderstorms through the afternoon. Once again, most of the activity should be over the higher terrain. A surface low pressure area over eastern Colorado tomorrow will produce a bit of a Denver Cyclone over the urban corridor that will help to keep moisture pooled against the foothills. Forecast CAPE values further east on the plains indicate only weak instability, so only isolated probability of precipitation forecasts will result. With only marginal instability, strong to severe thunderstorms are not expected. .LONG TERM...(Tuesday night through Monday) Issued at 314 PM MDT Mon May 21 2018 ...Summer-like weather expected much of this upcoming week... Weak short wave and associated showers and thunderstorms are expected to push off to the northeast Tuesday evening. Drier air works in overnight with gradual clearing expected. Very warm and drier southwest flow Wednesday will bring warmer temperatures and probably less thunderstorm coverage by then. The northeastern plains could still see a couple stronger storms in the afternoon with better low level moisture holding in place with southeast winds. CAPE could reach 1500-2000 J/kg, and bulk shear of 30-40 knots would be sufficient for a severe storm threat. However, the warmer air aloft and lack of short wave will likely keep any storm coverage limited. On Thursday and Friday, the flow aloft will turn more westerly and weaken with flat upper level ridging expected. As a result, we should see a continuation of warm temperatures but less thunderstorm coverage. High temperatures should push well into the mid to upper 80s across the plains. By Saturday, the upper level ridge will likely amplify over the state as the next upper level low drops into California. Expect another very warm and mostly dry day with such sharp upper level ridging. Would not be surprised if Denver reaches 90F at some point in the Thursday through Saturday period. The next upper low is advertised by most medium range models to open up and lift northeast across the Central Rockies late Sunday into Monday. Confidence decreases in the timing here, so we'll go with a slight chance of thunderstorms and offer a few degrees of cooling by next Monday. && .AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon) Issued at 314 PM MDT Mon May 21 2018 Minimal aviation impacts through tonight and Tuesday as the drier airmass will remain too stable for thunderstorms to develop on the plains. Winds this afternoon will be driven by outflow from decaying showers coming off of the foothills. Drainage southerly winds are expected overnight. Tomorrow should see east to southeast flow until shower activity in the afternoon causes variable and gusty winds. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && SHORT TERM...Dankers LONG TERM...Barjenbruch AVIATION...Dankers
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 1103 AM MDT Mon May 21 2018 COZ030>051-221715- 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- 1103 AM MDT Mon May 21 2018 This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...Today and Tonight Scattered afternoon and evening thunderstorms are expected, mainly over the mountains and parts of the Palmer Divide. The stronger storms may produce brief moderate to heavy rain and small hail. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday Drier and warmer weather will continue through the week. There will be a chance of of afternoon and evening thunderstorms on Tuesday with only a slight chance of storms Wednesday through Friday. A couple of storms on the eastern plains may be strong Tuesday and Wednesday with hail and gusty winds the main threats. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today.
Special Weather Statement
National Weather Service Denver CO
446 PM MDT MON MAY 21 2018
COZ041-046-212330-
Elbert/Central and East Douglas Counties Above 6000 Feet CO-
North and Northeast Elbert County Below 6000 Feet/North Lincoln
County CO-
446 PM MDT MON MAY 21 2018
...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN ELBERT COUNTY UNTIL
530 PM MDT...
At 444 PM MDT, Doppler radar was tracking a strong thunderstorm 10
miles northeast of Kiowa, or 35 miles west of Limon, moving southeast
at 20 mph.
Nickel size hail will be possible with this storm.
This storm will remain over mainly rural areas of northeastern Elbert
County, passing about 15 miles east of Kiowa.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
&&
LAT...LON 3951 10438 3954 10429 3934 10392 3919 10403
3913 10423 3913 10425
TIME...MOT...LOC 2244Z 319DEG 16KT 3945 10431
GIMMESTADThe Denver radar (KFTG), 54 km away, was scanning. The volume nearest the first event began at 23:16 UTC.
1 tornado, 1 hail. Local standard time, as filed.
A small tornado touched down briefly in an open field. No damage was observed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2018Every state in 2018This day in weather historyThe tornado archive for Colorado, 2018Warnings in Colorado, May 2018
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: 746060, 745954.