Spotty wind damage occurred in Cozad after midnight on this Friday morning, followed by severe winds associated with a wake low later in the morning. At 1200 AM CST, a large mesoscale convective system was in progress from the Sandhills southwest into the southern Nebraska Panhandle.
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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 GID wrote it up.
Spotty wind damage occurred in Cozad after midnight on this Friday morning, followed by severe winds associated with a wake low later in the morning. At 1200 AM CST, a large mesoscale convective system was in progress from the Sandhills southwest into the southern Nebraska Panhandle. The forward-propagating squall line extended from the Sandhills southwest into Custer County and was weakening. Where the outflow boundary became oriented more west-east, a few strong storms remained. These storms formed into a new squall line over Lincoln and Custer counties. As this line moved into Dawson County, some minor roof damage occurred in Cozad and a large pine tree was blown over and onto a house. This line weakened as it moved further east into south central Nebraska. After sunrise, the persistent mesoscale convective complex that had affected the area, throughout the nighttime and early morning hours, weakened and decreased in size. As this occurred, a wake low developed on its westward side and resulted in measured winds of 60 mph at the airport in Ord, along with significant fluctuations in pressure.
Two fronts separated three air masses over the U.S., one across the southern states and the other across the northern states. A chilly continental polar air mass was across the north, a warm and humid maritime tropical air mass was over the south, and these storms occurred in the modified continental polar air in between, far from any fronts. An upper-level trough was over the western U.S., while a ridge was over the Great Lakes. Fairly weak southwest flow was over the Central Plains. This MCS developed from scattered storms that initially formed within the lee trough near the Nebraska-Wyoming border the previous afternoon. Warm air advection and convergence associated with the low-level jet maintained the MCS through the night. Just prior to the squall line affecting Cozad, MUCAPE was around 1500 J/kg with mid-level lapse rates around 7.5 deg C/km. Deep layer shear was around 45 kts.
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 Hastings, NE wrote its last area forecast discussion before the first event at May 17, 11:31 PM CST, 2 hours 29 minutes earlier.
Area Forecast Discussion National Weather Service Hastings NE 1231 AM CDT Fri May 18 2018 .SHORT TERM...(This evening through Friday) Issued at 325 PM CDT Thu May 17 2018 There are still a few cumulus around the area this afternoon, but mostly sunny skies. Winds have been from the south and brought warmer temperatures and some additional moisture. The upper level ridge across the area will move to the east tonight and an upper level wave will affect the area mainly late tonight and into Friday. Even at this time, there are some minor differences in the models and when the precipitation will start and how much area will be covered in thunderstorms. The main thought is that the thunderstorms will hold off until after sunset before they get started and move into the area. Have slowed down the onset of thunderstorms tonight. Thunderstorms will continue into Friday and there could be a little bit of a break between the morning convection and the development of other thunderstorms during the afternoon and evening. Temperatures will be a little cooler on Friday with more clouds around. .LONG TERM...(Friday night through Thursday) Issued at 325 PM CDT Thu May 17 2018 A stronger upper level wave approaches the area Friday night. Thunderstorms are expected to develop late in the afternoon and spread across the area during the evening. The models are fairly similar with the system as it moves through the area and there is a good chance for precipitation across the area. Expect there could be some severe thunderstorms late in the afternoon and into the evening. Thunderstorms are expected to linger into Saturday. Once again, there could be a brief period without thunderstorms, but that will be short lived as another wave affects the area during the afternoon and evening. A few showers will linger into the overnight hours before moving out of the area Sunday morning. Sunday afternoon into Sunday evening will be a break between systems. From Sunday night through Thursday there continues to be an unsettled pattern that will bring on and off chances for showers and thunderstorms. Certainly there will not be precipitation all of the time, and there could even be portions of the area that see more breaks than others. There are several waves coming from a low in the western CONUS. Timing the waves and how strong they will be is a challenge. && .AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Saturday) Issued at 1222 AM CDT Fri May 18 2018 VFR conditions are forecast through the period. Have a mention of LLWS for EAR which had the stronger signal for LLWS compared to GRI. Chance for TSRA this morning, if storms make it to the sites will amend as needed. Some models trending north of TAF sites so felt a VCTS mention was all the was needed currently. && .GID WATCHES/WARNINGS/ADVISORIES... NE...None. KS...None. && SHORT TERM...JCB LONG TERM...JCB AVIATION...Beda
Hazardous Weather Outlook National Weather Service Hastings NE 336 PM CDT Thu May 17 2018 KSZ005>007-017>019-NEZ039>041-046>049-060>064-072>077-082>087- 181200- Phillips-Smith-Jewell-Rooks-Osborne-Mitchell-Valley-Greeley-Nance- Sherman-Howard-Merrick-Polk-Dawson-Buffalo-Hall-Hamilton-York- Gosper-Phelps-Kearney-Adams-Clay-Fillmore-Furnas-Harlan-Franklin- Webster-Nuckolls-Thayer- 336 PM CDT Thu May 17 2018 This Hazardous Weather Outlook is for south central Nebraska and portions of north central Kansas. .DAY ONE...This Afternoon and Tonight. There is a chance of thunderstorms within the outlook area mainly after 10 PM tonight, and lasting into early Friday morning. There is a Marginal Risk that a few storms could become severe, mainly west of a line from Kearney to Alma Nebraska, to Plainville Kansas. The main severe weather threat would be wind gusts to around 60 mph, although some small hail could also occur. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Periodic rounds of thunderstorms are possible nearly every day in the extended periods with the exception of Sunday. Strong to severe thunderstorms are possible on Friday, mainly during the late afternoon and evening hours. While all areas have at least some potential for severe weather, the greatest risk is across areas southwest of a Kearney, NE to Smith Center, KS line. Large hail and damaging winds are the main threats. Strong to severe thunderstorms may also occur Saturday afternoon, mainly across areas east of Highway 281. Once again, large hail and damaging winds are the main threats. Severe weather chances may return at times with thunderstorms next week, but specifics on timing and location of severe threats remains highly uncertain. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed tonight, mainly west of a line from Kearney to Alma Nebraska, to Plainville Kansas. && More information may be obtained at the following web page: https://www.weather.gov/hastings
The North Platte radar (KLNX), 131 km away, was scanning. The volume nearest the first event began at 07:58 UTC.
1 thunderstorm wind, 1 high wind. Local standard time, as filed.
A few local businesses sustained minor roof damage, and some tin was blown off a few outbuildings. A large pine tree was uprooted, landing on a house.
This wind gust was associated with a wake low. The pressure plunged 9 mb between 9-10 a.m. CDT. There was a 3 mb pressure drop from 9:55-10 a.m. CDT and then a 3 mb rise from 10-10:05 a.m. CDT. This gust coincided with the lowest pressure.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Nebraska in 2018Every state in 2018This day in weather historyWarnings in Nebraska, 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: 748382, 748383.