Torrential rainfall from slow-moving thunderstorms produced localized flash flooding in southwest Sioux County.
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The episode as NWS CYS wrote it up.
Torrential rainfall from slow-moving thunderstorms produced localized flash flooding in southwest Sioux County.
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 Cheyenne, WY wrote its last area forecast discussion before the first event at Jul 12, 1:46 PM MST, 1 hour 44 minutes earlier.
Area Forecast Discussion National Weather Service Cheyenne WY 246 PM MDT Thu Jul 12 2018 .SHORT TERM...(This evening through Saturday) Issued at 245 PM MDT Thu Jul 12 2018 Current KCYS radar loop shows slow moving thunderstorms across southeast Wyoming, mainly along and west of I-25. One thunderstorm prompted a Flash Flood Warning for the Badger Creek Fire area/burn scar due to a very slow moving cell just southeast of the Snowy Range. This activity has propagated a little further south and east into the Laramie Range early this afternoon. Some isolated flooding is possible along and just east of the Laramie Range into the I-25 corridor this afternoon and into this evening. Lower confidence further east across the Nebraska panhandle since storm motion is a little more pronounced, but can not completely rule it out. Areas east of the I-25 corridor will have a better chance of seeing a few severe thunderstorms this afternoon through late this evening as an upper level disturbance slowly move northeast across Colorado and into Nebraska. Shear is not that impressive, so only expect one or two severe storms at this time. Showers and thunderstorms may linger through midnight tonight east of I-25. Cooler temperatures will continue on Friday with northwest flow aloft. 500mb to 700mb temperatures will increase slightly through the day with quite a bit of dry air/subsidence above 500mb. This may be enough to limit overall convection through the day and into the evening hours. The best chance to see thunderstorms will be across southeast Wyoming, especially in/around the mountains. Increased POP between 25 to 50 percent across the mountains and adjacent valleys/high plains. High temperatures will generally be in the upper 70s to mid 80s. Saturday will be similar weather- wise, with maybe a later initiation of thunderstorms according to most models compared to Friday. It will be noticeably warmer with highs back into the low to mid 90s across most locations. .LONG TERM...(Saturday Night - Thursday) No major changes made to previous Long Range forecast through next week. Models are indicating northwest flow aloft developing across the forecast area, which tends to favor a more active and wetter weather pattern along the Front Range. /tt //Issued at 429 AM MDT Thu Jul 12 2018// A generally active pattern can be expected through the majority of the extended forecast period beneath quasi-zonal flow aloft. A few features to note. A brief bout of short-wave ridging will send 500 mb heights back near 595 dm on Saturday, setting the stage for hot and dry conditions once again with highs in the 90s. A weak upper- level disturbance/associated cold front is progged to swing across the area Saturday night/Sunday, bringing cooler temperatures along with good chances for precipitation. Daily chances for showers and thunderstorms should exist through Wednesday. && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) Issued at 1127 AM MDT Thu Jul 12 2018 VFR conditions will degrade this afternoon and evening to MVFR and IFR in some spots as scattered to numerous showers and thunderstorms develop. As of 1730z showers and storms were developing over the Laramie range and were slowly drifting southeast with cloud tops up to FL400. Storms should continue this evening and intensify across much of the area. Expect some low CIGS and possible fog at Nebraska terminals tomorrow morning as remnant moisture and cooler temperatures bring higher relative humidities. && .FIRE WEATHER... Issued at 149 PM MDT Thu Jul 12 2018 Fire Weather concerns will be low into the weekend and likely through most of next week. Slightly cooler temperatures and higher humidities are expected, with the exception of Saturday which may be the warmest day through Thursday of next week. A more active weather pattern is expected next week with a daily chance of showers and thunderstorms. This will keep daytime temperatures near normal or slightly below normal with daytime humidity ranging from 20 percent (west) to 40 percent (east). && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && SHORT TERM...TJT LONG TERM...CLH AVIATION...AL FIRE WEATHER...TJT
Hazardous Weather Outlook National Weather Service Cheyenne WY 631 AM MDT Thu Jul 12 2018 NEZ002-003-019>021-054-055-095-096-WYZ101>119-131245- Dawes-Box Butte-Scotts Bluff-Banner-Morrill-Kimball-Cheyenne- North Sioux-South Sioux-Converse County Lower Elevations- Niobrara County-North Laramie Range- Ferris/Seminoe/Shirley Mountains-Shirley Basin- Central Laramie Range and Southwest Platte County- East Platte County-Goshen County-Central Carbon County- North Snowy Range Foothills-Southwest Carbon County- Sierra Madre Range-Upper North Platte River Basin-Snowy Range- Laramie Valley-South Laramie Range-South Laramie Range Foothills- Central Laramie County-East Laramie County- 631 AM MDT Thu Jul 12 2018 This hazardous weather outlook is for portions of western Nebraska...east central Wyoming...south central Wyoming and southeast Wyoming. .DAY ONE...TODAY AND TONIGHT Thunderstorms are expected to develop over the higher terrain this morning, then spread across the high plains of southeast Wyoming and the western Nebraska Panhandle during the afternoon and evening. The strongest storms may produce brief heavy rainfall, gusty winds to 50 MPH, and nickel size hail. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY There will be daily chances for showers and thunderstorms across much of the region from Friday through Wednesday. Severe weather is not expected at this time. .Spotter information statement... Spotter activation will not be needed.
Special Weather Statement National Weather Service Cheyenne WY 132 PM MDT THU JUL 12 2018 WYZ103-106-122015- Central Laramie Range and Southwest Platte County WY- North Laramie Range WY- 132 PM MDT THU JUL 12 2018 ...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN ALBANY AND SOUTHWESTERN PLATTE COUNTIES UNTIL 215 PM MDT... At 132 PM MDT, Doppler radar was tracking a strong thunderstorm 10 miles southeast of Friend Park Campground, or 22 miles west of Wheatland, moving southeast at 20 mph. Half inch hail and winds in excess of 40 mph will be possible with this storm. This storm will remain over mainly rural areas of northeastern Albany and southwestern Platte Counties. LAT...LON 4214 10553 4222 10531 4189 10505 4178 10538 TIME...MOT...LOC 1932Z 335DEG 17KT 4212 10539 Lyons
Special Weather Statement
National Weather Service Cheyenne WY
137 PM MDT THU JUL 12 2018
WYZ116-122015-
South Laramie Range WY-
137 PM MDT THU JUL 12 2018
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN ALBANY AND
SOUTHWESTERN LARAMIE COUNTIES UNTIL 215 PM MDT...
At 137 PM MDT, Doppler radar was tracking a strong thunderstorm near
Pumpkin Vine, or 23 miles south of Laramie, moving east at 10 mph.
Nickel size hail and wind gusts up to 50 mph will be possible with
this storm.
Locations impacted include...
Pumpkin Vine, Tie Siding and Buford.
This includes Interstate 80 in Wyoming between mile markers 331 and
336.
LAT...LON 4108 10558 4115 10538 4112 10528 4100 10517
4100 10555
TIME...MOT...LOC 1937Z 248DEG 10KT 4099 10547
LyonsPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHEYENNE WY
147 PM MDT THU JUL 12 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0145 PM FLASH FLOOD 1 SSE WOODS LANDING 41.10N 106.01W
07/12/2018 ALBANY WY EMERGENCY MNGR
REPORT OF MUD AND DEBRIS ACROSS HIGHWAY 230 NEAR WOODS
LANDING.
&&
ALYONSSpecial Weather Statement National Weather Service Cheyenne WY 159 PM MDT THU JUL 12 2018 WYZ116-117-122045- South Laramie Range WY-South Laramie Range Foothills WY- 159 PM MDT THU JUL 12 2018 ...SIGNIFICANT WEATHER ADVISORY FOR EAST CENTRAL ALBANY AND WEST CENTRAL LARAMIE COUNTIES UNTIL 245 PM MDT... At 159 PM MDT, Doppler radar was tracking a strong thunderstorm 8 miles west of Horse Creek, or 14 miles northeast of Laramie, moving southeast at 10 mph. Dime size hail will be possible with this storm. Locations impacted include... Horse Creek. PRECAUTIONARY/PREPAREDNESS ACTIONS... Torrential rainfall is also occurring with this storm, and may lead to localized flooding. Do not drive your vehicle through flooded roadways. Frequent cloud to ground lightning is occurring with this storm. Lightning can strike 10 miles away from a thunderstorm. Seek a safe shelter inside a building or vehicle. && LAT...LON 4142 10548 4157 10538 4147 10505 4123 10521 TIME...MOT...LOC 1959Z 296DEG 7KT 4143 10535 Lyons
The Cheyenne radar (KCYS), 123 km away, was scanning. The volume nearest the first event began at 22:28 UTC.
1 flash flood. Local standard time, as filed.
Localized flash flooding was observed with at least six inches of flowing water over portions of Highway 29 south of Agate.
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, July 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: 779594.