Alert archive / Iowa / Severe Thunderstorm Warnings in 2017
Severe Thunderstorm Warning 248, NWS Omaha, NE
NWS Omaha, NE issued this severe thunderstorm warning at Sep 16, 2017, 8:58 PM CDT for Pottawattamie County, Iowa. It was in force for 32 min. No storm report in the archive falls inside the area while it was in force.
The area
The counties it named.
The facts
- Issued
- Sep 16, 2017, 8:58 PM CDT (01:58 UTC)
- Expired
- Sep 16, 2017, 9:30 PM CDT
- In force
- 32 min
- Issued by
- NWS Omaha, NE
- Area
- Storm-based polygon
- Hail
- 1.0 in
- Wind
- 50.0 mph
County Pottawattamie County, IA
The radar
The Omaha radar (KOAX), 69 km from the middle of the area, began a volume at 02:00 UTC, the scan nearest the moment this went out.
Open the radar archive at this moment
The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.
The nearest sounding before it
Topeka, KS (KFOE), launched 00:00Z, 2.0 hours before the alert went out and 260 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.
- Mixed-layer CAPE
- 1943 J/kg
- Mixed-layer CIN
- -49 J/kg
- Mixed-layer LCL
- 1257 m above ground
- 0-6 km bulk shear
- 28 kt
- 0-1 km storm-relative helicity
- 124 m²/s²
- 0-3 km storm-relative helicity
- 228 m²/s²
- Significant tornado parameter
- 0.6
- Supercell composite
- 6.2
What forecasters said that day
The local office's own words before this severe thunderstorm warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Omaha, NE wrote its last area forecast discussion before this severe thunderstorm warning went out at Sep 16, 6:00 PM CDT, 2 hours 58 minutes earlier.
Area forecast discussion, Sep 16, 6:00 PM CDT, 2 hours 58 minutes before
Area Forecast Discussion National Weather Service Omaha/Valley NE 600 PM CDT Sat Sep 16 2017 .SHORT TERM...(Tonight through Tuesday) Issued at 242 PM CDT Sat Sep 16 2017 A potent shortwave trough will eject east-northeast across the Dakotas and the ND-MN Red River Valley this afternoon into tonight with the southern fringe of mid-level height falls glancing the forecast area. At the same time, a cold front will steadily advance south through the remainder of southeast NE and southwest IA, ushering a cooler and drier air mass into the region. Pre-frontal showers and thunderstorms have limited the degree of destabilization within warm sector so far today. However, pockets of stronger heating will yield a moderately unstable and weakly capped environment by mid to late afternoon when surface- based storms will become increasingly likely. Latest convection- allowing model guidance suggests that this scenario is most likely to unfold across far southeast NE into southwest IA after 4 PM with additional storms forming nearer to the 850-mb front along and south of I-80 this evening. The most intense storms are expected to be those forming along the surface front where instability will be greater. Large hail and damaging wind gusts will be the primary hazards. A strong storm or two is also possible later this evening with the elevated activity mentioned above, and some hail cannot be ruled out. Precipitation will end from north to south tonight and the majority of Sunday looks to remain dry as high pressure builds through the area. On Sunday night into Monday, low-level warm advection will strengthen ahead of a low-amplitude shortwave trough tracking from the Rockies into northern and central Plains. This process in conjunction with deeper-layer forcing attendant to the approaching mid-level wave will support a good chance of showers and thunderstorms across much of the area. Locally heavy rainfall is possible, especially nearer to the NE-KS border. Both precipitation and clouds should diminish during the afternoon on Monday as the mid-level impulse shifts east of the region. Monday night into Tuesday, another powerful jet streak and associated shortwave trough will migrate from the Interior West into the northern High Plains. This will drive the deepening of a lee cyclone and the eastward advance of a cold front through the High Plains. This large-scale pattern evolution will support afternoon temperatures warming well into the 80s and perhaps lower 90s with breezy to windy conditions. .LONG TERM...(Tuesday night through Saturday) Issued at 242 PM CDT Sat Sep 16 2017 The above-mentioned shortwave trough will traverse the northern Plains and upper-MS Valley Tuesday night into Wednesday with the associated surface cold front weakening as it moves into the mid- MO Valley. Thereafter, medium-range guidance is suggestive that a longer-wavelength trough will become established over western North America by late week before edging east toward the Great Plains next weekend. Ahead of this trough, we will likely see near to above-normal temperatures with increasing precipitation chances by the weekend. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 559 PM CDT Sat Sep 16 2017 The surface cold front continues south through far southeast NE and southwest IA as of early evening with a trailing band of MVFR stratus across much of the area. Radar data indicate a gradual deepening of convection to the north of the surface boundary from KTQE to near KLNK. Latest model guidance suggests that some of this activity will further evolve into thunderstorms over the next couple of hours. As such, have mentioned VCTS at KOMA and KLNK through 03z. Otherwise, expect the MVFR ceiling to erode from northwest to southeast with surface winds diminishing and veering to northeast. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && SHORT TERM...Mead LONG TERM...Mead AVIATION...Mead
Hazardous weather outlook, Sep 16, 7:12 PM CDT, 1 hour 46 minutes before
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Special weather statement, Sep 16, 8:08 PM CDT, 50 minutes before
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</html>Special weather statement, Sep 16, 8:36 PM CDT, 22 minutes before
Special Weather Statement National Weather Service Omaha/Valley Nebraska 836 PM CDT SAT SEP 16 2017 IAZ079-090-NEZ067-068-170200- Mills IA-Fremont IA-Cass NE-Otoe NE- 836 PM CDT SAT SEP 16 2017 ...Significant Weather Advisory for NORTHWESTERN FREMONT... SOUTHWESTERN MILLS...NORTHEASTERN OTOE AND EASTERN CASS COUNTIES UNTIL 900 PM CDT... At 836 PM CDT, Doppler radar was tracking a strong thunderstorm 4 miles east of Murray, or 25 miles south of Omaha, moving northeast at 30 mph. Hail up to around dime size and winds in excess of 30 mph will be possible with this storm. Locations impacted include... Plattsmouth, Glenwood, Malvern, Pacific Junction, Murray, Union, Tabor and Hastings. LAT...LON 4078 9590 4095 9603 4114 9575 4098 9539 TIME...MOT...LOC 0136Z 233DEG 28KT 4091 9585 MILLER
Special weather statement, Sep 16, 8:46 PM CDT, 12 minutes before
Special Weather Statement National Weather Service Omaha/Valley Nebraska 846 PM CDT SAT SEP 16 2017 IAZ069-170230- Pottawattamie IA- 846 PM CDT SAT SEP 16 2017 ...Significant Weather Advisory for EASTERN POTTAWATTAMIE COUNTY UNTIL 930 PM CDT... At 846 PM CDT, Doppler radar was tracking a strong thunderstorm near Treynor, or 22 miles east of Omaha, moving northeast at 25 mph. Dime size hail and winds in excess of 30 mph will be possible with this storm. Locations impacted include... Oakland, Treynor, Carson, Macedonia, Hancock, Botna Bend Park and Old Town Park. This includes Highway 59 in Iowa between mile markers 41 and 61. LAT...LON 4116 9566 4123 9572 4146 9533 4117 9533 TIME...MOT...LOC 0146Z 234DEG 21KT 4120 9558 MILLER
The office that day
Everything else NWS Omaha, NE issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 16, 8:08 PM CDT | Special Weather Statement | OAX | Saunders | 37 min |
| Sep 16, 9:58 PM CDT | Special Weather Statement | OAX | Johnson | 32 min |
| Sep 16, 10:51 PM CDT | Special Weather Statement | OAX | Jefferson | 39 min |
| Sep 16, 10:59 PM CDT | Severe Thunderstorm Warning | OAX | Jefferson | 31 min |
| Sep 16, 8:36 PM CDT | Special Weather Statement | OAX | Mills | 24 min |
| Sep 16, 8:46 PM CDT | Special Weather Statement | OAX | Pottawattamie | 44 min |
| Sep 16, 9:16 PM CDT | Special Weather Statement | OAX | Shelby | 44 min |
| Sep 16, 10:15 PM CDT | Special Weather Statement | OAX | Pottawattamie | 45 min |
Nearby
Severe Thunderstorm Warnings in Iowa, 2017Every severe thunderstorm warning in 2017
Sources
The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.