textproduct: Omaha/Valley

KEY MESSAGES

- Potential for more severe weather today, mainly across southeast Nebraska and southwest Iowa. Large hail, damaging winds, strong tornadoes, and flash flooding will all be possible.

- Cooler weather moves in on Tuesday with potential for morning frost for northeast Nebraska on Wednesday.

- Another active pattern may set up going into next weekend with chances for more storms, and possibly severe weather.

DISCUSSION

Issued at 1155 PM CDT Sun May 17 2026

Today and Tonight...

We had a deceivingly cool, cloudy start to the day. Temperatures this morning started off in the 50s at 9 AM, and dipped into the upper 40s over northeast Nebraska. Farther south, however, Falls City had already warmed to 70 degrees, on the warm side of a cold front draped from Beatrice, to Offutt AFB, towards Shelby, IA. Spotty showers and a few rumbles of thunder developed behind the boundary this morning. A strong shortwave trough will continue to eject eastward this afternoon, bringing forcing for large-scale ascent. Despite the lingering cloud cover, very steep lapse rates aloft and daytime heating of a moist low-level airmass will likely support strong instability south of the cold front. Mesoanalysis depicting strong thetaE advection from central Kansas through southeast Nebraska and southwest Iowa depicted the abrupt resurgence of a volatile airmass. Storms have already begun to fire on the warm side of the boundary over northwest Kansas, and are expected to develop over far southeast Nebraska by 2 PM this afternoon. Initial isolated supercells will have the greatest potential for producing strong, potentially violent tornadoes, very large hail, and damaging winds, with the greatest risk in far southeast Nebraska. By 4 or 5 PM, CAMS depict more widespread clusters of storms developing, with the potential for supercell structures. While not as extreme as the possible intensity over far southeast Nebraska, these storms, primarily along and southeast of a line from Lincoln to Omaha will still be capable of producing large hail, damaging winds, and perhaps a tornado or two.

In addition to hail, winds, and a chance for tornadoes, heavy rain will also become an issue overnight. Last night's round of convection brought around 0.5" to 1" of rain across the forecast area. The potential for a few training storms with 3"+ per hour rates on top of the already saturated soils will create the potential for flash flooding across parts of far southeast Nebraska and southwest Iowa tonight. Therefore, a Flood Watch remains in effect until 7 AM Tuesday for southeast Nebraska and parts of southwest Iowa.

Tuesday and Beyond...

We'll see the cold front clear well to the south and east of our area by Tuesday, putting a cooler Canadian air mass in place across the region. Tuesday will start out cloudy once again, but really clear by the afternoon as high pressure builds over our area. High temperatures on Tuesday will only reach into the upper 50s to mid 60s. With clear skies and nearly calm winds, this lends to potential for frost early Wednesday. Overnight lows will drop into the mid 30s for northeast Nebraska to low 40s across southeast Nebraska and southwest Iowa. Cooler weather holds into Wednesday though we do see a reversal to southerly winds and start to advect moisture back into the region. An upper-level shortwave could potentially bring a few showers to the area Wednesday afternoon and evening, but the ensembles haven't picked up on this latest change in the deterministic guidance. In any case, this wouldn't be anything impactful.

A better chance for showers and storms moves in Thursday as the longwave trough that's been nearly stationary over the western US shifts eastward toward our area. With temperatures still in the sixties for highs, I wouldn't anticipate much of a severe weather threat with this system for our area.

Temperatures start to rebound on Friday though as we see enhanced warm air advection ahead of a deepening surface low which develops on the lee side of the Rockies over eastern Colorado and western Nebraska. Depending on the track of this system, we could potentially see more active weather next weekend with several chances for storms.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1244 PM CDT Mon May 18 2026

Widespread IFR/MVFR ceilings are observed across terminals this afternoon. Will see an area of scattered showers and storms overspread KLNK and KOMA after 21z. Have refined timing a bit with this issuance, but expect further refinements and adjustments. Storms that affect terminals will likely become severe with strong winds, very large hail, and the potential for a tornado. Have added a transition to -SHRA at KOMA and KLNK after 01/02z. Ceilings will bounce between MVFR/IFR overnight, before largely becoming MVFR late in the TAF period. Winds from the north northeast will turn to the north northwest this evening, with gusts gradually increasing to 25 to 30 kts, persisting for the rest of the TAF cycle.

OAX WATCHES/WARNINGS/ADVISORIES

NE...Flood Watch through Tuesday morning for NEZ065-066-068-078- 088>093. IA...Flood Watch through Tuesday morning for IAZ090-091.