textproduct: Omaha/Valley

KEY MESSAGES

- Isolated showers and non-severe thunderstorms remain possible early this evening. Probability of occurrence 10-20%.

- A Heat Advisory is in effect for northeast Nebraska Sunday and much of the area Monday. Expect heat index values in the 100 to 110 range in the afternoon. Overnight heat indices will remain in the mid 70s, providing little relief.

- Cooler weather returns by midweek, with high temperatures falling back into the 80s. Along with more seasonable temperatures, there will be increasing chances for showers and thunderstorms Wednesday night into early Friday.

DISCUSSION

Issued at 213 PM CDT Sat Jul 18 2026

Rest of today and tonight...

Satellite imagery continues to show an increase in cumulus across the area due to diurnal mixing of hot and humid air. Most dense coverage is along and north of a frontal boundary that is pushing into the area due to modest isentropic ascent along the 310K surface. CAMS continue to show isolated showers, and perhaps a thunderstorm or two, developing this afternoon along the boundary, which essentially will park itself essentially from Verdel, NE to Clarinda, IA later this afternoon. Very modest forcing for ascent is possible this afternoon and early evening from a jet streak moving across the Great Lakes region. H7 temperatures will be warm, 10-12C, and H5 temperatures -4 to 0C, which will lead to warm rain process, with perhaps a little glaciation in the upper mid- levels to permit charge separation and lightning. Localized heavy rainfall and wind gusts up 45 mph as storms collapse are the primary threats. Any convection that develops will dissipate with the setting sun, especially since the jet streak will be too far removed to assist with diabatic forcing.

Sunday and Monday...

The two most impactful days in the short term. Hot temperatures are expected, especially on Monday. The Extreme Forecast Index continues to highlight a 90+% temperature event for Monday, and a shift of tails of 1-2. The EFI has shown this extreme event occurring for the last 3 model cycles. Continued and expanded the heat advisory for northeast Nebraska for Sunday, where actual temperatures tomorrow will be around 100, and apparent temperatures 100-108. Conditions do not improve much overnight, with apparent temperatures 75 to 80. For Monday, actual temperatures from 100-107 are expected with heat indices 100-110 areawide. Dewpoints in the 70s will lead to wet-bulb temperatures in the 80s and 90s. Given there will be several outdoor sporting events/championships where children are participating, I decided to hoist a heat advisory for most of east central and southeast Nebraska along with western Iowa. The fly in ointment will be whether convection late in the day on Monday impact temperatures. Models have been advertising a disorganized MCS developing Sunday night and moving across mainly South Dakota. This will allow a stationary front to move slightly northward into northern Nebraska on Monday. The hot and humid airmass will lead to a lower tropospheric instability. I expect afternoon cumulus and towering cumulus to develop during the afternoon, with frontal and diabatic effects to develop isolated showers/tstorms. Dynamic forcing increases late in the day as a jet streak moves across the northern plains into the upper midwest. This jet streak digs further south than the one affecting the area today, thus coverage of convection may increase.

Tuesday through Saturday...

The passage of the jet streak and low level cool advection will push the front into Kansas. The most anticipated effect will be the decrease in temperatures. Temperatures on Saturday only will decrease about 10 degrees into the 90s, but as upper level heights decrease even further, temperatures the rest of the period will be in the 80s. Also something to look forward, are periodic chances of showers and storms, as a series of disturbances traverse the upper ridge axis over Texas, while simultaneously the polar jet remains active and will further increase opportunities for atmospheric ascent.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 628 PM CDT Sat Jul 18 2026

VFR conditions favored through the period, but will need to keep an eye on isolated shower and storm development early in the period and potential fog around 08-12Z. Fog appears most likely at OFK and LNK, but winds aloft still look strong enough to keep it pretty patchy if it does develop. In addition, there are some signs for potential MVFR ceilings as clouds first develop Sunday morning, but they should quickly rise above 3000 ft. Otherwise, winds will go from easterly to southeasterly and should remain under 10 kts through the period.

OAX WATCHES/WARNINGS/ADVISORIES

NE...Heat Advisory from 10 AM to 10 PM CDT Monday for NEZ015-018- 030>034-042>045-050>053-067-068-091-093. Heat Advisory from noon Sunday to 10 PM CDT Monday for NEZ011- 012-016-017. IA...Heat Advisory from 10 AM to 10 PM CDT Monday for IAZ043-055- 056-069-079-080-090-091.