7/3/25 - Average summer weather

• Iowa Weather History:

  • On July 3, 2001, severe thunderstorms in southern Iowa produced very large hail: 2.5-inch stones at Osceola, 3-inch at Otley, and 4-inch at Truro, causing widespread and extensive damage.

• Recent Severe Weather Trends:

  • Hail has been infrequent this year, with the most recent notable event in north central/northwestern Iowa a few weeks ago.

  • The primary severe weather mode this season has been wind, with only a few pockets of hail and very few tornadoes (no tornadoes in May, five reports in June, including a landspout).

  • Despite fewer severe storms, thunderstorms have provided good rainfall, especially in northern and western Iowa, aiding drought improvement.

• 7-Day Weather Forecast:

  • Expect average summer weather: several chances for thunderstorms over the next week.

  • Temperatures will be typical for the season, with daytime highs in the mid-80s and overnight lows in the mid to upper 60s.

  • Rainfall (QPF) is forecast at 0.5 to 1 inch, mostly thunderstorm-driven and variable.

  • The best chance for statewide rain is Saturday night into Sunday, with additional chances late Tuesday into Wednesday.

• Climate Outlook:

  • The July outlook initially showed a large dry area from the High Plains to the Gulf, but recent wet weather reduced this to a small bullseye over Nebraska, Kansas, Missouri, and Iowa.

  • The last ten years of Julys in Iowa have been 5–10% drier than average, influencing the forecast.

  • The first half of July still leans wet for most of Iowa; models suggest the second half could turn drier.

• Past Week’s Weather:

  • The past week was about 2°F above average for temperatures and below average for rainfall.

  • The state is transitioning to a quieter storm track, and soil moisture has improved thanks to late June rains.

  • Eastern Iowa, especially around Waterloo, Cedar Rapids, Washington, Wapello, Linn, and Black Hawk counties, remains drier and needs more rain.

• Specialty Crop Impacts:

  • Zucchini: Squash vine borer is active and affecting small plantings; some growers report a lull in fruit set, possibly due to poor pollination (weather or varietal timing).

  • Squash bugs: Adults are mating; now is the time to scout for eggs and treat nymphs with insecticidal soap or oils. Adults are hard to control; many growers opt to replant rather than spray.

  • Japanese beetles: Now appearing, mostly affecting basil (culinary and cut flower types), zinnias, and grape leaves.

  • Basil downy mildew: 'Cardinal' basil (popular for cut flowers) lacks resistance and is vulnerable. 'Thai Prospera' basil offers downy mildew resistance and may be a better filler for bouquets.

  • Garlic: Harvest is beginning. Use the "five green leaves, sixth browning" rule to time harvest for optimal bulb quality and storage.

  • Tomato spotted wilt virus: A grower in Kalona who lost most of his tomato crop to this virus in previous years now sees minimal infection, likely due to reduced thrips pressure. Onion thrips can also vector the virus, so monitor onions for thrips damage.

• Upcoming Resources and Events:

  • Dan will share links in the newsletter on strawberry plug planting, spring broccoli variety trials, root maggot information, and upcoming field days (flower field day in Decorah, urban ag field day in Waterloo, and a native plant propagation survey).

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