Iowa Weekly Growing Season Report

Preliminary weather summary for the week ending October 4, 2020

The final days of September into the beginning of October were unseasonably cool statewide with negative temperature departures ranging from six to ten degrees. The statewide average temperature was 50.2 degrees, 7.6 degrees below normal. Measurable rainfall was reported across Iowa as above average totals were observed in the southeast. Drier than normal conditions were reported across the rest of Iowa with departures across northern Iowa ranging from 0.50 inch to 0.70 inch below normal.

A cold front pushed through Iowa during most of Sunday (27th) bringing measurable rainfall across the state. Totals at 7:00 am on Monday (28th) were highest across southeastern Iowa where nearly 20 stations reported an inch or more; Bloomfield (Davis County) observed 1.00 inch while Cantril (Van Buren County) reported 1.43 inches. Rain amounts tapered off moving northwest with general totals between 0.25 inch and 0.50 inch. Northwestern Iowa collected a tenth of an inch or less with the statewide average total of 0.32 inch. Cloudy and cool conditions remained behind the front as daytime highs only reached the upper 50s and low 60s with a gusty northwest wind. Spotty showers formed throughout the day behind a large low pressure system moving over the Great Lakes with rain totals generally under a tenth of an inch at many Iowa stations. Cloud cover began to clear west to east into Tuesday (29th) morning allowing lows to dip into the upper 30s in southwestern Iowa while low to mid 40s were observed across the rest of the state. Stubborn clouds remained across eastern Iowa holding afternoon highs in the low 60s, while temperatures across the state were 10 to 15 degrees warmer under sunny skies and westerly winds. A weak cold front propagated through Iowa late in the day and into Wednesday (30th), bringing spotty showers across much the eastern half of Iowa. Rain gauge totals were light with Davenport (Scott County) reporting 0.17 inch. Totals farther west were generally under 0.10 inch where rain fell. High temperatures for the day were in the mid 60s and low 70s, near seasonal for early fall.

Thursday (1st) was a cloudy and cool day with temperatures only reaching into the 50s statewide under northwest flow. Very spotty showers were again reported across eastern Iowa, though amounts were light. Overnight lows into Friday (2nd) were some of the coldest of the season, as clear skies and no wind created radiational cooling. Some stations in northern Iowa reported lows in the 20s, likely producing the first killing freeze and ending the growing season. Southern and eastern Iowa observed lows in the low to mid 30s with a statewide average low of 33 degrees, 11 degrees below normal. Mostly sunny skies persisted through the day with afternoon highs rebounding into the 50s, though still unseasonably cool with light and variable winds. Cloud cover increased across western Iowa during the evening hours ahead of a disturbance that brought widespread rainfall over much of southern Iowa through Saturday (3rd). Dreary conditions persisted through the day with upper 40s reported at some southern Iowa stations; highs across the rest of the state were generally in the 50s. Skies cleared into Sunday (4th) morning as mid 20s were reported in northwest Iowa while 30s were reported across the rest of Iowa. Rain totals from the system were under 0.50 inch; Knoxville (Marion County) observed 0.49 inch. Rainfall amounts tapered off from to a few tenths to under a tenth north of I-80.

Weekly precipitation totals ranged from 0.01 inch at Rock Valley (Sioux County) to 1.67 inches at a gauge in Bloomfield (Davis County). The statewide weekly average precipitation was 0.37 inch, while the normal is 0.70 inch. Clarinda (Page County) reported the week’s high temperature of 82 degrees on the 29th, 10 degrees above normal. Spencer Municipal Airport (Clay County) reported the week’s low temperature of 24 degrees on the 2nd, 17 degrees below normal.