Highlights: Cool, wet conditions engulfed much of the Midwest, ending a period of favorable weather for corn and soybean development and maturation. Weekly rainfall generally totaled 1 to 3 inches across the northern Corn Belt. Significant rain (at least 2 inches) also fell in New England.

Meanwhile, favorably dry weather returned to the South for several days, although wet soils continued to hamper fieldwork and threaten the quality of unharvested cotton, rice, and soybeans. In addition, wet weather returned to the western and central Gulf Coast States toward week's end. Farther west, precipitation was mostly confined to the fringes of the Plains, allowing winter wheat planting and other fieldwork to proceed with few delays from Nebraska to northern Texas. On the northern Plains, mid-week showers slowed fieldwork but boosted moisture for wheat establishment. Elsewhere, Western showers were mostly confined to the northern half of the region, although moisture associated with the remnants of eastern Pacific Tropical Storm Olaf affected areas near the U.S.-Mexico border before shifting across the remainder of the South. Cool air settling across the contiguous U.S. held weekly temperatures at least 5 degrees F below normal in many locations across the Plains and the Midwest. Readings averaged as much as 10 degrees F below normal in Oregon. From September 29-October 1, frost and light freezes affected much of the northern Corn Belt. Although immature corn and soybeans lost some leaf canopy to the cold weather, most plants survived the outbreak.

Farther west, widespread freezes across the northern and central High Plains and the Intermountain West ended the 2009 growing season and slowed the emergence and growth of recently planted winter grains.

Early in the week, late-season heat lingered across the southern Plains and the West. Daily-record highs for September 27 included 111 degrees F in Palm Springs, CA; 107 degrees F in Phoenix, AZ; and 100 degrees F in Childress, TX. Meanwhile, high winds swept across the northern Plains and the Great Lakes States. On September 27, wind gusts were clocked to 66 miles per hour in Willmar, MN, and 59 miles per hour in Dickinson, ND. The following day, cold air reached the High Plains, where Alliance (22 degrees F) posted a daily-record low for September 28. Frosty conditions arrived across the northern Plains and upper Midwest by September 29, when Pierre, SD (29 degrees F), notched a daily-record low. In Grand Forks, ND (29 degrees F on September 29), the season's first freeze occurred earlier than last year (October 3, 2008), but was more than a week later than the normal first freeze date of September 20. By October 1, cool air settled across the Great Lakes region, where daily-record lows in Michigan included 26 degrees F in Marquette and 30 degrees F in Traverse City. In contrast, heat briefly affected the Nation's mid-section as far north as the central and southern Plains, where daily-record highs for September 30 reached 98 degrees F in both Liberal, KS, and Borger, TX. Meanwhile, sharply colder air arrived in the West. October opened with daily-record lows in Western locations such as Ely, NV, and Stanley, ID (both 14 degrees F). A day later, records for October 2 included 12 degrees F in Alamosa, CO, and 23 degrees F in Pocatello, ID. Grand Junction, CO (27 and 29 degrees F), started October with consecutive daily-record lows. Elsewhere in Colorado, Denver (26 and 31 degrees F) and Pueblo (25 and 27 degrees F) closed the week with consecutive daily-record lows on October 2-3. Other daily records on the Plains for October 3 included 16 degrees F in Alliance, NE; 29 degrees F in Garden City, KS; and 32 degrees F in Gage, OK.

On September 28, heavy rain accompanied blustery conditions in the Great Lakes region, where daily-record totals reached 3.55 inches in Buffalo, NY, and 1.28 inches in Marquette, MI. It was Buffalo's wettest day since June 22, 1987. In late September, rain and snow developed across the Intermountain West. In Utah, 11 inches of snow had blanketed Alta by month's end, while a wind gust to 68 miles per hour was recorded at the Great Salt Lake Marina. September 30 snowfall totaled 5.5 inches in Bozeman, MT. In early October, heavy rain developed across the northern Plains and upper Midwest, while a separate area of rain spread northeastward from southern and eastern Texas. Daily-record amounts for October 1 included 2.32 inches in Sisseton, SD; 1.98 inches in Fargo, ND; and 1.68 inches in Mason City, IA.

The following day, record totals for October 2 reached 1.62 inches in Lake Charles, LA, and 1.16 inches in Dayton, OH. At week's end, rain spread into the Northeast and expanded across the South. Portland, ME (1.90 inches), netted a daily-record sum for October 3. Meanwhile in previously drought-stricken southern Texas, San Antonio received 6.03 inches of rain in a 24-hour period on October 3-4.

Cold, mostly dry weather prevailed across the Alaskan mainland, while rain and snow fell in the southern part of the state. Valdez (29 degrees F) posted a daily-record low for September 28, while Yakutat's weekly rainfall reached 3.07 inches. Farther south, locally heavy showers developed across windward sections of Hawaii in early October. On the Big Island, for example, Hilo, received 3.11 inches of rain from October 1-3.