2002 Growing Season Weather Summary
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2002 Growing Season Weather Summary Jeff Andresen Michigan State University The 2002 growing season began quickly in response to a large upper air ridge across the central and eastern US, which brought a period of abnormally warm weather during the middle 2 weeks of the month. Mean daily temperatures at or in excess of 90F were recorded at some locations in the state (at least 35F above climatological normal high temperatures for the season), setting new maximum temperature records at many locations during the 16th-18th. Seasonal growing degree (GDD) accumulations, which had been near zero due to cooler than normal temperatures during much of March and early April surged to much above normal levels, resulting in rapid early growth and development of most overwintering crops, and allowing rapid progress of spring fieldwork and planting. Base GDD accumulations for the 8th-20th of April ranged from about 40 units in the far northern Upper Peninsula to more than 150 units in the southern Lower Peninsula, which is nearly double the normal accumulation for this time of year and versus the 2001 growing season totals. The unusual warmth came to an abrupt end on the 20th and again on the 25th with the passages of cold fronts through the region. The change in jet stream was accompanied by snowfall on the 21st and 22nd, and near-record minimum temperatures which fell into the upper teens and 20's F. on the morning of the 23rd. The cold temperatures caused extensive damage to many perennial crops, especially tree fruit and grapes. In contrast to the record warmth of April, much of May and June were cooler than normal, thanks to a persistent broad troughing upper air feature across the Great Lakes region. A series of frontal systems also brought above normal precipitation totals to much of the state. The cool, wet weather caused major delays in spring planting and slowed germination, growth, and development of all crops. In some areas, the conditions necessitated replanting. By mid-June, seasonal base 50F growing degree day totals lagged from 50-100 units behind normal, a dramatic change from the much above normal totals experienced at the beginning of the season. A return of an upper air ridging pattern across the Midwest during late June led to yet another major weather change which continued through much of the remainder of the growing season. This middle and latter portions of the growing season were characterized by warmer than normal temperatures, and during much of June, July, and early August, by much drier than normal conditions. During the period between the first week of June and the second week of July, rainfall totals were less than 0.25 inches across much of the Lower Peninsula. The dryness led to increasing levels of moisture stress in most spring and summer crops, but favored harvest of winter grains. Much-needed rainfall brought relief to the stressful conditions in early August. A drier the normal pattern developed across much of the state once again in late August and continued through the remainder of the fall season. By late September, sections of southern Lower Michigan were characterized by NOAA's Palmer Drought Index as experiencing 'moderate' drought conditions. A notable exception to the drier than pattern was western and central sections of the Upper Peninsula, where periodic heavy rainfall led to above normal precipitation totals and a Palmer Drought Index characterization of 'abnormally wet' conditions during much of the fall season. September and much of October were characterized by warmer and drier than normal weather, which favored maturation and drydown of summer crops as well as harvest activities. The first killing freeze of the fall season occurred during the last week of September and first two weeks of October over most of the state, which is near to a few days later than normal. Overall, for the 5-month May-September period, mean temperatures and growing degree day accumulations ranged from near to above normal statewide. From a climatological standpoint, the varying nature of GDD accumulations during the season was unusual. From previous studies, we know that it is uncommon in Michigan for significant GDD deficits (or excesses) that develop during the first half of the growing season to be reversed by the end of the season, and as was the case this year. Precipitation totals were also variable across the state, ranging from below normal totals much of the Lower Peninsula to much above normal levels in the Upper Peninsula. |