Climate Update - Fall, 1996

Dry and pleasant weather was the rule throughout the late Summer and early Fall across Minnesota. For some regions of the state, dry weather was a continuation of a very dry growing season. As of late-October, some locations reported less than 75 percent of normal precipitation for the season (see Figure 1). Some of the largest departures from normal * were:

Red Wing, minus 10.74 inches
St. Cloud, minus 9.34 inches
Caledonia, minus 8.52 inches
Mpls./St. Paul, minus 7.02 inches
_{* for the period April 1 - October 20}

For a few communities, the precipitation deficit was on par with the worst droughts of the century. Fortunately, moderate Summer temperatures led to reduced evaporation rates, mitigating the impact of the rainfall shortage. The Palmer Drought Severity Ind ex indicates that southeastern Minnesota remains in the "moderate drought" category as of this writing. Northwestern, central, and east central Minnesota fell in the "moderate drought" category for much of the Summer and early Fall. Ab undant mid-October rains pushed all but the Southeast out of the moderate drought designation.

The dryness manifested itself through crop stress, reduced stream flows, lower lake levels, and lowering of the water table in shallow ground water aquifers (see Figure 2). Shallow ground water aquifers are closely coupled with the climate on the surface, and react quickly to climate anomalies. Figure 2 shows the behavior of a shallow aquifer in the Anoka Sand Plain.

Compare the rise and fall of the aquifer with the climate index (Palmer Hydrological Drought Index). The drought of 1976; the wet period in the mid 1980's; and the drought of the late 1980's; are all quite apparent. Note the steady two foot drop in 1996 and the companion plunge of the climate index towards "negative" values.

A notable exception to the benign weather this Fall was the Mankato-North Mankato area deluge in early September. For the second time this year, the area received extremely heavy rains leading to urban flooding, mud slides and sewer backups. Rainfall tota ls exceeding six inches were reported.

Agricultural production across Minnesota will show mixed results, with those areas receiving adequate rainfall reaping the benefits of stress-free temperatures. Meanwhile, those areas with precipitation deficits may experience significant yield reductions . Many communities saw their first light frost in mid September, and all of Minnesota experienced a hard freeze in the first week of October.

While some hydrologic systems are at low levels, many Minnesota water resources remain at near-average levels. This is due to the lingering effect of the very wet weather experienced during the first half of the decade. In addition, October rains have helped to replenish depleted soil moisture reserves, leaving Minnesota in a more favorable condition entering the Winter freeze-up.

State Climatology Office
DNR - Division of Waters

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URL: http://climate.umn.edu/doc/journal/talkfa96.html
Last modified: October 28, 1996