Michigan drought update for August 9, 2012

More improvement with cooler temperatures and chances for rain is expected during the next week.

The combination of scattered showers and thunderstorms and relatively cooler temperatures brought some relief from long-term drought stress to many areas of Michigan during the past week. The less stressful weather was the result of a weakening and westward shift of the persistent upper air ridge that has been responsible for the drought.

As of August 8, three-month precipitation deficits (since May 9) across the state range from 1 to 3 inches from central sections of Lower Michigan to more than 6 inches in southwestern Lower Michigan. Plant available soil moisture levels in the top 5 feet of the soil profile of this area are currently estimated by NOAA’s Climate Prediction Center to remain from 1 to 5 inches below normal for this time of year. The most recent assessment by the U.S. Drought Monitor keeps just over 80 percent of the state in abnormally dry or some stage of drought conditions. That fraction has changed little during the past two weeks. Worst overall impacts in the state resulting from the drought continue across the lower tier of counties of the Lower Peninsula.

Latest forecast guidance continues to suggest a trend toward relatively cooler temperatures and more frequent chances for precipitation. During the next 24 to 48 hours, a fall-like weather system will bring a period of cool and wet weather. Look for occasional showers with some embedded rumbles of thunder overnight Thursday and Friday (August 9 and 10), with the threat of scattered showers continuing through the day Saturday (August 11). Rainfall totals, including the rain that began falling Thursday morning, are expected to range from less than 0.25 inches across far northern sections of the state to more than 1 inch in the south. Heaviest rains are expected across southeastern sections of the Lower Peninsula, where some localized 1- to 2-inch totals are possible. The rain should generally be light to moderate in intensity, which should minimize runoff.

Fair and mostly dry weather is expected Sunday (August 12) and for the first half of next week, with a slow, warming trend. Temperatures will remain at below normal levels Friday and Saturday with highs ranging from the upper 60s north to the upper 70s south and lows from the mid-50s to low 60s. Look for daytime temperatures to warm back into the 80s once again by Tuesday and Wednesday (August 14 and 15) of next week.

After the current round of precipitation, the next chance for significant rainfall will come late Wednesday or Thursday (August 15 and 16) of next week. Current forecast guidance suggests that it may be widespread. Further ahead, medium range forecast guidance is having a difficult time identifying a dominant jet stream pattern. In general, the guidance suggests a gradual flattening of the upper air pattern across North America, with mostly zonal, west to east flow.

The NOAA Climate Prediction Center 6-10 day outlook for August 14-18 calls for near normal mean temperatures and precipitation totals statewide, while the 8-14 day outlook for August 16-22 calls for above normal mean temperatures and precipitation totals. However, given the many discrepancies in the forecast guidance, forecaster confidence in these outlooks is relatively low.

In the long term, there is increasing evidence of the formation of El Nino conditions in the equatorial Pacific region. Should El Nino conditions develop later this fall, there would be a statistically elevated chance for milder and drier than normal conditions this upcoming winter and early next spring (this is now the current NOAA outlook for the Great Lakes region this winter). That in turn would increase the odds that soil water reserves – now at abnormally low levels due to the drought – in some areas of the state will not be completely replenished during the off season (as is almost always the case), and potentially a good reason to at least reconsider your crop insurance strategies for next year.

Additional information:

Dr. Andresen's work is funded in part by MSU's AgBioResearch.

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