September 8-14, 2007
Midwest Weekly Highlights - September 8-14, 2007
A Welcome Change
Autumn weather is right on schedule for the Midwest. September 1st marked the return to meteorological fall, and while last week felt anything but fall-like, a few frontal passages through the area helped to drop temperatures significantly. Day time highs started out warmer than normal, but with the progression of each cold frontal passage those warm temperatures quickly disappeared. The coldest of the air masses formed in Canada late on Tuesday and slowly worked its way east while gently drifting southward (Figure 1). Day time highs dropped at a slow but steady rate making for a pleasant second full week of September. In Minnesota, radiational cooling (relatively light winds, clear skies and dry air) caused lower than average overnight temperatures. As a result, many frost advisories were issued as temperatures dipped into the lower to middle 30’s. The first frost for areas north of I-94 in Minnesota is climatologically around the 16th of September, and frost was observed this week in some outlying areas. While the cold blast was a change it is not unusual for this time of year; only a few record low temperatures were broken. On September 13th in Hibbing and Little Falls, MN the low temperature dipped down to 25°F, coincidentally the coldest in the nation on that day.
Across the area the average temperature for this week has ranged from the upper 40's in Minnesota to the middle 70's in Kentucky (Figure 2). Indiana, Ohio and Kentucky were the only states to have temperatures remain slightly above normal. Warmest was Kentucky with an average departure of 2°F to 4°F above normal. Southern Illinois, Missouri and Michigan ranged from normal to below normal temperatures in their northern areas, and Wisconsin and Iowa ranged from 4°F to 6°F below normal. Minnesota was the coolest with temperatures ranging from 6°F below normal near the I-94 corridor to more than 10°F below normal along the Canadian border (Figure 3).
A nearly stationary frontal boundary combined with moisture from what was once Hurricane Henriette over the Pacific ocean produced torrential rainfall over southwestern Missouri Friday (September 7th) night into Saturday (September 8th). This area was plagued with flash flooding and many streets and roads had to be closed near Carthage, Missouri. The heaviest swath of precipitation from this system hit the four counties of Barton, Dade, Jasper, and Lawrence. Heaviest hit was Golden City, Missouri where a National Weather Service Cooperative Weather Observer recorded 2.35" on the 7th, 7.25" on the 8th and 1.30" of precipitation on the 9th (Figure 4). Outside of Missouri copious amounts of rain fell across eastern Indiana and portions of Ohio (Figure 5). While heavy at times these locations received only normal to slightly above normal rainfall. Areas outside of the heavy rains saw their departure from the normal grow, and in a bad direction. Northern Missouri and central Minnesota received only between 2 to 15% of the normal precipitation for this week. (Figure 6).
Lake Superior
NOAA Hydrologists indicated last month that Lake Superior was nearing record lows for the month of August. That trend continued into September and may continue into October as well. Records for Lake Superior date back to 1860, and the current record low depth for September was 183.06 meters (600.59 feet) back in 1926. Currently the monthly mean is at 183.009 meters (Figure 7) and is set to break the record (Figure 8) for this month. NOAA states that “Lake Superior, with a surface area of 31,700 square miles, is second in area only to the Caspian Sea, and is greater than the combined areas of Vermont, Massachusetts, Rhode Island, Connecticut, and New Hampshire. For every inch Lake Superior drops, 529 billion gallons of water are displaced. In the past decade, 12.7 trillion gallons of water have left Lake Superior.” Lake levels had been dropping at a predictable rate of 10 millimeters a year since 1978; in last decade levels have dropped an astounding 2 feet. There are a few factors that can go into the depletion of lake levels. The first factor is that the region has seen warmer air temperatures and less ice cover over the winter months, leading to an increase of evaporation during the winter months. Another factor associated with warmer temperatures is a smaller snow pack during the season. The less of a snow pack, the less runoff from the lake during spring. Of the Great Lakes, Superior is in the worst shape. Lake Michigan levels are below the long term means, but are not nearing record levels (Figure 9). All of the other lakes are very close to the long term means.
Drought Impacts
The drought is starting to hit farmers hard. Normally green pastures in Kentucky are starting to look like a desert, with hard grown grass crunching under your feet. Many farmers cut grass in the spring and summer to make hay that feeds their cattle in the winter when nothing is growing. Some farmers in Kentucky have been forced to feed hay to their cattle as early as June due in part to the drought induced lack of vegetation. Covington, KY is seeing drought that is comparable to the drought of 1936 with annual rainfall totals of only 19.04". When compared to 1936, the Tri-state area of Kentucky (near Covington) received 15.98" of rain through September. This may very well be a record breaking season for the area as all of Kentucky is in D2 Drought (Severe).
On Thursday September 6th, Ohio State Senator Sherrod Brown asked the Department of Agriculture to declare a disaster emergency for all of the 88 counties in Ohio. A late freeze in April damaged many fruit and vegetable crops, the drought and summer heat has since damaged crops and some of the flooding from August damaged many harvests. Overall the drought has slightly improved across the upper Midwest. The Upper Peninsula of Michigan saw a dramatic shift by upgrading a large portion of the area to D2 classification from D3. The most dramatic area of improvement occurred from rains that fell on September 7th in the Arrowhead region of Minnesota. The locally heavy rains helped to erode a modest section of drought. These areas shifted from D3 down to D1 (Figure 10) according to the latest Drought Monitor statistics (Figure 11). Missouri also benefited from heavy rain on the 8th of September (Figure 12). Only scattered light to moderate precipitation fell across the southern states, helping to intensify drought conditions. Overall rains seemed to miss the areas that are impacted by the drought the worst (Figure 13)
Hundreds of records were tied/set across the Midwest this past week. Only a fraction of the records are displayed.Daily Records September 8-14
Daily records for the second week of September can be viewed in Table 1 and Table 2.
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