July 1-10, 2005
Midwest Weekly Highlights - July 1-10, 2005
Drought Continues to Intensify
The first ten days of July did not bring any widespread precipitation to the Midwest. Only narrow border regions of eastern Kentucky, northern Minnesota, and southern and western Missouri received more than 2 inches of rain (Figure 1). Except for small areas in southern Missouri and central Michigan, none of the drought stricken regions of the Midwest received enough precipitation to partially relieve drought conditions. In fact, much of the dry zone stretching from southern Missouri to northern Michigan received less than 50% of normal precipitation for the July 1-10 period (Figure 2). Fortunately, temperatures remained below normal by 2-4°F in the dry swath from Lake Michigan to southern Missouri, with only the far southeastern Midwest mildly above normal (Figure 3). Most of the time during the 10-day period, surface high pressure centers from Canada dominated the region, keeping temperatures in check but also deflecting moisture away, too. The combination of dry air and abundant sunshine is still placing a large transpiration load on crops in the dry areas of the Midwest, and yield potential is in decline as corn silking season begins.
Current Drought Status
The latest U.S. Drought Monitor Map for July 5 (Figure 4, National Drought Mitigation Center) indicates that a large region of extreme drought (D3) has been designated in northern Illinois. The designation indicates a magnitude of drought that occurs only 3-5% of the time, and so is very significant in its potential impacts. This area in Northern Illinois has received less than 50% of normal rain since March 1 (Figure 5), and is at the core of a much larger swath that has received 50-75% of normal precipitation. This percentage amounts to deficits of greater than 8 inches in the D3 area (Figure 6). Parts of southern Missouri also have ongoing deficits of more than 8 inches, although recent showers have helped some of these districts. Soil moisture anomalies correspond to this pattern (Figure 7, Climate Prediction Center - CPC).
Illinois is the only state that is entirely within the Midwest drought belt, and recorded the second driest March-June period since 1895, 7.89 inches. Similar rain totals were measured during the history-making droughts of 1936 (7.65 in), 1988 (7.92 in), and 1934 (8.21 in). However, unlike those events, which were marked by a broad central continental high pressure center at the surface and aloft, and widespread dry conditions, the drought this year is narrowly focused and seems to be supported by anomalous troughs and ridges to each side of the core drought area (Figure 8, Climate Diagnostic Center). Instead of stationary surface high pressure forced by heating under a ridge, traveling high pressure centers plunging south from Canada are more commonly associated with the dry weather this summer.
Noteworthy drought impacts are beginning to occur in the Midwest. In the core drought region of Illinois, corn quality ratings are down to 37% poor to very poor, and soybeans are at 27% poor to very poor. Since silking season has begun for corn, any heat or moisture stress in July is reducing final yields. Both corn and soybeans appear to be tapping available deep soil moisture; crop conditions would be far worse now without abundant winter precipitation recharging the soil moisture before drought commenced. River flows are down significantly throughout the dry region (Figure 9, US Geological Survey). Fortunately, no serious drinking water shortages have developed at this time, although reservoirs are below normal levels in some locations.
Both Illinois and Missouri have activated their drought management systems. In Illinois, a Drought Response Task Force has met twice, and Farm Services Administration agents are documenting drought conditions in more than 89 counties. In Missouri, the governor has convened a Drought Assessment Committee, and a drought alert was declared in 23 counties.
Weather Systems During July 1-10
Only one weather system affected most of the Midwest during the first ten days of July. On the 4th of July, some fireworks displays and ball games were rained out by a cold front. While the precipitation was not continuous, several significant cells brought rain, winds and lightning to St. Louis, Chicago, and Detroit (Figure 10, University Corporation for Atmospheric Research - UCAR). This system did help to ameliorate the drought in Wisconsin (Figure 11a, NWS) and central Michigan (Figure 11b, NWS), and prevented further deterioration in Illinois southeast of St. Louis (Figure 11c, NWS). Unfortunately, not much fell in the core of the drought region in northern Illinois.
Several systems impacted the periphery of the Midwest. The remnants of tropical storm Cindy tracked across the Appalachians on July 6-8, but only eastern Kentucky received a substantial amount of rain. A low pressure system and cold front moved into Minnesota on the 8th, leading to heavy rains in northernmost Minnesota, and lighter rain to the south. Over most of the Midwest, though, this was a dry system. Finally, at the end of the 10th, some thunderstorms brought about rain in the southern Missouri drought area, but the rain was limited in areal coverage.
What Will Dennis Do?
Major hurricane Dennis slammed into the Gulf Coast on the last day of the period (Figure 12, College of DuPage). For several days, Dennis forecasts proved to be promising for bringing precipitation to the Midwest, and the projected storm path (Figure 13, Tropical Prediction Center) and precipitation forecast (Figure 14, Hydrometerological Prediction Center) on July 10 indicates considerable possibility for drought relief. The Climate Prediction Center issued a revised July to September drought outlook to reflect this possibility (Figure 15, CPC). As the period ended, precipitation from Dennis had just reached Kentucky (Figure 16, UCAR). It will be interesting to see how the third tropical system of the year to impact the Midwest (after Arelene and Cindy) behaves in the coming week, as models have it becoming nearly stationary in the southern Illinois/Indiana area. Some locations may go from drought to flood in a matter of days.