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American monsoon creates a stir. - 08.21.05
Strange climate patterns result as the American monsoon fires up in the Southwest.
An unusual climate feature of the American continent is the American monsoon that rises up in the southwest late every summer. In severe years like this one a high- pressure area over the Gulf of Mexico is far enough to the west that the clockwise rotation of the winds around the high feeds moisture into the Southwest. This is illustrated in figure 1.
Fig.1
The placement of the high over the Gulf States has also been problematic in the ongoing drought pattern that has hit the Midwest this summer. In the chart, the 45�° eclipse jet curve is placed along the east coast of Florida and the 72�° jet curve moves in a southeasterly direction from the PNW to the southern High Plains. High-pressure values on the eclipse points over the eastern Atlantic, translating to high-pressures on these two jet curves, have dominated the continental regimes this season. The lunar node is aspecting these eastern Atlantic points and has kept the high-pressure values consistently in play for most of the summer. High-pressure areas have oscillated east and west between the 45�° and 72�° jet curves all summer. In general a high has been somewhere between the lines most of the season. Over time, the high has grown to cover a large portion of the Gulf Coast.
As a result the monsoon is drawing strong currents of moisture off of the western Gulf of Mexico, into the wake of the clockwise circulation around the high. This has several outcomes. One being that there is a flood watch in western Texas, New Mexico and Colorado as a result of the very strong monsoon. The other outcome is that the moisture that rises up into the Colorado plateau has to go somewhere after it rains in the southwest. The prevailing pattern is for moisture to run up the eastern windward scarp of the central Rockies. The moisture then forms clouds due to the air lifting up and over the mountains. The moisture filled clouds drift to the east and gradually settle into the Plains bringing abundant rains there. Kansas City, for example has had four times the average amount of rain this August. This flow pattern is illustrated in figure 2.
Fig.2
Unfortunately, another outcome of the placement of the high so far to the west, is that it prevents the moisture from the Gulf of Mexico from running up into the Corn Belt. The high blocks the Midwest while the flow moves up into the Rockies. This has caused a drought pattern to prevail in eastern Iowa, Illinois and Indiana. Recent rains have relieved some of the drought but Chicago has had only an inch or so of rain in the past two months. It will take more than a heavy storm to relieve that deficit. The corn crop this year is threatening to be far below last years bumper harvest. However, with large reserves of corn in farmer's bins from last year, the commodities market has turned a deaf ear to the drought conditions. Recent rains in the three I's area (Iowa, Illinois and Indiana) seem to have saved the soybean crop that is just now filling pods. This extremely dry area was sandwiched in between the super abundant rains of Kansas to the south (from the monsoon) and the very beneficial rains in the Dakotas and Minnesota. These northern rains resulted from a zonal flow pattern from the northwest meeting the remnants of the southerly flow from the monsoon. It was not cool enough for the fronts to move all the way into the three I's area. This was because the blocking high didn't push the jet up into Canada in the northern Mountain States. It stayed too far to the south. The slack space between the two jet curves is an image of the roller coaster choppy weather patterns this season. The commodities market has been bounding sideways for good portions of the early summer and now it is in a tailspin since June as the fronts keep coming in but they only bring moisture to the northern and southern Corn Belt while the "donut" of the three I's is knee deep in dust. All told this has been a strange year weather wise for the Midwest, and we can't even blame it on El Nino or La Nina.