A long-awaited shift in weather patterns is beginning to take place around the world. Drought in Europe, portions of western Russia and Canada has been slightly “eased” recently, but drought remains in each of these areas. The changes noted so far have been welcome, but drought remains in each of these areas as well as in Australia.

In North America, cold air has been building into Canada’s Prairies, causing earlier-than-usual bouts of accumulative snow and cold rain. The cold in Canada was expected to intensify during the first half of October, and as it does it will run into the very warm and moist airmass that has been dominating the central United States. The clash in these two air masses will be dramatic, changing an already moist environment in the U.S. Corn Belt to one of extreme wetness.

The U.S. situation is unique and will likely bring several atmospheric ingredients together to produce copious amounts of rain, flooding, significant snowfall and some severe thunderstorms producing hail, damaging wind and possible tornadoes. The first ingredient to this explosive environment is abundant soil moisture, an influx of tropical moisture from the Gulf of Mexico and the eastern Pacific.

Soil moisture at the end of September was adequate to surplus in many areas from the southeastern Great Plains, Delta and lower and eastern portions of the Midwest into the northeastern states. A portion of the northern Midwest also has been abundantly moist. Most of these wetter biased areas will experience rising temperatures late in the first week of October and into the second week of the month. The heat will raise temperatures above average, drawing moisture out of the soil and into the atmosphere, resulting in warm and humid conditions.

The heat in the United States will become most anomalous in the south-central states northeast through the lower and eastern Midwest and Delta to the middle and lower Atlantic Coast states. The driving force for the warmth will be a ridge of high pressure over the southeastern states that will prevail early in October. The high pressure system will not only bring heat to the region, but it will draw tropical and subtropical moisture northward from Mexico, the Pacific Ocean and the Gulf of Mexico northward into the central and eastern United States.

Tropical Storm Rosa moved inland to northwestern Mexico in the first couple of days this month and that moisture was drawn northeast across the central and eastern U.S. by the high pressure ridge in the southeastern states. Rosa’s moisture further saturated the atmosphere and kept air temperatures above normal.

In the meantime, Canada was experiencing unusually cold temperatures in late September and early October. The cold was responsible for shutting down some harvest progress because of some snow that ended up falling across unharvested areas. Reinforcing shots of cold air moving from the arctic into Canada’s Prairies will be too great to be contained in the Prairies and will begin streaming south into the northcentral United States.

At the same time cold air is pushing southward from Canada and warm, moist, air is present over the central and eastern United States, a new trough of low pressure carrying its own moisture from the Pacific Ocean will be moving into the western United States. Cold air from Canada will meet up with the trough of low pressure moving into the western United States late in the first week of October, causing the trough to strengthen. As it fills with Canada’s cold air a series of storm systems will move across the United States producing repetitive rain events ahead of the deepening trough moving into the western states. The series of storm systems will end up occurring along a nearly stationary frontal system that will evolve along the leading edge of the western U.S. trough of low pressure. Each of the small storms will take some of the warm and moist conditions from the eastern United States and mix it with the cold and drier air pooling in the central and western states to create rain and periodic strong thunderstorms.

The super saturated condition of the central and eastern U.S. atmosphere will allow copious amounts of rain to fall as the colder air from Canada is dragged to the east across the United States and southeastern Canada. Strong to severe thunderstorms and rainfall of multiple inches will result from the southern Plains into the western Corn Belt late in the first week of October and on into the second week of the month. Rain totals of 3 to 6 inches will be widespread with a few amounts of 6 to 10 inches. The new rain over areas that already are saturated or nearly saturated will result in some significant runoff raising the potential for flooding.

In the meantime, some of the cold from Canada air will get far enough south to generate excessive amounts of snow in a part of the northern U.S. Plains and upper Midwest. The environment will be threatening to some livestock and unharvested crops in the northern Plains, Canada’s southeastern Prairies and upper Midwest. Some of these areas will end up with blizzard or near blizzard conditions and snowfall that may range from 6 to more than 12 inches.

The wet bias in the United States is not likely to prevail through the entire month of October. The cold air eventually will move across the entire North American continent and as it does it likely will dry out the air — at least for a while. Canada’s Prairies and the western United States should dry out first. The eastern United States will dry down a little later in the month, possibly after mid-month. The returning dry air, however, will help to support the return of better harvest conditions beginning in western Canada’s Prairies where a ridge of high pressure should evolve for a while sending temperatures above average during the second half of the month.

Needless to say, harvest progress in Canada, the U.S. Plains and western Corn Belt will not advance well in the next 10 days, but conditions will be good for a while in the Delta and southeastern states.

Some of the expected significant precipitation also will impact hard red winter wheat production areas where flooding rainfall could lead to some need for replanting. Moisture is needed most in Colorado, western Kansas and a few counties in the northwestern Texas Panhandle, but the situation was not serious. The situation in the northern Plains and southern Canada’s Prairies, however, could be more threatening to livestock and unharvested summer crops where excessive snowfall might occur along with some cold rain and windy conditions.