As many other weather advance forecasters have been touting, snowfall will be be occurring over the upper midwest and northern Rockies, specifically Northern Minnesota and North Dakota tomorrow. Snow is already falling over parts of South Dakota and the Black Hills, and this snow will spread NE towards North Dakota and Minnesota. Snow totals will probably exceed 8 inches in many areas NE of Grand Forks, and the snow will be blowing and drifting at times, and according to the local NWS office out of Grand Forks, ND, sustained winds will be ranging from 20-30 MPH, with gusts potentially exceeding 40 MPH, which would make this, by definition not quite a blizzard, but very close to it. (A blizzard is defined as a snowstorm with with winds of at least 35 MPH, and visibility less than a quarter mile for a period of at least 3 hours. Many of the impacts felt over Northwest MN and NE North Dakota will be blizzard-like, and it certainly will make travel very hazardous to nearly impossible at times.
Along with this weather system, there is another shortwave area of low pressure that will develop within this main trough of low pressure near the northern Rockies in a few days, and this will combine with energy near the tail end of a cold front that will be associated with this low pressure system that will produce snow over the upper midwest tomorrow, and will lead to the formation of a new area of low pressure. This new area of low pressure will move south of the I-70 corridor and off the New England coast in several days, and with cold air that will be coming into place from the low pressure that’s now over Montana, it is possible that some wintry precipitation may fall into the Pennsylvania Appalachians and areas northeastward into Quebec. However, the amount of cold air that will be available with this system is still in question, and it appears that 850 millibar values will be ranging from 30-36 degrees, which will not be too supportive of snow in the lower levels, but in elevations exceeding 1500-2000 feet, the air will be colder and snow may be able to fall and accumulate in some areas that receive more intense rates of precipitation. Regardless, much colder air will settle into the region, and widespread frosts and freezes will occur over the Northeast, Appalachians, and areas of the Great Lakes behind this low pressure system, and will put an end to the growing season over these areas.
The pattern that has helped to produce these early season chances for winter weather has been very favorable for large troughs over the eastern and central US, and is a pattern that is classic for large cold shots into the the eastern and central US, with a large ridge extending from the Gulf of Alaska and into NW Canada. Such large high latitude high pressure areas force areas of low pressure and troughiness over the US, especially east of the Rockies, and near the Hudson Bay. In this instance, this large area of general low pressure focused over the Hudson Bay and eastern US has forced blocking high pressure upstream just south of Greenland and Iceland, and when you have higher than normal pressures near Iceland and Greenland, you have a -NAO, and this -NAO has only amplified the effects of this cold air mass east of the Rockies.
This pattern of course can be drawn back to the Western Pacific landfall typhoon theory that was proposed by Joe Bastardi, and has been something I have taken and ran with the past several days, because now with another large trough over the eastern US, one only has to look to the Western Pacific to see that we have yet another typhoon currently near Japan. When you have a landfalling typhoon over the west Pacific, it strengthens the trough over eastern Asia, strengthens ridging over extreme eastern Russia, which in turn amplifies a low pressure area near the Bearing Sea, that forces higher pressures over the Gulf of Alaska and western North America. When you have higher than normal pressures over western North America, it forces lower pressures and a trough to dig in over the eastern US, and the troughing over the eastern US helps to enhance a colder than normal airmass, and increases the chances for winter weather.
In the longer ranges, it appears that yet another typhoon will form over the western Pacific and head towards Japan in several days, and that means yet another trough over low pressure will dig over the eastern US in about a week or so, and that trough will keep the weather unsettled and rather chilly east of the Rockies. However, there are signs that this pattern may finally break down once and for all thanks to the MJO finally starting to move out of the “igloo” and it may continue to move out of octants 5 and 6 towards Mid-October. If this does occur then a major pattern flip would unfold over the Northern Hemisphere, because as I have said in previous posts, with the MJO moving out of the western Pacific, that will raise the pressures over the Western Pacific and begin to focus low pressures over the Gulf of Alaska, and with low pressure near that area it bundles the cold air way up to the north, and it pumps a ridge to its southeast over the US and southern Canada, thus leading to warmer weather.
With this pattern change, we now have to be more concerned about a potential comeback with the hurricane season, because with these large cold air masses and with high pressure showing up over the US in the longer ranges, this means that with higher pressures over the United States it forces convergence and rising air over the SW Atlantic, Caribbean, and Gulf of Mexico, which would be favorable for tropical development near the US just like in the beginning of the hurricane season. With systems developing much closer to home, it also increases the chances for a landfall simply due to the fact that storms will developing much closer to land, and with wind shear and dry air increasing, and with the african wave train beginning to subside, conditions will continue to deteriorate over the deep tropical Atlantic, as they usually do in October, and this will help to focus tropical activity farther west.