BALTIMORE, MARYLAND — A developing jet stream shift is setting up a renewed period of cold air intrusions across the Eastern and Midwestern United States from Sunday, January 11, through Saturday, January 18. Forecast guidance highlights Illinois, Indiana, Ohio, Pennsylvania, Maryland, and New York as core impact areas, with colder air returning in multiple waves and creating a favorable background pattern for potential winter weather as mid-January unfolds.
Jet Stream Configuration Allows Repeated Cold Air Pushes
Upper-level analysis shows the polar jet stream bending southward, opening the door for Arctic-origin air to spill back into the Midwest, Great Lakes, and Mid-Atlantic. The first surge arrives early in the period, with additional reinforcing shots of cold later in the week as the trough reloads.
This setup matters because repeated cold intrusions help lock in below-normal temperatures, increasing the odds that any approaching disturbance could tap into cold air already in place — a key ingredient for snow rather than rain.
Deep Trough Signals Active Winter Background Pattern
The focus of the current forecast is on 500mb height anomalies, which depict the large-scale atmospheric pattern rather than individual storms. Consistent signals point to a deep trough centered over the eastern half of the country, a classic winter configuration that supports snow, ice, and sustained cold across multiple states.
At this lead time, it is normal for one model run to show widespread snowfall while another shows little or none. Those differences reflect uncertainty in surface details, not a lack of winter potential. As timing and placement of shortwave energy become clearer, confidence in specific impacts will increase.
Cold Air Expected to Reach the Ohio Valley and Mid-Atlantic
One notable feature of this pattern is how far south the cold air is projected to extend. Forecasts indicate cold air pressing through the Ohio Valley and Mid-Atlantic, placing states like Ohio, Pennsylvania, Maryland, and Virginia on the colder side of the pattern…