Subtle Weather Gives Way to Possible Pattern Shift

After a week of nice, and somewhat chilly weather following last week's massive storm system, which dropped literally multiple feet of snow across South Dakota, brought heavy rains to the Midwest and Ohio Valley, and tornadoes to Iowa, Nebraska and Missouri, we are now beginning to anticipate the next big pattern shift in our current weather pattern, which could have some foreboding signs for what awaits us this winter.

However, let's first begin with a brief analysis of the current weather.

Right now, we have a slowing and weakening cold front approaching the area from the Central Plains, the left-overs of a rapidly strengthening storm in the lee of the Rockies earlier this week. This cold front is driving an area of showers and thunderstorms from the Gulf coast, upwards into the middle Mississippi Valley. Very little shower and thunderstorm activity is occurring farther north in the Midwest, but a few showers and thunderstorms are expected to develop as afternoon instability increases and moisture transport increases in a very thin region ahead of the cold front. Even so, I would not expect much rain at all.

Current 500 MB map of the United States

After the cold front sweeps through, expect a gradual decrease in the mean temperature over the next three or four days. By mid-week, models are in general agreement that a series of split-wave troughs will creep into the country, and along with them, a few weak surface systems which would bring back the chance for showers and light rain. Even with these systems, I do not expect any kind of significantly warm air along with it. Temperatures will remain near normal in the mid-60's from about Monday through Wednesday. Behind these systems, temperatures will gradually drop, with highs by the end of the week only in the mid to upper 50's, a few degrees below average for this time of year.

After about 168 hours out, it is rather uncertain about what will happen. Models diverge here on the speed of a larger trough that will drop into the Midwest and eventually the East by the weekend. If the ECMWF is correct, the main trough will remain slower, with a series of smaller troughs bringing somewhat colder air. Finally, once the main trough begins to move, it will allow for the first wave of cold air of the season, with average temperatures likely 15-20 degrees below normal [meaning 40-45 here] by the middle of next week. As of right now, this is NOT set in stone, but remains a definite possibility.