Split-flow pattern to return

After the first real fall-like air mass of the season, a split-flow pattern will return to the Mid-South and temperatures will once again warm above normal. Rain chance look slim until the weekend of 10/12, when the first big winter storm of the season may wallop the northern Rockies and northern Plains.

In the wake of a chilly air mass, the Mid-South will once again warm up into the 80s this week as a split flow sets up across the central United States. An upper-level trough seen clearly late Tuesday will fizzle into a poorly defined front by Thursday as it nears the Mississippi River. There may be a few widely scattered showers from this system later next week from this system before it falls apart.

The key to the next system is the vort max associated with a deepening trough along the British Columbia coast. By Saturday, the 00Z GFS shows this as a full-blow winter storm over the northern Rockies that will bring the first significant snows to Denver. There is still a lot of variation in the models regarding the strength and position of this storm, but there is no question this will be the dominant feature in the 8-14 day period, as evidenced by the CPC long-range forecasts. As this storm deepens and moves into the northern Plains, a powerful cold front will sweep across the southern Plains into the Mid-South next weekend, which should bring widespread heavy rain along with severe weather to the region for the first time in months. One thing to watch for in the coming days is how the models handle the energy coming into the northern Rockies.

If the models bring the energy into the Rockies as a single deep upper-level storm, there is a better chance of heavy rain and severe weather for the Mid-South, since a deeper storm will carve out a deeper trough in the Plains which will lead to better dynamics and moisture convergence over the Mid-South. Another possible solution is that the upper-level trough will stall out over the Rockies and allow weaker pieces of shortwave energy to come out of the Rockies into the Plains. These weaker vort maxes will not lead to a series of weaker fronts that will bring the chance of showers and thunderstorms to the Mid-South, but nothing that should be heavy, since the jet dynamics will remain too far west.

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