Pleasant weekend in the books, unsettled holiday week ahead

An unseasonably strong cold front dove through the Mid-South early Saturday morning, bringing with it drier and cooler air just in time for the weekend. With highs in the 80s and dewpoints in the low to mid 60s, the sunshine has resulted in pleasant days, rather than nature's sauna. Surface high pressure that is overhead this weekend will shift east though, meaning we're back in southerly flow by Monday and humidity levels will begin to increase.

Sunday mid-day surface analysis shows our recent cold front down near the Gulf coast while high pressure dominates the eastern U.S., bringing pleasant conditions.

Well above the surface, the eastern U.S. is dominated by a large trough of low pressure, which means the potential for unsettled weather. That pattern includes the Mid-South as cold fronts move by to our north, with the potential for thunderstorm complexes generated by these fronts diving south. These complexes are called MCS's (mesoscale convective systems) and we've talked about them before. They can be unpredictable both in the long term and the short term and they can bring damaging wind and torrential rain, as well as a lot of lightning.

In the Mid-South, they are most common in "northwest flow," which means the wind at the mid levels that drives storm complexes is blowing from the northwest, and that's the pattern we'll be in to some degree most of this week and right into next weekend.

The pattern at the mid levels this week will be dominated by northwest flow over the Mississippi Valley, as shown in this 500mb (18,000') forecast for Wednesday evening from the GFS model. A huge dome of high pressure over the western U.S. and general trough of low pressure over the eastern U.S. results in northwest wind over the Mid-South, which is a conducing pattern to unsettled weather and potential MCS activity from the Mid-South into the Ohio Valley.

As far as the forecast is concerned, though there is a very slight chance of a thunderstorm tomorrow, chances increase a bit Tuesday, then scattered thunderstorms are in the forecast for the remainder of the week. However, the main factor in our daily rain chances will be any MCS's that form and move into the area. Rain chances will be likely when one moves through, then probably dry for the rest of the day or night behind one as the atmosphere "re-energizes."

At this point we don't have our eyes on any one particular time period when one could affect the metro, so rain chances are fairly broad-brush. That's not good if you're planning to attend (or organize) a holiday fireworks display, so the best advice is check the MWN Forecast multiple times throughout the week as the forecast could change drastically from one day to the next as we get a better handle on timing of individual storm systems. For now, here's what we're expecting this week:

Erik Proseus
MWN Meteorologist

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