It would be almost odd if all of this warm weather did not bring with at least one chance for severe thunderstorms and it appears that chance will be Wednesday evening. A boundary between seasonably cool air to the north and the mild air we have been experiencing is going to meander around the Ohio Valley during the next five to six days and produce multiple chances for rain.
Our first interaction with this front was last night as showers and even a few rumbles of thunder moved through. The frontal zone essentially washed out this afternoon and temperatures climbed back to near 60 degrees. Strengthening upper level winds and an area of low pressure will re-tighten this boundary tonight. Southerly winds will cause steady or even increasing temperatures through the 50s. Widely scattered showers will become likely although not as heavy as last night.
The forecast for Wednesday is still relatively uncertain with regards to details on any rain/storm development particularly in the latter part of the day. There is a good signal for a mostly dry period from mid-morning through early afternoon. During this time a few peeks of sun are possible and temperatures will rise into the upper 60s making it feel very mild for any last minute shoppers.
A round of showers and a few rumbles of thunder will be possible during the middle of the afternoon in the form of a weakening batch of rain moving in from the west. It will be windy all day with southerly gusts of 20-35 mph likely.
The risk for severe weather will be during the evening hours Wednesday from 6 p.m. though 1 a.m. Plenty of wind shear should be aligned with an adequate amount of instability to produce severe weather *if* organized thunderstorm activity is present. That is the big question though. The lacking ingredient will be strong upper and lower level forcing for thunderstorm development. It will not be nonexistent, but it certainly is not taking on the look one would expect for a severe weather outbreak.
For that reason, the severe threat remains marginal and relatively uncertain tomorrow night for us locally. Any storms that develop tomorrow evening will run the risk of producing damaging winds or even an isolated tornado due to very large amounts of wind shear in the atmosphere. The highest threat will remain south and west of Cincinnati where stronger support from the jet stream (forcing for storm development) and stronger instability will exist. An outbreak of severe weather is actually quite likely across Tennessee and central Kentucky tomorrow.
So keep an eye on the weather Wednesday evening as a few of those strong storms may sneak into the Tri-State, but the threat does appear just isolated for now.
The frontal boundary will move through very early Thursday morning but it will be weakening and actually will somewhat wash out again like it did today. This will mean a lingering very isolated shower remains possible mainly south of Cincinnati. Temperatures will be a little cooler but still very mild around 60 degrees.
We will cool into the 40s for Christmas morning before seeing a rebound into the 50s for the daytime hours. A developing southerly flow once again will funnel moisture back in our direction. Showers are expected to develop mainly south of Cincinnati during the day but move into the Tri-State Christmas (Friday) night.
Rain will be likely Friday night and through much of Saturday. As the boundary pushes north, the rain will move north by Saturday evening. Temperatures will surge again into the middle and upper 60s.
The boundary will start to sag south on Sunday bringing more rain. Temperatures will start in the 60 but cool into the 40s by Sunday night as the front moves south.
Another area of low pressure is currently forecast to pull the boundary north again Monday bringing more rain and another swing in temperatures.
The good news is that the wet pattern should relax going into next week. Temperatures are also expected to cool off. In fact, the longer term forecast over the next few weeks is indicating a pattern change across North America. We may actually head for “average” conditions rather than significantly above average. This would mean much cooler weather relative to much of December 2015 as we head into January 2016.