The weather through the first 27 days of November has been quite variable but normal overall (Temp = -0.01; Precip. = 0.00 relative to normal). The pattern over the next two weeks should remain active with a series of storms. The first of the storms is shaping up and should begin affecting the Mid-South Saturday night.
First, keep in mind that normals across south-central KY for early December are low 50s/low 30s, so storms this time of year are most likely to be rain rather than snow. Second, the SE ridge that has kept much of the Southeast in drought for the past 12 months is still a force to be reckoned with. Third, the mean La Nina storm track has a ridge in the Southwest and a trough in the northern Rockies.
Starting with Friday afternoon, one can see a strong sub-tropical fetch of moisture into the Southwestern U.S. that will bring needed rainfall to the desert. This SW storm is juxtaposed with a strong zonal baroclinic zone that extends from the central Plains into the Mid-Atlantic states (Roughly along I-70). At this point the SE ridge is flat.
As the upper-level trough interacts with the SW low on Saturday, the western trough will deepen and amplify the upstream SE ridge. Strong SW winds will beat back the shallow cold air and allow rain showers to overspread most of the Ohio Valley Saturday night into Sunday. Because the strong jet (>150 kts) is located on the east side of the trough axis, the trough will actually weaken through the weekend which will cause the primary low to weaken towards the Great Lakes.
Much like the last storm, a secondary low will develop along the frontal boundary Sunday morning and rapidly intensify due to the favorable location of the jet streak. This will be the time period where severe weather may be possible, since the right rear quadrant of the jet streak will be located over AR and western TN and will move across western KY. By Sunday night, cold air will sweep across the Midwest behind the cold front which will change over any lingering rain showers to snow showers.
Monday will be a cold and windy day with temperatures in the 30s and winds chills in the teens. Snow showers and at least some flurries are possible in the Mid-South with the best chance for snow in the Bluegrass. The core of the cold air will be primarily to our NE.
Some models have a weaker SE ridge with the surface low moving across the Ohio Valley such that the secondary low forms off the Atlantic coast. I disagree with this solution because of the lack of a negative NAO.
Storm #1 summary: Rain showers and possibly thunderstorms will be likely over the Mid-South Saturday night through Sunday evening. Rain amounts over 1″ are likely with 2″ possible in some areas. Rain may end as snow across the northern portions of the Mid-South. Monday will be blustery and very cold with flurries possible.
A deep low over the eastern Pacific early next week will provide the energy for the next storm late next week. A third storm should end this active pattern sometime around the 10th-15th of December as teleconnections hint at a more zonal, mild pattern with weaker storms for mid-month.
