Friday’s rain and clouds kept it cool; we’ve got more of that coming for Saturday and Sunday. It’s going to be very, very wet in Alabama and Southern Tennessee Saturday on the ‘warmer’ side of a developing storm system. Steady rain moves in Friday evening and sticks around ALL DAY Saturday: getting heavier and more widespread by the hour. There may be some brief periods of sleet and snow mixed with the rain over northwestern Alabama and Tennessee, but the ‘big’ snow misses us for now.
Clouds and rain keep temperatures flat-lined: hovering in the upper 30s and lower 40s tonight, Saturday, Saturday night and Sunday. In all, we'll get close to two (if not up to three) inches of rainfall through Sunday afternoon.
The temperature won’t be moving much, but this storm system will be on the move. Colder air builds in behind the main surface low Sunday potentially changing us from rain to a wintry mix or snow in some cases. Surface temperatures stay above freezing, and the light nature of the precipitation likely prevents any major, disruptive accumulations of snow or ice this weekend.
Could we get some legitimate snow? It’s not out of the question for a small accumulation of snow from Sunday night through Monday; however, with surface temperatures above 32ºF all weekend and into Monday, a major ‘disruptive’ snow is unlikely.
Why Sunday and Monday? Saturday looks like an almost all rain kind of day. It might start with flakes and sleet early then transition to a soaker through Saturday night. That rain develops because of something called warm air advection: a phrase we use to describe warmer air on the move. It’s actually one of the most efficient ways to get rain or snow because it creates the most ‘lift’ over the broadest area.
The warm air stops moving in and slightly colder air moves in behind it. Cold air ‘advection’ (similar idea, just cold air this time) isn’t quite as good at producing precipitation. In fact, it tends to reduce it because of the subsidence (sinking air) it creates. As light, leftover showers Sunday transition from rain to snow or a wintry mix, the precipitation will be so light that we don’t expect any significant accumulations.
A totally different system - an upper-air low - moves in overhead on Monday. Those features are often very good at creating ‘lift’ and producing fairly widespread precipitation. They also tend to create colder air around them, and that’s why we think there’s a good chance of snow showers throughout the day Monday. Some small accumulations (probably around 1” or less) are possible with the on-and-off snow showers beginning Monday morning going through early afternoon.