Gators like to wear “jorts”. That’s a fancier term (so they say) for cut-off jeans. While it may be a fashion statement on a tailgate, a “cut-off” is not something meteorologists want to see on a weather map. This type of weather feature is a menace, often challenging to forecast because it’s removed (or cut off) from the jet stream, the river of air that typically steers it.
We have just the setup later this week, and the forecast challenges that go along with it. Determining the timing, track, and strength of a potential “cut off” low that develops Thursday and Friday will almost certainly prove impossible until midweek. Until then, our forecasters will need to reflect the lower than average confidence on rain chances until the situation becomes clearer AND remind our audience(s) to check back in for updates.
April and May are common months for these type of weather systems in the Southeast, largely due to the separation that occurs between the westerly winds that retreat north and the weaker subtropical trade winds (from the east) that control our weather in the summer months. This weaker wind pattern is what allows tropical weather systems and sea breezes to encroach.
Leading up to the Thu/Fri timeframe, a weakening cold front will be the driving force behind an increasing southerly flow, warmer temps and a little more humidity. There is reasonable model agreement on this feature (or at least a band of convection) approaching north Florida Tuesday evening. The Storm Prediction Center has areas north of I-10 in a marginal risk for severe weather. I’ll be leaving Tuesday’s forecast dry, but we will need to communicate the possibility of a spotty shower or thunderstorm surviving into our region by late evening. At the very least, we will be leaning toward good chance (30-40%) POPS for t-storms on Wednesday. Our temps and sky conditions should closely follow guidance, as I see no reason to stray.
Thereafter, the challenge awaits. We have two camps of thought showing up in reliable long term model data. The GFS (the recent less trustworthy of the two in the days 3-5 time frame) shows a dampening of shortwave energy and a tendency to develop the upper-level area of low pressure further to our east. This could, in turn, lead to less coverage and certainly lower intensity of any convective precip Thu or Fri. The European model, at least in its last two runs, has showed a tendency for more maturation of this weather feature nearby or just to our north and west. While experience tells me this solution is unlikely, given the upstream progression of another storm system over the Central US (e.g. a “kicker”), we certainly can’t ignore the idea that convection may be stronger and more widespread Thu-Fri.
Both solutions, and most ensembles, agree that our weekend will not be spoiled by this cut-off low. Surface high pressure is likely to nose in by Saturday, with weak cool (more so dry) air advection shutting down precip chances for the majority of the weekend. I will reflect this in my updated 6-Day.
Notable changes from prior shifts is to reflect highest pops on Thu, quantify them a bit more on Wed, then keep options open Thu-Fri. Temps remain largely unchanged, although I will raise overnight lows a bit later in the week when more humidity will be present.[promote-10day]