Over the River and Through The Rain (and Storms)
You only need to be the proud owner of a window to know that ugly weather has setlled into the Palmetto State today. For some, it will get uglier later today and this evening. The cause of the rain is a storm system currently crossing the eastern part of the nation. I drew up a weather map to help explain.
A surface weather map hand-drawn by your humble author based onthe surface pressure and wind analysis at 9:32 a.m. EST from theStorm Prediction Center's Mesoscale Analysis website.
The storm over Indiana is pulling a warm front northward across South Carolina today. As is common in this setup, we have chilly air entrenched over much of the state due to cold air damming. In the 'wedge' of cold air, it's only in the 40s and 50s, but outside of that wedge, it's warm (as I write, it's 46° in Greer but 71° in Charleston); there isn't much middle ground. Warm and moist air streaming from the south is riding over this chilly air, enhancing the rainfall over the Upstate and adjacent areas, though much of the state is seeing rain.
As the day wears on, the wedge of cold will steadily erode, allowing the warm and humid air to infiltrate most of the state. This will result in an environment favorable for the cold front trailing the storm to produce a line of thunderstorms as it crosses our state late today and tonight. The setup will be one where some thunderstorms could cause locally damaging wind and even isolated brief tornadoes. As a result, the Storm Prediction Center (SPC) has covered most of our state with a level 1 of 5 risk area for severe thunderstorms for the rest of today and tonight.
The current Day 1 Severe Weather Outlook graphic from SPC with South Carolina highlighted.
It looks as though thunderstorms will reach the far northwest corner of the state around 5 p.m. and march steadily southeastward tonight. Our primary concern area for severe storms will be in the Upstate, Catawba Area, the northern Midlands and northern Central Savannah River Area, where the best combination of warmth, humidity, and wind shear will occur; however, most of the state needs to be on the lookout.
So, if you're traveling to grandmother's house over the next 24 hours or if you're staying home but in the risk area, stay vigilant for threatening weather. Obviously, wet roads require reduced speed, but you'll have to be even more cautious during downpours and thunderstorms. The risk for severe weather means you'll want to keep track of which county you're in while driving so you'll know if you're in a warning when one is issued. Your phone's emergency alerts and favorite weather app can help if they're properly configured. In addition to the rain and storms, be ready to deal with annoying crosswinds; there will be a gusty breeze this afternoon and tonight, even outside of thunderstorms.
Speaking of the wind, if you're traveling today across far North Georgia, Western North Carolina, and into Tennessee, locally high winds will be a concern for those traveling through the Appalachians. The highest spots and north-to-south and northwest-to-southeast oriented mountain gaps are the primary risk areas because the wind will be from the south to southeast. These winds should diminish toward nightfall.
The front's forward progress will slow after midnight as it reaches our Coastal Plain, causing rain and thunderstorms to linger into Wednesday in that area. It may be the early afternoon before the frontal rains finally push offshore. Meanwhile, an upper-level disturbance moving through the region will trigger a scattering of mainly afternoon showers on Wednesday across areas north of I-20.
Cooler air will push in later Wednesday as the cold front currently over the Upper Midwest reaches South Carolina. So, temperatures will run below average through the holiday weekend, though it won't be as chilly as expected back on Friday. Highs across South Carolina will generally range from the middle 50s in the Upstate to the middle 60s in the coastal Lowcountry each day, with lows generally in the 30s and lower 40s, mostly above freezing.
Thanksgiving Day looks dry with some sunshine, but a storm system passing by to our south may bring light rain to much of the state on Black Friday. Saturday looks mainly dry, with any showers confined to our coast, though sunshine may be limited. There is another chance for light rain on Sunday. Early next week looks tranquil then we get another chance for rain from a storm taking an "if this happens in January it might snow" sort of track through the region Thursday or Friday.
I covered the long-range here because this will be your Weather Alert for the week as I'll be traveling Friday, and no high-impact weather will occur past Wednesday through at least Tuesday. The storm later next week could be intriguing. More on that early next week, if necessary. If nothing else, it brings a good chance for another drought-denting rain to the northern part of the state.
The hurricane season isn't over, but it's unlikely we have any more effects from tropical systems in South Carolina this year. However, there are a couple of items of interest for possible development today. One is a little swirl over the Caribbean Sea, and the other is a developing storm over the North Atlantic southeast of Bermuda.
This loop of true color visible satellite images gives a wide-angle view of most of the Atlantic Basin; our two areas of interest are highlighted on the first frame.
The little swirl over the Caribbean probably will be nothing to worry about, but there is a closed circulation and a bit of shower and thunderstorm activity in the area. The National Hurricane Center gives this area only a 10 percent chance of becoming a tropical cyclone. The other area southeast of Bermuda is a developing extratropical storm. It is forming over waters warm enough to sustain a tropical cyclone, so there is a chance for it to make the transition from extratropical to tropical or subtropical as it churns up the eastern North Atlantic in the coming days. NHC gives it a 60 percent chance to become a tropical or subtropical cyclone, but it only poses a threat to the Azores.
We're probably done with tropical cyclones for the season here in South Carolina, but it's always best to keep those disaster kits fully stocked. We're at risk for non-tropical disasters, too. For preparation tips, SCEMD has you covered at hurricane.sc and earthquake.sc.