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Big cooldown for Friday; rain returns Sunday with strong storms possible Monday

/ April 10, 2020 at 12:07 AM

A dry cold front will swing through tonight, bringing temperatures down well below normal for mid-April for Friday and Saturday, dipping into the low 40s by Saturday morning. High pressure will bring pleasant weather into the area to kick off Easter weekend, but that high pressure system will slide offshore Saturday evening, giving way to a potent storm system for Sunday and Monday.

Severe weather episode across the South Sunday into Monday

Updated 8am Friday, April 10

Airmass RGB animation depicting an upper low over California and Nevada. This disturbance will open up and head eastward, triggering severe weather in the Southeast.

The stage appears to be set for a significant severe weather episode in the Southeast starting on Easter Sunday and lasting into Monday. This will be an impactful storm across a wide swath, with severe weather in the Southeast on Sunday spreading northeastward into New England on Monday and Tuesday. It’ll be snowing in the western Great Lakes states on the back side of the low, too.

As far as things go in the Lowcountry, our best risk of severe weather appears to arrive possibly early Monday. (Timing differences in the global models preclude me from being any more specific on this, unfortunately.)

Sunday

Easter Sunday looks to be a dangerous day for much of the Mid-South into the Southeast as confidence continues to increase in a major severe weather outbreak across LA, MS, and AL in particular, where the Storm Prediction Center has painted a very rare Day 3 Moderate Risk. Tornadoes, straight-line winds, and hail are all in play there. If you have family in that region, I urge you to ensure that they stay up to date with weather forecasts this weekend.

Here in the Lowcountry, a warm front looks to lift north of the area throughout the day, bringing a return to that warm and humid feeling to the air. We’ll already be feeling some of the upper-air effects from the storm system, which will allow showers to develop and move from southwest to northeast, following the warm front. Severe weather is not expected in the Lowcountry during the daylight hours.

The risk for severe weather will increase from west to east overnight Sunday into early Monday morning as the upper disturbance and associated surface low lift northeast into the Ohio Valley. Thunderstorms will congeal into a squall line that will march across the Carolinas beginning possibly as early as overnight Sunday; this squall line will have plenty of upper-air support with a 60-80-knot low-level jet being indicated in some of the guidance this evening. This suggests a pretty decent swath where wind damage will be possible. Again, the timing is still in question, with the GFS about six hours slower than the ECMWF on the last three runs.

Monday

If present timing bears out, the squall line and associated severe weather threat will sweep through the Lowcountry sometime Monday morning into early afternoon. All hazards will be on the table: hail, strong straight-line winds, and perhaps a tornado or two on the leading edge of the line. Expect around 1-1.5″ of rain in most locations by the time the event is over, with locally higher amounts. Beyond this, specifics are very difficult to get into at this stage.

Timing is important here. If the storm is slower, allowing more heating to develop ahead of the squall line, our severe weather risk could increase. Right now, the Storm Prediction Center has us at about at 15% probability of severe storms within 25 miles of a point. This seems rather reasonable this far out.

It’s also worth emphasizing that the scenario which looks to play out in the Deep South on Easter Sunday is not the scenario which is forecasted for the Lowcountry. The weather will certainly be disruptive, but the severe weather threat will almost certainly not be as widespread as it will be there as the upper disturbance and its associated surface low lift well to our north and west.

There’s still plenty of time to watch and see what the atmosphere actually does, and as such, changes and refinements to this forecast are a near-certainty. I know that the news is a scary thing right now on multiple levels. Unplugging is healthy and you should do this from time to time. However, I urge you that if nothing else, you keep an eye on the weather this weekend.

What you should do

More as it develops. For now, though, enjoy a cool couple days of hoodie weather!


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