Sunday may represent our first good shot at thunderstorms so far in 2019. However, a few of those could be on the strong side with gusty winds, especially for those of you who are a little further inland (think Berkeley and Dorchester counties). Let’s dig in…
Dense fog potential
There is the potential for dense fog to develop overnight into early Sunday morning. Be alert to the potential for visibility to drop below a quarter mile, especially near the coast and rivers where fog may be thickest.
Fog won’t last terribly long; it should dissipate by 10am as temperatures warm quickly into the mid-60s.
Temperatures: One more day of 70s
Another warm day is on tap for Sunday, but cloud cover should keep temperatures a little lower than what we saw today (77 in North Charleston!). Expect temperatures to run well above normal once again, peaking in the mid-70s in the early afternoon.
This will be the last day of 70s for a few days. The first cold front swings through early Monday, keeping temperatures down to the low 60s. It will be followed up by a reinforcing shot of cold air on Tuesday which may plunge temperatures below freezing in many spots away from the coast for Wednesday and Thursday mornings. (More on this cold snap in a future post.)
Severe weather risk: Low, but not zero
Isolated to scattered showers and thunderstorms look to begin to develop as early as 11am across inland locations as temperatures warm into the low 70s and convective temperatures are reached. As it stands right now, the better dynamics arrive in the area later in the day, so anything that develops ahead of the main line may play more of a spoiler role than anything else by tapping available instability and keeping temperatures low.
The main weather concern then turns to a thunderstorm complex that will be approaching the Lowcountry from the west in the late afternoon and evening hours. This system will be capable of producing strong tornadoes in southern Alabama and southwest Georgia tomorrow as its parent low pressure tracks northeast.
As low pressure tracks away from the cluster, the storms are expected to take on more of a squall line configuration. This line will bring the potential for damaging wind gusts into the Lowcountry, particularly for inland portions of Berkeley and Dorchester counties (especially along and west of 17-A). Small hail cannot be totally ruled out, either, and there is a small (but non-zero) chance for a tornado.
Timing for severe weather, based on latest model data, appears to be in the 4PM to midnight window.
The Storm Prediction Center currently outlines much of the Charleston Tri-County area in a Marginal Risk area for severe weather. This indicates a potential for a more sporadic severe weather threat — not a widespread outbreak by any stretch.
For the Lowcountry, this will take on a “high shear/low CAPE” setup. This essentially means that there is significant wind shear aloft that may overcome a relative lack of instability. Dynamically, the system is pretty impressive, packing a 50-55 knot low-level jet that will overspread the area as the line arrives. Thunderstorms could act to bring this jet closer to the surface in wind gusts, which is why damaging straight-line winds appear to be the main concern at this point.
There are going to be several limiting factors for tomorrow’s severe threat:
- Cloud cover. Cloud cover will help to keep temperatures in check, though at least some of this loss of insolation will still be supplanted with plentiful warm air advection.
- Timing of the line. With the line of storms arriving later in the day, past peak heating, available instability will increasingly become limited, which will make mixing down gusts from the 50-55 knot low-level jet increasingly difficult.
- The marine layer. Stable marine air (thanks to water temperatures around 60°) will cut the line of thunderstorms off from the fuel it will need to maintain its intensity.
- The line’s parent low pressure track. Surface low pressure will move northeast through the Upstate into central NC as the afternoon progresses. As the low pulls away to the north, low-level wind shear which may help induce storm rotation and increase the risk of severe weather will diminish. (There will still be plenty of wind shear available for maintaining thunderstorm updrafts, though.)
As always, changes in the track or an additional amount of sunshine could cause changes in the forecast. Best advice is to stay weather-aware tomorrow. Be sure you can receive warnings in multiple ways; smartphones and NOAA Weather Radio are good, while social media as a sole source is probably not wise.
We stand to get some beneficial rainfall from this system as it swings through the area tomorrow into early Monday. Rain amounts are expected to top out around 1/2-1″ with locally heavier amounts possible. The Drought Monitor has pretty much all of the Lowcountry and Grand Strand outlined as “Abnormally Dry.” This bears out as we are coming off the fifth-driest February on record, with a year-to-date deficit of 4.54″ at the airport as of the preliminary March 2nd climate report.
- Fog is possible in the morning. It may be dense at times.
- A few showers are possible at any time, but that should not cause you to cancel any daytime outdoor plans. The window for more widespread rainfall opens after 3-4 PM.
- The risk for thunderstorms increases by late afternoon into the evening hours.
- The line will be weakening as it approaches the coast. Thus, the greatest risk for severe weather is west of Charleston. Damaging wind gusts cannot be ruled out in portions of Dorchester and Berkeley counties, especially along and west of 17-A. Hail is a possibility, and a tornado cannot be totally ruled out (but looks very unlikely).
I’ll have updates here and on Twitter tomorrow as conditions warrant.
Updated March 2, 2019 at 11:45 PM with additional discussion based on new model data and NWS briefings.