textproduct: Charleston

WHAT HAS CHANGED

All sections updated.

KEY MESSAGES

- 1) Isolated to scattered showers and thunderstorms will be possible today and Monday. A few storms could be strong to severe.

- 2) Increasing rain chances mid to late week with the potential for locally heavy rainfall.

DISCUSSION

KEY MESSAGE 1: Isolated to scattered showers and thunderstorms will be possible Today and Monday. A few storms could be strong to severe.

Well after a rather active afternoon with strong storms and flash flooding, rain chances do look to decrease the next two days as the upper trough shifts just a bit east. With the main trough axis just east of the area; drier westerly to northwesterly flow should begin to work into the area tonight into tomorrow. This drier air in the mid-levels should help limit coverage of showers and thunderstorms during the afternoon. However, less storms does not always mean less issues. While PWAT values will be lower in the 1.7 to 1.8 inch range tomorrow, there should still be enough moisture in the low levels to support some isolated to scattered storms to develop along the afternoon seabreeze. With temperatures climbing into the low 90s across SC and mid 90s across GA and dewpoints behind the seabreeze in the 70s, instability will be quite high in the 2,000 to 2500 range behind the seabreeze. What storms that do form and cluster up to survive the drier air could get rather strong. On-top of the instability, the aforementioned drier air a loft could assist in downdraft production leading to rather efficient downdrafts. DCAPE values look to range in the 1200-1500 J/kg range behind the seabreeze, which is rather potent. With 0-6km bulk wind difference around 20-25 knots, some multicellular organization could be possible as storms slowly move towards the coast. Damaging winds will be the primary threat with the strongest storms and as a result a marginal risk (level 1 of 5) for severe weather is in effect for today for most of the area. This potential is also noted in some of the machine learning guidance that is hinting at some low end threat for damaging winds.

Monday: Monday looks to be a rinse and repeat of Sunday with rather similar conditions across the area. The only main difference between Monday and Sunday will be slightly richer moisture as an upper shortwave looks to pivot through the area. This shortwave will help bring PWATs back into the 1.8 to 1.9 inch range which may support increased coverage across the area and more clusters rather than isolated cells. Given the better PWATS but drier air still lingering around some wet microburst potential seems possible and would not be surprised if Monday gets a bit rowdy in the late afternoon.

While overall concern the next two days for heavy rainfall is lower given the lower moisture content, storms will still be capable of heavy rainfall if they sit long enough over an area. Given several locations are rather saturated after yesterdays heavy rainfall and flooding, we will have to keep an eye on where storms develop for any potential flooding issues.

KEY MESSAGE 2: Increasing rain chances mid to late week with the potential for locally heavy rainfall.

By the mid part of the week, the upper trough will begin to flatten out as upper ridging over the Atlantic begins to strengthen. A series of embedded shortwaves are expected to pivot through the upper trough Wednesday through Friday in very much a repeat of the last couple of days. A subtle surface boundary will slowly make its way into the area Wednesday evening into Thursday. With deep southwesterly flow a loft, PWATS are expected to climb back into the 1.9 to 2 inch range. Between the seabreeze each afternoon, the slow moving boundary and any remnant boundaries for each days storms, there should be plenty of low level focus for scattered to widespread thunderstorms to develop each afternoon. With PWATs approaching 2 inches and slow moving storm motions, heavy rainfall could start to become an issue for some areas as rainfall totals could quickly pile up. The biggest concerns likely come Thursday and Friday as the surface boundary encroaches on the coast where it will interact each afternoon with the seabreeze rather close to the flood prone metro areas of Savannah and Charleston. We will certainly have to keep an eye on this as we go throughout the week.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

VFR conditions prevail into the afternoon with isolated to scattered showers and thunderstorms developing during the late afternoon. Storm chances look best along the coast and as a result, PROB30 groups have been added to CHS/JZI/SAV. Winds will remain light out of the southwest turning slightly more southerly during the afternoon with the passage of the seabreeze. Storms should subside by the early evening with clearing skies by midnight.

Extended Aviation Outlook: Prevailing VFR with isolated to scattered showers and thunderstorms each afternoon potentially bringing temporary restrictions to aviation.

MARINE

Today through Friday: South to southwest winds will persist through the period. Conditions will remain below Small Craft Advisory levels, with winds averaging 15 knots or less and seas 2 to 3 feet. Any showers or thunderstorms that move over the waters have the potential to bring higher wind gusts and frequent lightning.

CLIMATE

Record High Minimum Temperatures:

August 24: KCHS: 76/2010 KCXM: 80/1975

August 25: KCHS: 77/1982

August 28: KCHS: 77/2020

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...None.