textproduct: Charleston

WHAT HAS CHANGED

All sections updated.

KEY MESSAGES

- 1) Locally heavy rainfall is possible today as a stalled front remains in the vicinity of the South Carolina Lowcountry.

- 2) Hot and humid conditions return to the South Carolina Lowcountry and Southeast Georgia during the middle of this week.

DISCUSSION

KEY MESSAGE 1: Locally heavy rainfall is possible today as a stalled front remains in the vicinity of the South Carolina Lowcountry. The stationary front that has been lingering in the vicinity of the forecast area the last couple of days has shifted slightly, taking on a more northwest to southeast orientation. With the region still located along the southern periphery of a mid-level trough, this frontal orientation is in alignment with the mean flow. As of the 03Z WPC Surface Analysis, the front is located in the vicinity of Myrtle Beach. Through the remainder of the overnight hours and into this morning the front is expected to sag southward towards the Charleston Tri-County. With the front oriented along the mean synoptic flow, rounds of showers and thunderstorms are forecast to ripple southeastward along the front through the day today. Heavy rainfall remains the main forecast concern today, with plentiful moisture across the region. The KCHS 00Z RAOB Sounding had a PWAT value of 2.36", which was well above the 90th percentile according to SPC Climatology. PWATs are expected to remain in the 2.3-2.5" range through the remainder of today. The heavy rainfall threat today will be heavily tied to the location of the front. The 00Z suite of guidance is in decent agreement that the front will likely set up roughly along I-26 in SC. This would paint the greatest heavy rainfall threat over the Charleston Tri-County. The 00Z HREF probabilities are eye-catching, with a 50% contour of 3-hr QPF >3" over the Charleston Tri-County at 21Z. Confidence on the exact positioning of the front is low and a slight shift northward or southward would greatly impact the location of the heavy rainfall threat. Another consideration is some models are depicting a weak low pressure center developing along the stalled front, which would aid in the heavy rainfall risk. Forecast soundings indicate sufficient instability for a risk of strong to severe gusts as well, and the Storm Prediction Center has outlined the entire forecast area in a Marginal Risk for severe thunderstorms.

KEY MESSAGE 2: Hot and humid conditions return to the South Carolina Lowcountry and Southeast Georgia during the middle of this week.

The mid-levels will consist of a very strong ridge over the Rockies and Plains early to mid week. Meanwhile, troughing will be along the Eastern Seaboard. We'll generally be on the eastern periphery of the ridge, with NNW flow overhead. At the surface, weak high pressure will prevail over or nearby early to mid next week. Hot and humid conditions are expected to return during the middle of the week. Tuesday and Wednesday look to be the hottest days of the week, with highs in the mid to upper 90s, with some spots possibly reaching the 100 degree mark across far inland GA. Even temperatures at the coast will be in the 90s. Dewpoints are expected to be in the low 70s far inland, but pool into the mid to upper 70s at the coast with the afternoon sea breeze. This will equate to heat indices in the 100-105 degree range inland, and the 108-112 degree range for our coastal counties on Tuesday. Though, the range could increase to 110-115 degrees for our coastal counties on Wednesday. If this pans out, at least our coastal counties would need heat headlines both days. The wild card would be afternoon convection. Tuesday is looking fairly dry, but Wednesday may have scattered convection, which would quickly lower temperatures. It could also lead to strong to marginally severe storms. The heat and humidity is expected to drop to near normal values on Thursday with the arrival of a front.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

VFR to start the 06Z TAF period at KCHS/KJZI/KSAV. A stationary front is located just to the north of Charleston and Berkeley Counties as of 06Z. Some models are hinting at the formation of some MVFR to even IFR cigs in the vicinity of this stalled front early this morning. A TEMPO group has been introduced at KCHS for MVFR cigs from 09 to 11Z. Confidence in possible impacts at KJZI was too low to include mention of restrictions at this juncture. The threat of restrictive cigs does not extend southward enough to impact KSAV.

Additional restrictions are possible at KCHS/KJZI this afternoon as showers and thunderstorms develop associated with the stalled front. The previous PROB30 group has been adjusted to a TEMPO group at both terminals as confidence in impacts to the terminals has increased. KSAV remains precip free at this juncture.

Extended Aviation Outlook: Brief flight restrictions are possible Wednesday and Thursday due to showers and thunderstorms.

MARINE

Through Friday: A stationary front nearby will continue southwesterly winds today. Winds and seas are forecast to increase late Tuesday into Wednesday, so Small Craft Advisories may be needed for most of our waters.

CLIMATE

Record High Temperatures:

July 28: KCHS: 101/1949 KCXM: 100/1936 KSAV: 102/1949

July 29: KCHS: 100/1993 KCXM: 99/1999 KSAV: 103/1993

Record High Minimum Temperatures:

July 29: KCHS: 80/2016 KCXM: 85/1999 KSAV: 82/1878

CHS WATCHES/WARNINGS/ADVISORIES

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