... The remnants of Tropical Storm Claudette will track northeast across the Southeast through Sunday and bring periods of heavy rain showers and thunderstorm across the forecast area. An active cold front pushes into the area Tuesday, before drier weather returns Wednesday through Friday.
NEAR TERM /THROUGH SUNDAY/... As of 230pm EDT Saturday: Several forecast challenges associated with the remnants of Claudette. Already seeing convection breaking out across the area well ahead of forecast and have made some updates to pops accordingly, but the evening shift will probably be chasing this all night. Increasing low-level shear with these tropical rainbands will need to be monitored. As the remnants move farther into the Deep South, they are expected to be picked up in the wavetrain and pushed farther east, with the center of the remnant circulation shifted south of our area. The complication is that all guidance is picking up on an area of 850-700mb convergence and deformation, and with subsequent runs we have increasing confidence as the hires models are showing this area expanding across north GA and into the Upstate/SW NC. Add to this the easterly flow north of the remnants with the orographic upglide, and so confidence has increase with us and WPC to bump up the QPF along the SC/NC border. HREF probs are showing 50-60% for 5"+ of rainfall in NE GA and stretching into the NW Upstate. For now, highest basin- average storm totals top out at 3-4" in the border counties but wouldn't be surprised if these amounts end up low. With this, there is enough confidence to issue a Flash Flood Watch, but the uncertainty is in the exact location. For now, we will highlight the NC/SC/GA border and adjacent escarpment areas but this may need to be adjusted this evening.
Tornado threat remains very uncertain as shear is very high but as always thermodynamic profiles are unclear in the tropical environment. Best instability remains well south but with the shear certainly cannot rule anything out. SPC Marginal remains in extreme southern zones, but CAMs are indicating that we could certainly see embedded low-topped storms or supercells within the larger rain shield even during the late overnight period so will need to monitor closely.
Of course diurnal range will be significantly reduced tonight through tomorrow with highs well below seasonal normals.
SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 125 PM Saturday...The pattern remains active thru the short range period. A departing upper wave associated with the TC remnants crosses the FA during the day Mon, while sfc-based CAPE increases to arnd 1000 J/kg per the NAM and GFS profiles. Expect afternoon convective activity, mainly across the mtns, where destabilization interacts with an incoming pre-frontal trof. Shear levels remain fairly low, so not expecting much more than general thunder, with a few cells possibly producing large hail and strong outflows. On Tue the frontal zone approaches and crosses the CWFA. Soundings indicated sbCAPE will be low-end, however, deep shear levels jump into the 30-40 kt range. This could make things interesting severe-wise along and ahead of the sfc convg zone during the afternoon. With PWATS remaining arnd 1.5-1.8 inches...there could be isol hydro issues both days as antecedent conds will likely be very moist most areas due to previous rainfall from the remnant tropical system. Temps will rebound to normal levels Mon as insol increases, but more widespread frontal cloudiness will again drop max temps a couple cats below normal on Tue. Mins will remain abt 5 degrees abv normal each night.
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 155 PM Saturday: Not much change was made to the ext fcst. The guidance still indicates a relative drying period as a broad upper trof axis swings east across the area thru the period. A developing subs zone will maintain broad sfc hipres and allow a weak cP airmass mix. Expect max and min temps to remain below normal thru the period while slowly rising each day. There will be a small chance of afternoon showers and general tstms across the wrn zones as a moist return flow ensues. By the end of the period a cold front will approach from the northwest and precip coverage chances will increase mainly across the NC mtns.