Area Forecast Discussion
Issued by NWS Columbia, SC
Issued by NWS Columbia, SC
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684 FXUS62 KCAE 121515 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 1115 AM EDT Mon Aug 12 2024 .SYNOPSIS... Scattered showers and thunderstorms expected each afternoon through Tuesday. Then drier air moves into the region allowing for a few slightly cooler days with only isolated showers and thunderstorms. Moisture returns to the region late this week and into the weekend as a frontal system moves into the eastern US. && .NEAR TERM /THROUGH TONIGHT/... Key Message(s): - Showers and thunderstorms expected across the eastern half of the forecast area this afternoon. 11 AM Update: In general, the patchy fog from this morning has lifted, but there are a few pesky spots still reporting some fog. Satellite imagery is showing that the low stratus from this morning is dissipating rather quickly now with the daytime heating. Areas along the northern Midlands and PeeDee are still seeing the low clouds, however. This is likely due to the rain that occurred overnight. Expect these clouds to continue dissipating over the next couple of hours, making way for another round of afternoon convection. The areas most likely to see thunderstorms are those that have cleared out from the clouds. Otherwise, read the earl-morning discussion for more details on today`s forecast. Early-morning discussion: Zonal upper level flow will persist overhead today. At the surface, a weak and diffuse boundary will be over the Midlands and will continue to provide a source of convective initiation. Moisture remains entrenched over the region, with dewpoints in the mid to upper 70s once again, and PW values from 1.8"-2.2", the highest values toward the coast. Strong heating with highs in the low 90s will yield moderate to strong instability, with 1500-2000 J/kg of SBCAPE. This should be plenty to generate scattered showers and thunderstorms during the afternoon and evening with much of the anticipated activity along and south of I-20. Wind gusts will be the main threat for severe thunderstorms as DCAPE values will again push toward 1000 J/Kg. A few transient shortwaves may enhance activity for a time, but widespread severe weather is not expected. The other concern remains the potential for locally heavy rainfall over already saturated or nearly saturated soils. WPC has maintained much of the central and eastern Midlands in a marginal risk of Excessive Rainfall. Expect the majority of convection to dissipate with the loss of daytime heating, however any residual outflow boundaries could interact to develop a few cells into the early overnight hours. Steering flow should also be a bit faster, around 15-20 kts. Lows tonight will be in the low to mid 70s. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... Key Message(s): - Damaging wind gusts possible Tuesday afternoon and evening An upper trough axis will be just east of the area on Tuesday. Low level moisture should pool over the forecast area with PWAT values between 1.75 and 2 inches. As the air mass destabilizes in the afternoon, convection will develop in an environment with deep-layer shear strong enough to support organized convection. West-northwest winds aloft with easterly low level winds should support 0-6 km shear values from 30 to 40 kts. Although 0-3 km lapse rates will be steep, poor lapse rates aloft may limit updraft strength and the overall severe threat. The HREF tends to favor convection initiating in the higher terrain of the Upstate progressing SE into the forecast area in the late afternoon or evening. Steep low level lapse rates and moderate shear could support damaging wind gusts with storms. The bulk of the convective activity should move east of the forecast area in the evening with a few lingering storms behind the main area. Highs Tuesday will be in the upper 80s to low 90s with lows in the low 70s. && .LONG TERM /THURSDAY THROUGH SUNDAY/... Key Message(s): - Drier air moves into the region mid to late this week - A frontal system may approach the area Friday into the weekend The GEFS and ECMWF ensembles continue to favor the amplification of a ridge over the central US this week with the axis of an upper trough offshore of the East Coast. This will direct northwest flow into the Southeast along with drier air for Wednesday and Thursday. PWAT values of 1.4 to 1.6 inches and weak lapse rates favor isolated to widely scattered convection each afternoon. Late week, models indicate the potential for an upper low to move into the Great Lakes region. The associated frontal system should swing into the Southeast near the end of the long term. As warm, moist advection strengthens ahead of the front we should expect to see PWAT values rise back to 1.75 to 2 inches through the weekend. This will support at least a chance of showers and thunderstorms. With troughing generally over the area for much of the long term we should see afternoon high temperatures slightly below normal in the mid to upper 80s. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... Generally VFR conditions expected outside of brief restrictions in diurnally driven thunderstorms and early morning stratus/fog. Convection is north of the terminals early this morning with mainly mid and high level clouds across the area. With shallow low-level moisture, near calm winds overnight and decreasing high clouds, fog and low stratus may develop toward dawn. Have included a mention of restrictions in the TAFs, possibly as low as LIFR/IFR but improving by 12/14z. As the air mass becomes moderately to strongly unstable this afternoon, scattered thunderstorms are expected to develop once again. Outside of convection, sfc winds will be variable at 5 to 10 knots. EXTENDED AVIATION OUTLOOK...Afternoon and evening convection and associate restrictions will be possible through Friday. Early morning fog and stratus could occur, especially at fog- prone AGS/OGB. && .CAE WATCHES/WARNINGS/ADVISORIES... SC...None. GA...None. && $$