626 FXUS62 KCHS 202001 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 401 PM EDT Sun Oct 20 2019 .SYNOPSIS... High pressure over the region tonight will begin to weaken on Monday. A frontal system will affect the area Monday night and Tuesday. High pressure will rebuild late Tuesday through Thursday before another storm system potentially moves in Friday or Saturday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Weak high pressure will prevail tonight in wake of low pressure lifting northeast away from the Mid-Atlantic coast. Quiet and dry weather is expected through the night. The main forecast concern will be the potential for fog late tonight. Areas inland, especially across interior Georgia, should see low condensation pressure deficits and temperatures fall below crossover temperatures. Model visibility progs pin that area for fog development, so we have included patchy fog in the grids. Low temperatures will range from the mid 50s far inland to low/mid 60s at the coast. && .SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/... Monday: We maintained a dry forecast as deep layered dry air persists above 850 MB for much of the region. Weak return flow across far Southeast GA will extend west along the Gulf Coast as a broad baroclinic zone will be in a genesis stage. Isolated showers may develop just prior to sunset in our far southern GA coastal zones, however we preferred onset of POPs to fall into the Monday night period. Skies should become partly cloudy most areas by afternoon with warm temps in the upper 70s to near 80 SC and lower 80s in GA. Monday night and Tuesday: Deep moisture advection is forecast on Monday night across the region as a warm front lifts north after midnight. We continue to trend upward with rain chances late night as models indicate a fairly extensive band of convective rains advancing north. Temps will rise overnight with many of our minimum temps likely occurring in the evening hours before clouds thicken and showers increasing. On Tuesday, A deep long wave trough will blanket much the U.S. east of the Rockies. Our area will see slow but steady mid level height falls as a cold front advances through the area reaching the coast in the afternoon. Showers and a few tstms will accompany and precede the front. The risk of severe weather does not look too impressive despite strong wind fields aloft and warm low-level temps prior to fropa. Latest models show instability parameters weakening during the afternoon hours as low level dew points decrease in a mixing low level environment. Highs will reach the lower to mid 80s most areas ahead of the front. Wednesday: Dry and cooler conditions as high pressure builds over the southeast states. Highs should only reach the lower to mid 70s from north to south. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Dry high pressure is expected to persist Wednesday night into Thursday before a broad upper trough pattern brings potentially unsettled weather into the weekend. There remain substantial differences in the models regarding timing of features late in the week. We expect an increase in rain chances beginning as early as Thursday afternoon but more likely Friday into Sunday. && .AVIATION /20Z SUNDAY THROUGH FRIDAY/... Sub-VFR ceilings are expected to scatter out this afternoon. Improvement to VFR is expected first at KSAV, then to KCHS within a couple hours after. Couldn't rule out some light fog towards daybreak, but confidence is not high enough to include any restrictions in the TAF at this time. Extended Aviation Outlook: Flight restrictions possible Monday night as a warm front lifts north through the area. Cigs could lower to MVFR/IFR at times with increasing chances for showers. It should become VFR on Tuesday with brief restrictions possible in convection rains along a cold front. VFR expected mid week with chances for increasing lower clouds and showers late week. && .MARINE... Tonight: Marine conditions will continue to improve this evening, with the remaining Small Craft Advisories to come down at 6 PM. The remainder of the night will be quiet with winds veering from the northwest to a more northeasterly direction by daybreak. Seas will be highest this evening, then subside to 2 to 3 feet on average overnight. High pressure weakening to the northeast will result in a light onshore flow Monday. The flow will veer to southwest by early Tuesday as a warm front lifts north through the waters. The surging will mainly be 15 kt or less. A cold front will move into the waters late Tuesday with much stronger surging Tuesday Night in cold air advection. We think SCA conditions are likely over GA waters beyond 20 NM with the best jetting occurring beyond 20 NM in northwest flow. There could be some gusts to 25 kt within 20 NM, but SCAs are less likely there. Winds will decrease during mid week as high pressure builds north of the waters. The decreasing trend will be short as onshore winds increase again by Thursday. Seas for much of the week will be in the 2-4 ft range, highest offshore with a period of higher seas likely near the Gulf Stream Tuesday Night and early Wednesday in gusty northwest flow. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for AMZ350- 374. && $$ NEAR TERM...ETM SHORT TERM... LONG TERM... AVIATION...ETM MARINE...ETM