Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 132045 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 345 PM EST Fri Dec 13 2019 .SYNOPSIS... An area of low pressure will track across the area tonight. High pressure should then build over the region Saturday and persist into early next week. A cold front will shift across the area Tuesday, followed by high pressure into late next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... The cold air damming regime has held strong today despite all model data suggesting it would erode by mid afternoon. This is a very common model weakness for this area. The surface low that has been developing along the coast has remained over the Gulf Stream as it tracks northeast with the cyclonic flow further entrenching the high pressure wedge over land. The main upper shortwave will gradually push northeast of the area through early this evening. Meanwhile, as the surface low moves toward the NC/SC border, the best isentropic ascent on its NW periphery will shift north of the area. Much of the precipitation should clear out from south to north through mid evening due to NVA in the wake of the shortwave. Late tonight a strong upper shortwave and the surface cold front will sweep through the area. Strong forcing for ascent is anticipated, especially given another round of strong upper jet divergence coincident with the PVA associated with the shortwave. A few hours of moderate to heavy showers are expected to sweep through late tonight. Isolated thunderstorms are also possible, mainly over the eastern half of the area where a bit more elevated instability will exist. Temperatures will rise little during the remainder of the afternoon through tonight. The cool northeast flow is likely to continue until daybreak Saturday when the cold front sweeps through. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/... Mid-level troughing over the Southeast U.S. Saturday morning will shift over the Northeast U.S. by Saturday night, causing semi-zonal flow over our area. This flow will continue on Sunday. Sunday night into Monday broad high pressure will be building over the Bahamas while troughing amplifies over the Central U.S., leading to southwest flow over our area. At the surface, low pressure and it`s attached from will be moving away from our area Saturday morning while high pressure moves in from the west. The high is forecasted to prevail over the Southeast U.S. late Saturday into Sunday, then shift offshore Sunday night. As the high continues to move further offshore on Monday, a front will approach from the distant west. Though, it`s not expected to reach our area in the short term. The only precipitation we are expecting in the short term is early Saturday morning, as the aforementioned low/front moves away. Some remnant showers, especially along the coast, should bring little, if any, measurable QPF. Then, the high will become the dominant driver of the forecast for the rest of the short term. Subsidence and dry air associated with the high will bring our area dry conditions into Monday. High temperatures should generally be in the 60s Saturday and Sunday. Highs rise well into the 70s on Monday as winds turn to the south/southwest, ushering warmer air into the region. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... The area will become warm-sectored Monday night into Tuesday ahead of a cold front expected to shift across the region Tuesday afternoon afternoon/evening. Temps will be the warmest of the week on Tuesday, peaking in the mid 70s across several areas. Sfc heating should also be sufficient to produce some instability along/near fropa, suggesting a few thunderstorms embedded in numerous showers until the front reaches the coast. Dry and cooler high pressure will then build across the area Tuesday night through late week. Temps will be some 15-20 degrees cooler following the front with highs generally peaking in the mid/upper 50s and overnight lows in the low/mid 30s away from the coast. A few showers could return next weekend as a coastal trough takes form along the Southeast Coast. && .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/... IFR, as well as possible LIFR conditions are expected to prevail through 23Z as a low pressure system continues to move through the area and lift northeast by 00Z. Until then, showers are expected to linger around both terminals, with heavier rain at times. By 00Z, showers are expected to lessen, with VCSH to prevail at both TAF sites. Fog and low clouds will support IFR to LIFR conditions at both terminals. Around 06Z, a cold front will start to move through the area, bringing more rain to both terminals and the continuation of lower ceilings and visibilities. By daybreak, showers are no longer expected with vsbys and ceilings improving with the passing of the cold front. By 15Z, VFR conditions are expected. Extended Aviation Outlook: VFR through Monday. Flight restrictions are possible at both terminals Tuesday due to showers/thunderstorms along a passing cold front. && .MARINE... Winds may eventually become south later tonight as the coastal trough shifts inland. However, speeds will be at or below 15 kt. Nevertheless, seas will be at or above 6 ft over the Charleston nearshore and GA offshore through the night, thus necessitating the continuation of Small Craft Advisories in those two zones. An area of low pressure and its associated front will be moving away from the coastal waters Saturday morning while high pressure approaches from the west. The interaction between these two features will lead to elevated winds for most of Saturday. The worst conditions appear to be Saturday late afternoon. Small Craft Advisories will be ongoing for most of the waters, except AMZ354 and Charleston Harbor where wind gusts should remain just below 25 kt. The winds are expected to ease late Saturday evening through the overnight hours as the high becomes more dominant across our area. All of the advisories should expire across the waters by daybreak Sunday. The high is forecasted to persist into early next week. A cold front will shift across all coastal waters Tuesday, producing another round of cold air advection across the region and the potential for Small Craft Advisories Tuesday night into early Wednesday. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory from 10 AM to 9 PM EST Saturday for AMZ352. Small Craft Advisory until 5 AM EST Sunday for AMZ374. Small Craft Advisory until midnight EST Saturday night for AMZ350. && $$ NEAR TERM...JRL SHORT TERM...MS LONG TERM...DPB AVIATION...MS/RAD MARINE...JRL/MS

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