Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 190601 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 101 AM EST Sun Jan 19 2020 .SYNOPSIS... A cold front is expected to move through late tonight into Sunday morning. In the wake of the front, a cold and dry air mass will build over the region early next week and will remain until Thursday. A low pressure system will bring warmer temperatures and showers beginning Friday. && .NEAR TERM /THROUGH TODAY/... Midnight update: Forecast on track, only minor tweaks to sky cover and POPs. Extensive mid and high level cloud cover has overspread the forecast area in advance of a cold front that will move into local counties prior by daybreak. Warm advection in advance of the front and the blanketing affects of the clouds will hold temps fairly steady or even allow them to climb a couple of degrees overnight. Through 6 am the bulk of the region will experience temps in the lower or middle 60s, far above normal, as a 35-45 kt low level jet spreads overhead between 06Z and 12Z. This will yield increasing southwesterly winds that reach as high as 20-30 mph at times overnight. Forcing aloft with strung out vorticity and the right entrance region of the upper jet, plus modest isentropic ascent will allow for scattered to numerous showers to spread in ahead of the cold front. The highest PoP of 50-60% will cover the west- northwest tier prior to 4 am, with the higher PoP spreading closer to the coast closer to daybreak. && .SHORT TERM /TONIGHT THROUGH WEDNESDAY/... Sunday: As the cold front progresses through the area during the morning hours, showers are expected to continually decrease until the afternoon, when cool and dry high pressure moves into the area. This will help decrease POPs quickly, with a mostly dry afternoon/evening. Temperatures are expected to be in the low to mid 60s. Throughout the night, temps will trend much cooler with lows in the high 30s, low 40s. Monday and Tuesday: As high pressure continues to prevail, temperatures will be much lower than we have seen in recent days. While mid 40s to low 50s are expected, temps could actually stay lower. Into the night, temps will drop into the low 30s along the coast while inland will see upper 20s. Tuesday will start off quite cold and warm up to similar temps as Monday, just a little chiller. It is interesting that a clipper-like system is expected to quickly ripple over the region on Tuesday, slowly closing off at H5. As the system passes over the CWA, H85 temperatures cool to -6 to -9C. Using a blend of MOS, highs on Tuesday are expected to remain 10-13 degrees below normal. The core of the mid and high level moisture is expected to pass to the south, however, cloud cover is expected to increase through the daylight hours on Tuesday. By late Tuesday, the mid-level disturbance will pass over the cold front over the western Atlantic, resulting in cyclogenesis east of the Gulf Stream. As a result, a few showers are forecast to develop across the outer GA waters, temperatures in the upper 40s to low 50s should support all liquid. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... A large area of sfc high pressure will dominate much of the East Conus with its center shifting across the Midwest midweek, then into the Northeast by Friday. Aloft, a large trough of low pressure will begin to shift offshore midweek, setting up a period of mid-lvl ridging through late week. The pattern will favor cold temps Tuesday night with lows in the mid/upper 20s away from the coast, before conditions gradually warm as winds become more directly onshore through late week. Temps will likely warm into the low/mid 50s Wednesday, then mid 50s well inland to upper 50s/lower 60s on Thursday. On Friday, onshore winds should prevail as high pressure shifts off the East Coast. A developing coastal trough could also bring some showers onshore. In general, temps should approach the mid/upper 60s. Chances of precip should increase during the weekend as low pressure over the Gulf of Mexico merges with a cold front approaching from the west on Saturday. Scattered to potentially numerous showers are possible during peak forcing/moisture across the area Saturday afternoon. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... VFR conditions at both terminals much of tonight and Sunday. However, scattered SHRA will move through the area with a cold front late tonight and Sunday morning, and this could result in several hours of MVFR conditions. We`ll be close to LLWS mid morning, but surface winds currently look to be too strong to prevent us from adding to the latest TAF set. Gusty surface winds will then persist behind the cold front through about sunset. Extended Aviation Outlook: VFR conditions are expected at both terminals Monday through the middle of next week. && .MARINE... Overnight: Increasing low level winds that reach as high as 35-40 kt in advance of the next cold front will be tempered somewhat by warm advection. However, given geostrophic wind fields that are as great as 30 or 35 kt, we have Small Craft Advisories in effect for the South Carolina Atlantic waters and the outermost Georgia waters. SW winds will reach as high as 20-25 kt and gusty across these marine zones, with seas as large as 5 or 6 ft within 20 nm and up to 7 ft further out. Conditions will be close to advisory thresholds in Charleston Harbor for several hours late tonight and Sunday morning. Sunday: A cold front will sweep across the waters on Sunday. Winds are forecast to veer from SW during the morning from the WNW by the afternoon. Conditions are expected to become gusty, with frequent gusts to around 25 kts across AMZ350 and 374. Seas across these zones are forecast to range between 4 to 7 ft. Small Craft Advisories will remain until 6 PM Sunday. On Monday, large high pressure centered over the Mid West will build SE across region. The pressure gradient across the marine zones should support gusts in the low 20s early Monday morning, decreasing to 20kts or less during the daylight hours. Tuesday through Wednesday night: Low pressure will organize and deepen offshore as a mid-level disturbance arrives from the NW. The marine zones will remain between the developing low to the east and high pressure centered to the NW. This pattern will likely yield Small Craft Advisory conditions outside the CHS Harbor Tuesday through Wednesday night with gusty NE winds and building seas. On Thursday, seas above 6 ft may linger across AMZ374 through much of the day. High pressure will build over the area on Thursday, with gradually lowering wind gusts and seas. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory from 4 AM to 10 AM EST this morning for AMZ352. Small Craft Advisory until 6 PM EST this evening for AMZ350- 374. && $$ NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE...

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