Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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608 FXUS62 KCHS 282007 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 407 PM EDT Fri Jun 28 2024 .SYNOPSIS... A weak front will linger near the area today. Atlantic high pressure will return over the weekend, while a trough of low pressure resides inland. A cold front will likely to impact the area early late Sunday into early next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... This Afternoon: Aloft a weak, elongated, positively tilted shortwave trough will be positioned over the southeast coastline. At the surface a stationary front will linger in the vicinity of the forecast area, slightly inland from Charleston County. With slight forcing for ascent from the lingering stationary front and some vorticity aloft, showers and some thunderstorms have already begun to spur across southeast GA. As the afternoon progresses greater coverage is anticipated, however the bulk of the activity will likely remain across far southern SC and southeastern GA where according to SPC Mesoanalysis, a pool of 1500 J/kg of ML CAPE resides. This morning`s RAOB sounding from KCHS showed an impressive cap, which according to mesoanalysis is still present with some lingering CIN across the Charleston Tri-County. Temperatures this afternoon have reached into the low 90s across the forecast area. At KCHS the dew point at 3 PM was actually 71F, significantly lower than previous days. Dew points have been adjusted downwards across the forecast area. Heat index values are only reaching to around 100F across the region. Tonight: Showers and thunderstorms will likely dissipate with nightfall and overnight conditions should remain dry. Some lingering low clouds and possible patchy fog may impact some areas in the early morning hours, especially areas which received precipitation. Overnight temperatures are forecast to dip into the low 70s inland with upper 70s along the direct coastline. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/... Saturday and Saturday night: The area will be dominated by a deep layer ridge, centered to the south and east. Very little in the way of upper level features to help force afternoon convection. However, with light southerly flow, ample deep layer moisture with PWs around 2 inches, and mean CAPE values of 1500-2000 J/Kg, expect scattered afternoon showers and thunderstorms. The main trigger will be the seabreeze, then the combo of the seabreeze and convective outflow boundaries. Have continued likely PoPs west of I-95 and chance elsewhere. With light steering flow, locally heavy rainfall will be possible. Convection should be diurnally driven, decreasing into the evening. Temperatures above normal, with highs in the lower to mid 90s and lows in the mid to upper 70s. Sunday and Sunday night: The pattern becomes a little more active during this period as a broad upper trough takes shape over the northeast U.S. and OH River Valley area. The associated surface cold front approaches from the northwest by late day/Sunday night, but should remain well northwest of the area through the day. However, the increased low level convergence upstream/northwest of the area will likely help to spark a line of shower/thunderstorms, which could propagate southeast into our northern area via outflow boundaries. The presence of some cyclonic flow at upper levels, better low level convergence, and CAPE values near 2000 J/Kg will lead to the potential for isolated strong to severe storms, especially over our SC region, which is where the SPC has a Marginal Risk. Main impact from stronger storms will be strong/gusty winds. Also, depending on cloud/convective coverage, temperatures could spike into the lower to mid 90s due due to some compressional warming ahead of the front. These temps combined with surface Tds in the lower to mid 70s, would result in max heat indices of 105 to 109, which would be marginal Heat Advisory conditions. Will continue to monitor this potential. Again, convection likely to decrease by evening with loss of heating. However, given the presence of the upper trough along with the cold front sagging into the area, would not be surprised to see isolated to scattered convection last through the night, especially north of the Savannah River. Monday: The cold front that was advancing into the area Sunday night is shown by models to stall over the region. Deep layer ridging builds north and west of the area, with low level easterly flow. Given the lingering front and sufficient moisture /PWs around 2-2.25 inches/, expect scattered to numerous showers/thunderstorms. Highs a tad lower than the previous day given the front and cloud cover. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... A slightly quieter weather pattern is expected for much of this period as a deep layer ridge continues west and north of the area with light south-southeast winds. With little to no upper level features to trigger convection, any convection during this period will mainly be triggered by afternoon heating and the presence of a seabreeze. Expect a weak front to linger over the area Tuesday, but then dissipate Wednesday and beyond. Given the lingering front on Tuesday, have continued likely PoPs, especially over the southern half of the area where the best moisture will reside. Wednesday and beyond, kept more climo level/chance PoPs. Given PWs remain 2+ inches much of this period, along with light steering flow, any stronger showers/thunderstorms could produce locally heavy rainfall. Temperatures generally near normal Tuesday, then possibly climbing back to above normal Wednesday and Thursday. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... KCHS: Isolated to scattered showers and thunderstorms are anticipated in the vicinity of the terminal this afternoon. Confidence in direct impacts to the terminal remain low, so have only included vicinity showers in the 18Z TAF. KJZI: Current trends suggest that showers and thunderstorms will likely remain inland of the terminal this afternoon. Therefore, no mention of thunder or precipitation has been included in the 18Z TAF. KSAV: Showers and thunderstorms are already forming across southeast GA to start the 18Z TAF period. Brief flight restrictions are possible through roughly 00Z tonight. Extended Aviation Outlook: Prevailing VFR. Brief flight restrictions are possible in showers and thunderstorms, mainly in the afternoon and evenings. && .MARINE... South to southwest flow will remain dominant across the coastal waters through tonight. Seas will run 3 feet or less. Extended Marine: No highlights are expected through the period. Generally southerly winds are expected to persist through Monday as a surface ridge remains east and south of the waters. Winds of 15 knots or less and seas 2 to 4 feet. Slightly stronger winds possible Sunday and Sunday night as the pressure gradient increases ahead of a cold front. Monday and Tuesday, a cold front is expected to stall over the waters, creating lighter winds, generally 10-15 knots from the south- southeast and seas 2 to 3 feet. Rip Currents: Latest guidance indicating very marginal Moderate Risk for rip currents on Saturday. Given surrounding offices going with Moderate, and we are going into a weekend, have opted to maintain Moderate Risk for Saturday. Low risk for Sunday. && .FIRE WEATHER... The South Carolina forestry commission reported low fuel moistures across portions of the area on Thursday. However, rainfall on Thursday and the potential for rainfall over the next few days will help to alleviate some of the low fuel moisture values. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...CPM SHORT TERM...CPM/RFM LONG TERM...RFM AVIATION...CPM/RFM MARINE...Adam/CPM/RFM