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Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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594 FXUS62 KCHS 272330 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 730 PM EDT Thu Jun 27 2024 .SYNOPSIS... High pressure will remain over the western Atlantic while weak fronts linger near the area through the end of the week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Tonight: Upper level troughiness lingers through the night and it`s unclear if the surface boundary actually pushes through or simply stalls/washes out across the region. The convection is looking to linger through the mid to late evening hours, moving off the coast and diminishing overnight. Overnight lows should dip into the middle 70s most areas (73-78F), warmer along the coast of course, with some fog possible particularly in areas that do receive decent rainfall. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... Friday: A rather fragmented mid-level pattern will be overhead as a weak mid-level ridge centers across Texas. Toward the Carolinas, vorticity will be elongated from the Atlantic southwest to the southeastern United States. The vorticity will start to get torn apart as it exists on the periphery of the aforementioned ridge. Looking down at 700/ 850 MB actually has the vorticity retrograding back west underneath the mid-level ridge and being picked up in the next wave. Towards the SC coast, the secondary weakness will remain though with forecast soundings advertising widespread instability (MLCAPE around ~1500 J/kg). Given this, have PoPs at likely for Friday with most of the convection being favored in the afternoon to evening hours. Expect high temperatures again in the low 90s as 850 MB temperatures remain around 19 degrees C. The other concern over the last couple of days has been the chance for another Heat Advisory Friday. Current thinking is that dewpoints will be a few degrees lower Friday compared to Thursday as enough convective overturning occurs for slightly more mixing. So the widespread 78/ 80 dewpoints of Thursday will be a degree or two less Friday. This coupled with high temperatures a degree or two lower will keep max heat index values around 105 degrees (or just shy of 108 degrees/ Heat Advisory criteria). Saturday and Sunday: This weekend looks rather active with multiple rounds of afternoon into evening showers and thunderstorms likely. In the mid-levels of the atmosphere, weak PV will continue to decay with mid-level ridging retreating west as a trough axis begins to amplify across the Eastern United States. Simultaneously, PWATs are forecast to climb to between 2.25" and 2.4". Instability will also be impressive, with MLCAPE values around 1800 J/kg Saturday and around 2000 + (J/kg) by Sunday. Likely PoPs are advertised for both Saturday and Sunday afternoon. High temperatures for both days are currently advertised to be in the low to mid 90s (thanks to 850 MB temperatures warming to 21 degrees C), but this could be moderated due to ongoing afternoon convection. Max Heat Index values are currently advertised to reach Heat Advisory criteria in places both Saturday and Sunday. A Heat Advisory might be required for the coastal zones this weekend. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Ensemble guidance is in fairly good agreement for the extended with a rather active period forecast Monday as a weak cold front approaches from the northwest. Tuesday into Wednesday the GEFS/ GEPS/ and EPS all indicate that mid-level ridging will slide east slowly building over the southeastern United States. WPC Cluster Analysis shows good agreement of this, with only slight differences in the strength and expanse of the 594 dam ridge. Sunday night into Monday: A cold front will approach the area from the northwest on Monday with showers and thunderstorms initiating across the Midlands of SC and Piedmont of NC. High temperatures Monday will be only around 90 degrees in most places given the likely coverage of storms. Tuesday: There is uncertainty on Tuesday with a weak backdoor cold front that is forecast to slide down the east side of the Appalachians. Guidance is indicating that the front makes it through the coastal plain of SC, before washing out and heading north by Wednesday. Synoptically, a mid-level ridge over the Southern Plains of the United States will nudge east Tuesday with a mid-level trough quickly exiting the east coast. This type of setup generally does allow a weak cold front to temporarily push south before retreating north. Most of the time though, convective enhancement to the front (via a reinforcing cold pool) is needed to really get the front through. Either way, this will bring a chance of showers and thunderstorm to the region Tuesday afternoon (less coverage compared to Monday) with highs only in the upper 80s. Wednesday: Mid-level ridging will nudge east and center across MS/ AL/ GA with air rapidly drying in the 500 - 750 MB level. This will really start to limit convective development with temperatures again warming back into the low to mid 90s. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... KCHS/KJZI/KSAV: Lingering rains and a few t-storms, mainly at KCHS and KJZI will taper off before midnight. Some low stratus and/or light fog could impacts the terminals late at night into Friday morning due to light or w=calm winds and the wet grounds. Flight restrictions are likely at all sites in the convection and again in the stratus/fog. The potential for convection Friday afternoon and evening will be reevaluated in later TAFs, but additional flight restrictions can occur. Extended Aviation Outlook: Prevailing VFR conditions through the period. Brief flight restrictions are possible each afternoon due to showers and thunderstorms. The highest chances of thunder will be Saturday, Sunday, and Monday afternoons thanks to the proximity of an upper level disturbance. By Tuesday, a weak cold front will wash north with mid-level high pressure taking control of the region. This will likely limit shower and thunderstorm development Tuesday and Wednesday. && .MARINE... South to southwesterly flow at 10 to 15 knots will persist across the coastal waters tonight. Showers and thunderstorms are likely to impact the coastal waters late this afternoon through this evening with briefly higher winds and waves expected. Seas are forecast to average 2 to 3 ft. Mariners on the South Carolina waters can expect some strong or severe storms early tonight. Extended Marine: Surface high pressure will remain anchored across the western Atlantic with southerly flow generally expected through the period. Each afternoon, a gradual backing of the winds to southeast is expected as a sea breeze forms, with winds strongest along the land/sea interface. A weak cold front will ooze southwest over the waters Monday into Tuesday, but the wind shift will be transient with a quick return of southerly winds forecast. Seas will be 2 to 4 ft. Rip Currents: A lingering 2 ft, 9 second swell coupled with some astronomical influences and typical sea breeze enhancements along the beaches support a moderate risk for rip currents for all beaches Friday and Saturday. && .FIRE WEATHER... The South Carolina forestry commission reported low fuel moistures across portions of the area today. Widespread coverage of showers and thunderstorms Saturday and Sunday will help to alleviate some of the low fuel moisture values. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM...Haines LONG TERM...Haines AVIATION... MARINE...