Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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879 FXUS62 KCHS 100253 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1053 PM EDT Sun Jun 9 2024 .SYNOPSIS... A cold front is expected to sweep across the forecast area on Monday, followed by an unsettled pattern mid to late week. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... First Half of Tonight: Latest Radar and satellite data shows scattered showers and thunderstorms well to the northwest of the region. However, this convection is moving rapidly east- southeast and may reach the northern portions of Berkeley counties within the next 1 to 2 hours. Have brought in slight chance PoPs a little earlier over that area to account for the recent radar trends. There were some reports of wind damage with this system well upstream, but conditions are not quite as unstable over our northern area. Thus, still feel severe potential is still low for tonight. Second Half of Tonight: CAMs guidance continues to show that the convection, currently over northern GA, will move eastward, possibly reaching our interior and northern SC counties after 08Z tonight/Monday. Have kept slight chance PoPs in the forecast to account for this. Again, severe potential seems too low to mention. Otherwise, a very mild night, with lows in the low 70s inland to the mid to upper 70s along the coast. && .SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/... Monday: The mid-levels will consist of a positively tilted trough amplifying over the East Coast as time progresses. Additionally, a weak impulse is expected to pass over our area towards the evening. There also may be a jet streak to our north overnight. At the surface, a cold front located approximately over our northernmost counties at daybreak will slowly shift southeast during the day, likely becoming located offshore to our southeast by the afternoon, and then transitioning to a stationary front during the evening and overnight. There will be a plume of moisture with the front, with PWATs peaking around 2" during the afternoon. The models even hint at higher values in some locations. Either way, these values are above the 90% mark for CHS per SPC sounding climatology. While NAEFS PWATs seem a little lower, there are signs that if the values were similar, then this would be nearly 2 standard deviations above normal. Lift around the vicinity of the front and the afternoon sea breeze will combine with the moisture to generate convection. The highest POPs will initially be across our coastal and inland GA counties, then spread north into our SC counties during the later afternoon and evening. Convection should decrease a bit towards midnight, remaining closer to the coast afterwards. The highest instability is along our GA coast, where MLCAPEs could reach 2,000 J/kg. There is a decent amount of shear there, with DCAPEs exceeding 1,000 J/kg. So a few marginally severe thunderstorms with damaging winds cannot be ruled out in the afternoon and evening. SPC has most of our area under a Marginal Risk and this seems reasonable. While severe is the main concern, rainfall potential is also up there. Depending on how the front, sea breeze, and boundaries interact, there could be training and backbuilding storms. Heavy rainfall is possible, with some spots getting 1-2", locally higher. This will mainly be along our coast, especially our GA coast. Temperatures will range from the mid/upper 80s across our northernmost locations, to the mid 90s closer to the Altamaha. Lows will range from the mid 60s far inland to the lower 70s near the coast. Tuesday: The positively tilted trough prevails over the East Coast during the day, shifting offshore overnight. The surface stationary front will meander just off our coast during the day and into the night. Additionally, High pressure will be centered to our northwest and gradually building into our region. Even though the highest PWATs will remain offshore, values should still generally range between 1.25-1.75" during the day. It appears there will be enough moisture and instability to generate scattered convection along the sea breeze. Though, more drier air later in the day could somewhat limit this potential. The convection will diminish during the evening, with it being dry just about everywhere overnight. Highs will peak in the upper 80s to lower 90s. Lows will range from the mid 60s far inland to the lower 70s near the coast. Wednesday: Weak mid-level troughing will approach from the Lower MS Valley. At the surface, weak High pressure will remain to our north while a stationary front will be located just to our south and southeast. There appears to be enough moisture across our area to support diurnal isolated to scattered convection across our GA counties, while our SC counties should have little, if any convection. Temperatures should remain slightly above normal. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... The general pattern remains unsettled and uncertain. A large, unorganized area of Low pressure could potentially develop somewhere in the Gulf of Mexico. Most models indicate that at least some of the deep layer/tropical moisture associated with this feature could spread northeastward toward our region, especially by late in the week. This would support diurnal convection, with the potential for locally heavy rainfall. Temperatures should be near to slightly below normal. && .AVIATION /03Z MONDAY THROUGH FRIDAY/... Tonight: VFR conditions will prevail at the terminals. A surface boundary/weak cold front will push southward through the region late tonight into early Monday. Still concerned that MVFR CIGS could develop behind the boundary Monday morning, particularly at KCHS/KJZI. However, given uncertainty, have kept out mention of MVFR CIGS, but continue to indicate the potential with scattered 2-3k ft CIGS, generally after 17Z Monday. Have also now added Prob30 mention for TSRA in the afternoon. There is a small chance for some storms to become strong to severe after 17/18Z Monday, especially around KSAV. Extended Aviation Outlook: Convection will bring the chance for periodic flight restrictions later Monday through Tuesday, and then again Thursday and Friday. && .MARINE... Rest of Tonight: A cold front is still expected to reach northern waters by 06Z, pushing through most of the coastal waters by daybreak Monday morning. Have introduced slight chance PoPs for the northern waters for isolated showers/thunderstorms, with the main impact being the potential for cloud to water lightning and strong/gusty winds. Outside of any thunderstorms, southwest winds will likely remain a bit gusty much of the night, with occasional gusts near 20 kt, especially over the South Carolina coastal waters, as the front approaches later tonight. Seas are forecast to build to 2-4 ft during the wind surge ahead of the cold front. Extended Marine: A cold front will slowly move through our waters on Monday, then become a stationary front to our southeast Monday night, possibly meandering through the middle to end of the week. Despite potentially unsettled weather, conditions are expected to remain below Small Craft Advisory criteria. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...Adam/RFM SHORT TERM... LONG TERM... AVIATION...Adam/RFM MARINE...Adam/RFM