Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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550 FXUS62 KCHS 191839 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 239 PM EDT Sun May 19 2024 .SYNOPSIS... A cold front will cross through our area later today. High pressure then prevails for most of this week, followed by another storm system potentially impacting our area late this week. && .NEAR TERM /THROUGH TONIGHT/... Satellite water vapor indicated the center of a mid-level vorticity maximum over south-central GA, tracking to the SE. A band of strong to severe thunderstorms developed along a cold front earlier this afternoon. This band will continue to slide south, tapping into a unstable environment. CAPE in excess of 2000 J/kg, DCAPE between 600-800 J/kg, and effective bulk shear around 30 kts may support strong to severe thunderstorms over the lower Savannah River Basin, including the City of Savannah this afternoon. These storms may produce damaging wind gusts and even hail up to the size of half dollars. PW values are forecast to increase to around 1.6 inches this afternoon. The combination of deep instability, adequate atmospheric moisture, and storm motions less than 25 MPH could result in pockets of torrential downpours. In fact, arriving 12z HREF data continues to indicate impressive probabilities of 3"/3hr within 40 km across portions of coastal SC and GA, especially a corridor from southern Charleston County south to coastal GA. Flood Advisories appear possible for these area this afternoon, possibly a Flash Flood Warning. Tonight: Short-wave trough axis will slowly push off the coast while surface high pressure wedges down from the north. Convection will run its course this evening with thinning cloud cover during the overnight hours. Cooler temperatures...dipping down through the 60s for lows. && .SHORT TERM /MONDAY THROUGH WEDNESDAY/... Monday: The mid-levels will consist of a positively tilted trough just off the Southeast U.S. coast in the morning, and a ridge just to our west. The ridge will slowly build into our area as time progresses. At the surface, High pressure centered well to our north will build down the coast as time progresses, with it`s southern periphery making its way into our area. The High will bring dry conditions with skies becoming mostly sunny/clear. Low-level thickness values support temperatures in the middle 80s. But we went a little below this due to the northeasterly surface winds and the expectation that surface evaporation should limit temperatures. Highs should peak in the lower 80s. Lows should range from the upper 50s far inland to the mid 60s closer to the coast. Tuesday: A positively tilted mid-level trough will be just off the Southeast U.S. coast in the morning, transitioning into a cut- off Low in the evening and overnight. Meanwhile, a ridge will strengthen over the Southeast U.S. Broad High pressure centered to our north in the morning will shift off the Mid-Atlantic Coast as the day progresses. Though, it`s southern periphery will continue to dominate our weather during the day and into the night. Subsidence will yield dry conditions with mostly sunny/clear skies. High temperatures should be in the mid 80s, except cooler at the beaches. Lows should range from the upper 50s far inland to the mid 60s closer to the coast. Wednesday: The mid-levels will consist of a cut-off Low meandering off the Southeast coast, while a ridge prevails over the Southeast U.S. At the surface, High pressure along the Southeast coast in the morning will shift offshore into the afternoon. A front will slowly approach from the north and northwest. Though, it won`t make it near our area as the High will remain the dominant synoptic feature. Some of the models hint at isolated weak showers trying to form along the inland moving sea breeze late in the afternoon. But it`s still a little too early to determine if the dry air in place will completely squash these weak showers. Expect at least partly sunny skies. Highs will peak in the mid to upper 80s, except cooler at the beaches. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... Mid-level ridging will be over our region Wednesday night, followed by west southwest flow on Thursday. A weak trough may pass to our north Friday night into Saturday. Surface High pressure in the western Atlantic on Thursday will shift further offshore as time progresses. A cold front could approach from the north and northwest later Friday, then lift north on Saturday. Expect mainly dry conditions Thursday, with increasing diurnal convection Friday and Saturday. High temperatures will be a few degrees above normal each day. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... KSAV: A cluster of strong to severe thunderstorms will reach the KSAV terminal by 19Z. The KSAV TAF will feature moderate thunderstorm at 19Z with a TEMPO from 19-23Z for gusts to 35 kts and IFR vis. The thunderstorms are forecast to push south and east of the terminal by early this evening. The challenge overnight will be the formation of MVFR ceilings, expected to develop by 3Z at KSAV. The stratus should mix out shortly after daybreak on Monday with steady NE winds. KCHS and KJZI: Prior to the 18Z TAFs, a cluster of showers and thunderstorms was located over KLCO, drifting SW. This activity will remain close enough to mention VCSH at both terminals through 21Z. AMDs may become necessary later this afternoon if the activity tracks over either one of the terminals. By late this afternoon, convection should drift south of the terminals. Steady NE winds with ceilings between 040-060 may remain through the night. Extended Aviation Outlook: VFR. && .MARINE... A brief period of gustier southerly winds will impact the coastal waters early this morning. Surface boundary will move down through the region as we go through the day and kick off another round of showers and thunderstorms during the afternoon. Winds veer northerly behind the front and will be increasing as we go through tonight. Monday: A cold front will be shifting offshore early in the morning. Meanwhile, High pressure centered well to our north will build down the coast and into our area as time progresses. The strongest gradient will occur in the morning, with wind gusts just short of 25 kt possible across much of the waters, and seas 3-5 ft. The gradient will gradually weaken into the afternoon and overnight, with seas gradually subsiding as well. Tuesday and Beyond: NE winds on Tuesday will shift around to the SE by later Wednesday as High pressure gradually shifts off our coast. This will lead to a more typical summer wind pattern on Thursday with the formation of the afternoon sea breeze. && .TIDES/COASTAL FLOODING... The combination of rising astronomical tides with the upcoming Full Moon and moderate NE winds will cause tides to be elevated early this week. Minor flooding is possible with the evening high tides Monday and Tuesday, mainly along the South Carolina coast. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...NED SHORT TERM... LONG TERM... AVIATION...NED MARINE...