Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 201201 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 801 AM EDT Thu Jul 20 2017 .SYNOPSIS...
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Atlantic high pressure will extend west into the southeast coast through this weekend as a surface trough remains inland. Unsettled weather will ensue toward the early to middle part of next week as a cold front approaches the area.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Today: The slowly weakening and retrograding mid level low pres area remains along/just off our coast while a very weak surface pressure pattern continues across the region. The atmospheric profiles appear fairly typical for this time of year with a decent early low level cap and generous deep layered instability for the afternoon hours with PWATs near 1.8" despite some drier layers aloft. Similar to Wednesday, we should begin the day with strong insolation and quick warming of land mass. Forecast soundings from the 00Z NAM and latest RAP output indicate an air mass capable of at least isolated to scattered convection this afternoon across the sea breeze corridor once convective temps in the lower 90s are reached. Storm motions are expected to be south and southwest down the sea breeze later today and probably result in some multi- cell clusters over southeast GA by 20-21Z. High resolution guidance favors best chances along the lower Savannah River area, then south into inland GA zones by later in the afternoon. We think with decent DCAPEs, hail CAPES and updraft potential, isolated strong to severe storms cannot be ruled out along and west of I-95 this afternoon, especially in GA. We raised pops to 30 percent across the board in this area and even considered values a bit higher in spots. Along the South Carolina sea breeze, we maintained 20 POPs. Tonight: The mid level low will continue a slow drift southwest toward northeast FL, while early evening convection either moves to the southwest and weakens. Skies should be mainly clear after midnight with lows in the mid 70s on average.
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&& .SHORT TERM /FRIDAY THROUGH SUNDAY/... Mid and upper level ridging over the deep south will pass overhead and offshore through the period. A surface ridge extending from the Atlantic high to the Gulf Coast will keep southwesterly low level flow, and the typical summertime warm and humid airmass, in place. Hot and mainly rain-free will be the story Friday and Saturday as deep layer subsidence precludes any precip threat aside from a few isolated storms along the sea breeze each afternoon. Ample sunshine will allow temps to climb into the mid 90s away from the coast each day, and heat index values will generally reach the low to mid 100s. Temps and POPs will begin to moderate back toward more climatological values Sunday as the upper level ridge shifts offshore and modest H5 height falls begin. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... Heights aloft will fall continue to fall early next week in response to large scale troughing shifting over the eastern US. Warm and humid airmass will remain in place at the surface as the area remains on the western periphery of the Bermuda High. An approaching cold front could provide further moisture enhancement by the middle of next week, and have a general trend of increasing POPs through the period to account for this feature. Temps will moderate from a few degrees above normal Monday thanks to plentiful solar insulation to a few degrees below normal by late week owing to increased cloud cover and a more unstable environment. && .AVIATION /12Z THURSDAY THROUGH MONDAY/...
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Mainly VFR. There are patches of thick stratus and fog around the coastal corridor at dawn but any restrictions should be brief. We have a VCTS at KSAV between 18Z and 22Z today. . Isolated tstms will be possible this afternoon in the coastal corridor, especially to the south of Charleston. We add a prob30 at KSAV on the 12Z TAF. Extended Aviation Outlook: VFR conditions will prevail.
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&& .MARINE... Today: Tranquil conditions with light and variable winds early, becoming southerly later today. Winds should see a slight uptick late today but still below 15 kt. The Atlantic surface ridge will tend a bit tonight with winds 10-15 KT at times. Seas through tonight 2 FT near shore and 2-3 FT well offshore. Typical summertime pattern will persist through weekend and into early next weekend as the waters remain under the control of the powerful Bermuda High. Light to moderate southwest breezes with enhancements and backing near the coast with the sea breeze each afternoon will be the norm. Incoming swell will be minimal, with seas of 2 to 4 feet in mainly local wind swell. && .TIDES/COASTAL FLOODING... Elevated tide levels due to the lunar perigee and new moon will result in the possibility for minor coastal flooding during the evening high tides this weekend into early next week, especially along the SC coast. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM...CEB LONG TERM...CEB AVIATION... MARINE...CEB TIDES/COASTAL FLOODING...

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