Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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729 FXUS62 KCHS 100215 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1015 PM EDT Thu May 9 2024 .SYNOPSIS... A cold front will approach the area tonight, then move offshore Friday. High pressure will prevail for the weekend into early next week. A storm system could affect the area by the middle of next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Now that the higher level clouds have pulled out from earlier convection, with the wet grounds we are seeing patchy low stratus form. Some guidance indicates that there could be fog developing as well. But we`re still anticipating no worse than about 2-3 miles, since geostrophic winds are just too much. So no mention in the actual forecast. Our attention turns to the west, where an MCS in Alabama and Georgia will approach overnight. But it is expected to weaken as it does so, as there are poor lapse rates, limited MUCAPE and 0-1 km bulk shear, and likely too much CINH. We do show some slight chance of showers in our Georgia zones close to daybreak however. An additional MCS in Mississippi and Louisiana, and maybe even a third from Texas would not get here until Friday. Temperatures really won`t move much through the night, with actual lows in the mid 60s to lower 70s. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... The forecast for Friday is quite tricky. A quasi-zonal flow will persist aloft, though we will see several potent shortwaves ripple through the area during the day. Given the high theta-e airmass across the Southeast, ample instability should be in place to support convective development with these upper vort maxima. Furthermore, the presence of 50-60 kt of 0-6 km bulk shear will favor organization of the convection once it become established. Most of the guidance continues to indicate the most impressive shortwave will move through southeast SC/GA between 15Z and 18Z. There is surprising agreement between the synoptic models and the CAMs that a large area of showers and thunderstorms will move across the forecast area between 9am and 3pm Friday. It appears that an MCS could be ongoing across south central GA at daybreak that then pushes east through our area. Thus, the greatest coverage of convection would occur over our southeast GA zones. This is also where the strongest convective indices are expected, so our primary focus for severe weather potential is in southeast GA and extreme southern SC. Damaging winds appear to be the primary threat assuming the convection becomes organized into a line. Isolated large hail or tornadoes can never be completely ruled out. Farther to the north in SC, at least scattered showers and thunderstorms will move through, but extensive cloud cover in the morning and less available instability should reduce the overall severe weather potential. Rainfall totals on Friday will range from 1-1.5" in southeast GA and 0.5-1.0" in southeast SC. The brunt of the convection is expected to be off the coast by 3pm. A secondary shortwave will drop into SC early Friday evening, pushing the cold front into the area. A big question mark is what convection, if any, develops out ahead of the front. It will heavily depend on what happens in southern SC with the first batch of convection and whether or not the airmass gets worked-over as a result. If convective coverage is limited during the early afternoon activity, a greater degree of destabilization could occur in southern SC, allowing for a more conducive airmass for convective development late Friday afternoon or early evening. For now we penciled in scattered PoPs across eastern Berkeley/Charleston Counties late afternoon and early evening. Saturday will be dry and noticeably cooler with highs in the upper 70s. Sunday will warm up a bit due to upper ridging, with highs in the mid 80s. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Early next week will briefly start off quiet before a warm front extending across the Deep South lifts north. Conditions look quite unsettled beginning late Monday night into Wednesday due to plentiful upper forcing and deep moisture building in. Several rounds of showers and thunderstorms are expected. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... KCHS/KJZI/KSAV: VFR has returned to all sites. With at least some clearing and due to the wet grounds, some stratus and fog will develop into Friday morning. Flight restrictions are likely for several hours, at least down into the MVFR category, but potential for even IFR. An MCS will move in from the west Friday morning, impacting especially KSAV into the early or mid afternoon. For now we show just -SHRA (also VCTS at KSAV), and additional flight restrictions are possible. If there is an MCS that impacts the terminals, strong winds and heavier rains could occur. Extended Aviation Outlook: VFR conditions will return for the weekend into early next week. Scattered convection expected Monday night and Tuesday. && .MARINE... Tonight: Expect winds to be mainly S-SW 10-20 kt. A few gusts up to 25 kt are possible at times, but not enough to justify a Small Craft Advisory. Seas will be in the 2-4 ft range. Low stratus and maybe some fog will develop overnight. Likely not enough fore an advisory, but possibly a Marine Weather Statement for Charleston Harbor. Friday: A decent SW gradient expected in advance of a cold front, though winds will be quite variable once convection moves offshore midday. Late in the afternoon and early evening, wind gusts could approach 25 kt, so it`s not out of the realm of possibility that a short-duration Small Craft Advisory is needed. Due to the low confidence we will hold off on any issuance with this package. Marine conditions will improve Saturday morning as high pressure builds in from the west. Winds/seas expected to increase Monday night into Tuesday ahead of the next storm system. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM...JRL LONG TERM...JRL AVIATION... MARINE...