Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
514 FXUS62 KCHS 091956 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 356 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/... Radar indicates the line of strong thunderstorms is moving off the coast of SC, and is near the coast of our GA counties. Instability ahead of the line has peaked, but both the instability and shear should sustain the thunderstorms for another hour. The enhanced wind threat persists down there and a tornado also cannot be ruled out. We continue to adjust the POPs/weather grids based on the radar trends. The CAMs have a better grasp of the overall line now, with the southern end moving slower across our GA counties. Once the line of thunderstorms moves offshore, expect 1-2 hours of stratiform precipitation, followed by clearing by mid-evening. The rest of the night should remain generally dry. However, a second MCS will arrive from the west after the pre-dawn hours Friday morning. Rain-cooled temperatures are expected to remain nearly steady around 70 degrees tonight. && .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 /20Z THURSDAY THROUGH TUESDAY/... 20z TAFs: Radar indicates the line of strong thunderstorms has moved east of the TAF sites. We amended CHS and JZI, to improve conditions, since the storms have moved offshore. But we`re holding off on amending SAV as the storms are still nearby. Behind the storms, stratiform precipitation will persist for about another 1-2 hours. The precipitation should end by this evening, with VFR persisting into part of the night. MOS and some of the ensembles then indicate IFR ceilings developing over the terminals late tonight, which we kept in the TAFs. Finally, another round of showers and thunderstorms is expected to bring impacts to the TAF sites late in the TAF time period. Extended Aviation Outlook: Scattered to numerous showers and thunderstorms could continue into Friday afternoon with flight restrictions and gusty winds possible within convection. VFR conditions will return for the weekend into early next week. Scattered convection expected Monday night and Tuesday. && .MARINE... Through Sunset: A line of thunderstorms is moving though the coastal waters. Some of these storms could produce gusts in excess of 40 kts and possibly a waterspout. The main line of storms should move east our waters and dissipate by about sunset. Tonight: Expect winds to be mainly SW 10-20 kt. A few gusts up to 25 kt are possible across the Charleston County waters this evening, especially across the far northeastern portion of the zone. But the time and areal extend don`t appear to be enough to warrant a Small Craft Advisory. Seas should be in the 2-4 ft range. 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...JRL MARINE...JRL