FXUS62 KCHS 101127 AFDCHS

Area Forecast Discussion National Weather Service Charleston SC 727 AM EDT Sat May 10 2025

.SYNOPSIS...

A front will remain stalled near our area through early next week. Low pressure will slowly move through Monday into Tuesday, followed by high pressure.

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.NEAR TERM /THROUGH TONIGHT/...

Early this morning, nighttime microphysics satellite product showed a band of low clouds associated with a backdoor cold front just off the coast near the NC/SC border. To the west, a sfc low is expected to organize over the Deep South, under a closed H5 low. The low is not anticipated to move much today into tonight as the closed H5 low becomes part of Rex Block. However, the circulation around the low will bring deep moisture across the CWA, with PW values ranging between 1.6 to 1.7 inches this afternoon through tonight. As the backdoor cold front reaches the forecast area around daybreak, it should begin its southward push. By this afternoon, H85 winds are forecast to shift from the south and increase to 15 to 20 kts. A west to east oriented band of isentropic lift should gradually expand across SE GA/SC this afternoon. The combination of the increased forcing and SBCAPE between 1000-1500 J/kg should support an expanding area of showers and embedded thunderstorms this afternoon, the greatest coverage of thunderstorms expected across SE GA and along the coast this afternoon. Isentropic lift should lift slowly north across SC Lowcountry tonight. SBCAPE sourced from the Gulf Stream will push along the GA/SC coast tonight, high resolution guidance indicates that convection may develop over the Atlantic and stream onshore. This process may lead to areas of very heavy rainfall, HREF indicate probabilities of 1" within 40 km increase to around 50 percent along with a 10 percent chance for 3" within 40 km. WPC has highlighted the region in their Excessive Rainfall Outlook. In addition, the environment across SE GA this afternoon may support some strong to isolated severe thunderstorms, with a risk of damaging winds and hail.

Temperatures today will be limited by thick cloud cover, steady ENE winds, and rounds of rain. High temperatures are forecast to range from the low 70s across the SC Lowcountry to the mid 70s across SE GA. Tonight, low temperatures are forecast to range from the low 60s inland to the upper 60s along the coast.

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.SHORT TERM /SUNDAY THROUGH TUESDAY/...

A very active period is forecast in the short term period, with numerous to widespread showers and thunderstorms forecast each day.

Aloft a mid-level closed low will be positioned over the southeastern states, while a the surface a front will remain stalled in the vicinity of the forecast area. Moisture will continue to be advected into the region, owing to the southwesterly flow aloft. PWATs are forecast to reach upwards of 1.8" each day through the period, which would be close to the daily maximums according to SPC Climatology. Several rounds of showers and thunderstorms are forecast through the period, with the greatest coverage likely from Sunday night through Monday night. Precipitation will likely be ongoing to start Tuesday, tapering off into Tuesday night. Generally 3 to 6 inches are forecast across the region through the period. It is worth noting that HREF probabilities show the potential (~30%) for upwards of 4 inches across portions of southeastern GA on Sunday. Given the impressive HREF probabilities the WPC continues to highlight the region in a Slight Risk for Excessive Rainfall on both Sunday and Monday.

High temperatures Sunday and Monday will be below normal, given precipitation and cloud cover, with low to mid 70s and some upper 70s along the Altamaha River in GA in the forecast. With expected cloud cover, overnight lows Sunday and Monday night will remain mild, only dropping into the 60s. Temperatures on Tuesday will return to near normal as precipitation wanes and some sunshine returns, with highs reaching into the low to mid 80s.

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.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...

The mid level closed low will begin slowly ejecting northeastward towards New England in the middle of the week. By the end of the week ridging aloft will build into the southeastern states. At the surface the stalled front will move into the Atlantic waters mid week, with high pressure building in thereafter. Isolated to scattered showers and thunderstorms will be possible on Wednesday, mainly diurnally driven. As ridging builds in aloft with high pressure at the surface a mainly dry forecast is in store through the remainder of the week. Temperatures initially will be around normal, with the potential to increase to well above normal by the end of the week.

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.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...

6Z TAFs: A cold front will slide south across the forecast area this morning as an area of low pressure organizes over the Deep South. As the low approaches from the west, the front should stall across the region. Forcing and instability will increase across KSAV by late this morning and KCHS/KJZI this afternoon. This environment will be ripe for rounds of showers and thunderstorms today through this evening. In addition, MVFR ceiling is forecast to develop by mid-morning and is expected to linger through the rest of the day.

Extended Aviation Outlook: MVFR or lower cigs and/or vsbys possible Sunday through Tuesday as a front remains stalled nearby and several rounds of showers/tstms move through.

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.MARINE...

A backdoor cold front will arrive from the north this morning, then drifting to the south during the daylight hours today. Behind the front, northeast winds should increase, approaching Small Craft Advisory (SCA) criteria across the nearshore SC waters. We will monitor trends upstream this morning, it is possible one or both SC nearshore zones could be highlighted with SCA today. Winds should settle to 10 kts with gusts around 15 kts by late tonight. The strengthening winds are forecast to build seas to 3 to 5 ft by this afternoon, diminishing to 3 to 4 ft late tonight. In addition, clusters of thunderstorms will likely push across the marine zones late this afternoon into tonight, Special Marine Warnings may be needed.

Sunday through Wednesday: A stalled front will linger in the vicinity of the coastal waters Sunday and into early next week. Southeasterly flow will increase Sunday, with 15-20 knots with gusts to around 23 knots forecast by Monday. Seas will build to 4 to 5 ft, with some 6 ft possible across the 20 to 60 nm offshore GA waters and the nearshore Charleston County waters on Monday and into Tuesday. Small Craft Advisories may be required.

Rip Currents, strengthening northeast winds will develop in the wake of a passing backdoor cold front today. The combination of a strengthening longshore current and building breakers may produce rip currents along the SC/GA coast today. A moderate risk will be posted until 8 PM this evening.

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.CLIMATE...

Record Precipitation:

May 10: KCHS: 1.45/1961 KCXM: 1.72/1949 KSAV: 1.29/1989

May 11: KCHS: 1.93/1952 KCXM: 1.57/1899

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.CHS WATCHES/WARNINGS/ADVISORIES...

GA...None. SC...None. MARINE...None.

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NEAR TERM...NED SHORT TERM...CPM LONG TERM...CPM AVIATION...CPM/NED MARINE...CPM/NED