FXUS62 KCHS 010619 AFDCHS
Area Forecast Discussion National Weather Service Charleston SC 119 AM EST Mon Dec 1 2025
.SYNOPSIS...
A storm system will pass through the region late today into Tuesday. High pressure then returns for the middle to end of this week ahead of the next frontal system that could impact the area Friday into the weekend.
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.NEAR TERM /THROUGH TONIGHT/...
During the pre-dawn hours, the cold front will surge southward across GA and the adjacent Atlantic waters. Behind the front, high pressure will build across the forecast area, remaining centered over the Mid-Atlantic States. By this afternoon, an H5 shortwave will ripple over the Southern Plains with a 150 kts H25 jet crossing the Arklatex. Sfc low pressure should gradually organize near the Mississippi Delta along the cold front. The developing low should support strengthening south H85 winds over the sfc ridge across the Southeast U.S. this afternoon through tonight. This afternoon, deepening isentropic lift and moisture should support thick cloud cover across the forecast area. Mostly cloudy to cloudy conditions combined with northeast sfc winds should keep high temperatures limited to the upper 50s inland to the low to mid 60s along the coast and extreme SE GA. Coniditons through the daylight hours should remain dry. However, isolated showers may cross extreme SE GA late this afternoon.
Tonight, high resolution guidance indicates that H85 winds will strengthen overnight, reaching 60 kts across much of the CWA by 12Z. The sfc ridge should remain across the forecast area tonight, until the sfc low tracks NE along the coast by day break. Models indicate strong forcing develop along and ahead of the sfc low. The deepening forcing along with PW values in excess of 1.5 inches should result in widespread rainfall after midnight. Rainfall rates will likely become moderate during the pre-dawn hours, thunderstorms possible near the coast. Low temperatures are forecast to range from the mid 40s inland to the low to mid 50s across the coastal counties.
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.SHORT TERM /TUESDAY THROUGH THURSDAY/...
Tuesday: In the upper levels of the atmosphere, a jet streak will start to splinter over the Ohio River Valley with an area of low pressure beginning to move northeast across southeast Georgia. Simultaneously, an area of high pressure over the Canadian Maritimes responsible for the northeast winds today, will slowly move east while widespread rain falls into the CAD. This precipitation falling into the CAD will act to reinforce the northeast winds and keep Tuesday morning rather cold and wet. However, the key question is when will the CAD weaken and by how much. Three subtle but important scenarios are possible with this system:
Scenario 1 (~50% chance): The CAD is slightly stronger and the area of low pressure rides northeast along a stalled boundary across inland GA and SC. Peak rainfall amounts of 1" - 2" from a Candler GA to Hampton SC to Berkeley SC county line.
Scenario 2 and 3 (50% chance): The CAD collapses more quickly/ weaker with the peak rainfall axis being in the Midlands or even approaching the Upstate of SC.
Either scenario has the peak rainfall amounts avoiding the urban area of Savannah and Charleston.
Hourly Rainfall Rates: Latest run of the HREF shows the most likely rates to be around .10"/ hour with some rates nearing 0.25" an hour. Probabilities of rainfall amounts exceeding 1" in 6 hrs are less than 20%.
Timing: Sprinkles will start 8 PM Monday to 12 AM Tuesday with peak precipitation rates between 3 AM and 2 PM Tuesday. Precipitation will then end from west to east 4 PM - 8 PM Tuesday as a cold front crosses GA and SC.
Wednesday and Thursday: Surface high pressure will move east over the Ohio River Valley with no precipitation expected. Winds initially Wednesday morning will be out of the northwest, with a reinforcing cold front then crossing the zones from the northeast. Expect temperatures to be 5 to 10 degrees below normal.
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.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
A return of multiple rounds of precipitation looks possible for next weekend as a long wave trough axis centers across the central United States. Some guidance is showing a more amplified pattern (~65%) while a mix of GEFS/ GEPS/ EPS members how a less amplified pattern (~35%). The more amplified pattern allows multiple rounds of shortwaves to traverse the region along with multiple rounds of precipitation. The less amplified pattern, keeps most of the rainfall further south and east of the region. At this point, precipitation for Friday into Saturday at times appears likely (>60%) with temperatures slightly below normal.
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.AVIATION /06Z MONDAY THROUGH FRIDAY/...
Prior to the 6Z TAFs, the sfc cold front was near KCHS and KJZI, pushing seaward. MVFR ceilings have developed near the front, impacting KCHS until 7Z. In the wake of the front, winds will shift from the northeast and ceilings should remain VFR. During the daylight hours, a sfc ridge will build across the terminals and low pressure organizes near the Mississippi Delta. Isentropic lift and moisture should increase from the south after mid-morning. KSAV is timed to see MVFR ceilings by 17Z, then reaching KJZI and KCHS by 21Z. HREF indicates that the leading edge of a shield of rain will reach KSAV between 3-6Z, highlighted with a PROB30. Ceilings are expected to lower to IFR with the arrival of the rain. Rain may reach KCHS and KJZI shortly after 6Z Tuesday.
Tuesday: A storm system will bring higher probabilities (50-80%) of flight restrictions tonight into Tuesday, with both low ceilings and lowered vsbys possible in addition to rain showers and isolated to scattered thunderstorms. Low level wind shear also appears likely (>60% chance) at all terminals Tuesday morning.
Wednesday through Friday: VFR through Friday morning. Late Friday, cloud bases will begin to lower ahead of the next storm system.
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.MARINE...
During the pre-dawn hours, the cold front will surge southward across GA and the adjacent Atlantic waters. Behind the front, high pressure will build across the forecast area, remaining centered over the Mid-Atlantic States. This pattern will support gusty northeast winds across the marine zones today, gusts reaching into the low 20 kts. This evening, low pressure is expected to approach from the west, resulting in winds veering from the south. South winds should continue to strengthen through the rest of the night, with gusts reaching 25 kts or more across the outer GA and Charleston County nearshore waters during the pre-dawn hours. Wave heights will increase late tonight, with 6 ft seas developing with the SC nearshore and outer GA waters during the pre-dawn hours. The wind and sea conditions will be highlighted with Small Craft Advisories.
Tuesday: A surface low will approach the region from the southwest. Northeast winds from the CAD will slowly weaken and turn from the southeast then southwest by the morning hours. Sustained winds of 15 to 20 kt with gusts up to 25 kt appear likely as cooler shelf waters limit mixing. Expect seas 5 to 8 ft. As such, a small craft advisory has been issued for the offshore Georgia waters and nearshore SC waters for Tuesday morning and evening. A cold front will then cross the waters Tuesday evening with seas slowly falling 3 to 5 ft.
Wednesday through Friday: Northwest winds veering from the north Wednesday morning 10 to 15 kt. Seas 2 to 4 ft. No precipitation is expected.
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.TIDES/COASTAL FLOODING...
Chances for minor coastal flooding return with the Tuesday early morning high tide, along the Charleston and Colleton county coast. Astronomical tides will then continue to rise with the morning high tide cycle through Friday and remain elevated through the weekend. Coastal Flood Advisories will likely be needed, primarily for the Charleston Harbor tide (Charleston and coastal Colleton counties).
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.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None. SC...None. MARINE...Small Craft Advisory from 4 AM Tuesday to 1 AM EST Wednesday
for AMZ350-374. Small Craft Advisory from 10 AM to 7 PM EST Tuesday for AMZ352.
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NEAR TERM...NED SHORT TERM...Haines LONG TERM...Haines AVIATION...Haines/NED MARINE...Haines/NED