FXUS62 KCHS 220839 AFDCHS
Area Forecast Discussion National Weather Service Charleston SC 339 AM EST Sun Dec 22 2024
.SYNOPSIS...
Arctic high pressure will build across the region today. A coastal trough or weak low will develop nearby on Monday, before lifting north away from the area Tuesday. High pressure is expected to return mid week.
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.NEAR TERM /THROUGH TONIGHT/...
Today: West-northwest flow will prevail aloft while high pressure centered near the eastern Great Lakes ridges down the Eastern Seaboard. Plentiful dry air and clear skies will prevail, producing a sunny but chilly day. Low-level thickness progs support highs reaching the upper 40s to low 50s for southeast SC and low to mid 50s for southeast GA. The day will start off quite chilly this morning, with wind chill values as low as the low to mid 20s at sunrise.
Tonight: The center of the surface high will settle more over New England while a coastal trough starts to take shape just off the coast. The overall trend will be for increasing cloud cover as offshore stratocumulus attempts to push onshore late. The main question is how much cloud cover makes it onshore and what impact does this have on low temperatures. Current thinking is that cloud cover will have the greatest impact late, and along the coastal counties. The forecast advertises mid to upper 20s inland, ranging to the mid to upper 30s at the beaches. These lows, combined with persistent northeast flow will yield wind chill values dipping into the low to mid 20s for many areas, with the potential for values at or just below 20 degrees right an hour or two either side of sunrise Monday morning. A reasonable case can be made for needing a Cold Weather Advisory for the inland tier of counties, but will hold off for now and see how guidance trends through the day.
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.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
High pressure remains anchored inland Monday, while a coastal trough sharpens offshore. There are some indications that a weak low could form within the trough aided by weak shortwave energy just off the GA/SC coast, before it lifts northward away from the area later Tuesday. This feature is expected to bring scattered showers to the area, mainly Monday night into early Tuesday. Drier air and lower rain chances are expected to return for the latter half of Tuesday. Monday will be unseasonably chilly, with highs topping out in the upper 40s to lower 50s. Tuesday will be more mild, ranging from the mid 50s near the Santee River to low 60s closer to the Altamaha in Georgia. Lows will be within a few degrees of normal.
High pressure will expand back into the area for Wednesday/Christmas Day. Aloft, mid level ridge overhead will give way to another shortwave approaching later in the day. Most signals point to a rain- free day, with the possible exception being right along the coast where a 20% PoP resides. Highs will average around 60/lower 60s, except mid 60s over far southeast Georgia.
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.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
Fairly persistent pattern late week with high pressure inland, and yet another coastal trough developing offshore. Ridge largely prevails aloft, with perhaps some weak shortwave energy moving through. No significant weather concerns at this time with PoPs no higher than 20-30%. Temperatures will trend on the warmer side of normal.
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.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
VFR conditions will prevail at KCHS, KJZI, and KSAV through 06z Monday.
Extended Aviation Outlook: Flight restrictions are possible in showers and low clouds associated with a coastal trough Monday night into midweek.
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.MARINE...
Today through tonight: High pressure across the Northeast will continue to drive elevated northeast flow across the local waters. Sustained wind speeds will be in the 15-20 knot range through the period, with frequent gusts around 25 knots. Small Craft Advisories are in effect for all waters outside of Charleston Harbor through the period. Seas are forecast to gradually increase, becoming up to 6 feet in the nearshore Georgia waters and 5-8 feet in the outer Georgia waters by sunrise Monday.
Monday through Friday: High pressure will persist inland Monday, while a coastal trough sharpens offshore. A weak low could form within the trough before it lifts north away from the area on Tuesday. A tight pressure gradient between the inland high and coastal trough will lead to gusty northeast winds Monday into Monday night. Small Craft Advisories will remain in place for all coastal waters outside of the Charleston Harbor. Conditions should improve as we head into midweek. Northeast winds will remain gusty through the latter half of the week, but current forecast keeps winds/seas below advisory levels. The exception possibly being over the outer Georgia waters where 6 foot seas could return.
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.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None. SC...None. MARINE...Small Craft Advisory until 10 PM EST Tuesday for AMZ350.
Small Craft Advisory until 1 PM EST Tuesday for AMZ352-354. Small Craft Advisory until 10 PM EST Tuesday for AMZ374.
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NEAR TERM...BSH SHORT TERM...ETM LONG TERM...ETM AVIATION...BSH/ETM MARINE...BSH/ETM