textproduct: Charleston

WHAT HAS CHANGED

Dewpoint values this afternoon and Friday afternoon were lowered to account for the dry air over the region. The Aviation Section has been updated to reflect the 18Z TAFs.

KEY MESSAGES

- 1) An impactful system arrives late this weekend, resulting in renewed precipitation chances and perhaps a few thunderstorms.

DISCUSSION

KEY MESSAGE 1: An impactful system arrives late this weekend, resulting in renewed precipitation chances and perhaps a few thunderstorms.

A substantial southern stream shortwave will track into the southeast as a surface low tries to develop off the Mid-Atlantic coastline. Quite a bit uncertainty remains with this system as it depends on how quickly phasing occurs with this shortwave and the northern stream energy. This significant uncertainty is reflected in the 00Z.LREF cluster analysis where Cluster 1 contains roughly 70% of the GEPS members and about 50% of the GEFS members, emphasizing the split of solutions and the lack of a dominant scenario. The Cluster 1 analysis would be supportive of the 06Z.ECMWF as it has a slower onset of precipitation. While, Cluster 2 contains roughly 40% ENS members and about 20% of the GEFS members. The Cluster 2 analysis would be supportive of a drier solution as it displaces the southern stream shortwave farther south and exhibits less phasing.

The 13Z.NBM leans more towards the Cluster 1 analysis and the forecast has been maintained to reflect this. As the region becomes warm-sectored ahead of an advancing cold front on Sunday, expect precipitation to begin early Sunday and persist into Monday. Regarding rainfall amounts, there continues to be a 80-90% chance of rainfall > 0.5" and a 60-70% chance of rainfall > 1" within a 24-hr period. WPC seems to agree with this sentiment, as the region has been placed in a Marginal Risk of Excessive Rainfall. There is even a possibility of a few weak thunderstorms developing on Sunday afternoon/evening as a little bit of instability appears to be present. These thunderstorms could produce localized pockets of higher accumulations in some areas. As stated before, a lot of uncertainty remains with this system and trends will continue to monitored over the next couple days.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

VFR will prevail at KCHS/KJZI/KSAV through the 18Z TAF period.

Extended Aviation Outlook: VFR expected to prevail through Saturday. The potential for flight restrictions will increase into Sunday as an area of low pressure moves into the region.

MARINE

High pressure will dominate over the marine waters this afternoon through Saturday. The center of high pressure is forecast to be positioned to the NW of the region through Friday, yielding in generally NE winds. The high pressure is then expected to shift eastward, positioned just off the southeastern coast. This will result in a wind shift across the local waters to the SE by Saturday evening. An area of low pressure will then approach from the west on Sunday, creating a pinched gradient across the local waters between the approaching low and the offshore high. Winds gusts could approach 25 knots on Sunday along with seas building to 6+ ft across portions of the waters, possibly necessitating Small Craft Advisories for the waters. The low is then forecast to push through Monday, possibly yielding another period of stronger wind gusts. There remains considerable uncertainty regarding the low and its track, so the confidence in this period is low.

CHS WATCHES/WARNINGS/ADVISORIES

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