textproduct: Charleston

WHAT HAS CHANGED

Updated for Dense Fog Advisory. The Aviation and Marine sections were updated.

KEY MESSAGES

- 1) Dense fog possible this morning across the South Carolina Lowcountry, Southeast Georgia and the adjacent coastal waters.

- 2) Unseasonably warm temperatures continue into the middle of next week, with increasing rain chances during the later half of this weekend.

DISCUSSION

KEY MESSAGE 1: Dense fog possible this morning across the South Carolina Lowcountry, Southeast Georgia and the adjacent coastal waters.

Dense fog continues to expand across Charleston and nearby areas. The Dense Fog Advisory was extended to include Coastal Colleton and Tidal Berkeley.

Early morning GOES-E fog products, VIIRS nighttime visible imagery and surface observations show areas of stratus expanding across interior Southeast Georgia with patchy sea fog over the coastal waters. The forecast confidence concerning the fog forecast is low with all of the near term high-resolution guidance and the 07/00z synoptic guidance initializing very poorly. Most of the guidance would suggest widespread dense fog is already in place across the coastal waters and nearby coastal counties which is just not the case. Conditions are supportive of stratus building down to produce fog across the interior through daybreak with 1000 hPa condensation pressure deficits progged to drop below 2 hPa as dewpoints depressions approach zero within a decoupled boundary layer. However, at the coast, southeast winds are expected to persist, which is typically not overly favorable for widespread sea fog formation given the limited the warm parcel residence times across the cold Atlantic shelf waters.

Given current observational trends and limited useful model data, it is not exactly clear how widespread inland fog will become or how much sea fog will develop and expand onshore through sunrise. The previous fog forecast was mostly maintained, although the "widespread" fog qualifier was removed until more definitive fog trends can be identified. A Dense Fog Advisory may still be needed over the coming hours, however.

KEY MESSAGE 2:

Deep-layered high pressure extending across the western Atlantic will prevail across the Southeast United States this weekend into the middle of next week, with ensemble situational awareness tables continuing to show that geopotential heights at various levels peak at or above the 90th percentile wrt climatology. This pattern favors a warm southerly flow under ample sunshine each day ahead of a stalling/dissipating front upstream Monday, with well above normal temperatures in the upper 70s to mid 80s, coldest along the coast.

Despite sufficient moisture, high resolution convection allowing models show persistent subsidence associated with this pattern which looks to hinder production of showers/storms over the area today. Scattered weak shortwaves work to flatten the ridge on Sunday bringing scattered chances (30-45%) for showers and thunderstorms, though models are indicating they will be fairly quick moving leading to low rainfall amounts at under a quarter of an inch, ending overnight into Monday. Not currently expecting any severe weather or flooding with this activity, but severe weather can't be fully ruled out per some of the AI/ML guidance. Another chance for light rain late Monday into Tuesday from a weak passing shortwave may present itself, though model confidence is low on the track thus leading to pops remaining at or below 30%. Warm temperatures continue ahead of a more substantial cold front arriving to the local area during the second half of the week, bringing normal temperatures and renewed chances for rain.

The latest forecast ties the record warm low temperature at Savannah on Tuesday, and is within 3 degrees of record highs and record warm lows Saturday through Wednesday.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

07/12z TAF Discussion: KCHS/KJZI/KSAV: Fog should lift at all terminals by 14-15z with VFR prevailing thereafter. Guidance is still hitting the potential for fog/stratus again late tonight/Sunday morning. Confidence is unclear as it appears its origins are from off the Atlantic where model performance has been poor. Opted for a much more optimistic forecast until better trends can be established.

Extended Aviation Outlook: Restrictive ceilings and visibilities are possible overnight into the early morning hours each night into early next week due to low stratus/fog. Chances for scattered showers and thunderstorms return Sunday afternoon/evening, leading to chances for temporary flight restrictions.

MARINE

Marine Dense Fog Advisory was expanded to include Charleston Harbor through 10 AM.

Through Tonight: Sea fog is the main concern over the waters through tonight. Satellite and webcams show patches of sea fog slowly expanding over the waters. It is unclear how widespread the fog will become especially with southeast winds likely limiting parcel residence times. The Marine Dense Fog Advisory was expanded to include the South Santee-Edisto Beach nearshore leg to match up with WFO Wilmington's advisory to the north. Otherwise, fairly light southeast wind swill veer to the south and southwest tonight as the gradient between high pressure centered well offshore and an approaching cold front tightens. The risk for sea fog will persist.

Sunday through Wednesday: High pressure will remain the dominant weather feature across local waters into next week, favoring a south/southeast wind in the 10-15 kt range and seas generally between 2-4 ft, well below Small Craft Advisory thresholds. Sfc winds could tip more south/southwest heading into early next week, but will continue to remain well below Small Craft Advisory levels between Atlantic high pressure and a stalling/dissipating front well inland. As that front continues to push eastwards, the pressure gradient rises and may result in winds reaching Small Craft Advisory levels Wednesday into Thursday, which will continue to be monitored.

CLIMATE

Record High Temperatures:

March 7: KCHS: 87/2023 KCXM: 84/2023 KSAV: 86/2023

March 8: KCHS: 86/1974 KCXM: 86/1951 KSAV: 86/1974

March 9: KCHS: 87/1974 KCXM: 84/1974 KSAV: 88/1974

March 10: KCHS: 90/1974 KCXM: 87/1974 KSAV: 91/1974

March 11: KCHS: 85/2015 KCXM: 82/1997 KSAV: 87/2015

Record High Minimum Temperatures:

March 7: KCHS: 63/1992 KCXM: 65/2023 KSAV: 68/1880

March 8: KCHS: 63/2022 KCXM: 65/2022 KSAV: 65/1880

March 9: KCHS: 66/2022 KCXM: 65/2022 KSAV: 65/2022

March 10: KCHS: 64/1974 KCXM: 65/1974 KSAV: 63/1909

March 11: KCHS: 63/2015 KCXM: 64/2016 KSAV: 64/1974

March 12: KCHS: 62/1985 KCXM: 64/1973 KSAV: 65/1973

CHS WATCHES/WARNINGS/ADVISORIES

GA...Dense Fog Advisory until 9 AM EST this morning for GAZ101- 116>119-137>141. SC...Dense Fog Advisory until 9 AM EST this morning for SCZ042>045- 047>052. MARINE...Dense Fog Advisory until 10 AM EST this morning for AMZ330-350- 352-354.