textproduct: Charleston

SYNOPSIS

A weak cold front will briefly stall near the Savannah River this morning before lifting north this afternoon. A cold front will move through the area Monday with high pressure prevailing for the rest of the week.

NEAR TERM /THROUGH TONIGHT/

Today: The upper-level ridge axis will pass over the region today. A weak backdoor cold font will continue to sink south early this morning and will likely become hung up near the Savannah River by daybreak. The front is expected to lift slowly back to the north as a warm front later in the day as surface high pressure propagates to the southeast and well offshore of the Southeast U.S. coast. Some shallow ground fog could pool along the shallow front itself and may result in a band of lower visibilities (roughly 3- 5SM) across far southern South Carolina as daybreak approaches. In addition, widespread dense fog developing over the Florida Panhandle and the Suwannee Valley is expected to expand across far Southeast Georgia over the next few hours, possibly oozing north to near the Altamaha River right around sunrise. The risk for dense fog looks greatest south of the Altamaha River, but it could get close. Weak isentropic lift noted along the 295-300K surfaces could spark a few showers in the vicinity of the northward moving warm front later today. The risk for some very light QPF looks highest across the Charleston Tri-County area. Pops around 20% were introduced to account for this. Highs today will range from the lower 70s over Southeast South Carolina to the mid 70s across Southeast Georgia. There are some signals that suggest a 4000-6000 ft cloud deck may end up a bit thicker in Georgia which may limit highs there a bit. While some statistical data support slightly cooler afternoon highs than what the 28/01 NBM is highlighting, the unknowns about cloud cover and possible breaks allowing for periods of greater insolation necessitate limiting any significant deviations from the NBM at this time.

Tonight: The area will be firmly in the warm sector as a cold front approaches from the west. Increasing wind fields and weak warm air advection will yield a fairly warm night with lows only dropping into the upper 50s to around 60 for most areas. Conditions looks somewhat favorable for the development of sea fog over the coastal waters overnight. It is unclear how widespread or dense this fog will become with near term models often over-forecasting the extent and degree of sea fog this time of year. Should any fog develop, some of this may brush the lower South Carolina coast, especially from Tybee Island northward. Patchy fog was introduced for the immediate coastal areas and as far inland as (roughly) the US-17 corridor in Charleston County. Adjustments to the fog forecast may very well be needed later today as shorter term trends become more apparent.

SHORT TERM /MONDAY THROUGH WEDNESDAY/

For Monday morning, we'll be watching a cold front move towards the area from the west, with a strong mid-level trough similarly moving towards the area. Expect breezy winds to quickly develop as the temperature inversion mixes out, allowing for the strong winds from the low-level jet to be brought to the surface. Sustained winds out of the southwest in the teens to lower 20s with gusts in the upper 20s to lower 30s are expected out ahead of the front. Temperatures will remain seasonably warm in the upper 60s to lower 70s, coldest for inland areas due to the cold front moving from west to east, with temperatures dropping throughout the afternoon hours. Behind the frontal passage, winds swing around to become out of the northwest, remaining similarly breezy amidst cold-air advection and increasing pressure advection.

Lake Winds: Given periods of sustained winds above 20 knots and gusts over 25 knots, a Lake Wind Advisory for Lake Moultrie will likely be needed starting Monday afternoon and continuing into the early overnight period on Tuesday.

In addition to the breezy winds, models continue to show a band of broken light rain showers developing along/ahead of the front Monday morning into the afternoon hours. However, given PWATs near an inch and rather meager instability, any rainfall amounts are expected to be light at under a tenth of an inch.

Much cooler air is brought in behind the cold front, with Tuesday morning temperatures expected in the lower to upper 30s, warmest along the coast. Wind chills into the mid to upper 20s are expected, so be sure to dress appropriately Tuesday morning as this will feel much cooler than it has been as of late. While not quite as breezy, northwest winds gusting into the mid to upper teens will be continuing throughout the day on Tuesday, with afternoon highs only expected to reach the lower 50s given the continued cold-air advection.

As the cold-air advection dwindles into the overnight period, winds will weaken allowing for radiational cooling to take affect for the rest of the overnight hours. Will likely see early morning temperatures dip down into the mid 20s inland, though winds currently look weak enough to not see wind chills below cold weather advisory criteria of 20 degrees or less. Closer to the coast, expect low temperatures Wednesday morning in the lower/mid 30s. Temperatures begin to moderate on Wednesday, with ample sunshine bringing the region back up into the mid 50s.

LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/

Upper level trough axis moves across the area overnight into Thursday, with a surface high pressure moving into the eastern Gulf. This will likely keep winds just strong enough to limit radiational cooling, though overnight temperatures into Thursday may dip close to freezing for inland areas, closer to the upper 30s for areas along the coast. Temperatures continue to moderate Thursday and Friday, rising into the upper 50s and lower to mid 60s respectively.

A weak shortwave looks to move towards/across the area on Saturday, accompanied by a surface low pressure system in some models, bringing a chance for light rain showers.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

28/06z TAF Discussion: KCHS/KJZI: A weak backdoor front will cross the terminals by 09z resulting in a steadier east winds. Shallow ground fog could briefly reduce vsbys at KJZI to MVFR thresholds prior to FROPA. A TEMPO group for MVFR vsbys was maintained through 08z to account for this. Otherwise, VFR. Isolated showers could develop near the terminals later this morning through early afternoon as the front lifts back to the north, but no meaningful impacts are expected. There is a chance that some degree of sea fog could impact KJZI later this evening as conditions favor its development offshore. The low-level flow will become favorable for any sea fog that forms to brush the coast. Confidence on impacts this far out is very low, so no mention was included for the 06z TAF cycle. VCFG or possibly even some vsby reductions may be considered for KJZI with the 12z TAF cycle.

KSAV: VFR will prevail through 28/06z. There is a brief window for some fog to impact the terminal just before daybreak as a weak front approaches from the north. Confidence for reduced vsbys is too low to introduce at this time.

Extended Aviation Outlook: Gusty winds are possible on Monday, along with a brief period where MVFR cigs are expected as weak rain showers move in along a cold front. Conditions improve shortly thereafter, with VFR conditions expected into the extended period.

MARINE

Through Tonight: A weak backdoor front will briefly stall near the Savannah River Entrance later this morning, then slowly drift back to the north later in the day. Winds will be east to northeast as high as 10 kt north of the front and variable to southerly less than 10 kt south of the front. The front should clear the South Santee-Edisto Beach nearshore waters by late this afternoon with south to southwest winds prevailing tonight ahead of a cold front. Winds tonight will increase to 10-15 kt.

Sea Fog: There is concern for the development of sea fog later today and especially tonight as warm air parcels advect over the cooler nearshore waters where sea surface temperatures are currently in the mid-upper 50s. HREF Grand Ensemble probabilities for vsbys <1NM increase to 50-70% across the Georgia and far southern waters by this afternoon and expand to 60-80% across all waters this evening. Models do have a history of being too aggressive with the degree and expanse of sea fog, especially given the marginal sea surface temperatures are in place, so these probabilities should be used with caution. There is too just much uncertainty to introduce anything more than patchy dense fog at this time, especially given model aggressive tendencies and marginal sea surface temperatures. Marine Dense Fog Advisories may become necessary if the sea fog does develop as much of the guidance suggests and vsbys 1 NM or less are realized.

Monday through Tuesday: Ahead of a strong cold front, Monday will see southwesterly winds increasing to 20 knots and gusts to 30 kts with seas building. A cold front will bring a shift in winds late Monday afternoon into the evening, continuing the breezy winds out of the northwest. Seas near 6 feet are expected well offshore in the waters from South Santee River to Edisto Beach SC, and also the waters from Savannah GA to Altamaha Sound GA roughly 40 to 60 nm out. Small Craft Advisories may have been posted for all waters, not including the Charleston Harbor as winds look to remain below advisory thresholds.

Wednesday and Thursday: Surface high pressure builds across the southeast on Wednesday, bringing improving conditions Wednesday into Friday.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory from 7 AM Monday to 7 AM EST Tuesday for AMZ350. Small Craft Advisory from 1 PM Monday to 4 AM EST Tuesday for AMZ352. Small Craft Advisory from 4 PM Monday to 4 AM EST Tuesday for AMZ354. Small Craft Advisory from 10 AM Monday to 1 PM EST Tuesday for AMZ374.