textproduct: Charleston

WHAT HAS CHANGED

Sea fog has yet to materialize and near term guidance is backing off. Grids/text products were updated to remove all mention. Dewpoints were also lowered a bit for this afternoon and high temperatures were nudged up in a few places.

KEY MESSAGES

- 1) Near record warmth today.

- 2) Hazardous conditions are likely on Lake Moultrie late tonight into Saturday.

- 3) Fire Weather Watches are in effect for southeast SC and most of southeast GA on Saturday.

- 4) Dry with above normal temperatures next week.

DISCUSSION

KEY MESSAGE 1: Near record warmth today.

The center of a 588 DM ridge will remain over the TX/Mexico, with the H5 ridge extending east across the Southeast U.S. At the sfc, a strong backdoor cold front is forecast to stretch across the Mid- Atlantic states southwest to the southern Appalachians by 18Z. In addition, a deepening frontal wave is expected to develop over the Foothills near the NC/VA line this afternoon. This pattern will support WSW sfc winds across the forecast area today. The return flow should result in H85 temps to warm to around 15C this afternoon. High resolution guidance indicates that a sea breeze will advance inland this afternoon. Given nearly full insolation, mild llvl thickness, and afternoon sea breeze, high temperatures should favor values in the upper 80s. These temperatures would challenge record highs for today, see Climate section.

KEY MESSAGE 2: Hazardous conditions are likely on Lake Moultrie late tonight into Saturday.

Winds will increase on Lake Moultrie late tonight into Saturday behind a strong southward moving cold front. Conditions could get hazardous on the open lake waters with winds reaching as high as 20- 25 kt with gusts up to 30 kt. Wave action could be significant with waves reaching 2-3 ft at times, especially over the central and southern portions of the lake. A Lake Wind Advisory is in effect from midnight tonight until early Saturday afternoon.

KEY MESSAGE 3: Fire Weather Watches are in effect for southeast SC and most of southeast GA on Saturday.

A dry cold front will be far offshore at daybreak Saturday. Meanwhile, High pressure will be building in from the northwest. The center of this High will pass far to our north late Saturday. The High will usher significantly drier air and breezy winds into our area, creating dangerous fire weather conditions.

As is typical for this type of spring pattern, models are failing to adequately capture just how dry it will be. Therefore, we went much drier than guidance, going with the NBM10 for dew points, which arguably might not be dry enough. But it matches up with minimum RH values in the HREF. Dew points will drop into the upper teens and 20s across most inland areas, but remain higher at/near the beaches. This will cause afternoon RH values to drop into the mid/upper teens very far inland, while generally being in the low/mid 20s across most of our area, with higher values at/near the beaches. These values will be reached late in the afternoon.

Additionally, cold air advection and pressure rises from the High will lead to gusty northerly, then northeasterly winds. The strongest gusts will be in the morning, peaking in the 25-35 mph range across our SC counties and the 20-30 mph range across our GA counties. Winds should gradually ease into the afternoon, which is when RH values will really drop. So the strongest winds and lowest RH values won't line up perfectly.

However, state, military, and federal land management agencies have reported some extreme fire behavior with controlled burns and a few wildfires over the past few days. This is on top of the ongoing drought.

Per coordination with neighboring NWS offices as well as various fire weather partners, a Fire Weather Watch has been issued for all of our SC counties, and most of our GA counties. The start time is 8 AM, which is probably too early for our area. But it was done to assist state messaging. The end time was initially going to be 11 PM, again for state messaging. But this was hard to justify with winds significantly easing around sunset and RH values really rising closer to the coast. So the compromised end time was adjusted to 8 PM, which is historically when conditions improve across our area. An upgrade to a Red Flag Warning would be with this afternoons forecast package.

KEY MESSAGE 4: Dry with above normal temperatures next week.

Mid-level ridging will prevail over the Southeast U.S. most of next week while surface High pressure is in the western Atlantic. This pattern will continue to bring dry conditions to our area. High temperatures will be slightly below normal on Sunday, then rise above normal on Monday. The warming trend continues Tuesday through Thursday.

AVIATION /13Z FRIDAY THROUGH TUESDAY/

VFR is expected to prevail through the 12z TAF period. MOS and forecast soundings indicates that southwest winds will develop gusts at KCHS and KJZI this afternoon with a sea breeze, both TAFs will feature gusts between 15 to 20 kts. KSAV may see occasional gusts between 17-20Z, highlighted with a TEMPO. Wind gusts should end around sunset. A strong cold front is timed to push across KCHS and KJZI by 8Z and KSAV by 10Z. Gusts should increase to 25 to 30 kts by the end of the 12Z TAFs.

Extended Aviation Outlook: VFR. There will be gusty winds behind a dry cold front on Saturday.

MARINE

The coastal waters will remain under a broad pressure gradient today through this evening. This pattern should support southwest winds between 10 to 15 kts with gusts near 20 kts. Seas will range from 1-3 ft.

Saturday through Tuesday: A dry cold front will be well offshore by daybreak Saturday. High pressure will then start building in from the northwest early Saturday, then shift off the Mid- Atlantic Coast into Sunday. This will bring gale conditions to all of our waters early Saturday, followed by near gale conditions later Saturday into early Sunday. We have Gale Watches in effect to account for this. Conditions will further improve on Monday. Though, seas could stay elevated across the GA waters beyond 20 nm into Monday night.

High Surf: Breaking wave heights could reach 5-6 ft along parts of the Georgia coast Sunday. A High Surf Advisory may be needed.

CLIMATE

Record High Temperatures:

March 27: KCHS: 87/2021 KCXM: 81/2021 KSAV: 89/2021

CHS WATCHES/WARNINGS/ADVISORIES

GA...Fire Weather Watch from Saturday morning through Saturday evening for GAZ087-088-099>101-114>119-137-138. SC...Fire Weather Watch from Saturday morning through Saturday evening for SCZ040-042>045-047>052. Lake Wind Advisory from midnight tonight to 2 PM EDT Saturday for SCZ045. MARINE...Gale Watch from Saturday morning through Saturday afternoon for AMZ330. Gale Watch from Saturday morning through Saturday afternoon for AMZ350-352-354. Gale Watch from Saturday morning through late Saturday night for AMZ374.