textproduct: Charleston

WHAT HAS CHANGED

Snow timing and amounts were updated based on short term trends. Minor adjustments to temperatures and wind chills tonight through Wednesday.

KEY MESSAGES

- 1) Risk for minor snow accumulations through early this afternoon across far interior areas. - 2) Cold temperatures in the low to mid 20s (upper 20s to lower 30s along the coast) possible Monday, Tuesday, and Wednesday morning.

DISCUSSION

KEY MESSAGE 1: Risk for minor snow accumulation through early this afternoon across far interior areas.

Correlation Coefficient (CC) and reflectivity data (Z) from both KCLX and KJGX suggest the freezing level continues to steadily lower as colder/drier air filters into the area. Widespread rains are in place and are beginning to mix with and even change over to all snow across the far interior. The rain recently changed over moderate snow around Millen, GA. Areas west and north of a Metter to Sylvania line may see a brief period (1-3 hours) of moderate snow before ending as the core of the strongest forcing aloft with the negatively tilted shortwave moves through. There have even been occasional convectively enhanced bands that have set up at times indicative of the alignment of strong 850-500 frontogenesis with pockets of negative EPV. One of these bands crossed over Dublin, GA, earlier this morning which yielded a period of heavy snow with vsbys <1/4 mile. This possibility had been discussed about for the past few days. Although ground temperatures are still warm, webcams to the west over east-central Georgia suggest rates will be sufficient to produce minor accumulations, mainly on grassy areas and other elevated surfaces such as roof tops. Snow amounts of 0.1-0.3" were maintained, which is just shy of Winter Weather Advisory criteria. Significant travel issues are still not expected, but isolated slick spots could occur on elevated bridges and overpasses. Elsewhere, while a few snow flakes could mix in as far east as I-95 before the rain ends, precipitation will remain all liquid.

The rain and snow will quickly end from west-east later this afternoon as low pressure offshore pulls away.

KEY MESSAGE 2: Cold temperatures in the low to mid 20s (upper 20s to lower 30s along the coast) possible Monday, Tuesday, and Wednesday morning.

Behind the departing surface low and exiting shortwave aloft, cooler air is ushered in tonight into Monday morning. Weak cold air advection (CAA) from a surface high pressure moving into the Gulf, combined with some radiational cooling, will bring overnight lows down into the mid 20s for inland areas rising up to the lower 30s along the coast. Probabilities for temperatures at or below 20 deg F have become fairly low (<10% for majority of the area), though a small footprint of 30% probabilities remain across portions of inland southeast Georgia. Winds will remain fairly weak overall, and don't look to be able to produce wind chills below 20 degrees across portions of inland southeast Georgia and up towards the mid 20s elsewhere. LREF probabilities for wind chills at or below 20 deg F remain near 40% range for the aforementioned portions of inland southeast Georgia, while the high res HREF and REFS both keep chances below 10%. Given the lack of clear signal and the general trend for winds to remain weak, have opted to forgo a Cold Weather Advisory at this time, though this will continue to be monitored.

Ahead of our next cold front, highs on Monday are only expected to reach into the upper 40s to lower 50s. The cold front pushes through during the late evening hours, with a surface high pressure moving into the southeast region from the central CONUS. This will bring another round of overnight lows in the mid 20s inland to lower 30s along the coast, with wind chills in the upper teens to upper 20s. Probabilities for wind chills at or below 20 degrees F are highest for areas west of the I-95 corridor, though they have decreased slightly with the latest LREF and HREF data ranging from 30 to 40%, while the REFS has probabilities < 10%. A cold weather advisory appears unlikely at this time, though the area to watch will continue to be portions of inland southeast Georgia.

Highs on Tuesday are again expected to be in the mid 40s to lower 50s. Our final cold overnight period from this event will occur as the previously mentioned surface high pressure slides by just to the north of the local area. We could see Cold Weather Advisory criteria (20 degrees F or lower) across inland areas from either temperatures alone if there is no wind (20-40% chance), or from wind chills if winds are a touch stronger (30-40% chance).

The later half of the week will see a return to near-normal highs and lows, though near-freezing temperatures may return for inland areas Friday morning behind a cold front.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

18/18z TAF Discussion: KCHS/KJZI/KSAV: Conditions will rapidly improve at all three terminals by late afternoon as rain ends and much drier/cooler air filters in from the west. VFR will then prevail from this evening through 19/18z.

Extended Aviation Forecast: There are no concerns.

MARINE

Through Tonight: Rain will be ending from west to east throughout the afternoon hours. As cold air advection continue out of the northwest, wind gusts into the lower to mid 20s will remain over the waters throughout the afternoon hours, strongest from 15NM out to 60NM. 6 foot waves look to remain confined close to the 60NM boundary, decreasing to 3 foot waves along the coast. While conditions will slowly improve and may dip below Small Craft Advisory criteria this evening, a resurgence in winds speeds above criteria is noted on high res guidance during the late evening/early overnight hours as a push of cold air moves onto the waters. Have thus extended the expiration time for all zones through 9Z. The Charleston Harbor looks to remain just below criteria, but that will need to be closely monitored this evening. Rain exits the area Sunday afternoon/evening, with winds subsiding into the overnight hours.

Monday to Thursday: No high confidence marine concerns in the extended. Northwesterly winds become breezy on Tuesday, with gusts up into the upper teens throughout the afternoon hours. Wave heights begin to trend upwards on Wednesday, continuing into Thursday as swell moves in from the Atlantic, though wave heights look to remain below 6 ft.

CLIMATE

Snowfall Records for January 18: KCHS: 0.4/1977 KSAV: 1.0/1893

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory until 4 AM EST Monday for AMZ350-352-354- 374.