Marine Weather and Tide Forecast for Isle of Hope, GA

KEY MESSAGES
- 1) Confidence continues to increase in an accumulating snowfall event across a portion of the SC Lowcountry and SE Georgia Saturday morning through Saturday night.

- 2) Extremely cold temperatures are expected across our entire area this weekend into early next week. Historically cold wind chills are expected Saturday night into Sunday morning.

DISCUSSION
KEY MESSAGE 1: Confidence continues to increase in an accumulating snowfall event across a portion of the SC Lowcountry and SE Georgia Saturday morning through Saturday night.

A sharp trough and closed 500 hPa low is forecast to dig southward out of the Great Lakes today, dropping into the southeastern states tomorrow morning. Simultaneously a strong surface low is forecast to develop off the southeastern coast before trekking to the northeast through the weekend. Friday night into Saturday morning will remain dry across the region, as forecast soundings indicate plentiful dry air aloft. As precipitation along the backside of the coastal low begins to impact the region the atmosphere will saturate, with rainfall forecast across inland zones beginning around 9 AM.
Rainfall will then expand eastward towards the coastline around noon. As the coastal low begins its trek northeastward cold air will be ushered into the SC Lowcountry, resulting in a change over from rain to snow sometime in the afternoon hours across most locations.
Wet bulb temperatures are expected to drop below freezing just after noon across inland zones, working eastward into the afternoon. This will aid in the change over from rain to snow as the atmosphere diabatically cools with the falling precipitation. Something unique to this event is the very cold temperatures are forecast to yield a snow ratio of nearly 20 to 1. This is very high for the region, resulting in a "dry" snow. Combined with elevated winds gusting to around 20 mph, visibilities could be reduced leading to difficult driving conditions. There is still a degree of uncertainty regarding snow totals, as they are highly dependent on the location of the offshore low. However, confidence continues to increase that the region will see accumulating snow this weekend. The current forecast features a slight uptick in snow amounts (owing to a slight uptick in QPF) which is supported by both deterministic and ensemble guidance. Highest snowfall amounts are forecast to be across the Charleston Tri-County area, generally 3 to 5 inches. Confidence decreases and uncertainty increases the further south you go, however a Trace to 1 inch is possible even south of I-16 in SE Georgia. Given the slight upticks in snow totals and increasing confidence, the Winter Storm Watch for Charleston, Berkeley, and Dorchester Counties has been upgraded to a Winter Storm Warning. Elsewhere, roughly along and north of I-16 in SE Georgia, the Winter Storm Watch remains in effect.

KEY MESSAGE 2: Extremely cold temperatures are expected across our entire area this weekend into early next week. Historically cold wind chills are expected Saturday night into Sunday morning.

The mid-levels will consist of a very strong trough over the eastern half of the U.S. Saturday through Monday, followed by it shifting offshore on Tuesday. But before it shifts away, it appears to peak in intensity Saturday night, which is also when an embedded Low is over our area. NAEFs indicates 500 mb readings in that Low will be approaching minus 6 standard deviations at that time, which is very impressive over our part of the country. This will line up with a storm system, that'll be impacting our area this weekend. It's already covered in Key Message 1, so we won't restate all of the details. The storm will usher in very, very cold temperatures to our area. Highs on Saturday will range from the mid 30s across the northern tip of Berkeley County, to the mid 40s near the Altamaha River. Saturday night, lows will mostly be in the teens, maybe the lower 20s at the beaches, due to a fresh snowpack. But breezy northwest winds on top of the snowfall will cause wind chills to drop into the single digits across our entire area. These are dangerous wind chills for our part of the country and is why we have a Extreme Cold Watch in effect. On Sunday, High pressure will start building towards our region. The combination of northwest winds ushering colder temperatures over a fresh snowpack (especially for our SC counties) will cause high temperatures to range from near freezing near the Santee River, to around 40 degrees near the Altamaha River. Even daytime wind chills across our SC counties will probably be in the 20s. Sunday night, lows will again be in the teens, maybe the lower 20s at the beaches. But lighter winds will equate to wind chills in the teens just about everywhere, which would prompt Cold Weather Advisories. Temperatures are expected to moderate mostly into the 40s on Monday, with lows ranging from the lower 20s inland the the upper 20s at the beaches. Given the potential for light winds Monday night, it's borderline whether we'll need Cold Weather Advisories in some locations or not.
Temperatures moderate further on Tuesday with highs ranging from the upper 40s near the Santee River to the upper 50s near the Altamaha River.

AVIATION /12Z FRIDAY THROUGH TUESDAY/
VFR conditions will prevail at KCHS, KJZI, and KSAV through the 12Z TAF period.

Extended Aviation Outlook: The probability of widespread flight restrictions will increase for Saturday and Saturday night as an area of low pressure develops off the coast. There is also increasing potential for snow and gusty winds at the terminals.

MARINE
High pressure will prevail through tonight, bringing a gradual increase in both winds and seas. Conditions deteriorate on Saturday as strong Low pressure develops off the Southeast U.S.
Gale conditions are expected to develop across our GA waters late Saturday afternoon, then spread north into our SC waters by Saturday evening. Gale Watches remain up for all of the ocean waters, and we may eventually need one for the Charleston Harbor. The strongest winds and highest seas will be Saturday night into Sunday morning.
As the Low moves away on Sunday, conditions will gradually improve.
High pressure will then return on Monday and persist through the middle of next week.

CLIMATE
Record Low Temperatures:

January 31: KCHS: 15/1966 KCXM: 19/1966 KSAV: 16/1966

February 1: KCHS: 21/1977 KCXM: 23/1900 KSAV: 23/1977

February 2: KCHS: 19/1980 KCXM: 17/1917 KSAV: 18/1917

Record Low Maximum Temperatures:

January 31: KCHS: 36/1948 KCXM: 34/1936 KSAV: 37/1909

February 1: KCHS: 38/1980 KCXM: 36/1900 KSAV: 38/1900

February 2: KCHS: 38/1980 KCXM: 38/1898 KSAV: 38/1951

Record Snowfall:

January 31: KCHS: 0.6/1977 KSAV: 1.3/1977

February 1: KCHS: no record established KSAV: no record established

EQUIPMENT
The KCLX radar remains out of service. We hope to have the radar restored by Saturday. Users should use adjacent WSR-88D sites, including KCAE, KLTX, KJAX, KVAX and KJGX.

CHS WATCHES/WARNINGS/ADVISORIES
GA...Winter Storm Watch from Saturday morning through Sunday afternoon for GAZ087-088-099>101.
Extreme Cold Watch from Saturday evening through Sunday morning for GAZ087-088-099>101-114>119-137>141.
SC...Winter Storm Watch from Saturday morning through Sunday afternoon for SCZ040-042-043-047>049-051.
Extreme Cold Watch from Saturday evening through Sunday morning for SCZ040-042>045-047>052.
Winter Storm Warning from 7 AM Saturday to 1 PM EST Sunday for SCZ044-045-050-052.
MARINE...Gale Watch from Saturday afternoon through Sunday afternoon for AMZ350-352-354-374.