textproduct: Charleston

SYNOPSIS

A cold front will push offshore early Sunday. High pressure then builds into the area through mid-week, followed by another cold front on Thursday.

NEAR TERM /THROUGH TONIGHT/

This Afternoon: Low clouds and fog have finally scoured out, although some degree of low-level cloudiness will likely linger across parts of Charleston County into eastern Berkeley County for a few hours hours. Temperatures are rising as insolation increases and are on track to peak near record levels at both KCHS and KSAV later this afternoon. Bands of showers developing over the west wall of the Gulf Stream will remain well offshore and a QLCS moving into western Georgia should remain to the west through late afternoon.

Tonight: A large band of showers/tstms associated with an approaching cold front will steadily weaken as it moves east tonight as the corridor of strongest forcing with the powerful shortwave moving across the Great Lakes and the right entrance region of the polar jet pass by well to the north and northwest. The leading edge of the QLCS moving into the western Georgia should largely outrun the main frontal band over the next several hours and should largely dissipate prior to reaching the far interior zones by early evening. While a few showers could still occur across far interior areas adjacent to the CSRA and east-central Georgia, most areas will remain dry this evening. Rain chances are not expected to increase all that much overnight as the front moves from west-east during the early morning hours Sunday. 10/12z guidance has continued with the drier trends noted with the 12/00z runs, which seem reasonable given the lack of significant forcing, meager deep-layer moisture and the absence of instability. Overnight pops were lowered to 20%, except 30-40% in the Allendale-Sylvanis-Metter corridor. Overnight lows will be closely tied to FROPA, ranging from the lower-mid 50s in the Allendale-Metter corridor to the upper 50s/near 60s elsewhere.

Lake Winds: Changes are needed to the going Lake Wind Advisory for Lake Moultrie. The latest NBM and HREF Grand Ensemble support yesterday's thinking that the shallow marine layer will likely keep frequent gusts below 25 kt over the open lake waters for the rest of this afternoon into tonight. Probabilities run near 0% of reaching Lake Wind Advisory criteria this afternoon (despite gusty conditions over land) and only climb to 10-20% tonight as the cold front works through. Pre-frontal warm air advection regimes just do not yield favorable mixing profiles on the larger lakes such as Lake Moultrie given the cold water temperatures that are in place this time of year. Water temperatures on Lake Moultrie are running in the mid-upper 50s. Probabilities do not really ramp up until after daybreak Sunday when the strongest cold air advection works its way through. It is only then does the marine-layer scour out and deeper mixing commences. Given these trends, the start time of the Lake Wind Advisory has been pushed back from 11 PM this evening to 6 AM Sunday.

SHORT TERM /SUNDAY THROUGH TUESDAY/

Cold front continues to depart the region Sunday, allowing clear skies to gradually return. With the aid of deep-mixing and a strong low level jet, expect northwesterly winds to become a bit breezy in the wake of FROPA. Currently have gusts up to 30 MPH possible for much of the daylight hours. Dewpoints also look to plummet during this time with the influx of cooler air, which may resulted in some elevated fire concerns across our area - more on this in the Fire Section below. Otherwise, look for temperatures to be notably cooler than days past, as high only rise into the low to mid 60s.

Dry and seasonally cool temperatures prevail heading into the new week as sfc high pressure builds overhead. As such, have morning lows Monday and Tuesday near/just below freezing, with afternoon highs only rising into the 50s to lower 60s.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Upper level trough deepens across the Ohio River Valley mid- week before pushing eastward toward the Atlantic. Meanwhile, at the sfc, will see another cold front eject across the region late Wednesday night into Thursday, potentially bringing a few light showers to the area. Outside of this, should see dry conditions prevail for the remainder of the extended period.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

10/18z TAF Discussion: KCHS/KJZI/KSAV: Gusty winds will impact all terminals for the remainder of the afternoon before subsiding a bit after sunset. A cold front will approach from the west tonight, crossing the terminals early Sunday morning with a wind shift to the west just before daybreak. There will be a risk for LLWS at KCHS and KJZI a few hours prior to FROPA, so WS015/24038KT was carried 08-11z to account for this. The risk for LLWS at KSAV looks a bit too marginal to mention with the 18z TAF cycle. There is a medium chance (40-50%) that a band of MVFR cigs will occur just ahead of the front. RAP soundings are the most aggressive with this band, but all of the 12z statistical guidance packages support VFR. VFR was maintained for now. A line of showers with the front should largely dissipate as it approaches the coast, so no direct impacts are expected at this time. Gusty west winds will prevail redevelop after daybreak Sunday with gusts near 25 kt.

Extended Aviation Outlook: Breezy northwesterly winds will prevail Sunday, with gusts up to 30 MPH possible through the afternoon. Otherwise, VFR conditions are expected.

MARINE

Through Tonight: Winds will increase tonight ahead of an approaching cold front. Guidance has trended slower with the ramp up to Small Craft Advisory conditions with the greater risk for frequent gusts to 25 kt now not occurring until Sunday morning with the exception of the outer portions of the South Santee-Edisto Beach nearshore leg where 25 kt gusts will likely start after midnight. A Small Craft Advisory begins for the South Santee-Edisto Beach leg at 2 AM Sunday.

Sunday through Wednesday: Winds become breezy in the wake of FROPA, with direction shifting from westerly to northwesterly by Sunday afternoon. With the aid of deep-mixing and a strong low level jet, have gusts between 25-30 kts for much of the daylight hours. Thus, SCA will remain in place for all our waters. Should see winds weaken into Monday as sfc high pressure builds overhead, allowing all SCA to expire. Tranquil marine conditions are then expected through Wednesday.

FIRE WEATHER

Elevated fire danger will be possible Sunday afternoon in the wake of a departing cold front, as drier and cooler air infiltrates the region. This combined with antecedent dry fuels, breezy northwesterly gusts up to 30 MPH, and falling dewpoints could promote fire growth/development. Latest guidance suggest relative humidity values may be a limiting factor and remain just above Red Flag Criteria, so have opted to forgo any headlines for the time being. Will continue to monitor trends in the coming shifts. Nonetheless, we encourage folks to be cautious with any activity that could cause a spark, as fires can spread quickly under these conditions.

CLIMATE

The low temperature at KCHS so far today is 60. If the low stays above 60 prior to midnight, the record high minimum for the date (60/1974) will be tied.

January 10: KCHS: 79/2008 KSAV: 81/1972

Record High Minimum Temperatures: January 10: KCHS: 60/1974

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...Lake Wind Advisory from 6 AM to 7 PM EST Sunday for SCZ045. MARINE...Small Craft Advisory from 9 AM to 8 PM EST Sunday for AMZ330. Small Craft Advisory from 2 AM Sunday to 7 AM EST Monday for AMZ350. Small Craft Advisory from 9 AM Sunday to 7 AM EST Monday for AMZ352-354-374.