Area Forecast Discussion
Issued by NWS Columbia, SC

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000 FXUS62 KCAE 221501 AFDCAE Area Forecast Discussion National Weather Service Columbia SC Issued by National Weather Service Greenville-Spartanburg SC 1001 AM EST Tue Jan 22 2019 .SYNOPSIS... Cold high pressure ridging into the forecast area this morning will shift off the coast today. Moisture will increase in the veering east to south flow on the backside of the offshore high and ahead of a cold front tonight and Wednesday. There will be increased cloudiness and spotty areas of light rain late tonight and Wednesday. The front will be in the area Wednesday night into Thursday morning and showers will occur. High pressure following the front will dominate Friday. && .NEAR TERM /THROUGH TONIGHT/... Skies are almost completely clear this morning with light easterly surface flow around surface ridge northeast of the area. Very dry dewpoints will increase this evening as surface flow becomes more southeasterly. This will also increase high temperatures about 4 degrees over what was seen on Monday. As next upper system approaches, some light rain becomes possible Tuesday night/Wednesday morning. Believe there will be increased low cloudiness and a chance of light rain or drizzle late. The guidance consensus supports pops around 30 percent. The NAM, GFS, and ECMWF depict very little QPF, about 0.01 of an inch. The NAM continues to be the coldest in the near-surface layer indicating a concern for freezing rain in the north section. It has had a cold bias this winter. We followed the more consistent GFS and ECMWF which have surface wet bulb temperatures above freezing even in the extreme north section. Also, precipitation will be light with limited evaporative cooling potential. Nearly all SREF members keep temperatures above freezing. We believe the chance of freezing rain is too low to include in the forecast at this time. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... Wednesday will start cloudy as increasing low level moisture and isentropic lift support plentiful low clouds through the first half of the day. There will be some light rain or sprinkles around, but little if any QPF is expected with significant dry air once you get above 6K feet, not allowing much depth to the stratus/stratocu. By afternoon, winds will turn southerly and increase, and some breaks may develop as mixing increases ahead of the approaching cold front. Temps will be noticeably warmer by afternoon, with maximum temps ranging from 60 near the NC border to 70 in the southern CSRA. Wednesday night...the cold front will rapidly move through the area. Despite its speed, a decent amount of rain will fall due to a combination of much above normal deep moisture (PW values more than 1.5 inches), strong diffluence aloft in the right rear entrance region of a jet, and strong mid level lift from an approaching sharp trof and associated vorticity. Rainfall totals will generally be around an inch, but local areas could see double that amount. Temps will be much above normal for most of the overnight, although it will start to cool towards daybreak as winds turn westerly behind the front and cold advection begins. Thursday...The front will continue its rapid trip eastward into the western Atlantic Ocean. There may be some lingering showers in the morning, most likely in the eastern half of the FA, but the chances of rain will essentially end by mid morning in the western and central areas, and noon everywhere. Temperatures will not change much during the day as the increasing sunshine will be counteracted by surface cold advection behind the front on cool northwesterly flow. && .LONG TERM /THURSDAY THROUGH MONDAY/... High pressure will move into the region for Friday and Saturday. The air mass origin will be more continental than polar, so I don`t expect a true arctic invasion, but temps will nonetheless fall back to a little below late January norms. For Sunday and Monday, the ECMWF and FV3 have come into much better agreement with the GFS, as all models are advertising a much flatter system coming out of the Gulf of Mexico, passing well to our east. The Canadian is now the lone outlier keeping a stronger low closer to the coast and threatening the area with precipitation. I have lowered POPs considerably for Sunday through Monday, but not all the way to zero in deference to the Canadian, along with a couple of the GEFS members that still bring in some rain. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... We have high confidence in VFR conditions through today. Low- level wind shear along with lowering ceilings will occur tonight. IFR ceilings may develop toward the end of the 24-hour TAF period. It will remain dry today because of the pressure ridge in the region. VFR conditions should continue. The surface ridge will be shifting eastward and bring easterly winds. The NAM and GFS MOS support speeds 5 to 10 knots. Moisture will increase tonight with continued onshore flow associated with the offshore high and ahead of a cold front well to the west. Expect a ceiling will develop and lower overnight. We followed the GFS MOS for the timing of developing MVFR and IFR ceilings. There is a diminished fog risk because of the cloudiness and a continued dry near-surface layer. The moisture should remain too shallow for rain through 06z because of the lingering affects of upper ridging. The moisture may become just deep enough for areas of drizzle or light rain after 06z. Uncertainty was too high at this time to include the precipitation and possible visibility restrictions in the terminals at this time. There will be increased shear associated with a low-level jet developing ahead of the front. Followed the NAM and included low-level wind shear in the terminal forecasts beginning around 04z. EXTENDED AVIATION OUTLOOK... MVFR/IFR conditions are likely Wednesday morning. The cigs could lift to VFR by afternoon, especially at AGS and DNL, as mixing increases, but it will come at the cost of slightly stronger southerly/southwesterly winds. Wednesday night as the front moves through, expect IFR conditions in clouds/rain. LLWS could also be a problem with the models forecasting winds in excess of 50 knots as low as 2K feet near the front. Thursday conditions will be improving from west to east as the front moves away, with VFR conditions likely at all terminals by some time during the afternoon. VFR conditions are then expected to continue into the weekend. && .HYDROLOGY... Minor flooding will continue on the Congaree River due to recent rainfall and upstream reservoir releases within the Broad and Saluda River basins. && .EQUIPMENT... The Columbia, SC (KCAE) WSR-88D is out of service due to a faulty voltage regulator. The part will be ordered but an estimated time of arrival is unknown at this time. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. && $$ SYNOPSIS...99 NEAR TERM...99 SHORT TERM...99 LONG TERM...99 AVIATION...99 HYDROLOGY... EQUIPMENT...

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