Area Forecast Discussion
Issued by NWS Columbia, SC

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904 FXUS62 KCAE 170745 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 245 AM EST Thu Jan 17 2019 .SYNOPSIS... A low pressure system will cross the region tonight and Friday, followed by a more powerful storm system over the weekend with much colder temperatures early next week. Another storm system will approach during the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... High pressure over the forecast area (FA) currently will lead to light winds through this morning. Though slightly drier low level air in place compared to 24 hours ago, along with some slight increase in high level cloudiness, patchy fog possible in favored locations. Otherwise, expect increasing mid level cloudiness later today ahead of a fairly fast moving upper level disturbance that will move through late today and this evening, providing a chance of light rain showers. && .SHORT TERM /FRIDAY THROUGH SATURDAY/... The forecast area will be between systems on Friday with the departing trough off the New England coast and the developing system over the Plains states. A weak shortwave ridge will traverse the region through Friday evening with dry weather expected and then the 500mb flow backs to a more southwesterly direction later Friday night into Saturday ahead of the approaching and strengthening storm system over the Mississippi Valley. Moisture advection will return over the area with Gulf of Mexico open as southerly 850mb winds increase to 30-40 knots and precipitable water values increase to just under 1 inch. Late Friday night and into Saturday there will be increasing isentropic lift which may result in isolated showers developing so will have slight chance pops to account for this and gradual increasing pops during the afternoon Saturday as the storm system approaches from the west and moisture transport increases further across the area. Temperatures will be mild and well above normal with highs in the 60s on Friday and in the 60s to around 70 in the southeast Midlands on Saturday. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... The upper trough and associated surface low will move east across the central Appalachians Saturday night which will push a cold front across the forecast area. The strongest moisture transport and deepest moisture with precipitable water values reaching over 1.25 inches just ahead of the front with 850mb winds increasing to around 60 knots. Despite very strong wind shear the instability is not present so there is minimal threat of severe weather. Expecting generally around a 3-6 hr window just ahead of the frontal passage when the precipitation is expected to move across the region sometime between the 00z-09z time frame. Rainfall may be heavy but the system will be moving through quickly enough to limit overall rainfall totals with ensemble QPF guidance still showing generally around 0.5 to 0.75 inches of average rainfall across the area. The upper trough axis will cross the forecast area on Sunday but deeper moisture will be shifting out of the area as precipitable water values rapidly drop to around a quarter inch by 00z Monday. Strong cold advection behind the cold front will commence with breezy northwesterly winds. A Canadian polar air mass will settle over the region Sunday night through Monday with well below normal temperatures expected. There is some uncertainty late in the forecast period with medium range models differing on timing and strength of the next weather system. The GFS is more progressive showing the next storm system will be developing over the middle of the country on Tuesday with yet another digging upper trough resulting in surface low development over the Plains which will then lift northeast into the Great Lakes region Tuesday night. This would bring another cold front across the region Tuesday night into Wednesday. However, the ECMWF is quite a bit slower with this next system showing a much deeper upper trough and not bringing precipitation back to the forecast area until Wednesday night into Thursday. Given these uncertainties will maintain a persistence forecast. Temperatures this period will be above normal on Sunday but then below normal on Mon/Tue with cold low temperatures on Sun/Mon nights with the ECMWF much colder. Temperatures will moderate and return to near normal or slightly above normal values by Wednesday. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... High pressure over the forecast area (FA) currently will lead to light winds through this morning. Though slightly drier low level air in place compared to 24 hours ago, along with some slight increase in high level cloudiness, patchy fog possible in favored locations. Will indicate tempo MVFR at CAE/CUB, with tempo IFR at the fog prone locations AGS and OGB. Otherwise, expect increasing mid level cloudiness later today ahead of a fairly fast moving upper level disturbance that will move through late today and this evening, providing a chance of light rain showers. Will indicate a tempo group for -SHRA and MVFR conditions late afternoon and evening. EXTENDED AVIATION OUTLOOK...CIG restrictions possible late Friday night and Saturday morning. Showers and associated restrictions late Saturday through early Sunday. Breezy conditions may occur Saturday night through Sunday. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. && $$

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