Area Forecast Discussion
Issued by NWS Columbia, SC
Issued by NWS Columbia, SC
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838 FXUS62 KCAE 041803 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 203 PM EDT Thu Jul 4 2024 .SYNOPSIS... Atmospheric moisture increases into the weekend with isolated to scattered showers and thunderstorms each day beginning Friday. Above normal temperatures are expected Friday and Saturday with Heat Index values up to 110 possible. Atmospheric moisture remains high through the long term supporting a chance of showers and thunderstorms each day. && .NEAR TERM /THROUGH TONIGHT/... Key Message(s): - Hot with heat indices between 100-105 this afternoon. Upper ridge over the Gulf coast region extending into the area. At the surface, high pressure dominates over the southeastern States. There is a weak trough over central NC extending south into the central Midlands. Cumulus is increasing near the trough due to some weak convergence and slightly higher low- level moisture than other areas. The air mass appears a little drier in the southern Midlands and CSRA where dew points are in the mid 60s. Temperatures trends on track for highs in the upper 90s. The air mass appears capped. The CAMS suggest some showers and thunderstorms will develop in higher terrain in NC and move east this afternoon, but these showers should stay north of the Midlands due to ridge aloft. Surface ridge weakens a bit and moves off the coast tonight. The models indicate low-level moisture will increase overnight with overall precipitable water around 1.90 inches by morning. The guidance low temps imply muggy conditions with lows only down to the mid to upper 70s and some high thin clouds. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Key Message(s): - A Heat Advisory is in effect from 11am to 8pm Friday - Low threat of severe thunderstorms and flash flooding Saturday Heat: Moisture increases on Friday pushing Heat Index values up to 110. MOS dewpoints in the afternoon are in the low to mid 70s which are several degrees higher than the previous day. With warming 850mb temps and only widely scattered convection expected, we will likely see highs in the upper 90s to around 100 degrees. Despite PWAT values around 1.7 to 1.9 inches, upper ridging over the FA should be sufficient to suppress widespread convection. Dewpoints continue to increase on Saturday with PWAT values over 2 inches. However increased convergence ahead of a front and some shortwave energy moving into the region will promote higher convective coverage than Friday. So confidence in a Heat Advisory for Saturday is limited. Convection and cloud cover should keep us cooler than Friday. Thunderstorms: An upper level trough will move into the Great Lakes region then into New England this weekend. The associated front will remain west of the area however increased convergence ahead of the front and rising atmospheric moisture will lead to scattered or numerous showers and thunderstorms for Saturday afternoon. Shortwave energy rounding the base of the trough may also support convection in the afternoon and evening. PWAT values as high as 2.5 inches indicates potential for flash flooding however the threat will be hampered by 10 to 20 kt cloud layer winds. The flash flooding potential may be limited to training storms or urban areas. A tall, skinny CAPE profile suggests limited updraft strength but precip loading may promote isolated downbursts in some of the deeper storms. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Key Message(s): - Daily afternoon thunderstorms expected for much of the period A fairly persistent synoptic pattern dominates the long term period. Global ensembles favor positive 500mb height anomalies over the Southeast with mean PWAT values very steady around 2 inches through the end of the long term. With near or above normal atmospheric moisture and weak ridging in place, we would expect a common summertime pattern of diurnal showers and thunderstorms with temperatures near or a little above normal. As is typical for the season, there could be an isolated severe threat each day. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... VFR forecast. Scattered cumulus this afternoon across central SC, fewer low clouds near the AGS area where it is slightly drier. In general, high pressure in place across the area. The ridge will move off the coast tonight and southwest flow will increase. This will result in increasing moisture into Friday. Overnight, expect cumulus to dissipate after sunset with a few mid and high level clouds at times. Guidance is not indicating any low clouds or fog overnight and the boundary layer appears mixed so low risk of fog. Winds will be southwest 5 to 10 knots this afternoon and become light after 00z. The air mass will become weakly to moderately unstable after 15z Friday. A few showers may be developing, especially in east- central GA. EXTENDED AVIATION OUTLOOK...Restrictions possible mainly associated with diurnally driven convection each day. The greatest convective coverage expected Sat/Sun afternoon. && .FIRE WEATHER... Key messages(s): -Hot and dry conditions continue through Independence Day. -Rainfall probabilities increasing Friday through early next week. Hot and dry conditions will continue through Independence Day with increasing moisture and chances of showers and thunderstorms Friday into early next week. Although there was some rain late in the weekend and into early this week the hot and dry conditions over the past few days and through Thursday will generally minimize any improvement from the rain. Moisture will begin increasing Thursday but rain chances will hold off until Friday with scattered afternoon and evening thunderstorms mainly along and north of I-20 then spreading eastward Saturday into early next week. Temperatures will also be a concern with afternoon highs in the upper 90s to around 100 which will push heat index values to 110 Friday and possibly 105- 110 Saturday. && .CAE WATCHES/WARNINGS/ADVISORIES... SC...Heat Advisory from 11 AM to 8 PM EDT Friday for SCZ016-018- 020>022-025>031-035-037-038-041-115-116-135>137. GA...Heat Advisory from 11 AM to 8 PM EDT Friday for GAZ040-063>065- 077. && $$