Area Forecast Discussion
Issued by NWS Columbia, SC
Issued by NWS Columbia, SC
639 FXUS62 KCAE 201042 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 642 AM EDT Wed Aug 20 2025 .SYNOPSIS... A retreating upper ridge breaks down today and allows Major Hurricane Erin to pass offshore of the United States. More typical rain chances should return by the end of week with cooling temperatures due to developing upper troughing. Cold front late in the weekend will usher in a drier and cooler air mass for next week. && .NEAR TERM /THROUGH TONIGHT/... Key Message(s): - Erin remains well off the coast while continuing to move northward - Near normal temperatures with less humid conditions Morning analysis shows a strong upper ridge centered over the four corners region and western Colorado with Erin slowly lifting northward through the western Atlantic, northeast of the Bahamas. A weak upper trough was noted between these features extending from the Great Lakes region through the OH/TN Valleys with an associated front over the Ohio Valley. A stronger area of subsidence around Erin should provide a rain free day across the forecast area. Hi-res guidance concurs with keeping our area dry with convection being limited to the sea breeze and across the Upstate and higher terrain of NC associated with the trough to our west. Forecast soundings show lower PWATs today with values dropping to around 1.5 inches resulting from the mid level subsidence and this is noted in the soundings along with deep mixing expected through the afternoon. Expect somewhat breezy winds today from the north to northeast around 10 mph with gusts as high as 20 mph at times due to an increased pressure gradient as Erin makes its closest approach before turning northeast away from the region tonight. Temperatures should be warmer today back near normal in the lower 90s. Dry conditions tonight with lows in the lower 70s. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... Key Messages: - Seasonal temperatures Thursday that then begin to cool Friday with a weak frontal boundary moving through the area. - More typical rain/shower chances Thursday before chances increase Friday with front moving through. - Heavy rainfall will be possible each day. On Thursday Hurricane Erin will continue to move away from the area and in it`s wake some weak troughing will move over the region with a frontal boundary slowly working into the area from the northwest through the day. Despite northerly to northeasterly flow continuing much of the day, some stronger insolation should allow temperatures to reach into the low 90s. A slug of moisture advecting off the Atlantic and into the Mid Atlantic region through Wednesday should start to move south with the front Thursday, raising PWAT`s back near 2" for the afternoon and evening. This deep moisture and forcing from the front should allow for a more typical afternoon/evening with isolated to scattered showers and storms, though BUFKIT soundings do suggest coverage could be toward the lower side due to some lingering subsidence in Erin`s wake. Overall, instability looks to be rather meager thus the risk for strong storms is lower, but skinny CAPE profiles and high moisture should yield efficient rainfall production in this activity, thus locally heavy rainfall will be the primary risk with this activity, especially if any storms train near the frontal boundary. The WPC has maintained its Marginal Risk for excessive rainfall (level 1 out of 4) for the area due to this. On Friday, the weak front stalls out near the southern FA, but some guidance is a bit more optimistic that it will fully push south by Friday. Either way, weak troughing will remain in place through the day and low level flow will become more southeasterly, allowing for continuing PWAT`s near to just above 2". Deterministic models also suggest there could be some more shortwave activity during the day, aiding in driving higher coverage in showers and storms during the afternoon and evening, especially toward the southern FA closer to the front. With thermodynamics fairly similar to Thursday, another day with the main risk being heavy rainfall and possible areas of flooding is expected where NBM probabilities for greater than 0.50" of rainfall is highest in the southern FA (around 35-45%). With the bulk of the CWA behind the front, some slightly cooler air is expected to filter in with afternoon highs that are in the mid 80s, but the southern FA should be closer to the upper 80s. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Key Messages: - Gradual warming trend returns Sunday into Monday before cooling into Tuesday. - Increased shower/storm chances for this weekend as a stronger front works through before drier conditions are expected in the early week. EC Ensemble and GEFS members remain in good agreement that deeper troughing will start digging into the upper Great Lakes Saturday, leading to some slightly stronger height falls through the day in the FA, but the deep trough is not expected to fully reach the area until Sunday and into early next week. In terms of sensible weather, this pattern should bring increased shower/storm chances this weekend as PWAT`s remain around 120% of normal with subtle upper forcing, as well as a more prominent cold front that will push through the FA Sunday from the northwest. Temperatures this weekend should only be slightly below normal and this continues into the early week before falling further below normal Tuesday and into mid week as deep troughing continues. Drier weather is also expected Monday and Tuesday as some of the driest air we have seen in a while pushes in behind the front where the mean GEFS solution shows PWAT`s that are nearly 1-1.5 standard deviations below normal. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... Satellite imagery showing stratus clouds building southwestward from NC but confidence is limited on whether they will reach terminals before mixing out by mid morning. Higher confidence this blanket of stratus will not make it to AGS/DNL but patchy stratus has been developing around that area as well so including a few hours tempo group all terminals for MVFR cigs until 15z. Higher clouds associated with Erin will likely spread over the region this afternoon. An increased pressure gradient may result in northeasterly winds around 6 to 10 mph with some gusts between 15 to 20 mph at times. Otherwise, no other significant aviation concerns through the end of the forecast period as winds should stay up a bit overnight preventing fog concerns. EXTENDED AVIATION OUTLOOK...Chances of restrictions increase Friday and over the weekend as deep moisture returns to the region. Showers and thunderstorms are likely on Friday and Saturday. && .CAE WATCHES/WARNINGS/ADVISORIES... SC...None. GA...None. && $$ SYNOPSIS... NEAR TERM... SHORT TERM... LONG TERM... AVIATION...