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Area Forecast Discussion
Issued by NWS Huntsville, AL
Issued by NWS Huntsville, AL
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043 FXUS64 KHUN 172325 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 625 PM CDT Wed Jul 17 2024 ...New AVIATION... .NEAR TERM... (Tonight) Issued at 115 PM CDT Wed Jul 17 2024 Medium/high chances for showers and storms are forecast this afternoon and evening across the Tennessee Valley as diurnally driven convection initiates along residual outflow boundaries in place over the area. Additionally, a more pronounced outflow boundary from convection along the AR/TN Mississippi Delta region is propagating toward northwest Alabama and triggering additional storms that will work their way into the area by 19-20z. We are primed for at least a few strong to marginally severe storms through this evening, with SBCAPE values around 3000 J/kg and at least some appreciable 0-3/0-6 km shear values of around 30 kts. This could lead to a few organized line segments/multicells as well as pulse storms capable of wet microbursts. Additional rounds of showers/storms will likely redevelop overnight as another shortwave ripples across the area -- along with the actual cold front. Thus, have kept medium chances in the forecast through the early morning hours. Main threat with any overnight convection will be locally heavy rainfall under the strongest cores. && .SHORT TERM... (Thursday through Saturday) Issued at 115 PM CDT Wed Jul 17 2024 We remain in an active pattern late this week under the influence of a broad mid/upper trough over the Ohio/Tennessee Valleys. Medium to high chances (40-70%) are forecast during this timeframe, with the highest values each afternoon/evening across the region. The highest coverage will likely be along and south of the Tennessee River, the area closest to where a weak front and/or convergence boundary will be stalled over central Alabama. The main threat with this activity will be locally heavy rainfall and lightning which will impact though with outdoor plans. In fact, hydro issues for localized flash flooding may become a concern later in the week if we get several days of rainfall. The higher rain chances and cloud cover will keep the dangerous heat at bay, however, as high temperatures will actually trend below normal for mid-July, peaking in the mid/upper 80s each day (about 5-7 degrees below normal). && .LONG TERM... (Saturday night through Tuesday) Issued at 329 AM CDT Wed Jul 17 2024 The local forecast area will remain to the east of a mid-level longwave trough (extending from the Great Lakes into the northwestern Gulf of Mexico) for much of the extended period, with initially light SSW flow aloft expected to strengthen by Monday/Tuesday as the height gradient contracts between a subtropical ridge retrograding across FL and a developing upper low over the MO Valley. As this occurs, a weak area of surface low pressure is expected to evolve across west-central TX Friday night, which will force the stalled frontal boundary to lift northwestward through the region once again on Saturday. Precisely how far north and west the front makes it is highly uncertain at this time, but regardless of position, we will be either sufficiently close to the boundary or within the moist warm sector, and this will promote several rounds of rain and thunderstorms from Sunday-Tuesday (both during the day and at night). Although shear may strengthen a bit by Monday/Tuesday, deep moisture and weak lapse rates will limit storm intensity, with lightning and locally heavy rainfall the main threats. Heat Risk will not be a concern through the end of the extended period. && .AVIATION... (00Z TAFS) Issued at 625 PM CDT Wed Jul 17 2024 Lingering shra/tsra have diminished/moved east of the area heading into the evening hrs this Wed, leaving just some mid/high cloud cover. Additional shra/tsra area possible overnight, as a weak frontal boundary approaches from the NW, with brief/tempo MVFR cigs/vis possible in/near any heavier shra. Mid level cigs near 4-5K ft are then expected during the day Thu, with further shra/tsra possible during the afternoon and a PROB30 group has been added later in the period. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...None. TN...None. && $$ NEAR TERM...AMP SHORT TERM....AMP LONG TERM....70 AVIATION...09