Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
593 FXUS64 KHUN 212358 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 658 PM CDT Fri Sep 21 2018 .UPDATE... For 00Z TAFS. && .NEAR TERM...(Tonight) Issued at 233 PM CDT Fri Sep 21 2018 Scattered showers and a few thunderstorms continue to develop over northern Alabama, especially east of a line from the Muscle Shoals area to northwest of Columbus, Mississippi. Expect this activity to continue in the evening hours, before retreating north a bit. However, still cannot rule out a shower or thunderstorm after midnight (only 20-30 percent chance though). Expect cloud cover to become high and thin and winds fairly light after midnight. This should allow temperatures to drop into the upper 60s to lower 70s by Saturday morning. .SHORT TERM...(Saturday through Sunday) Issued at 233 PM CDT Fri Sep 21 2018 As an approaching frontal boundary continues to edge southeast closer to the region, models still stall the main front somewhere across portions of Tennessee and northern Arkansas. Enough forcing and instability should be in place in northwestern Alabama and southern middle Tennessee to allow showers and thunderstorms to increase in coverage. Shear doesn't look great, but fairly deep moisture is in place ahead of the boundary. Kept higher pops (40-60 percent) in northwestern Alabama and southern middle Tennessee. Elsewhere kept mainly scattered chances of showers or thunderstorms. The boundary still doesn't move much Saturday night into Sunday night, keeping similar pops in the forecast. The biggest question much of this period, is will the higher changes of rain/frontal boundary remain further north than currently thinking. For now, sticking close to blended guidance. Shear doesn't look overly impressive through the period. Thus, normal general thunderstorm activity is expected. Lower daytime highs in the lower to mid 80s are expected. .LONG TERM...(Sunday night through Thursday) Issued at 233 PM CDT Fri Sep 21 2018 A cold front will be in the vicinity of the region during the early to middle part of the upcoming week. However, some uncertainty does exist as to the behavior of this boundary and what it will mean for PoPs and temperatures in the coming days. After a somewhat cloudy day on Sunday (with scattered to numerous storms), a slightly drier period may be in store for Monday and even Tuesday. Models are hinting that the aforementioned boundary may actually retreat back north and west on Monday as the Bermuda high temporarily tries to nose it's way back into the Piedmont region of the Southern Appalachians. The result will likely be a few less clouds, slightly higher temperatures (mid 80s), and more widely scattered convection. Areas to the north and west (closer to the boundary itself) would likely see the greatest potential for this activity. Still, with southwest flow and abundant moisture in place, there will be plenty of ingredients for some scattered showers and storms areawide as referred to above. A stronger shortwave trough over the Northern Plains will shift into the Great Lakes/Ohio Valley Tuesday night into Wednesday and attempt to force the front back south into Southern Middle Tennessee and Northern Alabama. Regardless, it will be close enough to warrant an increase in PoPs to likely across most of the region during this period. These numerous showers and storms will hopefully bring the region some much needed precipitation as moderate drought conditions have been starting to develop within the last couple of weeks. The best dynamics, however, will be well displaced of the region and thus am not expecting any severe risk with this activity. The status of the main "cold air" push associated with a stronger cold front to the north the models have been advertising is still quite uncertain at this time -- at least this far south. The ECMWF is now wanting to reestablish a ridge of high pressure late next week over Central Georgia and Alabama -- and potentially into the following weekend. The GFS on the other hand does show a stronger upper-low pushing from the Northern Plains into the Ohio Valley by Friday, which could push this stronger "autumn" front at least close to the area. Should this solution occur, it's possible we could see a taste of autumn to close out the last couple days of September. However, I'd still advice caution on totally buying into the GFS solution given the magnitude of this Bermuda High feature the models are advertising. Temperatures will still be relatively cooler, but should the ECMWF solution verify, we'd be looking at mid to upper 80s during the day and 60s at night -- with southerly flow maintaining the Gulf moisture over the region. Hardly a true taste of autumn. Stay tuned, a lot of details still to be worked out! && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 658 PM CDT Fri Sep 21 2018 A few areas of mod/heavy shra continue to develop across parts of the area heading into the evening hrs, especially near the KMSL airport and on into srn mid TN. These shra are likely to continue across mid TN and into portions of NW AL for much of the evening period, and a prevailing VCSH will be in place at the KMSL airport thru 06Z. Given the rainfall from today coupled with the light winds, some -br/MVFR vis are then possible at both airports heading into the early morning hrs. Any vis reductions should quickly improve with the onset of daytime heating Sat. Additional shra are then xpcted later in the day Sat, as a frontal boundary drops into the area. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...KTW SHORT TERM...KTW LONG TERM...AMP.24 AVIATION...09 For more information please visit our website at weather.gov/huntsville.