Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
525 FXUS64 KHUN 190325 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 925 PM CST Sun Feb 18 2018 .NEAR TERM...(Tonight) Issued at 914 PM CST Sun Feb 18 2018 The weak area of convergence/forcing that brought some scattered light to briefly moderate rainfall to portions of northern Alabama this evening has pushed further north. This convergence/forcing now is near a line from Rome to Nashville. Some lingering light rain showers are hanging on over eastern Jackson and DeKalb counties, but will push east into Georgia and eastern Tennessee shortly. Not sure how much further east the area of convergence over Georgia will make it, due to the strength of the surface ridge through daybreak. Guidance seems to pick up on this and redevelops some scattered showers over northeastern Alabama between 3 am and 6 am on Monday as an additional weak area of forcing moves north across the area. Thus, keeping isolated to scattered showers in the forecast through daybreak mainly near and east of the I-65 corridor. Further west, low clouds could break up a bit between now and 2 am. If this occurs, with very thin high clouds, some patchy fog may develop west of I-65 between now and 2 am. Lowered winds based on current observations a tad and kept this trend through about 3 or 4 am. Models show that next round of possible scattered precipitation toward daybreak occurring as another piece of weak energy moves north through the area towards daybreak into the early morning hours on Monday. This forcing looks weak also, but the increase in low level moisture and enough lift will likely allow mostly cloudy to cloudy conditions to redevelop west of I-65 after about 3 AM. Lows look on track and should be just a few degrees cooler than they are now, likely in the lower to mid 50s in most locations. Winds should stay high enough in most locations to not see widespread fog formation, but west of I-65, where clearing could occur, sheltered areas could see patchy fog formation. .SHORT TERM...(Monday through Tuesday night) Issued at 258 PM CST Sun Feb 18 2018 Earlier analysis of 12Z upper air data revealed an upper low moving southward along the Pacific NW coast. This low will help carve out a deep trough over the western CONUS, kept from moving eastward in part by a strong upper high situated north of the Bahamas and east of Florida. This more amplified pattern will result in slower eastward movement of the systems to our west eastward. It will also bring more warmer air northward across the region. Thus lower to mid 70s for highs are expected for Washingtons Birthday/Monday. Normals this time of year are in the mid to upper 50s. Even warmer temperatures expected tomorrow night and Tuesday. Nighttime lows will fall only into the mid 50s to lower 60s. Highs on Tuesday will rise into the mid/upper 70s. Record high temperatures tomorrow and Tuesday could be given a run for the money (especially on Tuesday). Respective standing records then are 79/1917 and 79/1986, in Muscle Shoals and Huntsville respectively. Another change from the recent wet trend, decided to keep Mon-Tue dry, but brought scattered showers back into the picture Tuesday night, as deeper moisture and better lift is realized across the Tennessee Valley. .LONG TERM...(Wednesday through Saturday) Issued at 258 PM CST Sun Feb 18 2018 The forecast area will be situated between an upper trough extending through the Intermountain West and a fairly strong subtropical ridge over the southeastern CONUS and eastern seaboard at the start of the long term period. A cold front will be meandering over the central CONUS and approach the TN Valley on Wednesday. Ahead of this front, moisture will continue to advect northward as southerly flow persists at the surface and southwesterly flow persists aloft. The upper trough over the west will weaken quite a bit as it progresses eastward, while the upper ridge maintains a strong hold to our southeast. This will make it hard for the cold front to make much progression, which is evident in the models forecasts, as they continue to struggle with the evolution of this system. At this point, it does seem clear that the front will make it at least into the Mississippi Valley, with rain chances increasing across the TN Valley during the day on Wednesday. The GFS continues to be the more progressive model, swinging the front through on Wednesday, before it stalls to our south. Meanwhile, the ECWMF hangs it up just to our north, leaving the potential for outflow boundaries to move into the region and generate precip. Still too far to go into much detail about mesoscale features, but for these reasons, have maintained the blended guidance of likely pops on Wednesday, with higher chances on Wednesday night given the possibility of the front sagging through the area. The front looks to be within the vicinity of the TN Valley from Thursday through Saturday. Meanwhile, southerly flow through the vertical column will keep a rather moist profile across the area. This will mean a continued wet pattern for the TN Valley at the end of the week. It's difficult to pinpoint which days will have the higher potential for rain, so have kept chance pops in the forecast for Thursday night and onward. The front looks to finally move through the area on Saturday, bringing a higher chance for showers Saturday and Saturday night, along with isolated thunderstorms. Still a lot of uncertainty, so undercut the guidance a little due the discrepancies noted in the midweek front. Temperatures through much of the extended period will be well above normal for late February given the strength of the ridge and upper level heights. Rain and cloud cover may help, but the slow movement of the cold front and continued WAA will likely overcome any precip to help temps warm into the upper 60s to upper 70s during the period. The warmest day will likely be on Wednesday, as the front remains to our north at this time. Overnight lows will be on the warm and muggy side, with temps remain in the upper 50s to lower 60s. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 522 PM CST Sun Feb 18 2018 A weak warm front will continue to keep MVFR cigs in place through the night. Some scattered showers may continue to affect both terminals at times this evening as this feature moves north, but due to low confidence/pop have kept only VCSH in the forecast from now to 04Z at KMSL and 05Z at KHSV. Will have to watch late tonight at KMSL if we get some brief clearing around and just after midnight. This may allow some brief light fog to form, but left out for now due to uncertainty. A 1000 to 1500 foot deck should return to KMSL around 07Z. Winds should stay between 5 and 10 knots through the night. By 16Z, expect strong winds to mix down aloft and some gusts up to 20 knots are possible through tomorrow afternoon. Expect cigs to come up as well to VFR around 5000 feet or higher tomorrow. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...KTW SHORT TERM...RSB LONG TERM...73 AVIATION...KTW For more information please visit our website at weather.gov/huntsville.