Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
315 FXUS64 KHUN 152006 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 306 PM CDT Sun Jul 15 2018 .NEAR TERM...(Tonight) Issued at 306 PM CDT Sun Jul 15 2018 Active afternoon across the Tennessee Valley, with scattered to numerous storms in progress as of 20z. Any diurnal convection will diminish after sunset. However, additional showers and storms associated either with the boundary that is entering NW AL or the boundary elongated to our west just across the MS border could linger into this evening and into the overnight hours. The combo of PWAT values remaining over 2", weak shear, slow storm motion and CAPE values of 2-3,000 J/kg into this evening will allow for a strong storm or two with heavy rainfall, gusty winds and frequent lightning as the main threats. Especially for locations that have already received rainfall, localized flash flooding is possible. Starting this morning off with mainly BKN/OVC clouds and the early start of convection put limited solar heating somewhat and probably the possibility of reaching heat advisory criteria across NW AL. However, decided to keep the heat advisory in place due to the fact that locations who have received a peak of sunshine have quickly rebounded their temps. Thus, a few isolated spots could see peak HIs close to 105 degrees. See the heat advisory for additional information. Otherwise, cloudy conditions will keep overnight lows at bay, with temps reaching the lower 70s. .SHORT TERM...(Monday through Tuesday Night) Issued at 306 PM CDT Sun Jul 15 2018 As an upper-level trough swings across southern Canada, it will continue to break down the ridge that was anchored across the Southeast. This will place us in a northwesterly flow pattern, allowing a series of disturbances to dive down into the region. At the sfc, a low moving out of the Great Lakes will pull a cold front into the TN Valley by Tuesday morning. With moist and unstable conditions, scattered to numerous showers and storms are possible Monday and Tuesday. Heavy rainfall, gusty winds and frequent lightning will again be the main threats with PWATS still ~2" and CAPE 1000-2000 J/kg. Steering flow will slightly improve, allowing for storms to have a lower chance of producing flooding. The increase in storm coverage and cloud cover will limit heating, and thus temps should only reach around 90 degrees. This will keep heat index values below heat advisory criteria over the next couple days. As the front pushes through late Tuesday and drier air filters in, storm chances will decrease allowing for a drier air mass to work in by Tuesday night. .LONG TERM...(Wednesday through Saturday) Issued at 306 PM CDT Sun Jul 15 2018 Large area of high pressure is xpcted to be in place across the Great Lakes/OH Valley states to start off this part of the forecast package, with a cold front located just south of the cntrl TN Valley. Some slightly drier air between H5-H85 should also be in place over the area thx to the passage of the front earlier, which should offset much in the way of rain chances except for perhaps the far SW corner of the forecast area where slightly better convergence near the front may allow for a few showers/tstms thru Wed. Temps will still be seasonably warm with highs in the upper 80s/near 90F, although the drier air will keep afternoon heat indices more in the lower/mid 90s. Rain chances begin to gradually increase Thu/Fri, as the front to the south rebounds to the north as a warm front. With the warm front moving nwd, a low pressure system out of the mid Plains states also looks to translate ewd into the Midwest/OH Valley areas, which should help with the influx of moisture into the region. The latter half of the global models are also suggesting an upper shrtwv/trough carving thru the Great Lakes, placing the region in more of a nwly flow regime. All of this should result in sct showers/tstms developing across the mid TN Valley by Fri and persisting into the weekend. Even with the increase in rainfall, highs still look to be fairly seasonal for this time of the yr, with temps again maxing out near the 90F mark for most locations, while overnight lows trend predom in the upper 60s to lower 70s. && .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) Issued at 1221 PM CDT Sun Jul 15 2018 Prevailing forecast will be VFR with a tempo of MVFR conditions this afternoon as thunderstorm coverage increases. Thunderstorms will diminish with sunset, however additional convection is possible before the end of the TAF period. Kept with a VCTS starting at 15Z due to low confidence in timing. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...Heat Advisory until 6 PM CDT this evening for ALZ001>003. TN...NONE. && $$ NEAR TERM...JMS SHORT TERM...JMS LONG TERM...09 AVIATION...JMS For more information please visit our website at weather.gov/huntsville.