Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
000 FXUS64 KHUN 190336 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1036 PM CDT Sat May 18 2019 .NEAR TERM...(Rest of tonight) Issued at 1035 PM CDT Sat May 18 2019 Regional radar indicates that an outflow dominant QLCS continues to push further east into western TN and north central MS. This is farther east in expectation than recent HRRR runs and the 18Z NAM/GFS. The line should encounter a much drier and capped airmass as noted in our earlier evening update. But can't ignore the current radar and have opted to add a low PoP of showers tonight in our far western portion of the forecast area (NW AL/Shoals area). .SHORT TERM...(Sunday through Monday night) Issued at 310 PM CDT Sat May 18 2019 The overall wx pattern is xpcted to turn a little more active going into the second half of the weekend period. An upper trough axis over the mid Plains states is xpcted to pivot NE into the Great Lakes on Sun. As this occurs, a sfc low will also move thru the Great Lakes states, dragging a weak frontal boundary ewd into the Mid South/lower MS Valley regions. As the sfc low continues to lift to the NE, the front will also translate ewd late Sun into Sun night. Sfc flow ahead of the front may be a little strong, as evidenced by an H85 jet out of the SSW near 40-50kt early Sun. This may translate into gradient wind gusts around 30 MPH Sun morning in the higher elevations of NE AL. Low level convergent flow along the front itself may result in a few strong tstms Sun afternoon into Sun night capable of brief wind gusts to 50 MPH. The front is then xpcted to stall invof the area, with a few showers/tstms remaining possible into the day Mon. Even with the front settling into the area, overall temps look to trend unseasonably warm, given a weak upper ridge pattern remaining in place over much of the Gulf region. Afternoon highs Sun/Mon look to remain in the lower/mid 80s while overnight lows trend in the lower/mid 60s for most locations. .LONG TERM...(Tuesday through Friday) Issued at 310 PM CDT Sat May 18 2019 At the beginning of the long term portion of the forecast on Tuesday morning, sfc high pressure will be situated to our north while another strong low pressure system will be taking shape well to our west over the central High Plains. As the sfc high to our north shifts eastward, flow will begin to back from the east and then south during the morning. A strengthening low-lvl temperature gradient will give rise to warm frontogenesis, but this is likely to take place just to our north. Although, there is still some uncertainty in the location of the developing warm front. Nevertheless, an axis of generally weak confluence will be present over the area during the morning into the afternoon. Global models also indicate a weak upper shortwave translating SSW-NNE across the area along the western flank of a building upper ridge. Although broad scale forcing will be generally low, some showers and thunderstorms may develop in the moderately unstable environment. A slight chance POP was thus introduced into the forecast for Tuesday afternoon. Otherwise, the long term portion of the forecast will be dominated by a highly amplified pattern across the CONUS with a deep trough in the West CONUS and a strong upper ridge situated over the East CONUS from Wednesday into next weekend. This will bring generally dry and hot weather to the TN Valley region during the period. Given the general agreement among the suite of global and ensemble guidance, this is a fairly high confidence forecast for the period. As stated in the previous long term discussion, GEFS probabilities indicate high confidence that 500 mb heights will exceed 2 standard deviations above the mean for this time of year across our area. What does this mean? Well, good confidence in above normal temperatures. While the guidance suite shows a range of temperatures generally in the mid 80s to lower 90s. Given the anomalous nature of the situation, the actual forecast high temperature values were placed above the main part of guidance, with values reaching into the mid 90s at some locations for Thursday through Saturday. Based on some of the data, temperatures even reaching the upper 90s would appear possible. Record high temperatures during this period are mainly in the mid 90s, so some records could be broken. While there is high confidence in the broad scale strong upper ridge, a few small showers or storms could occur each afternoon during the period. However, given the general limitation for broad scale ascent, any convection will largely be driven by very localized effects...potentially sfc temperature/moisture gradients. Anyway, the risk for showers and thunderstorms currently is too low to place POPs in the forecast, but will mention here for now. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 525 PM CDT Sat May 18 2019 VFR flight weather conditions are expected through tonight into Sunday morning. Southerly flow will increase markedly by 14Z with sustained speeds of 12-17kt and gusts of 22-25kt. An area of showers and a few thunderstorms will arrive in northwest AL including KMSL as early as 14Z, but more likely 17-21Z. It is much less certain if these will reach the KHSV area due to a more stable and drier airmass further east, but have maintained VCSH after 19Z. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...17 SHORT TERM...09 LONG TERM...KDW AVIATION...17 For more information please visit our website at weather.gov/huntsville.