Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
000 FXUS64 KHUN 211051 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 551 AM CDT Fri Sep 21 2018 .UPDATE... For 12Z TAFS. && .NEAR TERM...(Today) Issued at 202 AM CDT Fri Sep 21 2018 As has been advertised, the mid and upper level high has shifted east into the Carolinas. The ridge axis will be anchored across north GA into central AL. Mid level moisture was already increasing this morning as evidence by areas of mid level cloud development. The models may be over-emphasizing the potential of showers from this activity this morning and today. However, will not ignore the idea completely and keep a low PoP in for today, especially northwest AL more within the best moisture transport. As for temperatures, will continue for forecast above suggested blends by several degrees. With the upper high shifting east, don't foresee upper 90s or 100 again today, but lower 90s looks rather obtainable. .SHORT TERM...(Tonight through Sunday) Issued at 202 AM CDT Fri Sep 21 2018 The upper ridge position will remain anchored across north GA into central and northeast AL through tonight into Saturday. Tonight, clusters of showers and thunderstorms will continue within the moist south- southwest flow at 850 mb across middle TN southwest into northern MS, clipping far northwest AL. As the shallow surface boundary shifts southeast into middle TN, far northwest AL into northern MS, there will indeed be a sharp gradient in the potential for showers and thunderstorms. Locally heavy rainfall may clip far northwest AL during this period if the boundary and convergence does indeed slip southeast into this area. This may be somewhat short-lived as the models suggest the front and convergence will lift back northwest on Sunday. This will set up a good heavy rain pattern for areas from the Red River valley through AR, northwest TN and KY as numerous shortwave impulses propagate out of the southern Plains into the H valley.. For our areas, some or most of our central and southeast counties may remain dry both Saturday night into Sunday as the influence of the ridge and somewhat drier low to mid level flow will take place. .LONG TERM...(Sunday night through Thursday) Issued at 202 AM CDT Fri Sep 21 2018 A somewhat active pattern looks to continue through much of the next work week, as an upper trough begins to move eastward and into the Plains. This will allow for southwest flow in the mid to upper levels to strengthen, with a steady stream of moisture advecting northward into the TN Valley. Additionally, weaknesses within the upper flow pattern will generate at least some lift over the area, and keep the chance for showers and thunderstorms in the forecast for Monday and Tuesday. Meanwhile, the upper trough is expected to weaken a bit as it moves into the Mississippi Valley, though a cold front will continue to push eastward with the parent low over the northern Ohio Valley. Model discrepancies remain fairly high with regard to the system, as the latest forecast runs are a bit different than those yesterday. The weakening upper trough will be slower to move eastward Tuesday, as the strong subtropical ridge over the Atlantic holds. The surface low will continue its momentum eastward late Tuesday night, causing the cold front to become more east to west oriented as the southern extent of the front loses the upper forcing with flow aloft becoming more zonal over the southern CONUS. While the GFS continues to show an initial shortwave moving through and generating widespread precip on Wednesday, both the GFS and the ECMWF stall the front just north of the area. Models inconsistencies further increase after the end of the period, as the GFS shows a stronger closed low pushing eastward through the Great Lakes which would finally bring the front through the area on Friday. Meanwhile, the ECMWF has the upper low much further north, with zonal flow persisting over much of the eastern CONUS and the stalled front remaining north of the area. Given so much uncertainty, and the likelihood that model solutions will continue to differ for at least the next day or so, will follow closely to the blended guidance. This will make the highest chance for showers and thunderstorms on Wednesday, with the initial shortwave, with continued rain chances through the end of the week. Temperatures through the period will be closer to seasonal norms, as the upper ridge moves east and upper height falls allow for some cooling. Additionally, cloud cover will be fairly high and will combine with at least scattered thunderstorms to further help temps remain in the lower to mid 80s on Monday and Tuesday. The rest of the week will be highly dependent on just how quickly that front moves through, though an even greater coverage of cloud cover and precip will maintain highs in the upper 70s to lower 80s through the end of the period. Overnight lows will generally remain in the mid to upper 60s through the period. && .AVIATION...(For the 12Z TAFS through 12Z Saturday morning) Issued at 551 AM CDT Fri Sep 21 2018 Isolated to scattered showers this morning will continue this morning. Have included VCSH only through 15Z given the location uncertainty. With daytime heating, a few thunderstorms will also be possible. Outside of the showers and thunderstorms, VFR flight weather conditions are expected with high based cumulus at 050-060agl and pockets of ceilings at or above 100agl. The probability of showers or thunderstorms will persist into tonight, but is too low to include at KMSL or KHSV at this time. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...17 SHORT TERM...17 LONG TERM...73 AVIATION...17 For more information please visit our website at weather.gov/huntsville.