762 FXUS64 KBMX 042147 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 447 PM CDT Sat May 4 2019 .UPDATE... MESOSCALE UPDATE. && .SHORT TERM... Overall low pressure and surface front remain well back to the west of Central Alabama at this writing. Best convergence and mean moisture near MCV/upper disturbance moving over southern areas now. Best SBCAPE bubble was just east of the thunderstorm axis. Therefore, went ahead and expanded the Severe Thunderstorm Watch to the Georgia state line, even though it only goes another 1.5 hours. Mid level lapse rates are rather poor but there is enough shear to organize storms. The helicity values, low level flow, and convergence are not overly conducive to low level rotation and tornadoes. But there has been some mesocyclones and rotation aloft. Therefore the main threats will be damaging winds and large rain. Localized heavy rain is also possible, but storms will be moving 35-40 mph which should minimize the areal threat. Will monitor for a potential extension of watch in time also, but most strong to severe activity will be out of Central Alabama by 8 pm. 75 Previous short-term discussion: The shortwave trough will continue to advance toward the state this afternoon and evening with the surface low moving northeast from Louisiana across Mississippi and into northern Alabama tonight. The best dynamical forcing has existed across far southern Mississippi/eastern Louisiana and into southwest Alabama. As the surface low gains in latitude, this favorable area will creep further northward to include our southern tier of counties, roughly along the U.S. Highway 80 corridor. General unidirectional flow from the west/southwest will encourage bowing segments in linear convective formations which are expected to develop further north from southwest Alabama into our south- central counties this afternoon and tonight. The warmest temperatures and higher dew point values have been largely confined to our southern and southwest counties and these areas will have the most instability available for convective development and organization over the next few hours. The primary concern for this scenario remains damaging wind potential from bowing line segments. A secondary risk for large hail will exist across the same area due to steepening lapse rates with time due to height falls aloft as the upper trough nears from the west. Outside of strong to severe thunderstorms, the heavier activity will contain frequent lightning strikes and torrential downpours which could cause ponding of water in low-lying and poor drainage areas though persistent storm motions from 30-40 kts will help to limit flash flood potential in the more vulnerable areas. As we get past sunset, surface instability will quickly wane but the steepening lapse rates aloft will continue to support at least isolated thunderstorms along with lingering shower activity through much of the evening and into the overnight hours. The severe weather threat is expected to end from west to east from early evening across our southwest counties to later tonight, generally before midnight, across our southeast counties. 05 Modified previous short-term discussion: Today and Tonight. Storms this afternoon and evening will likely track south of the remnant boundary, generally south of the I-20/59 corridor. This is the area that is already seeing dewpoints in the upper 60s to near 70. With daytime heating, instability will likely increase to 1000- 2000+ J/Kg in this area, leading to the more robust storms of the day, some of which could be severe. High resolution guidance has not handled the evolution very well, giving drastically different data in each run, which isn't a surprise given the weak forcing and mesoscale nature of the propagation. With that said, some guidance keeps hitting on the more robust line of thunderstorms moving through Southern AL during the mid- afternoon. If this were to take place, it would have the better chance to produce damaging winds when compared to the more disorganized thunderstorms. Therefore, I'll increase the risk for severe storms capable of producing damaging winds to a "slight" risk generally along and south of the Hwy 80 corridor in South- Central AL. Locations north of this could still see strong to severe thunderstorms, but confidence in the coverage is relatively lower. At this time, the tornado potential is extremely low given the unfavorable low level wind profiles. By late tonight, any thunderstorm activity should be east of our area, ending any severe threat for Central AL. 25/Owen .LONG TERM... /Issued at 0300 AM CT/ Sunday through Saturday. Low level ridging builds in across much of the Southeastern CONUS with zonal flow aloft Sunday through early Tuesday. This will keep the area mostly dry with a gradual warming trend. Afternoon highs on Tuesday could reach into the upper 80s to near 90 degrees. A persistent trough remains over the Western US through mid-week and into the second half of the week. Several impulses move through the base of the trough, each bringing increased chances of thunderstorms for at least the northern half of Central AL through Saturday. For now, will not add any mention of severe potential with these systems as timing of any individual impulse remains uncertain. 25/Owen && .AVIATION... 18Z TAF Discussion. Active afternoon and evening in store across central Alabama with the majority of the TAF sites impacted. Currently most locations are experiencing MVFR ceilings except the far south which have cleared and lifted to VFR conditions. Isolated TSRA was noted just east of KBHM at 17z with more organized convection across Mississippi. This convection will increase in coverage and overspread the TAF sites this afternoon/evening. Have included a period of TSRA at all areas roughly between 21z and 01z with more widespread light precipitation after that time period. Ceilings will lower to the IFR range overnight before slowly improving late Sunday morning. 15 && .FIRE WEATHER... Showers and thunderstorms expected today across Central AL. Gusty winds may become erratic in proximity to the thunderstorms. There are no fire weather concerns at this time. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 61 79 57 84 59 / 80 20 10 0 0 Anniston 62 80 58 85 60 / 80 20 10 0 0 Birmingham 63 80 60 87 63 / 80 10 0 0 0 Tuscaloosa 62 82 59 88 63 / 80 10 0 0 0 Calera 62 80 60 86 62 / 80 20 0 0 0 Auburn 63 79 62 85 63 / 70 40 10 0 0 Montgomery 65 83 62 88 64 / 80 30 10 0 0 Troy 64 82 62 87 64 / 70 40 10 0 0 && .BMX WATCHES/WARNINGS/ADVISORIES/... None. && $$