115 FXUS64 KBMX 242005 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 305 PM CDT Sat Oct 24 2020 .SHORT TERM... /Updated at 1107 AM CDT Sat Oct 24 2020/ Through This Afternoon. The combination of a mid-level shortwave trough and associated weak surface low over southwestern Central AL is producing plenty of lift with ample moisture for widespread showers and a few thunderstorms. The heaviest rain is found in a north to south oriented line which is moving generally northeastward across I-65 at this hour. For the most part, rain rates are light with pockets of moderate to heavy, soaking rain which could lead to accumulations of an inch to an inch and a quarter in some spots. Instability and shear are too weak for any severe weather worries, but MUCAPE around 700-1000 J/kg will be sufficient for a few rumbles of thunder throughout the day. The rain will continue to shift into eastern AL this afternoon with lowering PoPs in the west. The aforementioned surface low is part of a larger system over eastern Canada with a trailing front over the eastern CONUS that will slowly move into Central AL through tomorrow. Temperatures will be slow to rise due to the rain, so highs will near 60F northwest behind the front to mid 70s southeast ahead of the front. Tonight Through Sunday. Some lingering showers will persist in the east through midnight, but dry air aloft quickly moves in behind the shortwave by tomorrow morning which greatly reduces our rain chances. However, the rain will leave saturated surface conditions which will likely support patchy fog across most of the area from ~07-13Z. Whatever is left of the weak surface front will erode over the area tomorrow while mid- level flow becomes zonal as a flattened ridge moves into the northern Gulf, so we really won't see much of a temperature change. 86 .LONG TERM... /Updated at 0250 PM CDT Sat Oct 24 2020/ The latest model output keeps the longwave pattern and its subsequent evolution similar to previous runs with little deviation. The GFS continues advertising a weaker low/trough Wednesday through Friday, and therefore quicker than ECMWF/UKMET/CAN. Will lean toward the consensus and away from the GFS at this time. Deep tropical moisture moves out of the Caribbean and into the Gulf of Mexico Monday and Tuesday. This airmass then enters the Lower Mississippi Valley and parts of the Southeast Tuesday night through Thursday. This moisture surge will be out ahead of the low/trough moving in. Therefore, rain chances are somewhat limited Monday-Tuesday and are relatively high Wednesday and Thursday. Dry conditions are anticipated after the low/trough exits eastward late Friday. NHC has a rather high chance of some tropical development affecting the Caribbean/Gulf, see NHC for specifics. Therefore, the specifics and areas of best lift and forcing are still to be determined. But some threat of locally heavy rain may develop. At this time, will not mention but certainly something to keep an eye on. Overall, the temperature trends remain above normal. 75 Previous long-term discussion: /Updated at 0318 AM CDT Sat Oct 24 2020/ Sunday night through Monday night: The center of a mid-level subtropical ridge will migrate from the western Gulf coast Sunday night to just north of the Bahamas by Monday night. This will be in advance of a positively tilted trough digging into the western CONUS. A closed low is expected to develop at the base of the trough over Arizona as it becomes detached from the stronger northern stream flow. This will place Central Alabama under southwest flow aloft. At the surface, the stalled front across the area will be dissipating, while another stronger cold front approaches from the northwest Monday night in advance of a 1040mb high over the northern High Plains. This front will be decelerating, however, as it becomes parallel to the flow aloft and encounters the ridge. Dry air aloft as well as a subsidence inversion associated with the ridge will prevent any appreciable rainfall Sunday night through Monday night. However, with some moist isentropic lift underneath the subsidence inversion due to low-level southerly flow can't rule out some patchy drizzle or a very light shower depending on the depth of the low-level saturation. Temperatures will continue to be above normal. Tuesday through Friday. A more active/wet pattern is expected to develop by midweek but confidence in details remains low. The closed upper low will eventually move eastward across the southern CONUS but models vary on its strength. These systems do also sometimes tend to trend slower especially given the strength of the downstream ridge. Also, NHC now indicates that the broad area of low pressure over the western Caribbean is likely to become a tropical depression as it moves towards Cuba over the next day or two. Models now seem to be indicating that the strong Bahamas ridge may limit recurvature enough for the system to move into the Gulf, though models vary regarding whether it will continue to have a weak closed surface circulation at this time. Confidence in details will remain low until the system actually forms. Models are coming into agreement on tropical moisture associated with this system lifting northward ahead of the closed upper low and associated cold front, though there is uncertainty regarding where the cold front that initially moves in Monday night will stall out. Will continue to indicate a gradual increase in PoPs through midweek. The potential tropical disturbance would limit the threat of severe weather with the closed low itself, but would have to be monitored in case the low-level wind fields associated with the disturbance end up being stronger. Will also have to monitor for any heavy rainfall potential during this time as well. 32/Davis && .AVIATION... 18Z TAF Discussion. This afternoon, a weak surface low is producing showers near the eastern terminals and OVC skies with ceilings that have been up and down most of the morning. These showers should move out of Central AL late this afternoon. A slot of dry air is moving northeastward from the Mobile area which will allow for VFR ceilings at the southern sites. Otherwise, low ceilings are advecting into the area from Mississippi and will linger around TCL for most of the day, potentially reaching as far east as BHM and EET. Generally expect drops into IFR at times through the afternoon with the exception of TOI/MGM. However, surface conditions remain saturated overnight and expect fog to develop at most terminals beginning as early as 05-06Z and persisting through at least 14Z. Visibilities and ceilings will drop into IFR, potentially LIFR at times, through that time period before slow improvements late in this TAF cycle. NOTE: AMD NOT SKED will be used for TOI until further notice due to missing data. 86 && .FIRE WEATHER... Moisture values will remain elevated through much of the coming week. Scattered showers and a few storms will impact eastern areas through this evening. Winds will generally be light outside of any stronger thunderstorm activity, with speeds below 6kts. Rain showers will end from west to east overnight, with rain-free conditions returning Sunday. The front will stall and dissipate across the area tomorrow, but drier air remains to our west. Low ceilings and fog will be possible tonight and early Sunday morning as low level moisture remains high. Afternoon relative humidities remain above 60 percent each day. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 61 73 59 79 61 / 30 10 10 10 10 Anniston 62 75 62 81 63 / 40 10 10 10 10 Birmingham 60 74 61 81 64 / 20 10 10 10 10 Tuscaloosa 58 73 60 82 63 / 10 0 10 10 10 Calera 60 73 61 81 64 / 20 10 10 10 10 Auburn 64 75 63 81 64 / 50 10 10 10 0 Montgomery 64 75 62 84 66 / 30 10 10 10 0 Troy 64 76 63 83 66 / 40 10 10 0 0 && .BMX WATCHES/WARNINGS/ADVISORIES/... None. && $$