Area Forecast Discussion
Issued by NWS Birmingham, AL
Issued by NWS Birmingham, AL
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949 FXUS64 KBMX 081126 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 626 AM CDT Wed May 8 2024 ...New AVIATION... .SHORT TERM... (Today through Thursday) Issued at 355 AM CDT WED MAY 8 2024 Key message: - Multiple rounds of strong to severe storms are possible tonight through Thursday night with damaging winds and large hail possible. Timing and location of the highest threat areas remain uncertain. Today through Midnight: For today, we will be in a preparation state across the area before the first of several waves of showers and storms move into the area. By the afternoon, isolated to scattered showers and a few storms will be possible. A few stronger storms will certainly be possible as the area will be a tad more stable that the south. Areas in the south will reach the low 90s by the afternoon, so any shower/storm that develops down here certainly will be strong. Most activity will dissipate after sunset, albeit briefly. At this time there does not appear to be organized severe weather threat through the early evening hours tonight. 16 After midnight tonight through Thursday afternoon: The rex block over the western CONUS and Plains will be transitioning to an omega block over the eastern Pacific and western CONUS tonight. As this occurs the upper low over South Dakota/Nebraska will break into three piece. The western piece will become an upper low forming near the Grand Canyon, the middle piece will become a shortwave that eventually dives southward across the Mid South Thursday night, and the eastern piece will get absorbed into a northern stream trough over the Great Lakes. Meanwhile a strong subtropical ridge will be centered over the Bay of Campeche. At the surface a somewhat disorganized but sub-1000mb low pressure area will move eastward from Missouri to the Ohio Valley. A trailing cold front will move only slowly southeastward, finally reaching Central Alabama Thursday night, while a warm and humid air mass will be present ahead of it. Convection developing over the Mid-South will grow upscale into an MCS tonight aided by a 35kt LLJ which has trended weaker with recent runs. Convection along the trailing outflow from this MCS will eventually sink southward into our northern counties late tonight, with the arrival time trending later. Any isolated cells that are able to develop ahead of this line this evening would be potentially capable of all modes of severe weather, though increased capping/warming 700mb temps make this a low probability chance at this time. The MCS should be weakening as it moves into our northern counties late tonight/early tomorrow morning as the LLJ veers/weakens and shear vectors become parallel to the outflow boundary. However, the unusually warm and moist air mass and steep mid-level lapse rates will keep CAPE values above 1000 J/kg, so it may still be capable of producing severe weather. Of more concern is the slower trend with the progression of the outflow boundary, with the potential for the MCS to re-intensify or a new MCS to develop as daytime heating occurs ahead of the outflow boundary, potentially aided by a subtle shortwave in the morning. CAPE values increasing to 2000-3000 J/kg by late morning, 0-6 km bulk shear around 50 kts, and plenty of dry air aloft/DCAPE would become very favorable for damaging winds mainly along and east of I-65 if this occurs, before the MCS pushes into Georgia. Therefore the severe risk has been upgraded to a Level 2 out of 5 slight risk. (Note: we`ve combined the late tonight risk and the tomorrow daytime risk on one threat graphic; an additional threat graphic covers the potential next wave tomorrow night). While this scenario is starting to become more plausible, and could warrant a further increase in severe risk, it`s also plausible that the line could push into Georgia before strengthening too much. Will have to keep watching model trends as this will be heavily dependent on mesoscale lifting by the outflow boundary as the only source of forcing. Any individual cells that can develop would also become capable of producing hail given the steep lapse rates, potentially larger than quarter size. It still looks like there will be some subsidence developing by afternoon with weakly anticyclonic flow and some drying aloft, to the west of the MCS. Though, some isolated severe storms may still be possible during this time, ahead of another potential round of severe storms discussed below in the long term section. 32/Davis && .LONG TERM... (Thursday night through next Tuesday) Issued at 355 AM CDT WED MAY 8 2024 A subtle mid-level speed max/southern stream shortwave is expected to help initiate convection ahead of the front over the ArkLaTex Thursday afternoon. As this feature moves eastward, it`s unclear if these storms will grow upscale into an MCS or if there will just be various clusters of storms. With a very unstable air mass and steep mid-level lapse rates of 7.5 to 8 C/km persisting south of the front, as well as strong bulk shear, the severe threat is expected to persist or re-develop Thursday evening through the overnight hours. In addition, a shortwave digging across the Mid- South will result in height falls across the area. Will indicate a Level 2 out of 5 slight risk focused across the southern half of the area for a continued threat of damaging winds as well as large hail with any supercells. Low-level shear appears too weak for a threat of tornadoes at this time. The cold front will push through the area Friday morning, providing welcome relief from the heat and storms. The upper low over the southwest CONUS will eventually move eastward early next week. Models have trended a bit quicker and wetter with this system 32/Davis && .AVIATION... (12Z TAFS) Issued at 622 AM CDT WED MAY 8 2024 MVFR ceilings have developed at all sites. There could be a brief drop to IFR at spots, but the predominate will be MVFR. The ceilings will slowly rise and become VFR by 16-18z. Showers and thunderstorms are possible again this afternoon and have the northern sites in a VCSH for the afternoon hours then clearing out after 21 to 23z. Winds will become 5-10 kts during the day and then remain that way through the night. MVFR clouds will redevelop after 6z with showers and storms moving in from the north. 16 && .FIRE WEATHER... Isolated to scattered showers and storms are possible this afternoon with greater rain chances overnight and Thursday. Rainfall amounts will average 0.5-1.0 inch under heavier storms. Afternoon minimum RH values will be above 45-50 percent this afternoon and then higher on Thursday. 20-foot winds will be 8-12 mph this afternoon and Thursday. Wind gusts to around 25 to 30 mph are possible near convection. Most of the rain will end by Friday afternoon, with a dry forecast through the weekend and first of next week. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 88 67 86 61 / 30 70 90 40 Anniston 88 69 85 64 / 30 50 90 50 Birmingham 88 70 86 63 / 30 50 90 50 Tuscaloosa 89 71 88 65 / 30 50 80 50 Calera 88 71 86 64 / 30 50 90 60 Auburn 87 72 85 67 / 20 20 80 60 Montgomery 91 72 89 67 / 30 20 80 60 Troy 91 72 89 68 / 20 10 70 60 && .BMX WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...16/32 LONG TERM....32 AVIATION...16