Area Forecast Discussion
Issued by NWS Birmingham, AL
Issued by NWS Birmingham, AL
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691 FXUS64 KBMX 090918 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 418 AM CDT Thu May 9 2024 ...New MESOSCALE UPDATE... .MESOSCALE UPDATE FOR SEVERE WEATHER THROUGH LATE MORNING... Issued at 418 AM CDT THU MAY 9 2024 A Mesoscale Convective System was moving southeast across Northern Mississippi and much of Southern Tennessee. The overall storm motion was southeast around 30 mph with a quick storm track projecting arrival times near 6:30 am for Gadsden, 7:00 am for Birmingham and 7:30 am for the Anniston metro areas. Further west, the arrival times for activity is more uncertain as activity is moving more eastward over the Mid-South Region. Locally, showers have rapidly developed over the past 30 minutes, likely in response to the arrival of 100 kt winds at 200 mb progged by the RAP 13 km model currently. This activity is expected to continue to develop and move east-northeast in the established low-level flow from the southwest in the 700 mb - 925 mb layer. A defined shortwave trough at 500 mb was analyzed by mesoscale modeling over North-Central Louisiana and is progged to move northeast over the area later this morning, further supporting additional convective activity. The environment is very supportive of continued convective activity as the 09/00z BMX sounding from last night contained nearly 3500 J/kg of SBCAPE that fed the intense storms over the Tennessee Valley Region. Mesoscale data suggests current instability values are a bit lower, typical for this time of day with the forecast low temperatures occurring, with values from 1600-2000 across the west and northwest portions of the area while lower instability values found across the far east/southeast. 0-6 km Bulk Shear values range from around 40 kts over North Alabama to near 50 kts over the southern portion of the area. These values are sufficient to support storm organization and persistence, of which already a few heavier showers ahead of the heavy convection moving southeast are exhibiting deviant storm motions with a storm split that recently occurred over Northeast Marshall County. Through late morning, we will be monitoring the progress of the MCS as it continues to move generally southeast into the forecast area. We will be closely watching shower activity that is expected to continue to develop and move northeast. This activity will have the potential to further develop into thunderstorms as it traverses the unstable and sufficiently sheared environment. Discrete mature convection ahead of the MCS will have the best potential of producing tornado activity along with damaging winds being a secondary risk. The MCS itself will have the best potential for producing damaging winds, though an embedded tornado or two will remain possible. 05 && .SHORT TERM... (Today through Friday) Issued at 115 AM CDT THU MAY 9 2024 Key Messages: - A Mesoscale Convective System dives southeast into the area before sunrise and push southeast through the morning and into the afternoon hours. While gradually weakening in the morning, it may re-intensify before it exists our southeast counties late morning into the afternoon. Damaging winds will be the primary risk, with large hail and a few tornadoes being possible as well. - Some thunderstorms may redevelop across North-Central Alabama late afternoon into the early evening that will have large hail potential, this risk will decrease in the evening as another MCS approaches our south-central counties from the west. - The second MCS appears to track a touch to the north of the previous forecast, so the severe chances have increased across the southern areas. Damaging winds will be the primary risk, with large hail and a few tornadoes being possible as well. We will be watching a MCS that is currently across western TN. This MCS should dive southeast into the area before sunrise and push southeast through the morning and into the afternoon hours. While gradually weakening in the morning, it may re-intensify before it exists our southeast counties late morning into the afternoon. There may be a line of showers and storms that develops as well and will merge with this first area. Highest confidence right now would be with the MCS to or northwest moving down and then spreading out. Damaging winds will be the primary risk, with large hail and a few tornadoes being possible as well, especially if there is a merge of lines. There will be a brief lull before the next system moves in. Conditions are shaping up for a secondary round of strong to severe thunderstorms late tonight through Friday morning. This activity will likely develop along the cold front which will be nearly parallel to I-20 as a mid-level shortwave quickly moves east across the area. The airmass will still be very warm and unstable south of the front with dewpoints in the lower to mid 70s and steep 7.5-8 C/km lapse rates leading to large CAPE profiles (MLCAPE ~3500 J/kg). Shear values will be amplified by the mid- level speedmax/shortwave which will result in eff. bulk shear values around 60 kts. This environment will foster intense convection to our west which will rapidly grow into a large MCS with damaging wind potential maximized along embedded bowing segments as the system moves east, across the southern portions of Central Alabama early Friday morning. There are questions regarding how far north the threat extends given the uncertain position of the front and remnant cold pool from the line of convection this morning/afternoon which could suppress the greatest risk to the southern third of the area. Anything that develops south of the cold front will have the potential to become severe given the moist, unstable environment. Damaging winds are by far the primary threat, but intense updrafts may lead to large hail in the Enhanced risk area. The cluster of storms will begin to exit the area around 7 AM Friday morning as the cold front continues to push south through the area, bringing a much more pleasant airmass to the region. && .LONG TERM... (Friday night through next Wednesday) Issued at 245 AM CDT THU MAY 9 2024 Dry conditions return Friday night as the system exits to our east. Humidity will be lower on Saturday with highs in the upper 70s to lower 80s under sunny skies. A mid-level ridge will move across the area over the weekend as an upper-level low transitions from the Four Corners to the Central Plains. Deep moisture returns on Monday, with an increasing potential for another period of rainy and stormy conditions through the early part of next week as a warm front lifts north across the region. 16 && .AVIATION... (06Z TAFS) Issued at 115 AM CDT THU MAY 9 2024 Almost all sites have already dropped to MVFR ahead of the next round of showers/storms. We may briefly see sites drop to IFR before the band gets in, but the biggest impact should be the storms as they move into the northern TAF sites after 10z and closer to 12z. This round will slide south of the northern sites by 16 to 17z and out of the southern sites by 19 to 20z. Conditions will improve to VFR for most of the rest of the cycle, but begin to decrease at TCL by 3z ahead of the next round of showers and storms along a cold front. 16 && .FIRE WEATHER... Multiple rounds of showers and storms are expected to affect the area through Friday morning. Rainfall amounts will generally range from 1 to 2 inches. A drier airmass will return on Friday as a cold front passes through the area with min RH of 35 to 40 percent on Saturday. 20ft winds will be out of the south- southeast at 8 to 10 kts. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 86 61 78 49 / 100 30 20 0 Anniston 85 64 79 52 / 100 50 30 0 Birmingham 86 64 79 54 / 100 50 20 0 Tuscaloosa 87 66 81 55 / 100 60 20 0 Calera 85 66 80 55 / 100 60 30 0 Auburn 82 69 81 57 / 90 80 50 0 Montgomery 86 69 84 57 / 90 80 50 0 Troy 86 68 83 57 / 90 80 60 0 && .BMX WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...05 LONG TERM....16 AVIATION...16