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Area Forecast Discussion
Issued by NWS Birmingham, AL
Issued by NWS Birmingham, AL
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296 FXUS64 KBMX 170552 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 1252 AM CDT Sat Aug 17 2024 ...New AVIATION... .SHORT TERM... (Tonight through Sunday) Issued at 904 PM CDT FRI AUG 16 2024 Showers and thunderstorms have already started decreasing in coverage this evening. Went ahead and decreased the pops for the remainder of the night, but held on to some mention just after midnight. Overall moisture convergence has decreased while the surface based parameters have become stable. Have removed severe wording for the overnight hours. Increased cloud cover quite a bit as we are dealing with the thunderstorm blow off. These clouds will slowly erode through the night. Lows at or slightly above normal in the 70s. On Saturday, it appears that thunderstorms will develop during the afternoon hours will decent coverage. Severe wording will be maintained and hot and humid conditions continue. 75 Previous short-term discussion: (This afternoon through Saturday) Issued at 1257 PM CDT FRI AUG 16 2024 With the rain diminishing by midnight, expect a break in the action through at least mid-morning until another wave of scattered to numerous thunderstorms moves into the area from the northwest. Model continuity is really all over the place in terms of the evolution of the storms, but nonetheless, the environment will once again be supportive for damaging winds in generally the same areas as today, the northern two-thirds. Moisture remains on the higher end with afternoon dewpoints remaining in the mid 70s, so heat will be a concern again tomorrow. The Heat Advisory has been extended through tomorrow afternoon, and expanded to include a few more counties on the eastern extent where heat indices will reach 105F before any upstream rain or associated outflow can reach the area and drop temperatures. 86/Martin && .LONG TERM... (Saturday night through next Thursday) Issued at 349 PM CDT FRI AUG 16 2024 The cold front that will move through the area Sunday is expected to spark thunderstorm development across middle and southern portions of Central Alabama by Sunday afternoon and evening. Confidence has increased somewhat from the previous forecast cycle, with the introduction of a Slight risk area from Demopolis to Clanton to LaFayette and points south. Bulk shear values of 30-40 kts and high DCAPE values will work in favor of a damaging wind threat as the line moves south. Depending on storm mode, lapse rates will be favorable for at least some small hail with these storms as well. Depending on timing of the storms, another Heat Advisory may be needed across the south on Sunday afternoon, as a humid airmass will still be in place ahead of the front. Otherwise, Monday through much of the week looks dry. Rain and storm chances return to the southeastern counties Thursday and Friday afternoon. Temps and dew points will be lower and conditions will be much more bearable. 12 Previous long-term discussion: (Saturday night through next Thursday) Issued at 257 AM CDT FRI AUG 16 2024 Key messages: - A somewhat conditional risk of severe storms with damaging winds continues Sunday afternoon and evening, depending on how storms evolve Saturday/Saturday night. - One more day of heat indices at or above 105 degrees appears likely on Sunday, before a less humid and not as hot air mass moves in for much of next week. A highly amplified pattern for mid to late August will persist through the long term period, with strong subtropical ridging remaining centered over the High Plains flanked by a trough/upper low off the coast of the Pacific Northwest and an amplifying trough over the eastern CONUS. Showers and storms will probably be ongoing Saturday evening, some of which may be strong to severe. Some ensemble members bring down some additional storms from the north late Saturday night into Sunday morning though the majority of members are dry. Another shortwave in northwest flow aloft down the back side of the trough moves in Sunday as the cold front moves into the area. The environment will be conditionally favorable for severe storms on Sunday as 0-6km bulk shear strengthens to an unseasonably strong 30-40 kts and mid-level lapse rates begin to steepen, with plenty of dry air aloft/DCAPE. Severe storm potential will be dependent on any outflow boundaries from Saturday night`s convection and how much moisture gets scoured out/if the mid-level dry air is too dry to sustain updrafts. Convergence will be limited along the front as winds veer to the northwest ahead of the front due to lee troughing. But there is enough signal for convective initiation in the latest guidance to message a marginal risk of severe storms. Mesoscale trends will continue to be monitored as we get closer in case any increase in storm coverage/risk level becomes apparent. A heat advisory will probably also be needed for at least some of the southern counties. Behind the front, a drier and "cooler" air mass for late August will move in with highs in the upper 80s to lower 90s and lows well into the 60s a couple nights with low humidity. Late in the period the main trough lifts out but a weakness will get left behind. Depending on how quickly this weakness retrogrades some moisture may begin to return by the end of the period. As high pressure pushes eastward and weak wedging develops, easterly winds will keep the heat at bay. 32/Davis && .AVIATION... (06Z TAFS) Issued at 1234 AM CDT SAT AUG 17 2024 Currently the area is between 2 MCS structures. The first is in Georgia and dissipating. A brief rain shower could slide through ANB but most of the activity remains east. A second MCS is well to the NW but will put an outflow boundary into Alabama by sunrise. This boundary will be between EET and MGM by 18z. Looks like we may have one round of showers and storms in the south early afternoon, then a second round develop across the north after 21z. This round will slide south and could work back into MGM after 3z. 16 && .FIRE WEATHER... A few rounds of showers and storms will move by through Sunday afternoon. RH values will remain above 40 percent through the weekend. A dry air mass returns next week, with no rain expected Monday through Wednesday and RH values from 30 to 40 percent. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 94 71 93 67 / 60 30 30 10 Anniston 94 71 92 68 / 60 50 30 10 Birmingham 95 73 94 69 / 60 40 30 10 Tuscaloosa 95 73 94 70 / 60 50 30 20 Calera 94 73 93 70 / 60 50 30 20 Auburn 93 73 94 70 / 50 40 40 40 Montgomery 97 74 97 72 / 50 30 40 40 Troy 92 72 97 71 / 50 30 40 50 && .BMX WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 9 PM CDT this evening for the following counties: Bibb-Blount-Dallas-Fayette-Greene-Hale-Jefferson-Lamar- Marengo-Marion-Perry-Pickens-Shelby-Sumter-Tuscaloosa-Walker- Winston. Heat Advisory from 10 AM this morning to 9 PM CDT this evening for the following counties: Autauga-Chilton-Coosa-Elmore-Lowndes- St. Clair-Talladega. && $$ SHORT TERM...75 LONG TERM....12 AVIATION...16