Area Forecast Discussion
Issued by NWS Birmingham, AL
Issued by NWS Birmingham, AL
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
191 FXUS64 KBMX 162050 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 350 PM CDT Fri Aug 16 2024 ...New LONG TERM... .SHORT TERM... (This afternoon through Saturday) Issued at 1257 PM CDT FRI AUG 16 2024 Central Alabama is positioned between a large ridge over the Desert Southwest, and an upper-level low over the Great Lakes region. Both features will gradually drift east through tomorrow. This will place us within a zone of MCS activity and persistent northwest flow with a few rounds of convection developing over the Midwest then moving into the Tennessee Valley. There`s already one boundary across northwest portions of the area, but activity along the boundary has diminished since this morning. CAMs are indicating higher chances for storms this afternoon as another outflow boundary is sent southeast from Missouri. Much of the more favorable forcing will remain north of Alabama, so convection this afternoon will be outflow and instability driven, and expected to be mostly scattered in coverage. As temperatures rise into the mid 90s, MLCAPE values will increase to around 2500-3000 J/kg and DCAPE to around 1000 J/kg, so storms will contain mainly a risk for isolated strong, straight-line winds as they move from north to south late this afternoon and into the evening. Some risk for strong winds may persist as far south as Clanton and Alex City, but intensity will begin to wane into the evening hours as temperatures drop. Speaking of the mid 90s, a Heat Advisory continues for mainly the western half of the forecast area this afternoon where dewpoints are in the mid 70s. 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... (18Z TAFS) Issued at 1257 PM CDT FRI AUG 16 2024 VFR conditions are expected for most of this TAF cycle, but some scattered convection later this afternoon and into the evening may cause periodic aviation impacts at mainly the northern terminals. Expect convection to wane in coverage as it moves from north to south across the area, so MGM may see little to no impacts. Coverage will dissipate by 06Z, and some high clouds will linger into tomorrow. Sfc winds will take on more of a westerly heading by 15Z tomorrow at 5 to 8 kts. 86/Martin && .FIRE WEATHER... A few rounds of showers and storms will move through this afternoon through Sunday afternoon. RH values will drop below 40 percent in far southeastern portions of Central Alabama this afternoon, but otherwise 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 70 93 70 91 / 50 60 50 40 Anniston 73 92 70 90 / 50 60 50 40 Birmingham 75 94 72 93 / 50 60 40 40 Tuscaloosa 75 93 73 94 / 40 60 30 40 Calera 75 93 72 92 / 40 60 40 40 Auburn 73 92 72 92 / 20 50 40 40 Montgomery 75 96 73 97 / 20 50 40 40 Troy 73 94 72 96 / 20 40 30 40 && .BMX WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 9 PM CDT Saturday 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 to 9 PM CDT Saturday for the following counties: Autauga-Chilton-Coosa-Elmore-Lowndes-St. Clair- Talladega. && $$ SHORT TERM...86 LONG TERM....12 AVIATION...86