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FXUS64 KBMX 070043 AFDBMX

Area Forecast Discussion National Weather Service Birmingham AL 743 PM CDT Mon May 6 2024

New SHORT TERM, AVIATION

SHORT TERM
(Tonight through Wednesday)
Issued at 720 PM CDT MON MAY 6 2024

Clouds will form late tonight as southerly, moist flow continues.
Additionally, a brief period of patchy fog is also possible around sunrise. The best chances for fog will be south. The lower clouds will increase in height and thin somewhat by afternoon.
Scattered thunderstorms will develop mainly during the maximum heating of the day. The discussion below still applies for Tuesday afternoon.

75

Previous short-term discussion: (This afternoon through Tuesday)
Issued at 103 PM CDT MON MAY 6 2024

A cold front moves into the Mid-South region tomorrow, and a very subtle weakness in the low to mid-level flow will move across the Lower MS River Valley and towards the Tennessee Valley during the afternoon. Although forcing will be very weak, the airmass will quickly destabilize during peak heating. MUCAPE is progged to rise to around 3000 J/kg across the west where dewpoints will stay near 70F, and eff. shear of 40 kts will support some scattered strong to severe thunderstorm potential. Stronger storms will be capable of producing damaging winds up to 60 mph and quarter size hail with highest thunderstorm coverage expected along and north of I-20.

86/Martin

LONG TERM
(Tuesday night through next Sunday)
Issued at 326 PM CDT MON MAY 6 2024

Not many changes needed in the extended this afternoon, other than minor changes rain chances. Will have more details for the Wed night/Thu system once we are in the time range of CAM models. For now, will continue to highlight the key messages below.

Key messages:

- The warmest day of the spring so far is expected Wednesday with heat indices in the mid 90s.

- One or more rounds of showers and storms will result in a threat of damaging winds, large hail, and localized minor flooding Wednesday night possibly into Thursday, especially across the northern half of Central Alabama. However, confidence on details remains low at this time.

Isolated to scattered showers and storms may linger into the evening hours on Tuesday before weakening, though some activity could persist across the far northern counties in closer proximity to a stalled cold front and lingering boundaries.

A rex block will be in place to start the period with an upper low over the Northern Plains and an anticyclone over the Canadian Prairies. The upper low will eventually split with the majority of its vorticity going into a trough over the Great Lakes by Thursday and a lesser portion going to an upper low over the Southwest CONUS as part of a developing omega block over the eastern Pacific/West Coast. Meanwhile a strong subtropical ridge will be centered over the Bay of Campeche. At the surface the stalled frontal boundary will lift northward as a warm front across the Ohio Valley in response to a broad but sub-1000mb area of low pressure moving from Missouri to the southern Great Lakes. A fairly strong late spring cold front will eventually move through Central Alabama Thursday and Thursday night.

Dry air aloft and weak ridging should keep any diurnal convection isolated to widely scattered Wednesday while strong low-level southwesterly flow results in the warmest day of the spring so far. Those that are especially sensitive to heat impacts may need to take precautions given the lack of acclimation to the heat this early in the season. Robust convection should develop to our northwest ahead of the cold front Wednesday afternoon and evening in a very unstable and sheared air mass, aided by a vort max moving through the Mid-Mississippi Valley. This convection will probably eventually grow upscale into one or more MCSs potentially moving towards our northern counties Wednesday night aided by a modest LLJ. With weak forcing there is quite a bit of model spread regarding timing as is typical in this setup. The ECMWF and its ensembles bring convection in during the evening hours while other guidance holds off until after midnight. An earlier timing would coincide with more instability and a greater threat for severe storms, but given mild overnight lows and steep mid-level lapse rates with an EML there would still be at least an isolated severe threat with the later overnight timing. Damaging winds and large hail will be the main threat. The tornado threat while very low may be non-zero. Some guidance does indicate some marginal SRH developing depending on whether a secondary surface low forms.
Given the uncertainty over timing, convective mode, and whether storms will be surface-based, will hold off on any brief tornado mention at this time.

Fast zonal flow will be in place Thursday as the cold front moves in, with little in the way of height falls until evening when troughing begins to deepen over the eastern CONUS. An impressive overlap of CAPE and shear may be present, but this will be highly dependent on how much convection occurs Wednesday night and Thursday morning and any leftover cold pools. Additionally, low-level flow will be veering and weakening, limiting convergence, while moisture dries up aloft. There will probably end up being at least an isolated threat of severe storms, but will hold off on messaging past Wednesday night given the limiting factors mentioned above. There is also the possibility for an MCS to move along the Gulf Coast Thursday night which could cause locally heavy rainfall and some stronger storms across our southern counties.

Behind the front, a welcomed relief from the heat is expected going into the weekend with highs in the 70s to lower 80s and lows in the 50s. There are some model disagreements regarding potential shortwave activity by Sunday, but ensembles support keeping PoPs at 10 percent or less on Sunday.

32/Davis/14

AVIATION
(00Z TAFS)
Issued at 720 PM CDT MON MAY 6 2024

The terminal forecast trend was continued this cycle. Some convection will be around this evening but will be isolated enough to leave out for the time being. The activity will dissipate by 3z. Southerly low level flow is quite moist and will become saturated toward daybreak. There is some isentropic lift that will occur and expect MVFR ceilings after 08-10z at all terminals.
Several locations will also see IFR ceilings which should be rather brief, 4 hours or less. The MVFR ceilings will rise and become VFR by 16-17z. Scattered thunderstorms will be possible in the afternoon for the northern terminals. Starting off with a PROB30 mention. Winds will be south southwest 5-10kts.

75

FIRE WEATHER

Isolated to scattered showers and storms are possible each day through Wednesday, with greater rain chances Wednesday night and Thursday. Rainfall amounts will average 0.5-1.0 inch under heavier storms. Afternoon minimum RH values will be above 40-45 percent each afternoon through mid week. 20-foot winds will average less than 10 mph from the south to southwest Tuesday, increasing to 8-12 mph Wednesday. Wind gusts to around 25 mph are possible near convection.

PRELIMINARY POINT TEMPS/POPS
Gadsden 64 86 67 89 / 20 50 30 30 Anniston 66 86 68 88 / 20 40 20 20 Birmingham 68 86 70 89 / 20 50 20 20 Tuscaloosa 68 87 70 90 / 20 50 20 20 Calera 67 86 69 88 / 20 40 20 20 Auburn 66 86 70 88 / 20 10 10 10 Montgomery 67 90 70 92 / 20 20 10 10 Troy 66 90 69 91 / 20 10 0 10

BMX WATCHES/WARNINGS/ADVISORIES
None.

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