949 FXUS64 KBMX 131807 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 106 PM CDT Tue Aug 13 2019 .UPDATE... For 18Z Aviation. && .SHORT TERM... /Updated at 0338 AM CDT Tue Aug 13 2019/ Today and tonight. Some adjustments have been made to our heat-related products for today based on observations from Monday. The airmass remains largely unchanged with only a small increase in moisture content noted in model guidance for this afternoon. The effects of ongoing drought conditions should result in an area of deeper mixing and dewpoints falling into the upper 60s to lower 70s this afternoon. Therefore, the Excessive Heat Warning has been replaced with a Heat Advisory across a large portion of our northern and eastern counties including the Birmingham metro area. PWAT values greater than 2 inches will be most common along and south of Interstate 85 today, and this is where scattered showers and storms are expected. To the northwest, convection should remain very isolated. For tonight, we'll be watching a front move in from the north and the potential for thunderstorms. Convergence along the front and strong instability may lead to a band of strong to severe storms across Tennessee during the late afternoon and early evening. However, short-range guidance generally agrees that convergence along the front will become more diffuse across our forecast area, and the storms to our north will probably weaken as they move into our northern counties. Therefore, no mention of severe storms will be added to the HWO for tonight. 87/Grantham .LONG TERM... /Updated at 0338 AM CDT Tue Aug 13 2019/ Wednesday through Monday. A westerly flow regime becomes prevalent on Wednesday as the ridge axis focuses back over the Rockies while troughing deepens into the eastern CONUS. At the surface, a developing low will move across the Ohio Valley as an associated cold front passes through the forecast area late Tuesday into early Wednesday morning. The front will slow generally across our far southeastern counties by Wednesday afternoon. Should see much better convective initiation and higher rain chances south of I-20 during the afternoon, especially near and south of Montgomery, as instability values rise in the convergence zone due to diurnal heating. Have added a Marginal Risk of severe storms Wednesday afternoon, generally south of a line from Alexander City to Demopolis, due to moderate to strong instability ahead of the front with the main concern being localized downburst winds within slow moving thunderstorms. Additionally, hot temperatures will remain across the south and ahead of the front with highs expected to reach the mid 90s among a moist pre- frontal warm sector with dewpoints in the mid 70s. There will likely be a couple of hours during the late morning to early afternoon where heat indices will reach Heat Advisory criteria briefly before rain and cloud coverage develops enough to reduce temperatures, so a Heat Advisory will be issued for Wednesday until 6 PM for our far southern tier of counties. Dry conditions and slightly cooler temperatures among a less humid post-frontal airmass will be the story for Thursday through at least Sunday as ridging builds back in behind the front. Nonetheless, highs will remain in the low 90s with lower humidity values helping to keep heat indices below 100F. Our highest rain chances through the weekend will be focused in the far southeast within vicinity of the decaying front. A disturbance may begin developing early next week over the Southeast which will increase our rain chances, but there still remains much disagreement between guidance on where exactly this development will set up, so capped PoPs at 25 percent for Monday. 86 && .AVIATION... 18Z TAF Discussion. Isolated showers and storms have developed across the southeast early this afternoon, with a VFR cu field elsewhere. A storm could impact MGM or TOI this afternoon, with a brief wind gust and heavy rain. The activity in the southeast will diminish early this evening. A weak front is approaching from the north and will drop into the area early Wednesday morning. Models have been inconsistent with the amount of rain activity along the front, and have trended drier with recent model runs. Cannot rule out a shower or storm at northern terminals late tonight/early Wednesday, but confidence is low. A slight wind shift to the northwest and north is expected Wednesday morning, with speeds below 5kts. 14 && .FIRE WEATHER... Look for isolated showers and thunderstorms this afternoon. The best rain chances will be in the south and east. Otherwise, very hot and humid conditions will persist. Better chances for wetting rains will come on Wednesday along and ahead of a frontal system. Humidity values will remain elevated through the forecast period. No critical fire weather conditions are anticipated at this time. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 96 74 91 69 91 / 20 50 20 10 10 Anniston 97 76 92 71 91 / 20 50 40 20 10 Birmingham 99 77 92 72 92 / 20 40 30 20 10 Tuscaloosa 99 78 94 73 94 / 20 30 40 20 10 Calera 99 76 93 72 93 / 20 30 40 30 10 Auburn 95 76 93 73 91 / 30 30 70 50 20 Montgomery 99 78 95 74 94 / 30 30 70 50 20 Troy 97 76 95 74 92 / 40 30 70 60 30 && .BMX WATCHES/WARNINGS/ADVISORIES/... Excessive Heat Warning until 9 PM CDT this evening for the following counties: Autauga...Barbour...Bibb...Bullock... Chilton...Dallas...Elmore...Fayette...Greene...Hale...Lamar... Lowndes...Macon...Marengo...Marion...Montgomery...Perry... Pickens...Pike...Russell...Sumter...Tuscaloosa. Heat Advisory from 9 PM this evening to 6 PM CDT Wednesday for the following counties: Autauga...Barbour...Bullock...Dallas... Elmore...Lowndes...Macon...Marengo...Montgomery...Pike...Russell. Heat Advisory until 9 PM CDT this evening for the following counties: Blount...Calhoun...Chambers...Cherokee...Clay... Cleburne...Coosa...Etowah...Jefferson...Randolph...Shelby...St. Clair...Talladega...Tallapoosa...Walker...Winston. Heat Advisory until 6 PM CDT Wednesday for the following counties: Lee. && $$