Area Forecast Discussion
Issued by NWS Birmingham, AL
Issued by NWS Birmingham, AL
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686 FXUS64 KBMX 170601 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 101 AM CDT Fri May 17 2024 ...New AVIATION... .SHORT TERM... (Tonight through Saturday) Issued at 845 PM CDT THU MAY 16 2024 The 00z Raob from BMX indicates that we have gained about a quarter inch of precipitable water since this morning. Winds through the atmospheric column increase slightly and become southerly all the way up by midnight or so. The model soundings have some dry air that we need to overcome and this will occur from top down moistening. Sped up the arrival pops slightly overnight as we should have a chance of light rain a bit earlier west, and then the rain/storms spread quickly west to east and cover much of the area by Friday morning. The evolution/strength of storms through early Saturday will largely be mesoscale dominated. The forecast discussion below is still largely valid. Several waves will have the potential of kicking off showers and storms. Each wave will have an impact on how the atmosphere responds and how much instability will be available. It appears there will be plenty of shear for organized storm development. We will monitor the areas of storms and their placement as we move through the overnight hours. Additionally, it still appears the best axis for heavier rainfall remains over the southern half of the area. Overall, some changes to temp, dew points, rain chances, but the message remains the same. 75 Previous short-term discussion: (This evening through Friday) Issued at 1255 PM CDT THU MAY 16 2024 A tranquil but warm day is ongoing across the region with a brief period of upper level ridging at 500mb. A weak surface ridge is also just off to our northwest, producing light northerly winds in the lower levels. We`ve rapidly warmed at the surface early this afternoon into the 80s in most locations, with 1000-850mb thicknesses supportive of highs in the upper 80s, perhaps close to 90 degrees across the far south. Our weather will quickly deteriorate overnight tonight as a shortwave trough begins to develop and eject eastward out of the four corners states. Northwesterly flow aloft will become southwesterly after midnight, with rapidly moistening conditions aloft. The first of several upper level shortwave impulses will advance eastward during the morning hours on Friday, with shower and storm activity expected to be ongoing across southern and Central Mississippi. These storms are expected to move across southern Alabama and the Gulf Coast region, with some uncertainty in terms of the northward extent of the storms. Following that round of convection, confidence decreases in terms of what our environment will look like behind it. Guidance trends are currently depicting a break in the action by the afternoon hours, with potential re-development of scattered to numerous showers and storms during the afternoon. Another more potent shortwave is expected to arrive Friday night, which will bring the best chance for severe storms as well as flash flood potential. Storms will likely train over the same areas as the flow becomes southwesterly across the atmospheric profile with PWATs progged to rise over 2 inches. The latest trends with the CAMs this afternoon depict the highest rain chances a little more to the south, and the Moderate Risk of Excessive Rainfall was also adjusted accordingly. Based on mesoscale trends that occur tomorrow, we certainly can`t rule out being "cut off" from the greatest moisture due to MCS development and the risk areas going even further south when all is said and done. Although further updates will be needed, 2-4 inches of rain remain in the forecast across our southern counties with isolated higher amounts. The severe weather risk has also shifted farther south as a result, with the best moisture and instability across the southern half of Central Alabama. With all that said, the setup will be very messy and conditional based on where MCS activity develops and moves through the next 36 hours. Large hail and isolated damaging winds will be the main hazards, with an isolated tornado threat possible across our far southern counties in the Slight Risk area. More isolated severe storms are still possible elsewhere, but much less of a chance as you go northward. 56/GDG && .LONG TERM... (Friday night through next Wednesday) Issued at 345 PM CDT THU MAY 16 2024 We will continue the trend from the short term. The main changes to the extended are with the latest guidance shifting the best instability and moisture/rainfall amounts overall further to the south. Will continue to mention severe for Fri/Fri evening for the SRN half of the area. We will also continue to mention the threat for heavy rain, especially in the SRN portions of C AL. However, with the trends of lower rainfall amounts expected over the Fri/Sat timeframe and the fact that the areas with the highest expected amounts have not had a great deal of qpf over the past week will forgo a flood watch at this time. Will reassess with the next set of guidance over the mid shift to determine which counties if any may need a watch. Sunday evening through Tuesday evening shows a return to rain free but warming conditions each day. Another system approaches by the end of the extended with low pops returning by next Wednesday. 08 Previous long-term discussion: (Friday night through next Wednesday) Issued at 255 AM CDT THU MAY 16 2024 Friday night through Saturday. A second wave of southerly moisture works into the area Friday night into Saturday morning. As the morning progresses rainfall becomes more widespread ahead of the upper low that will move through early Sunday morning. The consensus of the models indicate another 1 to 1.5 inches of rain with this swath of rain from generally north of Birmingham and to the the east. If this heavier band does develop and falls over the areas that receive the most rainfall on Friday then flooding may once again be a threat for much of the area on Saturday. Watches will likely be needed with the afternoon forecast update. Sunday through Wednesday. The upper level low exits most of the area by Sunday morning, however a few models tries to warp some additional rainfall along the backside of the low. Will keep in PoPs through the afternoon on Sunday. Deep-layer ridging is depicted in medium-range & ensembles thereafter, which supports a period of dry, warm weather that appears to extend into early next week. Highs in the 90s could be possible by then. On Wednesday we will begin to see the next system take shape to our west. A shortwave will ride along that boundary and clip our northern areas, with generally isolated to scattered showers/storms. A wetter pattern looks to be shaping up for the end of next week, but will be discussed over the next few days. 16 && .AVIATION... (06Z TAFS) Issued at 101 AM CDT FRI MAY 17 2024 Unsettled weather is expected for this forecast period as a couple waves of rain and thunderstorms impact the area. Terminals start off VFR with the potential of MVFR/SHRA/TSRA by 12-14z. The rain and storms will move west to east through the day on Friday, with a few waves of activity possible at each terminal. Predominant ceilings will be MVFR with lowering to IFR during the afternoon. Winds will be light and variable through early Friday morning, then veer from southeast to south through the day at 5-10kts. 14 && .FIRE WEATHER... Widespread rainfall and thunderstorms return to the area tonight through Saturday, along with some lingering scattered activity hanging around through Sunday. Minimum relative humidity values remain well elevated through Saturday. 20 foot winds become southeast to south on Friday and increase to 8 to 10 mph, and then become southwesterly on Saturday. Drier conditions return by Sunday evening. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 75 64 80 62 / 70 70 80 50 Anniston 77 67 79 64 / 80 70 80 50 Birmingham 78 68 80 64 / 80 70 80 40 Tuscaloosa 78 67 81 64 / 80 60 70 30 Calera 77 68 80 65 / 80 70 80 40 Auburn 78 69 78 66 / 80 70 90 40 Montgomery 81 69 80 66 / 80 70 80 40 Troy 81 69 79 66 / 80 70 90 40 && .BMX WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...75 LONG TERM....08 AVIATION...14