664 FXUS64 KBMX 292048 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 348 PM CDT Mon Oct 29 2018 .UPDATE...Short term and Thursday severe threat. .SHORT TERM... Through Tonight. Afternoon temperatures are right where they should be for late October with readings in the lower to middle 70s. Winds will go calm after sunset and with a dry air mass in place, temperatures will fall quickly this evening. Boundary layer winds will pick up from the east and southeast after midnight, and keep temperatures a little warmer across the southeast counties. Some valley and river fog possible later tonight, but no widespread fog issues expected. 58/rose .LONG TERM... Tuesday through Monday. Significant timing differences still between the slower ECMWF model and the faster GFS/NAM solutions. The faster models would likely result in a less threat for severe as forcing outruns better instability. The air mass would not likely have much time to recover Thursday for an increased severe threat over the southeast counties. The slower ECMWF model would allow for some air mass destabilization Thursday afternoon, but axis of higher forecast CAPE values do not even reach south Alabama until after sunset Thursday, thus limiting threat. Will continue with a very low confidence threat for Thursday, but not highlight any specific severe threat timing. 58/rose .PREVIOUS DISCUSSION... The dry cold front is lingering north to south across Central AL early Tuesday and gets pushed eastward as an effective warm front as we go through the day. This warm air advection just to our west will allow the high temps in our western locations to reach into the upper 70s to low 80s while the eastern counties remain in the low to mid 70s. Otherwise, a generally pleasant day on Tuesday with partly cloudy skies. On Wednesday, a trough digs southward through the Rockies and into the Central Plains as the high pressure over the Carolinas gets pushed further east into the Atlantic. A weak upper level low in the Bay of Campeche gets phased in with the deepening trough and moves through Southern Louisiana and Mississippi Wednesday afternoon. This specific feature is really nothing more than a weak shortwave with a little more moisture associated with it thanks to its source region, but it does provide just enough lift to generate some scattered rain showers generally west of I-65 Wednesday afternoon and evening. Rain totals should be on the lighter side with this due to the lack of significant forcing. Meanwhile, the main upper level trough continues to deepen into the Southern Plains Wednesday evening and into the overnight hours. Models still disagree on just how deep that trough digs, which has impacts to our weather on Thursday. However, models do agree on a surface low developing in the ArkLaTex region late Wednesday and lifting northeastward into Thursday morning. This will push a cold front west to east across Central AL during the day on Thursday, increasing rain chances. Enough instability will be able to work its way in that I can't rule out a chance for thunderstorms as well. Overall, I've increased PoPs Thursday into Thursday night to 80-90%. The model differences in the evolution of the trough on the synoptic level add uncertainty into the potential for any severe weather with this frontal passage. I'm edging my forecast closer to the GFS since it's been the more consistent run to run over the past 2-3 days. The ECMWF is roughly 6 hours slower due to digging the upper level shortwave trough further south and becoming more negatively tilted as it crosses the MS River. The ECMWF solution would lead to better dynamic forcing overlapping the thermodynamics, which would increase our chances for severe weather. The GFS, which has been more consistent, maintains the upper level jet lags behind the low level jet, and pushes a pre-frontal shortwave through that becomes the main trigger for rain/storm development vs. the cold front. Regardless, models do agree that some very modest destabilization can occur Thursday afternoon despite the cloudy skies, but we're still only expecting 400-600 J/kg of MUCAPE. With the track of the surface low being through North MS and the TN River Valley, plus the strong low level jet, I do expect ample shear to be in place. Therefore, I will introduce a low confidence mention in the HWO for severe weather Thursday with the possibility of a few tornadoes. The low confidence is due to the model differences in timing and trough evolution, which would change the the area of concern and/or change the overall threat completely. We will continue to monitor the model trends in the coming days and adjust any severe forecast accordingly. By midnight Thursday night/Friday morning, the front should be well east of our area, ending rain and storm chances for Central AL . Cooler and drier air moves in as the main trough axis slides through the Southeastern CONUS during the day Friday. Another shortwave slides through as this happens, but lack of any significant moisture return should limit any precipitation chances, so I've left out any mentionable PoPs Friday and Saturday. Rain chances increase slightly Sunday evening into the first of next week as another trough dips into to the Central US, but models disagree on moisture availability, so I've limited rain chances to 15-20% for the end of the extended period. 25/Owen && .AVIATION... 18Z TAF Discussion. VFR conds expected thru the period. A cold front has pushed thru area bringing drier air into the region. Light north winds will become calm by 00z. 58/rose && .FIRE WEATHER... A dry cold front is pushing southward this morning through the area. Drier and cooler air will spread into the area behind the front. RH values will fall into the 30s this afternoon. 20 ft winds maintain a northerly component through the day, but remain below 5-6mph. Airmass will begin to moisten tomorrow, ahead of the next weather system. Rain chances increase Wednesday and Thursday, with the passage of another front. There are no fire weather concerns at this time. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 42 74 54 75 62 / 0 0 0 10 80 Anniston 45 75 55 76 63 / 0 0 0 10 60 Birmingham 49 77 60 77 65 / 0 0 0 10 80 Tuscaloosa 50 80 61 79 64 / 0 0 0 20 90 Calera 47 77 58 77 64 / 0 0 0 10 80 Auburn 49 74 54 76 62 / 0 0 0 0 30 Montgomery 49 79 56 81 66 / 0 0 0 10 60 Troy 47 78 54 80 65 / 0 0 0 10 40 && .BMX WATCHES/WARNINGS/ADVISORIES/... None. && $$