589 FXUS64 KBMX 110555 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 1255 AM CDT Thu Apr 11 2019 .UPDATE... For 06Z Aviation. && .SHORT TERM... Through Tonight. Temperatures have risen into the lower to middle 80s this afternoon under clear skies. The temperature at Tuscaloosa Airport reached 87 at 3 pm, which ties the previous record high set in 2013. Winds will be calm at most locations this evening under clear skies. The boundary layer winds will increase after midnight as the pressure gradient tightens ahead of a weak cold front moving out of Texas. This will help keep temperatures from falling much after midnight, with many locations staying above 60 degrees. 58/rose .LONG TERM... Thursday through Friday: Deep layer southerly to southwesterly flow strengthens on Thursday, ahead of a powerful mature extratropical cyclone centered near Omaha. This will promote warm and breezy conditions over Central Alabama, but winds should remain below wind advisory criteria. Very dry air will remain in place aloft. However, broadly confluent low-level flow will be present between the cyclone and high pressure off the East Coast. Models suggest that just enough low-level moisture will pool over the area with 60F dew points and isentropic lift for a narrow north-south band of light shower activity to develop by afternoon. However, they vary on placement, and will just add in slight chance PoPs for the eastern two-thirds of the area. Scattered shower activity will potentially linger overnight in the eastern counties with continued isentropic lift. A band of showers will develop along the cold front aided by a shortwave trough, and approach the northwest counties late in the night. Models have trended slower with the front and PoPs have trended downward. Nothing strong or severe is expected overnight due to a lack of instability due to only modest moisture return and warm temperatures aloft. The cold front is forecast to stall out on Friday as it becomes parallel to the flow. Models are trending slower with the front and further north with where it stalls. The GFS/Canadian actually keep it north of the area while the NAM/ECMWF still bring it into our northwest counties. Trended PoPs accordingly with the highest PoPs in the northwest closest to the front. Models indicate some instability developing which could allow for some thunderstorm development, with strong deep layer shear present. Thus a couple stronger storms can't be ruled out. However, low-level shear will be weak and large scale subsidence/height rises are expected and mid-levels remain very dry. Therefore severe storms are not expected at this time for Friday. The front will begin to lift back northward as a warm front Friday night ahead of the next system. Rain chances will continue along the warm front due to isentropic lift with isolated thunder possible. Saturday and Sunday: GOES-West water vapor imagery depicts an active wave train over the northern Pacific. The shortwave trough/PV anomaly that will be responsible for the potential severe weather this weekend is well-defined on water vapor imagery just south of the Aleutians. This system will interact with another trough west of British Columbia before diving down the backside of the longwave trough over the western CONUS carved out by the current system over the Plains. This trough will be located over the Southern Plains on Saturday, with a closed low forming over Oklahoma. Lately models have been trending more amplified with the trough, giving the mid and upper level winds a more meridional component, and more positively tilted with the southern end (possibly due to latent heating from convection strengthening the downstream ridge), not becoming neutrally tilted until later in the day on Sunday. The main system will be well west of the area on Saturday afternoon. Precipitation along the warm front will begin to lift northward from the area, but a moisture axis may bring some additional showers or storms. Shear would be supportive of an isolated severe storm Saturday afternoon however instability may be limited. Considerable strong to severe convection is expected to develop from East Texas into Louisiana and southern Arkansas Saturday afternoon due to height falls and a very humid air mass ahead of a cold front. Upscale growth to a QLCS is expected Saturday night over the ArkLaMiss due to strong forcing and the meridional component to the upper-level flow, though some embedded supercells may be possible with a partial component of the deep layer shear vectors perpendicular to the line. Meanwhile a deepening surface low will track from northeast TX to southeast MO. This QLCS is expected to reach our western counties after midnight. Strong deep layer and low-level shear/SRH will be present. The ECMWF indicates the potential for 1000-1200 J/kg of CAPE over our western counties. The GFS has weaker instability, though its forecast soundings can often be suspect during the overnight hours and when contaminated by convection. The QLCS appears capable of producing damaging winds and embedded tornadoes. The potential for supercells ahead of the line is unclear but if this occurs this could happen as early as the evening hours. However, the moisture axis that is over the area moves east with a relative minimum in moisture between this axis and the axis of moisture along the QLCS, so confidence is very low in this potential. Instability drops off over our eastern counties overnight with a pocket of lower dew points noted. These lower dew points seem a little odd, but may be due to low-level wind trajectories being over land (south Georgia and the FL peninsula) longer and subject to drier air mixing down, rather than the trajectories being over the Gulf. The forward speed of the QLCS will be key in determining the severe threat for Sunday across the eastern half of the area. Often QLCSs do move faster than predicted once a cold pool develops, and there is the chance that the QLCS outflow could out-run the instability and/or the upper forcing. But as long as this does not occur, then some strengthening would be expected with daytime heating on Sunday, with the possibility (though very uncertain) of supercell development ahead of the line. The ECMWF shows a slower progression with the system but it does often show a slow bias with QLCSs. SPC has a slight risk for roughly the western half of the area for Saturday night and roughly the eastern half of the area for Sunday. Will combine this onto one graphic for the event. Whether or not this threat level will increase will be dependent on the uncertainties mentioned above with the speed of the QLCS relative to the upper forcing, and the amount of instability present. The relatively highest confidence in severe storms appears to be in the western counties. It's also possible that there could be a relative minimum where the threat is more marginal, but this can be refined in later updates. Further adjustments to the forecast and timing are likely given that this is still a few days away. Monday through Wednesday: Dry conditions are expected behind the front Monday and Tuesday, but models are in good agreement on another strong shortwave trough moving through the southern CONUS, bringing another potential severe threat in the Wednesday-Thursday timeframe. 32/Davis && .AVIATION... 06Z TAF Discussion. VFR and breezy conditions characterize the terminal forecast this period. A small window of some patchy fog near TOI. Pressure gradient tightens today with gusts near 20 kts possible. Winds start off rather light this morning then veer southerly by the afternoon. Winds reduce somewhat after 00Z but still stay around 7 to 10 kts 16 && .FIRE WEATHER... Rain-free conditions are expected through Thursday morning, with a slight chance of showers along and east of I-65 during the afternoon. Wind speeds will increase quickly this morning and help bring in slightly higher moisture values. A cold front moves into the area into Friday, bringing rain chances to parts of the area. A stronger and more potent system will bring in showers and storms Saturday night/Sunday. Otherwise, no fire weather concerns at this time. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 83 63 76 59 77 / 20 40 50 40 40 Anniston 83 63 78 61 78 / 20 30 40 30 30 Birmingham 84 63 77 61 78 / 20 20 50 40 40 Tuscaloosa 86 64 77 62 78 / 10 30 50 50 50 Calera 82 63 77 62 78 / 20 20 40 40 40 Auburn 83 63 78 62 78 / 20 30 10 20 10 Montgomery 86 63 81 63 82 / 20 10 20 20 30 Troy 84 63 81 61 81 / 20 10 10 10 10 && .BMX WATCHES/WARNINGS/ADVISORIES/... None. && $$