123 FXUS64 KBMX 211958 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 158 PM CST Fri Dec 21 2018 .SHORT TERM... Through Saturday Night. Upper level trough axis is moving eastward this afternoon, with drier mid and upper level air now spreading into west Central Alabama. Low level moisture remains high, trapped under an inversion just above 900mb, and is the cause of the extensive low stratus clouds and patches of light rain lingering across central and eastern counties. Northwesterly winds have been rather strong today due to a tightened pressure gradient with consistent gusts in the 18-22kt range. For the rest of this afternoon and early evening, light rain will gradually end as deeper moisture pushes eastward. Winds will diminish this evening as well. Low levels remain saturated under drier air aloft, and stratus will likely persist for much of the overnight period, with skies beginning to clear early tomorrow morning. Cannot rule out river/valley fog late tonight but cloud cover should prevent widespread fog development. Lows tonight will be in the upper 20s to mid 30s. Tomorrow and tomorrow night will be dry as a surface high moves across the southeastern CONUS and flow aloft becomes zonal. With skies also clearing through the morning, highs will warm into 50s. Warmer temperatures expected tomorrow night, as a weak system approaches the area. Lows will be in the mid 30s east to lower 40s west. Could see scattered showers moving into the northwest before sunrise Sunday. 14 .LONG TERM... Sunday through Tuesday. Much of the country will be under an upper-level split-flow regime with no particulary amplified troughs/ridges heading into Sunday and early next week. This setup will act as a broad thoroughfare for transient shortwaves to traverse from west to east across the eastern two-thirds of the US. The first and more prominent shortwave is expected to approach our region in the Sunday timeframe where downstream airmass modification supports enough moisture return to produce scattered light rain showers across central Alabama. Most of this light rain activity should stay focused along a weak low pressure area and associated frontal boundary and should be near the I-20 corridor ~12 PM Sunday. A southeastward progression is expected with diminishing coverage/intensity of rain showers heading into the overnight hours. Cooler & drier air advects into the region as a stable continental airmass/high pressure area settles across the southeastern CONUS into Christmas Day. Another perturbation is expected to pass by to our north on the holiday and bring the possibility of an isolated shower to the area, but moisture will remain limited due to the antecedent high pressure system. Highs in the 50s/60s will be the overall theme in the afternoon though temperatures will be a little cooler in areas receiving cloud cover & light rain Sunday/Monday. Wednesday through Friday. There are continued indications of a more potent & amplified disturbance to enter the Desert Southwest around Wednesday. Downstream conditions will undergo broad moisture/temperature increases as mid/upper-level ridging develops across the Southern Gulf Coast states. This sets the stage for the busy upper- tropospheric circulation to tap into northwestern Gulf moisture as the trough ejects from the southern Rockies into the Plains by Thursday. With low predictability within the split-flow regime this far out it's difficult to forecast the trajectory of the wave and where associated cyclogenesis/surface features develop. So, the general theme of the long-term forecast is best advertised as a period of wet & unsettled weather to move into our area, particularly in the Thursday/Friday timeframe. A slight chance of thunderstorms has been introduced on Thursday given the overall evolving synoptic pattern indicating the potential for instability to become available as well. For now the primary threat will be periods of moderate/heavy rainfall to affect the area and further support a continuance of the busy hemispheric pattern & above average precipitation for central Alabama. 40/Sizemore && .AVIATION... 18Z TAF Discussion. A highly amplified upper trof axis is moving eastward, out of the area at mid day. Extensive low stratus remains across the area with heights hovering between MVFR and IFR. Areas of light rain continue across much of the east, but only slight decreases in visibilities are occurring. Northwesterly winds have been gusting up to 22-25kts. For the remainder of the afternoon and early evening, light rain will end across all terminals with cigs remaining around or below 1500ft. Some localized IFR cigs are also possible. Tonight, cigs will improve slightly, but only to around 2000-2500ft, with northwesterly winds diminishing to 4-6kts. Guidance shows lower levels re-moistening overnight at MGM and TOI, and will show lower cigs working back into those areas overnight. With sunrise Saturday, cigs will continue to improve, especially across the north where sct cigs are expected. With high pressure building across the area, winds will be light and variable. 14 && .FIRE WEATHER... Patchy rain will end across the east by this evening. Cannot rule out localized river/valley fog late tonight. However, persistent low clouds will linger across much area through tonight, preventing widespread fog. Strong winds will diminish this evening. Drier conditions expected Saturday and Saturday evening, before scattered light rain showers return Sunday. With expected relative humidity values remaining above critical values, there are no fire weather concerns at this time. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 30 51 35 53 32 / 10 0 10 40 10 Anniston 30 51 36 56 34 / 10 10 0 40 20 Birmingham 32 53 40 55 36 / 10 0 10 40 10 Tuscaloosa 32 56 42 59 36 / 0 0 10 40 10 Calera 31 54 39 57 36 / 10 0 10 30 10 Auburn 33 51 38 59 40 / 10 0 0 20 20 Montgomery 33 55 38 64 41 / 0 0 0 20 20 Troy 34 56 37 65 44 / 0 0 0 10 20 && .BMX WATCHES/WARNINGS/ADVISORIES/... None. && $$