439 FXUS64 KBMX 010022 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 622 PM CST Fri Nov 30 2018 .UPDATE... For 00Z Aviation. && .SHORT TERM... Through Tonight Rain showers continue across the north this afternoon, in response to increased lift associated with a shortwave rotating around a weakly amplifying ridge. This activity will continue to slowly lift northward this afternoon and evening. To our west, a strengthening trough will move into the Plains this evening, quickly taking on negative tilt and pushing into the Midwest by Saturday morning. A shortwave embedded within the broader trough, just off the Gulf coast, will push northeastward as well, into southwest coastal AL and the FL panhandle. An increasing low level jet and upper level jet will accompany these features. Across Central Alabama, widespread rain will move back into the area from southwest to northeast late tonight, with widespread coverage expected by sunrise. With southerly flow and added moisture, temperatures will remain int the 50s and lower 60s tonight. 14 .LONG TERM... Saturday through Friday. --Widespread rain and a few storms on Saturday; attendant severe weather risk is marginal-- Widespread rain will be ongoing across central Alabama during the start of the forecast period/6AM Saturday as a 500mb shortwave trough moves northeastward across the north-central Gulf Coast region. Forecast soundings during the morning show nil surface-based and limited room for elevated instability per the SPC HREF; thus, the main theme for this activity will be rain (some heavy) with perhaps a few instances of thunder. Severe weather is not anticipated during the morning round of rain/storms despite the presence of wind shear as it's not coupled with a necessary amount of instability. Farther south, there's a better setup for some severe activity. Heading into the afternoon, the aforementioned 500mb shortwave trough will be well downstream of central Alabama; however, there will still be a large-scale trough atop the CONUS, driving a stacked low pressure system heading into the Midwest. A plume of increased surface dew points are projected to overspread central Alabama during the afternoon, ahead of a surface front well toward our west. This combined with daytime heating should result in a swath of weak to moderate instability. At the same time, there will be ample deep- layer wind shear given the configuration of the upper trough and parent surface low/front. If storms were to form in this environment, severe weather would be a threat; however, there's not a clear signal for renewed, robust activity during the afternoon to evening time frame. This is so not only at the surface, but aloft as well --(1) with the surface front lagging upstream (2) near neutral 500mb heights/lack of forcing. There will also be a steady eastward progression of decreasing mean relative humidity values aloft, which should tend to begin overlapping the region of coupled shear/surface- based instability parameters. So this forecast update will maintain a 'Marginal Risk' for severe weather Saturday afternoon into the early evening hours, with fairly low confidence with respect to any robust storm development (or any at all). For what it's worth, CAMS don't really show much in the afternoon. Flooding is not a big threat with this system, either. The highest totals will be across the southern portions of the forecast area, where a steadier plume of activity should exist. 89^GSatterwhite The main cold front pushes into Central AL Saturday evening and into the overnight hours, but by this point, the front has weakened due to the associated surface low lifting northward into the Great Lakes region. The upper level trough also begins to flatten at this time, leading to slight height rises across Central AL. So while enough moisture remains across the area, I'm not sure there will be enough frontal convergence for significant rainfall to occur with the frontal passage. I've kept at least chance PoPs in the forecast, but overall coverage should be diminishing during the overnight hours. Rain chances end from west to east across the area during the early morning hours on Sunday as the front pushes south and east of our area and becomes stationary across Southern AL and the Florida Panhandle. A weak shortwave impulse moves through the base of what remains of the trough on Monday, which could briefly lift the stalled frontal boundary northward. I've kept mention for 30-40% chance of rain south of I-20 during the day on Monday to account for this. Another upper level shortwave trough slides quickly through Ohio River Valley Tuesday into Wednesday, finally kicking the stalled front our of our area and ushering in a cooler air mass into the Southeastern CONUS by Wednesday. Surface high pressure builds into the area along with upper level ridging Thursday into Friday, leading to mostly clear skies and efficient radiational cooling for cold mornings during the second half of the week. 25/Owen && .AVIATION... 00Z TAF Discussion. Conditions will become restrictive overnight as a rather potent storm system moves in. Mid level ceilings and light rain are already affecting a few northern sites, but should see a slight break in the rain before the area is overtaken with rain. Ceilings will lower through the evening hours and reach MVFR after 06z, and then hit IFR before 12z most locations. The clouds/increased lower moisture will encroach from the south and west. By Saturday afternoon, these ceilings will rise into the MVFR range with rain and thunder possible. Winds will start off with ENE/E/ESE and gradually veer to the south be Saturday afternoon. Wind speeds will increase overnight and into Saturday with sustained around 10 and some gusts to around 20kts. Winds aloft will increase into the 30-40kt range and will monitor these speeds. At this point, it appears to be just below and LLWS mention. 75 && .FIRE WEATHER... Wet conditions continue tonight and tomorrow. One area of showers will move out of northern areas early this evening, before more widespread activity returns late tonight. Rain, and possibly a few thunderstorms, expected tomorrow and will end from west to east during the afternoon and evening. Low clouds and patchy fog are possible Saturday morning. No fire weather concerns are expected at this time. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 54 65 54 69 48 / 80 90 40 10 10 Anniston 55 67 57 71 51 / 80 90 50 10 10 Birmingham 58 68 56 71 51 / 80 90 20 10 10 Tuscaloosa 60 71 55 72 52 / 90 80 20 10 10 Calera 57 68 57 71 52 / 90 90 20 10 20 Auburn 55 66 61 72 55 / 80 90 50 30 30 Montgomery 59 71 61 74 55 / 90 90 40 20 30 Troy 58 70 63 75 57 / 100 90 50 30 40 && .BMX WATCHES/WARNINGS/ADVISORIES/... None. && $$