239 FXUS64 KHUN 291915 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 215 PM CDT Mon Oct 29 2018 .NEAR TERM...(Tonight through Tuesday Night) Issued at 215 PM CDT Mon Oct 29 2018 The ridge of high pressure at the surface will shift east into the central and lower Appalachians tonight. The 8h ridge will also shift east of middle TN and AL as well. Isentropic lift may induce a band of high based stratus (040-060agl) late tonight but should exit rather quickly on Tuesday. Most areas tonight should be milder with lows in the m-u40s, although a few colder eastern valleys could dip into the l40s. On Tuesday, another nice day is ahead with good low level warm air advection and sunshine returning after the morning clouds exit to the northeast. Highs should easily reach the middle 70s, and won't rule out upper 70s for some areas. Model soundings do not show strong indications of low cloud development Tuesday night. Overnight lows should still be mild with steady south-southwest flow. Looking at m50s-a60 at this time (coolest east, warmest west). .SHORT TERM...(Wednesday through Thursday) Issued at 215 PM CDT Mon Oct 29 2018 The short range guidance (i.e. NAM) seems to be leaning toward a slower solution as has been advertised by the previous ECMWF and Canadian. This is in regard to a possible QLCS that will develop on Wednesday along a deep southwesterly flow in mid to upper levels across TX northeast through the southeast Ozarks into the OH valley. The warm sector looks to be largely capped due to limited deep moisture return further east, including north AL and southern TN. So have backed off on the PoP on Wednesday in this regard. The QLCS may just get close to far northwest AL by 00Z/31. With a deepening of the trough axis and low level flow backing, the progression of the precipitation may be held up a bit. Instability magnitude is still a question mark for our area, with CAPE values increasing to only 500 j/kg or less in advance of the line late Wednesday evening. However, high shear will be sufficient for at least a marginal severe weather concern. 2km bulk shear vectors do increase to 30-35kt and 1km SRH values increase to above 300 m2/s2 in response to the LLJ acceleration late Wednesday night. The main period of concern west of I-65 will be from 03-09Z, and areas further east from 09-15Z. Have drawn a sharp gradient in the PoP forecast as such, with areas along the I-59 corridor likely remaining dry until Thursday morning after 12Z. Will continue to address the potential for strong to severe wx possible in our HWO and graphics. The QLCS will exit to the east with MCS stratiform precipitation or showers lasting into early Thursday afternoon before ending. .LONG TERM...(Thursday night through Sunday) Issued at 215 PM CDT Mon Oct 29 2018 The extended portion of the forecast begins Thursday in the wake of the line of storms that marched across the area overnight Wednesday into Thursday. Compared to the overnight model runs, not a lot has changed, with the exception of another model/two getting on board with the slowing down of the upper system as it traverses the area. Overall, the timing of the GFS was followed, albeit a bit slower than it's advertising, but not as slow as the slowest solution/ECMWF (it's a full 12+ hours slower than its counterparts). This should have the bulk of the precip pushing out of NE AL by 18/21Z Thursday, with some light rainfall expected post-fropa through the late aftn/early evening hours. With the CAA expected in the wake of the fropa, daytime temps Friday will be about 10 degrees cooler than Thursday, topping out around 60 degrees (after starting out in the mid/upper 40s). Morning lows Saturday will start off in the low 40s (with even a few upper 30s possible in NE AL/Srn Middle TN). Concurrent with this timeframe, models show a quick-moving shortwave rounding the base of the upper trof, and this should bring us another brief round of light rain/showers overnight Friday into Saturday. Am not expecting much other than a few hundredths at most during this time, and PoPs are relatively low (~20%). A general warming trend is expected through the weekend, with daytime temps topping out in the lower 60s Saturday and the middle 60s Sunday. Morning lows will once again start out cool on Sunday, but with winds becoming more southerly overnight Sunday, morning lows Monday will climb to 45-50 degrees across the area. It's at this point in the forecast that details become murky. While the GFS keeps an upper level system well N of the area during Monday/Tuesday, the ECMWF is far more progressive with this system, sparking another round of showers/storms for us during this time. PoPs have been retained at 20% coverage attm since this is the end of the forecast period, and the uncertainty is so large. Beyond this timeframe though (and just outside the forecast window), the ECMWF is highlighting another shot at strong storms possible for midweek. The GFS has rain for our area, but the strength/placement of upper level features is quite different. Either way, we're heading into our second severe weather season in the TN Valley, climatologically speaking, so folks should get safety plans in place anyway in the event that something come to fruition out of either events in the forecast period. Stay tuned for further information coming to light in the next few days! && .AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon) Issued at 1143 AM CDT Mon Oct 29 2018 VFR flight weather conditions are expected during the next 24 hours. A band of clouds based ~040agl will arrive around 09Z at KMSL and 12Z at KHSV. These clouds will exit close to the end of the forecast period. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...17 SHORT TERM...17 LONG TERM...12 AVIATION...17 For more information please visit our website at weather.gov/huntsville.