Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
875 FXUS64 KHUN 230538 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1238 AM CDT Mon Apr 23 2018 .UPDATE... For 06Z TAFS. && .NEAR TERM...(Tonight) Issued at 731 PM CDT Sun Apr 22 2018 Deepening low pressure system across the Ozarks/Mississippi Valley will continue to shift eastward into the Tennessee Valley overnight. A strengthening 850 mb jet is rotating into Northern Alabama from the southeast ahead of this low, while a pronounced dry slot has developed across Mississippi into Southwest/West Central Alabama. A meso-low has developed across Northwest Alabama, which in conjunction with the low-level jet, has generated some strong wind gusts in the 25 to 40 mph range across much of the Huntsville CWA. Over the past couple of hours, these gusts were noted across the Shoals, with KMSL gusting as high as 30-40 mph. Have expanded the Wind Advisory across the entire area to account for these strong winds which may be capable of producing some localized tree and power line damage through around 06z. In addition to the strong gradient winds, deep moisture continues to advect into the region from the SE/SSE. Have noted an uptick in reflectivity on radar over the last hour or two as the low-level jet kicks in. with this broad area of moderate to locally heavy showers generally producing about 0.3 to 0.6 inches per hour within the heaviest bands. In general, think the flash flood threat is fairly low given the higher FFG values -- and the fact that the heaviest activity is moving gradually east with time. However, will need to watch for some areal flooding concerns on a localized level in areas where training does occur. Forecasted rainfall totals of 1.5 to 3 inches through Monday morning seems on track given the latest radar trends and model data. The greatest rainfall potential will occur from 00z to 06z, before drier air moves in from the west, weakening this activity and eventually tapers it off late tonight. Most models, especially mesoscale guidance, continue to suggest show this abrupt end to precipitation occurring in this 06-08z timeframe from west to east as dry air entrains in. This will also coincide with the LLJ shifting north and west of the region, diminishing lift over the area. Due to the cloud cover, precipitation, and breezy/gusty, southerly winds, temperatures will remain quite mild and in the 50s overnight. .SHORT TERM...(Monday through Tuesday) Issued at 250 PM CDT Sun Apr 22 2018 As the upper low and vort max move over the area on Monday we can expect a few isolated to scattered showers and storms to develop. Models over the last 24 hours have shifted the low track a bit more to the north and have adjusted PoPs in that direction. Could be a situation where the further south you are on Monday the lower the PoPs and higher your chances for a few peeks of sunshine. Temps will end up a few degree warmer Monday compared to todays values with highs in the mid to upper 60s. The low begins to pull away from the area on Tuesday but some lingering wrap around moisture could allow for a few light showers and have continued lower end PoPs through Tuesday afternoon. Highs on Tuesday end up close to Mondays values. .LONG TERM...(Tuesday night through Saturday) Issued at 250 PM CDT Sun Apr 22 2018 Weak CAA on the backside of the departing system could allow for a shallow inversion to develop Tuesday night and with the recent rains could support some fog potential. Don't have anything in the forecast at this time but something to keep an eye on. Tuesday night through Wednesday afternoon will be one of the few dry periods in the forecast. A weak trough is forecast to drop S/SE out of the northern Plains towards the Gulf Coast. Models differ on just how far south to dig this feature and could be the difference between only a few light showers Wednesday night/Thursday to more scattered to widespread rain on Thursday. Because of this uncertainty have kept PoPs more broad brushed but tried to show some gradient north to south in PoPs. Beyond Thursday models begin to diverge on another trough that is forecast to drop SE out of the northern Plains. The GFS has the core of the trough over the OH Valley with the TN Valley remaining dry. The GEM has the trough moving across the TN Valley bringing another round of showers on Friday. The ECMWF on the other hand is between these two solutions with only a few light showers. Ensembles are also not very supportive to any of these solutions and have just slight chance PoPs for Friday afternoon to account for these differences. Winds remains out of the N/NW through the extend period and should allow for a few cool mornings with the colder morning likely occurring Saturday morning. Clearer skies over the weekend would support temps in the 70s despite the weak CAA. && .AVIATION...(For the 06Z TAFS through 06Z Monday night) Issued at 1239 AM CDT Mon Apr 23 2018 Very strong winds continue near the KHSV airport, with the ASOS reporting gusts near 50KT still. These winds are xpcted to diminish after 01Z, although cigs near/just below 1K ft look to become entrenched across much of the area heading into the early morning hrs. Cigs may then lift more into the MVFR range or 1-2K ft Mon morning, with the onset of daytime heating/mixing. VFR conds may develop late in the TAF period, as cigs lift above 3K ft. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...Wind Advisory until 1 AM CDT early this morning for ALZ001>010-016. TN...Wind Advisory until 1 AM CDT early this morning for TNZ076-096-097. && $$ NEAR TERM...AMP.24 SHORT TERM...Stumpf LONG TERM...Stumpf AVIATION...09 For more information please visit our website at weather.gov/huntsville.