Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
632 FXUS64 KHUN 191135 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 635 AM CDT Sun Aug 19 2018 .UPDATE... For 12Z TAFS. && .NEAR TERM...(Today) Issued at 412 AM CDT Sun Aug 19 2018 The night time microphysics view from GOES-16 indicated broken to overcast conditions developing over the region. This was sort of being confirmed by isentropic upglide in the 305K (~800-900 mb) region. Cloud bases across most of the area were for the most part ranging between MVFR (1000-3000' AGL) and IFR (500-1000' AGL). Along with the increase in clouds, light showers were in progress across parts of the region, mainly over southern middle Tennessee, moving ESE around 10 mph. Short-term guidance has the upglide continuing, but weakening somewhat into the afternoon. Precipitable water amounts over the Tennessee Valley should decrease somewhat this morning into the 1.3-1.5" range, then begin increasing towards the evening. Even though moisture levels will be lower, the upglide should keep more clouds than sun in the forecast, along with scattered showers and t-storms. With slightly less moisture, highs should warm this afternoon into the mid and upper 80s. .SHORT TERM...(Tonight through Tuesday) Issued at 412 AM CDT Sun Aug 19 2018 An upper system currently moving to the east across NE Wyoming will result in the formation of a surface low central High Plains this evening. This new surface low will deepen as it moves to the NE, reaching the Great Lakes region before daybreak Tuesday. A cold front trailing SW of the surface will move towards the Tennessee Valley, reaching the region Tuesday night. Precipitable water values should increase tonight and on Monday, reaching the 2" range for much of the day. This increase in moisture and instability will bring widespread showers and thunderstorms to the region Monday afternoon and night. Some of the storms during Monday afternoon/evening could become strong to marginally severe, with strong winds the main threat. The high amounts of water will obviously result in locally heavy rainfall, as well as a potential of an increase in lightning activity in the stronger storms. Despite the clouds, temperatures before rain commences should rise into the mid and upper 80s. Even though the front will arrive until after this period, overall atmospheric moisture values should go on a downward trend during Tuesday. Will keep scattered showers and thunderstorms in the forecast on Tuesday, with highs again in the mid/upper 80s. .LONG TERM...(Tuesday night through Saturday) Issued at 412 AM CDT Sun Aug 19 2018 Lingering showers and thunderstorms will begin to taper of towards the SE in the wake of a frontal passage across the cntrl TN Valley early in the day Tue. Even with the diminishing rainfall, iso showers/tstms will still have some impact on locations along/east of the I-65 corridor Tue night into Wed, especially with ample amounts of buoyant energy and modest deep layer/effective shear values near 35-40kt. This should translate into a continuing line/cluster of tstms affecting the wrn portions of the local area thru Wed, before lingering convection finally weakens and moves off to the SE. Given the low level dynamics in place coupled with adequate amounts of instability in the 1-2K J/kg range Tue night into early Wed, a few strong storms capable of gusty outflow winds, hail and brief heavy downpours are all possible. Rainfall will then begin to taper off Wed night, as an area of low pressure at the sfc quickly moves ewd into the Midwest/OH Valley regions and weak upper ridging out of the srn Plains translates ewd into the wrn/cntrl Gulf regions. Even with cloud cover and rainfall diminishing, overall temps look to remain near/slightly below normal for most of next week. Afternoon highs from Tue on predom look to be mainly in the mid/upper 80s range while overnight lows look to remain in the 60s for most nights going into the new work week. && .AVIATION...(For the 12Z TAFS through 12Z Monday morning) Issued at 635 AM CDT Sun Aug 19 2018 Overall moisture values in the atmosphere were on the decrease, with IFR CIGs likely to rise into the MVFR range, then VFR by the early afternoon. Despite a slightly drier atmosphere, on-going ascent just above the surface, and still sufficient moisture will keep VCSH going through the late morning. Daytime heating and a more unstable environment will be more conducive for t-storms in the afternoon and early evening. Uncertain with storm timing precludes adding it to the TAF at this time. Shower/t-storm chances are possible late at KMSL, where greater instability preceding a frontal boundary will be realized. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...RSB SHORT TERM...RSB LONG TERM...09 AVIATION...RSB For more information please visit our website at weather.gov/huntsville.