Area Forecast Discussion
Issued by NWS Huntsville, AL
Issued by NWS Huntsville, AL
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128 FXUS64 KHUN 072011 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 311 PM CDT Tue May 7 2024 ...New NEAR TERM, SHORT TERM... .NEAR TERM... (Tonight and Wednesday) Issued at 311 PM CDT Tue May 7 2024 Upper level southwest flow with subtle shortwaves are expected aloft over the Tennessee Valley this evening and overnight. Meanwhile, a trailing cold front from a surface low over the Great Lakes will slowly approach the Tennessee Valley overnight as well. Overall, the environment is conducive for storm development this evening with dewpoints in the 70s, along with instability values over 2000 J/kg, bulk shear values between 20-30 knots, and mid level lapse rates between 6.5-7.5 deg C/km. In addition, a low level jet will be present tonight, but likely remain around 25 knots over our area. However, guidance suggests the LLJ will be stronger to our north. Over the past hour or so, light showers have streamed over northern Alabama and southern middle Tennessee with only a few flashes of lightning detected. If storms can get going, they have the capability of becoming severe and producing damaging winds and hail. Hi-Res models also indicate another round of showers and storms tonight, perhaps beginning just before midnight, and continuing into Wednesday morning. The big question is whether or not these storms, which will move south of Tennessee this evening, will make it far enough south into our local area. If they do, confidence is low whether they will make it south of the Tennessee River. CAMs solutions differ widely with what scenario will play out. Ultimately, should storms enter our area, they have the potential of producing damaging winds and hail. Make sure to have multiple ways of receiving warning information tonight! For the rest of the day on Wednesday, low to medium (20-50%) chances of showers and storms are mostly forecast; however, not anticipating these to be severe at this time. For temperatures, it will be fairly warm tonight due to elevated moisture, with lows only dropping into the mid 60s to lower 70s. Highs Wednesday are then forecast to top out in the 80s. && .SHORT TERM... (Wednesday Night through Thursday Night) Issued at 311 PM CDT Tue May 7 2024 The "main event" in terms of severe weather will come in the form of a mesoscale convective system (MCS) traversing the Tennessee Valley Wednesday night into Thursday morning. Upper level southwest flow will continue, but more potent upper shortwaves are shown by models to ripple over the region Wednesday night into early Thursday. In addition, another low pressure system looks to develop and track over the Midwest by Wednesday evening, progressing east into the Ohio Valley by Thursday morning. Model instability will be lower overnight; but, even so, values are shown by guidance to be around 2000 J/kg. Bulk shear values range between 30-50 knots as well, with a stronger LLJ to between 35-40 knots over the region. Midlevel lapse rates are also higher, between 7-8 deg C/km along with 0-1 km SRH between 200-250 m2/s2. Therefore, the ingredients are in place for all modes of severe weather Wednesday night into Thursday morning: damaging winds, hail, and embedded tornadoes. Models have also been fairly consistent with the timing of this MCS, with it reaching northwestern Alabama around midnight and moving southeast over the local area during the overnight hours, exiting around 8AM. The Storm Prediction Center has the majority of our area in a Slight Risk (level 2/5) of severe weather, with portions of our southern middle Tennessee counties in an Enhanced Risk (level 3/5). Again, please make sure to have multiple ways to receive warnings, especially ones that will wake you up in the middle of the night! Another concern is the potential for localized flooding, especially where storms train over the same locations repeatedly. At this point, our forecast storm total rainfall ranges from 1-2 inches, with locally higher amounts possible. Turn around, don`t drown if you encounter flooded roads - find an alternate route! Once the MCS moves south of the area Thursday morning, residual chances (low to medium; 30-50%) of showers and some storms remain possible through Thursday evening. && .LONG TERM... (Friday through Monday) Issued at 427 AM CDT Tue May 7 2024 Prevailing NW flow aloft will exist across the region for much of the extended period, allowing a cooler and drier Canadian airmass to be advected deep into the southeastern CONUS. Highs will be in the 70s, with lows in the 50s, and although conditions will remain dry for most of the region, at least a couple of well- defined vorticity lobes will track southeastward across the TN Valley on Friday/Saturday, warranting a very low POP for light showers. && .AVIATION... (18Z TAFS) Issued at 1258 PM CDT Tue May 7 2024 Unsettled weather will comprise the forecast through midweek. Light showers have developed over the region this afternoon. Anticipating low to medium (20-50%) chances of showers with a few storms by mid-afternoon and into this evening. Some of these storms may become severe, bringing the risk of damaging winds as well as hail. A brief lull is then possible by mid-evening before another round of showers and a few storms may develop and move across the area later tonight (mainly north of the TN River). A few of these storms could become severe with damaging winds and hail the main threats. Low chances (20-30%) of showers/storms will then persist Wednesday morning. Reduced CIGs to MVFR and possibly to IFR are forecast late tonight through Wednesday morning as well. South/southwest winds between 10-15 knots will continue through this evening, with some wind gusts to around 20 knots this afternoon. Winds are then expected to decrease to between 5-10 knots Wednesday morning. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...None. TN...None. && $$ NEAR TERM...26 SHORT TERM....26 LONG TERM....70 AVIATION...26