066 FXUS64 KHUN 231819 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 119 PM CDT Thu Jul 23 2020 .UPDATE... For 18Z TAFS. && .NEAR TERM...(Rest of Today) Issued at 1132 AM CDT Thu Jul 23 2020 A mid-level ridge axis will continue to expand westward across central portions of GA/AL/MS today, to the north of TD 8 moving westward over the Gulf of Mexico. To the north of the local area, a couple of weak, convectively-induced vorticity maxima are expected to pivot cyclonically through the Mid-MS and OH Valley regions, in the flow around an amplifying shortwave trough over southern Ontario/Quebec. Latest thinking is that widespread showers and thunderstorms occurring to the southeast of a weak cold front in the OH Valley region will result in the development of a differential heating boundary, which could sink southward into the CWFA and focus the development of convection this afternoon. However, it appears as if there will be a sharp N-S gradient in precipitation coverage, due to both the expected locations of the low-level boundary and zone of weak mid-level subsidence associated with the expanding ridge axis aloft. We have adjusted POP/weather grids to reflect this reasoning, and raised max temps by a degree or two, due to the notable lack of cloud cover this morning. Similar threats of strong to locally damaging winds in the 50-60 MPH range, heavy rainfall and frequent lightning will exist with the strongest storms this afternoon. .SHORT TERM...(Tonight through Saturday) Issued at 216 AM CDT Thu Jul 23 2020 Convection will gradually diminish with time over the course of the evening, resulting in a dry and partly cloudy night. Moist boundary layer conditions from the rainfall will likely result in some patchy fog late tonight into early Friday morning. The aforementioned boundary will become more diffuse in nature, and with stronger S/SE flow developing, it may actually pivot further to the north into Middle and East Tennessee. Regardless, with a stronger southerly fetch, this moist, tropical air mass isn't going anywhere. The center of the high may actually shift a little bit closer to our area on Friday, but don't expect much of a change to our forecast other than it being a degree or so warmer. Showers and thunderstorms should be more scattered in nature on Friday, potentially being more numerous along the higher terrain of the Cumberland Plateau region. A similar setup can be expected for Saturday, but with slightly warmer temperatures, our heat index values start to creep back into the 100 to 105 degree range once again. .LONG TERM...(Saturday night through Wednesday) Issued at 216 AM CDT Thu Jul 23 2020 With high pressure centered just to the northwest of the area early next week (Sunday and Monday) we expect more of the same, with highs in the low to mid 90s and heat index values peaking between 100 to 105 degrees. Subsidence from the ridge and the lack of any forcing mechanism may help to cut-back on PoPs slightly as they may be a little more widely scattered in nature during this period. However, evidence is starting to indicate we may be in for a bit of a pattern change by Tuesday and Wednesday of next week as the center of the upper high begins to retrograde back into the Plains and Intermountain West. This will allow a stronger upper low to drop SE into the Great Lakes region, sending a cold front through the Ohio Valley by the middle of next week. Several shortwaves/impulses are shown to rotate around this parent low that will make their way across the Tennessee Valley and Southern Appalachian region, bringing good chances for showers and storms both days. It appears this upper-trough may become the more dominant feature in the eastern CONUS for much of the later half of next week, resulting in cooler temperatures (mid to upper 80s highs) and good precipitation chances. && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) Issued at 119 PM CDT Thu Jul 23 2020 VFR conditions currently exist at the HSV/MSL terminals, with few- sct high-based Cu and SSW flow arnd 5 knots. However, we will continue monitor the development of SHRA/TSRA associated with a subtle low- level convergence boundary dropping southeastward from Middle TN. At this point, we feel that coverage of convection invof the airports will be too low to include in the TAFs, but will monitor for amendments. Mid/high-lvl convective debris clouds will thicken across the region overnight, reducing the potential for vsby reductions. That said, some patchy BR/FG will be possible btwn 08-13Z, but primarily in locations that experience rainfall today. Conditions appear to be more favorable for the development of convection late in the forecast period, and a PROB30 group for TSRA has been included at both terminals btwn 24/16-18Z. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...70/DD SHORT TERM...AMP.24 LONG TERM...AMP.24 AVIATION...70/DD For more information please visit our website at weather.gov/huntsville.