571 FXUS64 KHUN 201937 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 237 PM CDT Sun Sep 20 2020 .NEAR TERM...(Tonight) Issued at 237 PM CDT Sun Sep 20 2020 Another beautiful early autumn day across the Tennessee Valley region with high pressure continuing to build into the region from the north. The end result has been a mostly to partly sunny day with comfortable temperatures in the 70s and low RH values. The weak afternoon Cu field will quickly dissipate by early this evening with the loss of heating. This will result in a setup for good radiational cooling once again, thanks to the dry air mass in place. With dewpoints slipping into the 40s overnight, would not be shocked to see us cool off another 3-5 degrees lower than last night, with many locations bottoming out in the 50-55 range. These would be the lowest temperatures readings we've seen since late Spring. .SHORT TERM...(Monday through Tuesday) Issued at 237 PM CDT Sun Sep 20 2020 With high pressure setting up to the northeast of the area on Monday, expect a mirror image of the weather again tomorrow as fairly light east to ESE breezes reinforce a drier air mass. After a fairly cool start, plenty of sunshine will allow temperatures to warm into the mid 70s in most locations in the afternoon. The center of the aforementioned ridge will begin to pivot into the Carolinas and Southern Appalachians on Tuesday, with winds veering to a more southerly direction. We'll be watching the progress of Tropical Storm Beta as it is projected to track toward the TX/LA border region during this time and we should begin to see a gradual uptick in moisture. Strong subsidence from the ridge will keep any precipitation well to our southwest, but we should see an uptick in cloud cover on Tuesday, especially later on in the day and into the overnight hours. The Tennessee Valley region will begin to experience better chances of rain from "Beta" in the middle to later half of the week as discussed in the section below. .LONG TERM...(Tuesday night through Saturday) Issued at 237 PM CDT Sun Sep 20 2020 The upper ridge over the southeast breaks down in earnest during the day on Wednesday, with zonal to weak southwesterly flow developing aloft over the Tennessee Valley. This should finally allow the remnants of Tropical Storm Beta to move east instead of to the north. Moisture advection and some upper level forcing associated with this system will likely push into Mississippi and areas just east of the AL/MS border on Wednesday. However, deeper moisture and better forcing should be held mainly over MS, so only 20 to 30 percent chances of rainfall in the forecast for now. Both GFS and ECMWF keep instability south and west of northern Alabama. The ECMWF is definitely a shift towards a more stable solution. So for now keeping thunderstorms out of the forecast, despite some bulk shear between 30 and 40 knots and 100-200 helicity shown in model guidance. Despite some warming 925 temperatures, abundant thick cloud cover should keep highs in the mid 70s to around 80 degrees. The warmer 75 to 80 degree temperatures should occur near and east of the I-65 corridor. Moisture advection increases Wednesday night, as a fairly strong upper level trough axis associated with the storm system moves into northern Arkansas. Shear increases and there may be just enough instability aloft for some isolated to scattered thunderstorms. Would think that some small hail and gusty winds would be the biggest threats, despite bulk shear continuing to be 30 to 40 knots. Lows should be warmer due to the moist airmass in place, only dropping into the upper 50s to lower 60s. Could see some heavier rainfall along with some of those elevated storms later in the evening. PoPs will likely need to be increased to likely or categorical if this solution holds on the next few model runs. Thursday looks wet as well, as the trough axis moves further east into western Tennessee. Strong forcing and an even more moist atmosphere looks to keep at least a high chance if not likely PoPs in the forecast. There looks to be more instability, but less shear in place, so more scattered thunderstorms look possible, but there should not be very strong. Keeping high chance throughout the day on Thursday, but again may likely need to be increased. Most models are now weakening this trough axis as it moves into the northeastern CONUS, while trailing right through or just north of the TN/AL border. This sets up a wet and below normal temperature pattern for the area through cooler period through the weekend. Cloud conditions with highs in the 75 to 80 degree range and lows in the lower to mid 60s are expected much of that period. A much stronger frontal boundary puts an end to this by late Sunday night in most guidance. This front looks to bring much cooler and drier air in the region to begin the new week. && .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) Issued at 1240 PM CDT Sun Sep 20 2020 VFR conditions will prevail at each terminal through the period, with light east to ESE winds and a mostly clear sky. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...AMP.24 SHORT TERM...AMP.24 LONG TERM...KTW AVIATION...AMP.24 For more information please visit our website at weather.gov/huntsville.