269 FXUS64 KHUN 241407 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 907 AM CDT Fri Apr 24 2020 .NEAR TERM...(Rest of Today) Issued at 907 AM CDT Fri Apr 24 2020 The upper disturbance responsible for thunderstorm activity seen yesterday is now moving off the Atlantic Coast, and high pressure is settling in over the Tennessee Valley. Morning satellite trends show clouds thinning out a bit faster than originally anticipated, so changes were made to reflect this in the forecast. Despite northerly flow, abundant sunshine should allow temperatures to rise into the mid 70s across several locations this afternoon. Expect dry conditions through the day today, although thunderstorm activity will be ongoing to our west as another disturbance tracks over the Southern Plains and lower Mississippi Valley. This will ultimately be responsible for the return of rain and thunderstorms on Saturday. Otherwise, no significant changes were made to the near term forecast. .SHORT TERM...(Tonight through Sunday night) Issued at 436 AM CDT Fri Apr 24 2020 Another mid-level trough embedded within the cyclonic flow aloft will dig southeastward from central CO into eastern KS/OK today, with this feature predicted to deepen as it advances across the Ozarks and Mid-South region by 12Z Saturday. Low-level flow across the TN Valley will initially veer to ESE late this evening, as the system's surface cyclone begins to track eastward across northern AR, with an even greater increase in southeasterly flow anticipated after Midnight. Due to this, we expect lows in the m-u 50s to be achieved this evening, with patchy fog development also possible in a few of our normally fog-prone valleys late this evening/early Saturday morning. However, mid and high-level cloud cover will increase rapidly between 6-12Z, with elevated convection expected to spread eastward in the strengthening warm advection regime to the east of the approaching disturbance. This activity will be ongoing around 12Z and should persist across much of the region in the 12-18Z timeframe before beginning to shift northeastward in tandem with the cyclones warm sector. Although severe storms are not anticipated with this particular round of convection, frequent lightning and small hail will be possible in the strongest cells. During the day on Saturday, models indicate that the deepening mid- level trough will assume a slight negative-tilt, with the developing surface low expected to track east-northeastward into south central KY by 00Z Sunday. A second round of thunderstorms will likely evolve along a surface trough/wind shift axis trailing southward from the low as it approaches the I-65 corridor early Saturday afternoon, with this activity developing eastward across northeast AL/southern TN through mid-afternoon. Deep-layer bulk shear in the 55-65 knot range indicates that this activity will be organized, and depending on the thermodynamic environment in the wake of early morning precipitation, it will have a greater risk of producing strong-severe wind gusts and hail. Although the chances of a brief tornado cannot be completely discounted, forecast soundings suggests that low-level flow will be weakening and veering with time, which will reduce this threat compared to wind and hail. Another band of showers will accompany the synoptic cold front as it drops southeastward during the late afternoon/early evening hours, and with postfrontal stratus expected to linger for much of the night, temps should only fall into the u40s-l50s by Sunday morning. Low clouds will likely maintain a presence across the region through late Sunday morning/early Sunday afternoon, until the arrival of a subtle reinforcing cold front related to a strong vort max digging southeastward into the TN Valley. Weak lift associated with this feature may generate a few light showers from Saturday night-Sunday morning, with the arrival of drier air resulting in a gradual clearing trend by late Sunday afternoon. Conditions will be favorable for radiational cooling Sunday night, as a ridge of high pressure settles across the TN Valley, with lows Monday morning falling into the l-m 40s. .LONG TERM...(Monday through Thursday) Issued at 436 AM CDT Fri Apr 24 2020 The extended forecast starts out on Monday, April 27th. High pressure in place will provide a tranquil day across the TN Valley. Look for a dry forecast with daytime highs a few degrees below normal in the upper 60s to lower 70s and overnight lows in the upper 40s to lower 50s. On Tuesday, our next system will dive into the Northern Plains and develop a sfc low. As it deepens and shifts into the Upper MS Valley, high pressure in place will slide eastward. Daytime highs will be a little warmer and more seasonable, reaching the mid 70s. By Tuesday night, the sfc low deepens further as it reaches the Great Lakes region and pulls a cold front into the region. Will see showers and thunderstorms return to the forecast late Tuesday afternoon into the evening hours ahead of the approaching cold front. Coverage of showers will increase through the night to become more numerous with a few thunderstorms possible. Winds will be a little breezy Tuesday afternoon into the overnight hours due to the increase in the pressure gradient with sustained winds ~10kts and gusts 15-20kts. Forecast soundings have too much disagreement to narrow down hazards at this time, however heavy rain looks possible. The cold front will finally move through on Wednesday and bring showers and thunderstorms to an end from west to east by the evening hours. Behind the front, the pressure gradient will slack, allowing for northerly winds to be light. However, will see cloud cover decrease and overnight lows a tad cooler, in the lower 50s. As for Thursday, look for dry conditions and seasonable temps as high pressure builds back into the region. && .AVIATION...(For the 12Z TAFS through 12Z Saturday morning) Issued at 646 AM CDT Fri Apr 24 2020 Satellite imagery and sfc observations indicate that postfrontal stratus will continue to impact the HSV/MSL terminals early in the forecast period, with bkn-ovc cigs in the 2500-4000 ft layer thru 15-16Z. Beyond this point, it appears as if a slight increase in northerly flow will provide sufficient dry air advection in the boundary layer to allow stratus to scatter into stratocu that will persist throughout the aftn. After a brief period of clearing early this evening, both mid/high-lvl clouds and SE flow will begin to increase ahead of an approaching storm system, with VFR cigs falling to arnd 8 kft early Saturday morning. Showers and perhaps a few elevated TSRA will quickly overspread the region from the west btwn 06-12Z, and this has been addressed with VCSH and PROB30 groups. In spite of the increase in precipitation coverage, cigs are expected to remain VFR thru the end of the current forecast period. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...25 SHORT TERM...70/DD LONG TERM...JMS AVIATION...70/DD For more information please visit our website at weather.gov/huntsville.