342 FXUS64 KMRX 222249 AFDMRX AREA FORECAST DISCUSSION National Weather Service Morristown TN 649 PM EDT Mon Mar 22 2021 .UPDATE... FOR 00Z AVIATION. && .SHORT TERM...(Tonight through Tuesday)... Mostly clear skies continue to prevail across the eastern Tennessee Valley this afternoon. Some low cumulus has formed across the Cumberland Plateau, southeast Tennessee mountains and southwest North Carolina mountains as east to southeast low level flow continues around surface high centered to the east of the Appalchians. Some thin cirrus is also moving from the west into the region from a southwest US upper level trough and associated surface cyclone. Temperatures at mid afternoon are in the upper 60s to lower 70s. This feature will continue to progress to the east into the Plains States as upper level ridging now overhead shifts east of the Appalachians overnight tonight. Clouds, mainly high level variety will increase overnight with temperatures only falling into the 40s. The plains system closes off into an upper level low tonight with the surface low moving into eastern Kansas by sunrise Tuesday. Showers and some thunderstorms will move into the southern Plains and late tonight the Mississippi Valley. On Tuesday the system will move east with the main low moving north and the southern end of the system hanging back over the Mississippi Valley. Eastern Tennessee will be in the middle part of the system with some possible showers spreading into the southern sections by afternoon but only very light rainfall amounts expected. Cloud cover will limit high temperatures over southern sections of the area with temperatures warmer in the north where cloud cover will be less dense and some breaks are possible. Instability is expected to be too low for thunderstorms. TD .LONG TERM...(Tuesday night through Monday)... We start the period in deep south and southwest flow aloft with an upper ridge to our east and troughing to our west with one upper low over the central Plains/Mississippi River Valley Region and another over the Desert Southwest. The first low will lift out to the north/northeast while the second ejects out of the Desert Southwest and tracks east and northeast. The first will pull nudge a cold front toward our area, but this front will stall out to our west until the second system comes along and pulls it east through our area Thursday night as the associated surface low tracks through the Ohio River Valley and into the eastern Great Lakes. Some weak mid/upper level short wave energy ejecting out of the trough to our west may provide enough support for some showers Tuesday night into Wednesday, but precip amount look to be on the light side and will keep PoPs in the slight chance/chance range. The second system looks to have much better support with a period of favorable jet dynamics as we get into the right entrance region of the jet to our north with a possible boost from a second jet further southwest. The low level jet will strengthen out of the southeast and south as well. PW values will be anomalously high for this time of year, so heavy rain will be possible Thursday into Thursday night ahead of and near the cold front. The risk for localized flooding remains, especially across the south and Plateau as downslope winds should help to lower amounts further northeast. Right now the system looks fairly progressive which would help to mitigate the flooding threat, but those details should become clearer as we get closer. As for those aforementioned downslope winds, mountain wave enhancement looks likely at this point later Thursday into Thursday night, so will keep the possibility of strong winds across the higher elevations and foothills of the eastern mountains in the HWO along with the flooding threat. Will keep mention of thunder mainly south and Plateau Thursday and all areas Thursday night, although right now models are keeping convective energy minimal. However, shear will be strong so the possibility of severe storms will have to be monitored as the system draws closer. Once this system exits, drier air will be moving in Friday and Friday night. Models struggling a bit further out with some significant disagreements, but a strong cold front looks to move through at some point in the Saturday night/Sunday time frame, along with some additional showers. As colder air pushes in, there may even be a few snowflakes over the highest peaks Sunday night/early Monday, although confidence in the details is low that far out. LW && .AVIATION... 00Z TAF DISCUSSION. Clouds will increase and cigs will start to lower, especially at CHA, but VFR conditions are expected for the entire period all sites. Winds will be light overnight, then will become south and southeast generally less than 10 kts during the day. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 52 66 55 69 57 / 0 30 40 30 50 Knoxville McGhee Tyson Airport, TN 46 69 52 68 53 / 0 10 20 20 20 Oak Ridge, TN 47 69 52 69 55 / 0 10 20 20 30 Tri Cities Airport, TN 42 68 48 69 48 / 0 10 20 20 10 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$