450 FXUS64 KMRX 191852 AFDMRX AREA FORECAST DISCUSSION National Weather Service Morristown TN 252 PM EDT Tue Oct 19 2021 Key Messages: 1. Continued comfortable weather through the short term period, with a slight warming trend into Wednesday. 2. Some additional fog possible overnight/early Wednesday morning following a pattern such as recent fog occurrences. Discussion: Overall, the short term period can be summarized by the continuation of fantastic conditions for the region. On the synoptic scale, the recent omega pattern seen within the upper level flow will continue to slowly transition eastward, bringing slight H5 height increases across the area Tuesday afternoon/evening. During this time frame, a surface low pressure system will be tracking ENE off the eastern side of the Rocky Mountains while high pressure dominates closer to home. Additionally, southerly low level flow combined with aforementioned height rises will continue the trend of temperatures at or above seasonal normal for most locations. A lack of available moisture and any significant synoptic support will continue to keep conditions dry this evening. Lastly, weak shortwave energy will help the northwesterly upper level flow carry some higher level clouds downstream from the todays convection well to our west. Additionally, the timing of the clouds and the extent of coverage will likely have an impact on how overnight/early morning fog plays out. Most recent hi-res guidance is suggesting that some higher level cloud coverage will exists during the overnight hours, which could act to reduce the amount of radiational cooling that takes place and lessen the impact of fog. Increased cloud coverage combined with the higher MaxTs on Tuesday will also allow overnight lows to break the seasonally cooler trend and approach values more towards seasonal norm. Dry conditions will remain in place throughout the day Wednesday as the aforementioned pattern continues an eastward shift and the ridge axis moves atop eastern TN. Moisture will begin to increase ahead of the front associated with the Colorado low, however, any direct changes to the dry weather pattern will not occur in this period and will be talked about in the next section. KS .LONG TERM...(Wed night through Tuesday)... Key Messages: 1. Some showers and a few thunderstorms for late Wed night into Thu night 2. Mainly dry Fri through Sat with near normal temperatures. 3. A bit warmer Sun into early next week, but precip coverage and magnitude of warming is uncertain. Discussion: An upper low will move into the Great Lakes region and open up as it pulls northeast. A weak cold front will approach our area Thursday and move through Thursday night. Low level moisture will increase ahead of this front as low level flow strengthens from the southwest, but the main upper forcing with the jet will stay to our north. Models show sufficient convective energy for showers and at least a few thunderstorms ahead of the front mainly Thursday into the first part of Thursday night, although there is still significant uncertainty about the magnitude. It does appear that there will be sufficient low level shear that provided enough CAPE, a few strong to severe storms may develop. This will bear watching as we get closer. A broad trough aloft will be over the Eastern US for Friday into Saturday but will be shifting east, with high pressure over our area at the surface. We should be mainly dry with near normal temperatures for this period, although there may be a few showers north associated with some weak short wave energy Friday night. Forecast uncertainty is still fairly high for the Sunday through Tuesday period, with more spread in the model solutions. Short wave ridging aloft looks likely for Sunday but with flow turning more southerly again, weak isentropic lift may touch off a few showers mainly north. Models are in poor agreement late but another weak front is expected to approach by Mon/Mon night followed by stronger ridging aloft beginning to build in Tuesday. Given the model spread for these later period, the NBM PoPs look reasonable with slight chance to chance PoPs for Sunday night into Tuesday for some showers. Temperatures should be at least a bit above seasonal normals for this period. LW && .AVIATION... 18Z TAF DISCUSSION. Mostly VFR conditions for this TAF period at all terminals with some very high level FEW/SCT clouds making way into the region. Included MVFR fog at TRI and CHA to follow pattern persistence overnight and into early Wednesday morning, however, there remains some uncertainty to how exactly the fog will evolve as lingering cloud cover overnight could impact the extent of radiational cooling. KS && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 47 76 57 75 56 / 0 0 20 60 40 Knoxville McGhee Tyson Airport, TN 46 74 55 74 55 / 0 0 10 50 50 Oak Ridge, TN 45 73 55 74 53 / 0 0 10 60 40 Tri Cities Airport, TN 41 72 47 72 54 / 0 0 0 30 50 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$