114 FXUS64 KMRX 210747 AAA AFDMRX AREA FORECAST DISCUSSION...UPDATED National Weather Service Morristown TN 347 AM EDT Wed Jul 21 2021 .SHORT TERM...(Today and Tonight)... Key Messages: 1) Drier and slightly warmer today with subsidence and height rises. 2) Hazy afternoon and evening due to smoke from Western and Canadian wildfires being advected around the eastern edge of a Western/Central CONUS ridge. Discussion: Upper ridge across the Western and Central CONUS will expand eastward, and subsidence along the eastern periphery is already evident across our area in WV imagery. As a shortwave across WV this morning moves eastward, additional height rises are forecast. This will allow temperatures to be slightly warmer and result in clearing sky conditions. However, smoke from wildfires across Canada and the NW CONUS will be advecting across the area from the north around the eastern periphery of the ridge. The subsidence across the area will also bring some of this smoke closer to the surface with the HRRR-Smoke showing near surface smoke concentrations of 30 to 40 ug/m3 during the afternoon across far northern East Tennessee and into SW VA. This will likely lower air quality, thus the AQA for the Tri-Cities area, and limit visibility to 4SM to 6SM during the afternoon hours for areas generally north of Interstate 40. There will be a slight chance of an afternoon shower, and potentially a thunderstorms, across far SE TN and SW NC closer to the surface front. However, with drier air moving in, believe most locations should stay dry. With increasing high pressure across the area tonight, dry weather is forecast with a mostly clear sky. Some patchy fog will be possible, especially near river valleys. In addition, continued haze is expected with some lower surface visibilities across northern East Tennessee and SW VA. JB .LONG TERM...(Thursday through Wednesday)... Key Messages: 1) Drier conditions expected for Thursday with only a gradual increase in showers and thunderstorms on Friday. 2) Much warmer temperatures this weekend and into early next week associated with increasing heights aloft. Heat index readings will also increase into the mid 90's across many valley locations. Discussion: Upper lvl ridging will dominate the plains and into the Southeast through the extended range which will keep conditions drier but with an increase in temperatures. On Thursday, the region will be between an upper lvl high across the northern GoM, and a shortwave that will be lifting northeast. At the surface, high pressure will descend into the Ohio Valley with a continued influx of drier air limited precipitation chances to the far southern valley. The high shifts east across the central Appalachians into Friday with northwest flow aloft continuing. Guidance suggests a couple of rounds of energy will translate through this flow on Friday which may promote a gradual increase in shower and thunderstorms across the high terrain. Heights gradually build over the weekend period in response to the overall strengthening ridge over the Plains. Surface flow will begin to veer to the southeast as the surface high becomes situated over the western Atlantic. An increase in low lvl moisture will accompany the increase in heights. As a result, Saturday and Sunday will feature a more typical summertime pattern with diurnal chances of showers and thunderstorms. Approaching early next week, guidance depicts a northern stream disturbances dropping into the Great Lakes with a weak cold front moving through the Ohio valley. A resulting amplification in heights will result in more northwest flow developing overhead. While any resemblance in a front will be hard to find across the local area, the lowered heights aloft may support a gradual increase in showers and thunderstorms on Monday. Temperatures will increase over the weekend and on Monday as highs approach the low to mid 90s across much of the valley, with low to upper 80's elsewhere. Finally, heights once again increase on Tuesday but with diurnal showers and thunderstorms expected. The main story during this time will be the increase in temperatures as thickness values increase with highs in the low to mid 90's and heat index values in the mid to upper 90's. Diegan && .AVIATION... 06Z TAF DISCUSSION. With northerly flow and drier air across the region, dry weather is forecast through the period. There will be a small chance of some isolated rain showers or thunderstorms in the vicinity of CHA this afternoon, but probability currently too low to include in the TAF. Guidance indicates haze and smoke from western wildfires will advect across the area this afternoon primarily affecting TRI, and to a lesser extent, TYS. Based on current forecast smoke concentrations, would expect MVFR vis this afternoon at TRI with vis of 4 to 5SM. Kept VFR vis at TYS with lower smoke concentrations but did bring vis down to 6SM. Winds remain light and generally from the north. JB && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 88 71 91 70 91 / 20 10 30 10 40 Knoxville McGhee Tyson Airport, TN 89 68 92 68 93 / 10 10 10 10 20 Oak Ridge, TN 90 68 91 67 92 / 10 10 10 10 20 Tri Cities Airport, TN 88 62 88 62 91 / 10 10 10 0 10 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$