438 FXUS64 KMRX 172314 AAA AFDMRX AREA FORECAST DISCUSSION...UPDATED National Weather Service Morristown TN 714 PM EDT Sun Oct 17 2021 .UPDATE... FOR 00Z AVIATION. && .SHORT TERM...(Tonight and Monday)... Key Message: 1. Cold. Patchy frost will be possible across parts of southwest VA and northeast TN Surface high pressure centered over the ArkLaTex region has provided the southeast with abundant sunshine. On the east side of the high where the surface pressure gradient is a little tighter, the winds are generally north to northwesterly with a few occasional gusts up to 20 mph. Clear conditions will persist overnight with the winds decoupling. Areas of frost will likely develop late tonight across parts of southwest Virginia and parts of northeast TN, perhaps for southwest NC. However, confidence is low for frost to develop across SW North Carolina. Monday will be another stellar day as high pressure remains nearly stationary centered over Tennessee. Daytime highs will generally be in the 60s and 70s. AC .LONG TERM...(Monday Night through Sunday)... Key Messages: 1. Dry weather with a warming trend through Wednesday is expected, followed by showers and isolated thunderstorms on Thursday. 2. Towards next weekend, the trend will be a return of dry and seasonally cooler weather, possibly like what has been seen lately. Monday Night through Thursday To start off the period, mid/upper shortwave ridging will be centered over the Mississippi River Valley with surface high pressure dominating much of the eastern U.S. A closed low will also be in place over the Northern Rockies. This initial setup will continue with height rises promoting a warming trend back to near normal during the day on Tuesday. By Wednesday morning, the aforementioned closed low will have ejected into the High Plains with continued cyclogenesis leading to a developed surface low pressure system that will track towards the Great Lakes. During this time, the surface high will shift eastward with both of these features lending southerly flow and Gulf moisture advection, especially to our west. This will continue the warming trend through Wednesday with its associated cold frontal boundary being the main forcing mechanism for a return of rain chances before its passage on Thursday night. The recent trend in model runs has shown a more dynamic and possibly a sufficiently unstable setup for showers and isolated convection. There has also been a slower trend for the frontal passage with this recent model run as well. With the surface low and upper jet still far removed from the region to the north, these factors are fairly marginal at this point. Nevertheless, indications of the vertical wind profiles and instabilty of potentially >500 J/kg along and near the Cumberland Plateau will justify low probability HWO wording. This is also given the limited confidence, being that the event is still 5 days. Nevertheless, the main message to be gained will be a return of showers and isolated thunderstorms on Thursday before the front moves through, likely by Friday morning. Friday through Sunday By Friday, the front will have moved through the region, shifting the pattern to a more northwesterly low-level flow pattern. With lingering moisture indicated near and below the 850mb level, a few sprinkles can't be ruled out in the mountains early in the day. Otherwise, drier and seasonally cool weather will prevail into the weekend with surface high pressure in place and near to below normal heights. With a lower sun angle and a similar setup to what we are currently seeing, another chance for frost exists by Sunday morning as the surface high will be in closer proximity to the area. BW && .AVIATION... 00Z TAF DISCUSSION. Clear conditions will prevail through this TAF period at all sites. Winds will be around 5 kts or less. While fog can't be completely ruled out at TRI near sunrise, dewpoints have really dropped today, making the chance of fog too low to mention at this time. DGS && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 44 70 46 73 49 / 0 0 0 0 0 Knoxville McGhee Tyson Airport, TN 43 69 43 72 48 / 0 0 0 0 0 Oak Ridge, TN 42 69 44 71 47 / 0 0 0 0 0 Tri Cities Airport, TN 37 66 40 71 43 / 0 0 0 0 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...Frost Advisory from 4 AM to 8 AM EDT Monday for Cherokee-Clay. TN...Frost Advisory from 4 AM to 8 AM EDT Monday for Johnson- Southeast Carter-Sullivan. VA...Frost Advisory from 4 AM to 8 AM EDT Monday for Russell-Scott- Washington. && $$