Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
768 FXUS64 KMRX 040540 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 1240 AM EST Thu Dec 4 2025 ...New DISCUSSION, AVIATION... .KEY MESSAGES... Updated at 1240 AM EST Thu Dec 4 2025 Dry weather today before increasing precipitation chances tonight into Friday. - Probabilities for minor impacts from ice and snow are trending upwards across the northern Cumberland plateau, southwest VA and extreme northeast TN for tonight into Friday morning - Very low probability of rainfall this weekend. && .DISCUSSION... Issued at 1240 AM EST Thu Dec 4 2025 Dry today with continued below normal temperatures. Increasing precipitation chances tonight into Friday morning. The good news is that the latest HREF probs mostly align with the previous forecast. The bad news, the last two runs of the HRRR are well above the HREF means in terms of snowfall amounts. This makes for a low confidence forecast. Latest HREF guidance shows probs for at least 0.5 inches across southwest VA are in the 30 to 50% range. Probs for at least 0.5 inches for extreme northeast TN are generally from 50 to 70%. There are also low probs, 10 to 20%, of at least 0.5 inches across the northern Cumberland Plateau and areas along and near the TN/KY state line. Upping the prob amounts to 1 inch yield much lower values, around 30%, but for very isolated locations for both southwest VA and extreme northeast TN. The LREF members shows slightly higher prob values, and with more spatial coverage, for the 0.5 and 1 inch prob values. LREF shows moderate probs of 1 to 2 inches across southwest VA and into extreme northeast TN. The REFS output aligns fairly well with the LREF ensemble probs. Then we have the HRRR. The latest two runs of the HRRR show even higher values than what the REFS and LREF ensembles means suggests. The HRRR wants to paint a solid 2 inches in across the northern Plateau, and 3 to 4 inches in across southwest VA and extreme northeast TN. Because of all this, uncertainty in snowfall amounts is high. These higher end amounts would result in travel impacts while the lower HREF amounts suggest little to no impacts. With this forecast package, have trended snowfall amounts slightly upward, above NBM, based on latest model data and trends. In addition to the snow, NBM also painting in some light icing across these same areas. Please stay tuned to the forecast as the snowfall forecast will likely continue to change given the current variability. Please plan ahead for potential impacts with this system. Areas from Knoxville and south should remain all rain through the event. The bulk of the precip will have ended by Friday afternoon, but a few light showers may linger into the evening hours. NBM still wants to hold on to some slight chance POPs for Saturday and Sunday but it seems warranted so will leave them in the forecast. Rain chances continue into next week as an active pattern will be in place across the country. As of now, Tuesday look like it should be dry though and is most likely to be the nicest day of the forecast period. && .AVIATION... (06Z TAFS) Issued at 1240 AM EST Thu Dec 4 2025 Overall, limited aviation impacts are anticipated with clear skies for the rest of the night into the early morning. Patchy freezing fog is possible in some places, but the probability remains low at the sites. Throughout the day on Thursday, light northeasterly winds will persist with increasing cloud cover around 5,000 to 10,000 feet AGL. Light rain will then move into the region later in the evening, which will likely lead to some reductions. However, this looks to be around or after 06Z, so no reductions were included with this issuance. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 49 38 49 39 / 20 90 40 20 Knoxville McGhee Tyson Airport, TN 45 35 44 38 / 10 90 60 20 Oak Ridge, TN 45 34 44 35 / 10 90 40 20 Tri Cities Airport, TN 44 32 42 35 / 0 90 60 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ DISCUSSION...99 AVIATION...BW