Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/12/20

Area Forecast Discussion
National Weather Service Grand Junction CO
434 PM MST Wed Nov 11 2020 .SHORT TERM...(Tonight through Thursday night) Issued at 230 PM MST Wed Nov 11 2020 One minor ripple in the broader upper level trough over the region is crossing northwest CO at this time. coincident weak elevated instability will peak between now and late afternoon, and as the HRRR and NAMNest models have pegged, convective bands have developed across far NW CO. Expect these to continue through early evening, impacting the mountains of NW CO with areas of less than 2 inches of snow accumulation. The next shortwave trough over eastern ID right now will combine with a strengthening upper level jet coming west to east across UT tonight to provide enhanced lift (in addition to orographics) across the same areas of northwest CO, but will also allow for scattered snow showers farther south such as over the Elks and from Vail Pass to Monarch Pass. Available moisture is somewhat limited, but high snow-to-liquid ratios should yield a total of 3 to 6 inches of snow north of Rabbit Ears Pass and 1 to 3 inches over the Flat Tops and over the Gore and Elk Ranges. Gusty winds to 45 mph over those higher elevations will cause blowing and drifting snow as well. Otherwise, it will be a mostly clear to partly cloudy and cold night for the rest of the area. This system will exit Thursday morning and the snow shower activity along the Divide will diminish. Northwest flow will transition to zonal during the day into Thursday night. Temperatures will remain about 10 degrees below normal. .LONG TERM...(Friday through Wednesday) Issued at 230 PM MST Wed Nov 11 2020 A stronger and wetter trough will plow into the Pac NW Friday and bring stronger forcing over northeast UT and much of western CO centered on late Friday night into early Saturday morning. Westerly upslope flow will be enhanced by this dynamic lift and moisture content will be greater. Snow chances will increase over northeast UT and northwest CO Friday evening and expect the highest snowfall rates between 09-15Z with 6-hourly rates of 3-5 inches...highest over the Gore, Park, Flat Top, and Elk Ranges. This event may require an advisory for those ranges considering 8-10 inch totals and considerable blowing snow. With the strongest forcing and best moisture remaining north, the San Juan mountains will be lucky to receive 1 to 4 inches of snow. Lower elevations of west-central and northwest CO and northeast UT will likely see up to an inch, but the I-70 corridor of the Grand Valley looks to stay mainly dry. Snowfall will diminish Saturday afternoon and night in the wake of the trough axis passage and the northwest upslope flow dries out. However, light snow showers will likely persist for the northern ranges of the Divide through Sunday. Upper level heights rise early next week as a ridge aloft develops over our region and temperatures will rise above normal by Tuesday...with these same dry and above normal temperatures continuing Wednesday. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 427 PM MST Wed Nov 11 2020 A disturbance clipping northeast Utah and northwest Colorado will continue to produce scattered and intermittent light snow overnight, particularly at KHDN and to a lesser extent KVEL, KEGE and KASE. During periods of snow, expect reduced visibility and ceilings that approach ILS breakpoints. Most snow showers will end Thursday morning, with a gradually clearing sky to follow. Otherwise, VFR conditions expected elsewhere for the next 24 hours. Winds will generally be light and terrain driven. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...BM LONG TERM...BM AVIATION...MDM
National Weather Service Morristown TN
905 PM EST Wed Nov 11 2020 .UPDATE... EVENING UPDATE. && .DISCUSSION... Cold front is moving through the area this evening with winds shifting to the NNW/N behind the front at obs sites. Rain continues to shift east with highest PoPs early tonight across the eastern half of the forecast area. This rain will continue shifting east overnight with PoPs decreasing late tonight and ending for most areas by daybreak Thursday. Some drizzle may linger early Thursday with some light rain showers across the higher elevations due to orographic lift, but precip will be isolated and decrease quickly through the day. With the low FFG and continued moderate rain, will continue the FFA at this time. Most of the moderate precip will be exiting the area in the next hour, and if this trend continue, may cancel the watch prior to the 12z expiration. JB && .AVIATION... 00Z TAF DISCUSSION. Poor flight conditions forecast overnight as a cold front with widespread rain slowly moves east across the area. Steady rain is coming to an end at CHA but will continue for the next 6-12 hours at TYS and TRI. Even after rain has ended at sites, cigs will remain low with some -dz through Thursday morning. General improvement in conditions is expected near the end of the TAF period as drier air arrives. JB && .PREV DISCUSSION... /ISSUED 319 PM EST Wed Nov 11 2020/ SHORT TERM (Tonight and Tomorrow)... Showers, with a few rumbles of thunder, will decrease west to east tonight with lingering chances tomorrow in the Tennessee/North Carolina mountains. Locally heavy downpours and isolated flooding in low-lying and poor drainage area is still possible. Temperatures will be seasonally mild but closer to seasonal norms. Current Setup: Currently, the long-discussed cold frontal boundary is located along western areas of the County Warning Area (CWA). Aloft, mid/upper-level troughing is dominating in the western two- thirds of the CONUS with tropical cyclone Eta located ~50 miles west of the western Florida coast. This Evening/Tonight Throughout the evening, eastward progression of the frontal boundary will continue with the CWA being located at the right-entrance region of a 60-80kt jet streak. Low-level convergence associated with the frontal boundary and upper-level divergence enhanced via direct ageostrophic circulation in the upper jet will both provide continued forcing for convection. Deep moisture remains in place ahead of the frontal boundary with post-frontal low-level moisture evidenced by 925mb-850mb saturation. By this evening, the front will be located along the eastern periphery of the area. Given the deep moisture and marginal dynamics, PoPs will remain high into the evening. RAP indications of pre-frontal surface- based instability above 500 J/kg will carry slight chance of thunder into the early evening. Pre-frontally low LCL heights with freezing levels above 14,000 feet, combined with the aforementioned considerations, suggests that notable rainfall rates are possible in heavier showers and thunderstorms, which has already been seen along the Cumberland Plateau. Also, SW flow has allowed for some training of cells with eastward movement increasing. Given these characteristics and latest high-res indications, localized flooding continues to be possible with an additional 1 to 2 inches possible in eastern portions of the area with locally higher amounts possible in the Tennessee mountains and into Washington County, VA. Based on lower flash flood guidance values, a Flood Watch is in effect in the mountains of Blount County up to northeast Tennessee and Washington County, VA until tomorrow morning. This is based on expected rainfall of 2 to 3 inches or more, ground saturation, and post-frontal upslope flow tonight. Tomorrow Heading into Thursday, much of the troughing and jet dynamics remain to the north. Deep moisture will have pushed off to the east with lingering low-level moisture and NW flow keeping slight chance/chance PoPs in the eastern high elevation areas before the moisture finally moves off to the east at the end of the period. Otherwise, seasonal temperatures prevail, given continued cloud cover and mid/upper heights close to normal. BW LONG TERM (Thursday Night through Wednesday)... Key Messages: 1. Dry weather returns Friday and Saturday with plenty of sunshine, and temps will still average 4 to 8 degrees above normal. 2. Showers will move through the region Sunday into Sunday night, but rainfall amounts will be light. 3. Dry conditions return early next week, but temps will finally cool to near normal. Discussion: Thursday Night through Saturday Night... Drier air will work into the region Thurs night as surface high pressure builds in from the N and W. The cold front will only slowly shift E through the Carolinas since the mid/upper flow remains somewhat WSW ahead of another shortwave digging into the desert SW. At the same time, the remnants of Eta will also move along the boundary near the GA and CA shoreline further slowing the front. This will cause some moisture to linger over the far eastern mountains, so clouds and a few stray showers will in that area Thurs night. The surface high will win out Fri with mostly sunny skies developing areawide. Since the upper trough stays well to our N moving across the Great Lakes and the flow over our region remains WSW, highs will remain mild in the mid/upper 60`s. The aforementioned desert SW shortwave will phase with a stronger shortwave crossing the Rockies into the Plains by Sat which will rebuild downstream ridging across the TN Valley and SE CONUS, with the surface high shifting to the E coast. This will set up southerly flow, with the resultant WAA boosting highs into the upper 60`s to near 70 for Sat making for a beautiful start to the weekend. Clouds will begin to increase ahead of the system Sat night. Sunday and Sunday Night... The mid/upper shortwave will move from the Plains across the Midwest and Great Lakes Sun and Sun night. Its axis will become negatively tilted resulting in a deepening surface low moving from the Great Lakes into Ontario, with the associated strong cold front crossing our CWA Sun. Deterministic and ensemble guidance have come into good overall agreement on a afternoon and evening fropa. Lift from a 150 kt upper jet over the OH Valley will combine with warm, moist advection ahead of the front to produce a band of showers, but the surface high holding on for so long near the E coast and relatively fast moving nature of this system will limit the quality of moisture return. This will result in the showers being tied closely to the boundary limiting QPF to a trace to a few hundredths of an inch. Kept PoPs in the chance range Sun. Drier air will quickly pour in behind the front Sun night, so most areas will dry out except for a few lingering showers from SW VA down the eastern mountains. Temps will remain warm ahead of this front with upper 60`s/low 70`s Sun before falling sharply into the low 40`s Sun night in the post fropa CAA. Monday through Wednesday... A fairly deep but progressive mid/upper trough will dig into the eastern CONUS behind the system Mon through Tues with strong surface high pressure centered near the MS Valley. This will place our region in dry, cool NW flow with highs near normal in the mid 50`s and overnight lows in the 30`s. Slight moderation will occur by Wed as the upper trough begins to lift out and height rises take place. Garuckas && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 58 70 49 68 44 / 50 10 0 0 0 Knoxville McGhee Tyson Airport, TN 57 66 49 65 41 / 80 10 0 0 0 Oak Ridge, TN 55 66 46 66 41 / 70 10 0 0 0 Tri Cities Airport, TN 57 64 50 64 37 / 90 30 10 0 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...Flood Watch until 7 AM EST Thursday for Blount Smoky Mountains- Cocke Smoky Mountains-Johnson-Northwest Carter-Sevier Smoky Mountains-Southeast Carter-Southeast Greene-Sullivan-Unicoi- Washington. VA...Flood Watch until 7 AM EST Thursday for Washington. && $$