Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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403 FXUS64 KMRX 170537 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 137 AM EDT Fri May 17 2024 ...New AVIATION... .UPDATE... Issued at 951 PM EDT Thu May 16 2024 The main issue tonight is fog development, and whether the high clouds approaching from the west will impact fog. The NAM and LAMP guidance are quite bullish on fog, but the LAMP has been trending toward less fog at TRI for the past few runs. Timing the leading edge of cirrus spreading across Middle TN takes it to TRI around 0630Z. The current forecast has patchy fog in NE TN and SW VA, and that will continue unchanged given the uncertainty. Expect that rain will begin to spread into southern sections late tomorrow morning as the cloumn moistens from the top down. Instability will be lacking so no strong/severe storms are expected, and there will probably be only isolated thunderstorms in the afternoon. && .SHORT TERM... (This evening through Friday) Issued at 244 PM EDT Thu May 16 2024 Key Messages: 1. Patchy fog overnight across northeast TN and southwest VA. 2. Chances for showers increase tomorrow morning across the southern TN Valley. Then, rain spreads from southwest to northeast into tomorrow afternoon. A few storms are also possible, but non severe. Discussion: High clouds, associated with the showers and storms across the ArkLaTex region, spread into the area overnight from southwest to northeast. These high clouds likely prevent fog across most areas except for northeast TN and southwest VA, where high clouds don`t arrive until daybreak. Fog will be patchy to scattered with visibility reduction in some areas. For Friday, a shortwave will be moving across the Missouri River Valley and into the Ohio River Valley. This shortwave will bring increasing chances of rain, and a few storms, across our area. Meanwhile, a shortwave will also be moving through the subtropical jet across the southern Gulf States. This southern convection will likely inhibit any meaning instability from developing across our area. NBM and HREF probabilities show roughly a 20 to 40% chance of SBCAPE greater than 500 j/KG during the day. Whatever instability is able to develop will be shallow as there is a very strong mid-level cap in place from 850 to 500mb, which would prevent any mature updrafts. So while a few storms are possible, none are expected to be severe and the main theme of the day will be scattered rain showers with overcast skies and slightly below normal to near normal temps. && .LONG TERM... (Friday night through next Thursday) Issued at 244 PM EDT Thu May 16 2024 Key Messages: 1. Wet pattern setting up Friday night and Saturday. 2. Drier and warmer Monday and Tuesday as ridging builds. 3. Cold front and storms move into the area around next Wednesday. As the upper trough amplifies across the Lower Mississippi Valley on Friday night, southwesterly unidirectional flow is expected across our region. Upper-level diffluence will promote widespread synoptic ascent with overcast sky conditions and the potential for periods of rainfall. Upper-level heights begin to decrease late Friday night as the trough axis shifts eastward with DPVA across the Tennessee Valley, and at the surface, an area of low pressure will move east- northeastward from the Lower Mississippi Valley. This will bring a surface warm front northward near our area. At this time, the majority of surface based instability is expected to remain south of our area. However, there is a low chance that this higher instability arrives in our area late Friday night after 06z with low probabilities of strong to severe thunderstorms. Any storms that do become strong would produce frequent lightning, heavy rain rates, and potential strong wind gusts. Scattered rain showers continue on Saturday as the upper-level trough axis is directly over the Tennessee Valley and Southern Appalachians. This will promote widespread light convection with rain showers, and perhaps a few thunderstorms, with gusty wind, heavy rain rates, and potential small hail. Convection will decrease with the loss of surface heating on Saturday night, and as the trough axis moves east of our area, subsidence on the west side of the departing trough will limit precipitation, especially west of Interstate 75. The highest precipitation chances on Sunday will be across the eastern counties of our forecast area near the TN/NC state line. Ridging bring drier weather and warmer temperatures on Monday and Tuesday with temperatures on the high-end 90th percentile of the distribution near 90 across our southern valley locations in the Chattanooga vicinity on Tuesday. A quick moving shortwave and surface cold front will approach the region on Wednesday with a chance of scattered showers and thunderstorms. If this front can move through the region, drier weather would be expected late week; however, if the front stalls near the Tennessee Valley, continued periods of wet conditions will be possible late next week. && .AVIATION... (06Z TAFS) Issued at 115 AM EDT Fri May 17 2024 Still uncertainty about cloud impact on fog development early in the period, but for now will go with MVFR/IFR conditions at TRI. Otherwise, showers and perhaps some rumbles of thunder will spread across the area from SW to NE today and will continue into tonight. Given lower probability and timing uncertainty will leave thunder out of the forecast for now. Will likely see conditions lower to MVFR/IFR at CHA, with conditions likely lowering to MVFR at TYS and at least briefly to MVFR at TRI. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 75 66 79 64 / 80 60 80 50 Knoxville McGhee Tyson Airport, TN 76 63 76 63 / 80 70 90 70 Oak Ridge, TN 76 63 77 62 / 80 70 90 60 Tri Cities Airport, TN 77 60 77 61 / 80 60 90 60 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...DGS LONG TERM....JB AVIATION...