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Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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508 FXUS64 KMRX 141924 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 324 PM EDT Sun Jul 14 2024 ...New SHORT TERM, LONG TERM... .SHORT TERM... (This evening through Monday) Issued at 306 PM EDT Sun Jul 14 2024 Key Messages: 1. Hot again on Monday with increasing moisture across the southern valley and plateau. 2. Higher risk of diurnal convection on Monday afternoon, mainly across the plateau and southern valley. Discussion: General persistence pattern continues with synoptic conditions potentially resulting in slightly higher chances for diurnal convection on Monday afternoon. Temperatures will be within a degree or two of the past couple days with increasing moisture resulting in higher heat index values between 100 and 105F for the southern valley near Chattanooga. While the 850mb ridge remains across the Southeast CONUS, a weakness or col at 500mb will shift slightly eastward and will be across Middle and West TN. These slightly lower heights aloft, and increased moisture to our west, will result in some higher convective coverage across the Midsouth and portions of the Lower Tennessee River Valley. This is evident in RAP soundings which show increasing moisture across the Cumberland Plateau and portions of the southern valley near Chattanooga on Monday afternoon. While LFC heights are around 3km this afternoon, they lower to around 2km on Monday afternoon due to increased moisture. Instability is also forecast to go from around 500 J/Kg this afternoon to 1500 to 2500 J/Kg on Monday afternoon. This thermodynamic environment will increase DCAPE to around 1000 J/Kg across the plateau and southern valley on Monday afternoon with a low risk for stronger, potentially severe thunderstorms capable of damaging downburst wind gusts. Further north across the central valley through northeast TN and southwest VA, drier air remains with more limited rain and thunderstorm chances. Daily Record High Maximum Temperatures Date Chattanooga Knoxville Tri-Cities Oak Ridge 07-14 103(1954) 101(1954) 98(1954) 101(1954) && .LONG TERM... (Monday night through next Sunday) Issued at 306 PM EDT Sun Jul 14 2024 .LONG TERM... Key Messages: 1. Extreme heat will continue on Tuesday with highs in the mid to upper 90s and heat index values into the 100s across much of the area. 2. Scattered storms are expected on Tuesday with more numerous coverage Wednesday and Thursday. Lower chances continue into this weekend with temperatures dropping to below normal. Monday Night through Thursday At the start of the period, quasi-zonal flow will be in place aloft with weak embedded shortwaves and surface high pressure receding to the south. During this time, 500mb heights will still be above 5,900m with near record 850mb temperatures reaching to 21 Celsius by the day on Tuesday. A shift to weak southerly flow will advect some moisture into the area, which will increase humidity in comparison to recent days. Accordingly, temperatures will not reach quite as high as the days prior, but heat index values will still rise into the 100s. The increase in moisture will also bring chances for more scattered convection, mainly along the higher terrain due to weak forcing overall. On Wednesday, troughing from the north will deepen, leading to height falls and further suppression of high pressure. A frontal boundary will be noted north of the Ohio River Valley. As this front approaches from the north, additional, more widespread chances of convection exist on top of terrain-based development. By Thursday, the front will likely reach near the area, providing additional lift and further reduction in temperatures. It is still unclear how much coverage there will be because of the significant drought and recent trends. But the pattern does look promising for more substantial rain chances, which are very much needed due to worsening drought. Friday through Sunday Late in the week and into the weekend, the main question will be how far south the frontal boundary reaches, which will affect the available moisture and overall forcing. Much of this timeframe will see more of a troughing pattern, keeping temperatures more moderated and even slightly below normal. Based on these indications, daily rain chances were maintained, but confidence is still limited based on the persistent dryness recent model biases. Daily Record High Maximum Temperatures Date Chattanooga Knoxville Tri-Cities Oak Ridge 07-15 103(1977) 98(1995) 96(1995) 100(1980) 07-16 105(1980) 100(1980) 100(1988) 103(1980) 07-17 103(1980) 101(1980) 94(1980) 103(1980) && .AVIATION... (18Z TAFS) Issued at 115 PM EDT Sun Jul 14 2024 VFR conditions and light winds are forecast. There is about a 10 percent or lower chance of some showers in the vicinity of terminals between 18z and 00z this afternoon, but the probs are too low to include in the TAF. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 75 98 74 96 / 10 30 20 50 Knoxville McGhee Tyson Airport, TN 73 97 74 95 / 0 20 10 40 Oak Ridge, TN 72 98 73 95 / 0 20 10 40 Tri Cities Airport, TN 68 95 69 93 / 0 10 10 40 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...JB LONG TERM....BW AVIATION...JB