Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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000 FXUS64 KMRX 240715 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 315 AM EDT Thu May 24 2018 .SHORT TERM (Today and Tonight)...
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Weak ridging has built into the region with low level moisture slowly pushing back in. With the moisture and daytime heating...expect diurnal convection to develop over the area this afternoon. The area with the best chance of shower/thunderstorm activity will be over southern areas and along the higher elevations of the Appalachians. The convection should decrease after sunset but may continue to see a few showers linger over the southeastern mountains through the night. As for may be a bit warmer this short term with highs in the 80s and lows in the 60s across most valley locations. .LONG TERM (Friday through Wednesday)...The main focus over the extended forecast will be on the system to the south across the Gulf of Mexico and how it will impact the Southern Appalachians over the holiday weekend into early next week. Start to see some moisture return on Friday as the ridge axis moves to the east and a weak upper level trough approaches from the west. Models indicate that PW values across the Tennessee Valley will increase into the 1.4-1.7 inch range which are well into the 90th percentile for late May. Therefore, have increased the pops Friday afternoon into the 40-60 percent range. The trough is weak and there is not much of a forcing mechanism, otherwise, pops would be much higher High temperatures will be in the low to mid 80s with SBCAPE values during the afternoon into the 1000-1500 J/Kg range. However, 0-6 km bulk shear is less than 15 kts and do not anticipate any strong to severe storms at this point. Already seeing some significant differences in the models with the system in the Gulf of Mexico by Saturday. Regardless, PW values will remain elevated across the area with deep southerly flow. There may be a bit more forcing as the weak shortwave trough moves closer to the area on Saturday. Cloud cover will also be increasing ahead of the system from the south and highs should be a few degrees cooler than on Friday. Most of the models suggest that Sunday may actually start off dry with the precipitation confined to the Gulf States. The chances for precipitation on Sunday and Monday will be highly dependent upon the track of the system. The GFS continues to be the most eastward of the models and brings in the highest chance for precipitation Sunday throughout the remainder of the forecast period. The ECMWF keeps the system well to the south and west of the area throughout the forecast period. However, with this solution the forecast area remains under deep southerly flow and would expect numerous to widespread afternoon showers and storms. The Canadian model is between these two solutions. For now, have continued with elevated pops generally from Saturday afternoon onward. Depending upon model solution, there could be some localized flooding issues early next week. The run total accumulated precip. from the GFS is 2-4 inches with a modest 0.5-1.5 inches on the ECMWF through mid week next week. Highs temperatures leaned more towards raw model guidance with the increased precip. chances and cloud cover. Highs will generally be in the low 80s with lows in the 60s.
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Chattanooga Airport, TN 88 68 84 69 / 30 20 40 30 Knoxville McGhee Tyson Airport, TN 86 66 84 67 / 30 20 50 30 Oak Ridge, TN 86 66 84 68 / 20 20 40 30 Tri Cities Airport, TN 84 63 82 64 / 20 20 40 20
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