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

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000 FXUS64 KMRX 290721 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 321 AM EDT MON AUG 29 2016 .SHORT TERM (Today and Tonight)...
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Current water vapor imagery and RAP upper air analysis indicates that the center of the ridge has retreated some out over the Atlantic. However, a weaker 593 dm high is centered just to the NW near the Ohio River. At the surface, a high pressure center is in place across the Great Lakes with Tropical Depression 8 just off the Carolina coast. The boundary layer across the forecast area remains moist with dewpoints in the upper 60s to low 70s. Just a bit to the NE, into VA and WV, dewpoints are in the upper 50s to low 60s. This will be a major factor of consideration for PoPs later today. For now, expect there will be some areas of patchy fog this morning with the moist boundary layer but expect fog should lift rather quickly after sunrise. For today, the low-level pressure gradient between the high to the NW and low associated with Tropical Depression 8 to the SE will lead to NE low level flow. As mentioned earlier, much lower dewpoints and drier air exist just to the NE in WV and VA. These winds will advect in much drier air with PW values dropping down into the 1.2-1.5 inch range. These values are near average for late August. Model soundings indicate much weaker lapse rates and SBCAPE values under 1000 J/Kg even in the most aggressive models. Therefore, expect there will not be the coverage of shower/storms seen over the last couple of days. Continued with just a small mention of shower/storms across the area later this afternoon but do not expect any strong or severe storms with the lower instability values and weak mid-level flow. With upper level heights in the 590-593 dm range, expect another hot day with high temperatures topping out in the low to mid 90s in most valley locations. .LONG TERM (Thursday through Sunday)... High pressure in control Wednesday and Thursday for continued hot and humid conditions. Strong diurnal heating will allow isolated to scattered convection to develop across the region with the best chance over normally favored higher terrain. Models trending toward bringing in a weakening frontal boundary on Thursday. Model consistency has been poor with this feature in regards to timing...strength and position. Confidence not high with current scenario but will trend forecast towards this solution for an increase chance of more organized convection Thursday afternoon. Behind the boundary...drier... slightly cooler air can be expected. Could see isolated diurnal convection over higher elevations on Saturday..otherwise...the trend is toward a dry weekend.
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Chattanooga Airport, TN 94 70 94 71 / 10 10 10 10 Knoxville McGhee Tyson Airport, TN 94 68 92 69 / 10 10 20 10 Oak Ridge, TN 94 70 92 69 / 10 10 20 10 Tri Cities Airport, TN 92 64 90 66 / 20 10 30 20
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