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

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000 FXUS64 KMRX 230706 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 306 AM EDT Wed May 23 2018 .SHORT TERM (Today and Tonight)...
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The current weather pattern shows flow aloft becoming weakly northwesterly with a broad...diffuse boundary slowly settling into the region. Overall...this should limit convective development with the best chance of showers and thunderstorms expected over higher elevations. Any activity lingering into the evening should come to an end with much of the overnight hours expected to be dry. Will see little change in the temperature pattern with highs today reaching into the upper 70s and 80s and lows tonight mainly in the 60s across most valley locations. .LONG TERM (Thursday and Tuesday)...The main story in the long- term forecast will be elevated pops throughout much of Memorial Day weekend into early next week. On Thursday, the upper level ridge will be overhead with PW values near to slightly below normal for late May. There will be an inverted trough across the region and there could be a few showers/storms across southeastern portions of the forecast area and the higher elevations where PW values will be slight higher. Overall, expect most locations will remain dry on Thursday. Thursday will be the hottest day of the forecast period with highs in the low to mid 80s under the ridge. Any ongoing precipitation should come to an end Thursday night with the loss of daytime heating. Deep southerly flow will develop on Friday as the ridge axis passes to the east. Moisture advection will push PW values up into the 1.5 inch range near the 90th percentile for late May. Have continued with around 50 percent chances for afternoon showers/storms on Friday. A wet Memorial Day weekend is forecast as a system moves northward across the Gulf of Mexico. There are still some difference on timing and locations with the GFS continuing to be further to the east than the ECMWF. Regardless, both global models keep the system to the south or west of the forecast area throughout the holiday weekend. It is a little too early to get into specific amounts but it does appear that rainfall amounts will range from around 1-2 inches across the forecast area with locally higher amounts. With the tropical atmosphere in place, lapse rates will be near moist adiabatic and do not anticipate any strong to severe storms. The main impact over the weekend will be localized flood from prolonged rainfall, especially in areas of poor drainage. Temperatures will be slightly cooler with persistent cloud cover and precipitation expect highs will be in the upper 70s to low 80s. Due to the increasing confidence, have gone with 50-70 pop throughout much of the holiday weekend. Both the GFS and ECMWF indicate that the tropical moisture will linger into early next week and have continued with elevated pops throughout the remainder of the extended forecast.
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Chattanooga Airport, TN 86 67 86 68 / 30 20 40 20 Knoxville McGhee Tyson Airport, TN 82 64 86 66 / 20 10 30 10 Oak Ridge, TN 82 64 86 66 / 20 10 30 10 Tri Cities Airport, TN 80 59 81 61 / 20 10 20 10
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