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

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000 FXUS64 KMRX 191916 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 316 PM EDT Fri May 19 2017 .SHORT TERM (This Afternoon through Saturday)...
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Current water vapor imagery and RAP upper air analysis indicate that the shortwave trough from earlier is now pushing eastward into Virginia. Current radar imagery indicates that most of the convection is on the east side of the Appalachian mountains in Virginia and North Carolina. For the remainder of the afternoon, expect a few isolated to scattered diurnally driven showers and storms will be possible and have continued with 20-40 PoPs across most of the area. As for the bigger picture, a closed low is spinning across Colorado with an enhanced risk for severe storms across portions of the Southern Plains. At the surface, a stationary boundary stretches from a surface low in Oklahoma to the Ohio River Valley. For tonight, expect most of the convection will begin to decrease due to the lack of diurnal heating with mild overnight lows in the 60s. The upper level trough currently across Colorado will eject to the northeast on Saturday across the Central Plains. Closer to home, a ridge will amplify across the Southeastern U.S. The ridge axis will be across the area throughout much of the day with PW values dropping down into the 1.0-1.2 inches. These values are around the 50th-75th percentile for mid-May. Due to the anticyclonic flow aloft, decreased PoPs during the day on Saturday with highs in the mid to upper 80s. The ridge does begin to break down later in the day as a shortwave trough rotates around the periphery of the ridge. Therefore, increased PoPs late in the day with best chances across the Southern Plateau counties. .LONG TERM (Saturday night through Thursday)... Precipitation chances really start to ramp up as we move into Saturday night/Sunday. As the front approaches the wind fields start to turn more southerly and increase in speed, bringing in in more moisture to our area. On Saturday evening/night there is moderate CAPE available for storms to work with, but not much in the way of mid/low level shear. So we could see a few storms pulse up quickly and threaten to produce strong gusty winds or some hail, but widespread severe weather is not anticipated on Saturday (nor Sunday). As the front actually gets closer the precipitation should become more widespread with the best chances for rain all week coming on Sunday/Sunday night. Will have to monitor precipitation amounts on Sunday as PWAT values of around 1.5" or higher, putting us into the 90th percentile for this time of year. Some places could see several rounds of thunderstorms run over them leading to localized flooding. Once we get into the work week things quiet down as the precipitation will exit off to the east throughout the day and temperatures are expected to be around normal. There will only be a brief lull in precipitation before a second system zips through the area. This one should move through quickly and only bring a round of rain on Tuesday night/Wednesday. It will also cool temperatures down, with highs on Thursday struggling to make it to the 70`s. Quiet weather is then expected through the rest of the work week.
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Chattanooga Airport, TN 68 89 69 80 / 0 60 70 80 Knoxville McGhee Tyson Airport, TN 67 89 67 78 / 10 20 60 80 Oak Ridge, TN 67 89 68 79 / 10 20 60 80 Tri Cities Airport, TN 62 87 63 78 / 20 50 30 70
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