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

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000 FXUS64 KMRX 201855 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 255 PM EDT Thu Jul 20 2017 .SHORT TERM (Tonight and Friday)...
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There will be very little change to the general weather pattern over the next 24 hours as a large midlevel high pressure ridge will remain to our west. However, the ridge does drift slightly to the south tomorrow, which allows a weak vort max and a surface trough to track into our NE sections. Forecast soundings show weak capping across the area, but the forcing may be enough to produce scattered showers and thunderstorms in SW VA and NE TN in the afternoon, while the rest of the area will likely remain capped. Temperatures will continue to be well above normal, and with slightly higher dewpoints expected tomorrow, heat index values may touch 100 in the southern Valley for a couple hours. .LONG TERM (Friday night through Wednesday)... High pressure will weaken and slowly move to the SE through the weekend...while a low pressure and assocaited weak frontal boundary strengthens over the Great Lakes and moves towards the southern Appalachians. Winds will shift to out of the SW and W...bringing a slow increase in moisture Saturday through Monday. Scattered showers and thunderstorms are possible Saturday and Sunday afternoon...with a greater increase in coverage across the area for Sunday. Instabitlies are between 3000 - 4000 J/kg...with weak winds throughout the atmosphere. PW values around around the 90th percentile for this time of year. Any showers and storms that develop Saturday and Sunday have a greater threat for heavy rainfall and damaging winds as the main threat. Monday through Monday night...the weak boundary will move through the area in the afternoon...allowing scattered showers and thunderstorms to begin developing in the morning and increase in coverage through the afternoon. Instabilities will remain around 3000 J/kg...PW values in the 90th percentile...and winds fairly uniform but weak throughout the atmosphere. Severe weather is not expected with these storms...though heavy rainfall and localized flooding remain a large threat. Showers and thunderstorms should weaken and decrease in coverage through the night Monday. Tuesday and Wednesday...slightly cooler temperatures will remain through both days as the flow shifts to out of the NW. Isolated showers and thunderstorms are possible Tuesday afternoon...but mainly in the higher elevations of east TN...southern TN Valley and SW NC. Wednesday should remain dry and mostly clear as high pressure sets up.
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Chattanooga Airport, TN 75 95 75 93 / 10 20 10 30 Knoxville McGhee Tyson Airport, TN 73 93 73 92 / 10 20 10 30 Oak Ridge, TN 74 93 73 92 / 10 20 10 30 Tri Cities Airport, TN 67 91 70 91 / 10 40 20 30
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ DGS/JW is the U.S. government's official web portal to all federal, state and local government web resources and services.