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

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000 FXUS64 KMRX 201911 AAA AFDMRX Area Forecast Discussion...UPDATED National Weather Service Morristown TN 311 PM EDT Mon Mar 20 2017 UPDATED FOR LONG TERM DISCUSSION .SHORT TERM (Today and Tonight)...
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A 850-700 mb shortwave trough over MI/WI/IA is progged to track SE across the Ohio Valley today and reach the central Appalachians this evening. Ahead of it, a 850 mb theta-e gradient/warm front will cross the area this morning, and associated isentropic lift will bring broken clouds for most of the morning and early afternoon. Warm advection and partial sun today should bring temps into the 60s in most spots, with lower 70s near CHA. The best lift and moisture with the trough stays north of our area closer to the upper jet, but we will see increasing moisture and instability through the day as the theta-e axis shifts south into KY/SW VA. Precip chances will rise across northern areas this evening but will keep coverage scattered due to limited moisture and fairly weak lift in our area - the categorical POPs of the GFS MOS seem overdone. Elevated instability will be present and warrant a mention of isolated thunderstorms tonight. .LONG TERM (Tuesday Night through Monday)... Front will be slow to progress Tuesday night becoming nearly stationary across the area. Ample deep moisture, model PWs at about the 90th percentile, coupled with potential training of storms along the boundary and we could see some isolated heavy downpours during the overnight. Current flash flood guidance across much of the area is at roughly 1.5 inches in an hour and 2 to 2.5 inches over three hours. Latest model QPF guidance seems to be indicating highest pcpn amounts on the order of an inch or so, therefore would expect mainly localized flooding issues to be possible in this event. Also, south of the front, over the southern third of East Tennessee and SW Virginia, instability Tuesday night remains a bit elevated with CAPE values of 500-750 J/kg. This, along with sufficient shear could lead to a few organized thunderstorms and some possible training thunderstorms across this area, mainly during the first half of the overnight. After some residual POPs from the slowly moving front on Wednesday, we then dry out across the area into Saturday. At the same time, we will once again start to warm above seasonal normals for the weekend and beyond. Next frontal system moves into the area Saturday increasing POPs through Sunday before pushing east of the area on Monday. With warming temperatures, some model indicated instability, and increasing shear with the approaching system on Saturday, prospects of some strong thunderstorms are possible Saturday and Sunday with this next system.
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&& .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 55 77 54 64 / 10 60 70 30 Knoxville McGhee Tyson Airport, TN 49 72 48 58 / 30 70 80 20 Oak Ridge, TN 52 72 49 61 / 30 60 80 20 Tri Cities Airport, TN 49 68 45 57 / 50 50 70 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ MJB/EJH

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