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

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000 FXUS64 KMRX 212010 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 310 PM EST Sat Jan 21 2017 .SHORT TERM (Tonight and Tomorrow)...
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We have entered into a fairly active weather pattern that looks to be with us through most of the week. With it we have the threat of severe weather...mainly hail and some damaging winds tonight and Sunday. Then we have a heavy rainfall potential and possible flooding issues by Sunday night and Monday. Finally we have chances of frozen pcpn at elevations above 3500 ft by Monday morning. We gradually dry out by mid week before next system brings pcpn, possibly in the form of snow, back into the area by Friday morning into the weekend. First in a series of shortwaves is now moving NE out of the area. Water vapor indicating some drying behind this first shortwave that HRRR picks up on keeping POPs to minimum until overnight tonight when the next shortwave begins to push across the area. With it, gradually increasing POPs from SW to NE overnight. With enough instability, MUCAPE in excess of 1000 J/kg, and ample SFC-3 km shear (50+ kts at KCHA) that threat of severe weather, mainly winds, hail will be possible in the overnight hours. Then, by tomorrow afternoon, rather strong middle level low, currently over Colorado/New Mexico will drive eastward toward Northern Mississippi and Northern Alabama. Associated surface low looks to move NE across middle TN during the day with warm frontal boundary just reaching into out southern counties as this low begins to rapidly occlude. With some elevated instability in place, threat of severe hail with localized damaging winds are possible across portions of our area mainly S of I-40. Similarly, PW values exceeding an inch throughout the area, will help to push rainfall totals in excess of 1 inch across the southern half of the area. .LONG TERM (Sunday Night through Saturday)... As the parent surface low center further occludes Sunday into Monday, cold air aloft will bring increase snow chances, particularly to elevations above 3500 ft where those areas could see up to a few inches by late Monday morning. Additionally, deformation zone on back side of the upper low will likely keep pcpn bands extending across SW Virginia, NE Tennessee and central to northern portions of the Appalachian mountains which is expected to likely add another Guidance suggests ample moisture with this system particularly Sunday and Monday could result in some possible flooding and flash flooding issues as 3 day QPF totals look to be near 2 inches across much of the valley and Plateau while the Appalachians could see 3 inches, with localized totals of over 3.5 inches. On a positive note, pcpn totals for the exiting system look to be less than earlier forecasted at 0.5 inches or less across the area. In lieu of issuing any flood watch, will opt to update the Hydrological Outlook while continuing to highlight the heavy rain potential for the Appalachians and Gatlinburg burn scar. Short period of mid week drying precedes the next system moving in the area for Friday and Saturday with some prospect of frozen precipitation possible.
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Chattanooga Airport, TN 54 62 47 50 / 80 90 70 50 Knoxville McGhee Tyson Airport, TN 53 66 48 52 / 80 80 90 80 Oak Ridge, TN 53 64 48 53 / 70 80 90 70 Tri Cities Airport, TN 50 65 48 53 / 50 80 100 90
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