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

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000 FXUS64 KMRX 211900 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 300 PM EDT Sun May 21 2017 .SHORT TERM (This Afternoon through Monday)...
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Widespread showers continue this afternoon across NE TN and SW VA as a shortwave trough moves through the Southern Appalachians. Rainfall totals today were a little lighter than forecast with amounts generally under an inch with radar estimates of up to 1.5 inches in portions of Clay and Cherokee counties in North Carolina. So far, there have been no reports of flooding and do not anticipate any issues at this time. The cold front is still back to the west of Nashville and there are some showers developing along the Plateau ahead of the front. Expect this activity will be more scattered and have chance PoPs for much of the evening and overnight hours. SBCAPE values are currently up into the 1000-1500 J/Kg range across middle TN with more stable values to the east from the widespread cloud cover today. Expect a few rumbles of thunder will be possible this afternoon and into the overnight but expect any chance for a strong to marginally severe storm is low. Due to this, went ahead and updated the HWO to include no hazards. Even with the recent rainfall, 3-hr FFG values are still in excess of 2 inches across most of the area. The cold front will make swift progress to the east tonight as shortwave trough rotates around the broader low across the Great Lakes and Ohio River Valley. PoPs will decrease from west to east late tonight. The front looks to get held up along the mountains tomorrow with lingering showers in the higher elevations on Monday. Noticeably cooler and drier air is forecast on Monday. Dewpoints will drop down into the upper 40s to mid 50s with highs in the mid to upper 70s across most valley locations. .LONG TERM (Monday night through Saturday)... Unfortunately models are still not in great agreement with how to handle the weather systems in the early to middle parts of the work week. They do agree that a surface low will slide up the stalled out frontal boundary and will bring precipitation wherever that low decides to traverse. However there is some discrepancy on the strength and especially the timing of the low as it moves through. GFS wants to move a quick moving low through that brings rain to the Southern Appalachian Mountains and the Eastern Tennessee Valley, the NAM wants to move the same low through but spread precipitation all the way west into Middle Tennessee, while the ECMWF has a very weak low but keeps the boundary closer to us so we see a longer period of sustained rainfall. So at this point confidence is very low with how much rain and how long rain will last through the middle of the week. Have gone with at least low end precipitation chances through the middle of the week, but will hopefully be able to trim chances as the models come into better agreement. After taking a break from precipitation another system will move through the second half of the work week. Depending on the track of the upper level low in this system we could get wrap around precipitation all the way into Thursday night, although it would likely be pretty light QPF-wise. Temperatures will then begin to rebound at the end of the week before a shortwave zips through and looks to bring precipitation chances to the region over the weekend.
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Chattanooga Airport, TN 64 79 61 76 / 40 10 30 30 Knoxville McGhee Tyson Airport, TN 64 78 58 75 / 50 10 20 30 Oak Ridge, TN 63 79 60 77 / 40 10 20 30 Tri Cities Airport, TN 61 76 57 75 / 50 20 30 30
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