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

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000 FXUS64 KMRX 220714 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 314 AM EDT Tue May 22 2018 .SHORT TERM (Today and Tonight)...
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With recent rainfall...patchy fog will be possible towards sunrise...mainly over northern locations. Otherwise...will continue to see a moist air mass in place Tuesday morning allowing for a few showers to develop across the region. However...by this afternoon...a weak/broad frontal boundary/trough axis will slide into the area. This will generate a weakly unstable atmosphere and allow a marginally organized band of convection to develop and move through the Southern Appalachian Region late this afternoon/early evening. With the deep moisture in place...the main concern will be heavy rains. This may allow for localized urban flooding. .LONG TERM (Wednesday through Monday)...A frontal boundary will be located near the Southern Appalachians to start the long-term period with a shortwave trough racing across the Mid-Atlantic and Northeastern U.S. Drier air will advect into the forecast area behind the departing cold front with PW values in the 0.9-1.2 inch range. These values are near to slightly below average for late May. Model soundings also indicates significant dry air in the mid to upper levels. Due to this, have only mentioned around 20- 30 pops with values decreasing from northwest to southeast throughout the day. An upper level ridge will build in by Wednesday night behind the departing trough bringing an end to any precipitation chances. The boundary will be stalled to the south of the area on Thursday. Moisture values remain similar to Wednesday and only expect a small chance for a shower or storm across the southern tier of counties into the mountains. Overall, expect most locations will stay dry with the upper level ridge axis just to the west. The ridge will weaken and the axis will shift to the east on Friday. Model soundings indicate that moisture will increase with southerly to southwesterly flow. PW values will increase to near the 90th percentile for late May. Therefore, have 40-50 pops for Friday afternoon with more scattered showers and storms possible. The GFS and ECMWF both diverge a good bit over the weekend with the system to the south in the Gulf of Mexico. Regardless, moisture will increase across the area with the weakening ridge and continued southerly flow throughout the atmosphere. Model soundings indicate PW values near 2 inches over the weekend into early next week and have gone with 50-70 pops throughout much of the remainder of the forecast period. Depending upon the track of the system, there could be some flooding issues with the prolonged rainfall. With the increased moisture content, lapse rates will be near moist adiabatic and do not anticipate any strong to severe storms with the showers and storms over the weekend into early next week. Temperatures on Wednesday and Thursday will be in the mid 80s for most valley locations with the ridge in place. With rain chances increasing over the weekend and into early next week, expect highs will be a bit cooler in the upper 70s and low 80s.
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&& .PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN 82 67 87 66 / 70 50 30 10 Knoxville McGhee Tyson Airport, TN 81 65 86 64 / 70 50 20 0 Oak Ridge, TN 81 65 86 63 / 70 40 20 0 Tri Cities Airport, TN 80 63 82 58 / 60 50 30 10
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ MJB/MA

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