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

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000 FXUS64 KMRX 230815 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 415 AM EDT Mon Oct 23 2017 .SHORT TERM (Today and Tonight)...
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A deepening upper level low will swing rapidly northeast from the Mid Mississippi and Ohio Valley region today on its way through the Eastern Great Lakes by the end of the short term period. A strong southerly flow ahead of the low is pulling a broad swath of moist air out of the Gulf of Mexico and this moisture is being lifted ahead of the upper trough and surface cold front. Therefore, categorical pops were used for showers today and there may be just enough instability for a thunderstorm across the southern third of the forecast area. Slightly drier air will flow into the region behind the cold front from west to east through the day allowing the more persistent rain to become a little lighter and more scattered in nature. The chance for showers will continue tonight ahead of a reinforcing cold front building southeast through the strong cyclonic flow present within the Eastern U.S. mean trough. Much drier air behind this front should bring an end to the light precipitation across most of the forecast area by daybreak Tuesday. High temperatures will be tricky today due to the fact that the lowest readings around sunrise are elevated in the strong southerly flow regime but cold air advection will be filling in behind the initial front relatively quickly today. Tonight`s lows will drop into the middle and upper 40s. .LONG TERM (Tuesday through Sunday)...The cold front and lead shortwave trough will be to the east of the area to start the long-term forecast. A highly amplified pattern will being to take shape on Tuesday as another trough dives out of the Mid- Mississippi River Valley into the Tennessee River Valley. The atmosphere will be dry behind the front with PW values ranging from around 0.4-0.6 inches, which is around the 10th-25th percentile for late October. Overall, there is sufficient lift for precipitation but the lack of moisture will really limit any showers to the higher elevations with dry conditions elsewhere. Cold air advection will drop high temperatures into the upper 50s to mid 60s across most valley locations on Tuesday. Cold air advection Tuesday night into Wednesday morning will drop overnight lows into the mid 30s to low 40s. Expect the pressure gradient will remain elevated enough for some light winds overnight Tuesday night and should prevent any widespread frost from forming. However, there could be some patchy frost in the sheltered valley areas Wednesday morning, especially for Northeast Tennessee and Southwest Virginia. The trough axis will shift to the east on Wednesday with northwesterly flow aloft. Wednesday will be the coldest day of the forecast period with highs only making it into the 50s across most valley locations. By Wednesday night, surface high pressure builds into the region. Ideal radiational cooling conditions will setup Wednesday night into Thursday morning with lows in the 30s. Due to this, expect a widespread frost on Thursday morning. For now, will mention this in the HWO. A shortwave ridge moves in on Thursday with dry conditions and moderating temperatures. The GFS and ECMWF are both in good agreement with a highly amplified pattern again over the weekend with a deep trough across the Eastern CONUS. The models differ slightly on the timing of the system but both suggest that the weekend will be cool and wet. For now, have 30- 50 PoPs throughout much of the weekend with below normal temperatures.
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&& .POINT TEMPS/POPS...
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Chattanooga Airport, TN 68 48 63 41 / 100 10 0 0 Knoxville McGhee Tyson Airport, TN 68 48 61 40 / 90 10 10 10 Oak Ridge, TN 67 47 61 41 / 100 20 10 0 Tri Cities Airport, TN 68 46 61 36 / 100 60 20 10
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...Wind Advisory until 3 PM EDT this afternoon for Johnson- Northwest Carter-Southeast Carter-Unicoi. High Wind Warning until 1 PM EDT this afternoon for Blount Smoky Mountains-Cocke Smoky Mountains-Sevier Smoky Mountains- Southeast Greene-Southeast Monroe. VA...None. && $$ 20/MA

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