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

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FXUS64 KMRX 210715

Area Forecast Discussion
National Weather Service Morristown TN
315 AM EDT Sun Jul 21 2019

.SHORT TERM...(Today and Tonight)...
Another warm, muggy night reflected in the temperatures across the
area early this morning. Most locations are in the lower to mid
70s and dewpoints are nearly identical. Patchy fog has developed
possibly with a few areas with locally dense fog reducing
visibilities, however, the fog is not widespread.

Some early morning convection is likely with current regional
radar showing a lone storm developing just south of Roanoke, VA
and a few light reflectivities showing up across the southern TN
Valley. Expect this to flare up a little over the next several
hours and persist into the morning and gradually increase in
coverage through the afternoon. Cloud cover from the showers will
cause daytime temperatures to be slightly cooler than previous
days. As such, don`t expect heat index values to be nearly as hot.

Storms that develop today will have the capability of producing
locally heavy rainfall and gusty winds. Steering flow is weak so
storms will move slowly with lots of low level moisture to work

Tonight, shower activity should slowly diminish by late evening
with another surge of developing showers possible towards sunrise.

.LONG TERM...(Sunday through Saturday)...
The bottom line of the extended period will continue to be the big
pattern change early week with much below normal temperatures for
mid to late week. Weak mid to upper level trough axis (what is
currently assisting in thunderstorm development this afternoon) is
expected to be oriented SW/NE across the region Sunday night into
Monday morning which may enhance a few showers and thunderstorms. As
a stronger shortwave dives southeast across the upper Mississippi
Valley, this will result in height falls across the Ohio Valley and
Southern Appalachians. A seasonably anomalous surface cold front
will move southeast with this trough and enhance boundary layer
forcing and precipitation coverage. Guidance is in good agreement in
indicating a prefrontal trough moving west to east across the region
on Monday afternoon with widespread scattered convection likely.
Instability will be marginal at 500 to 1500 J/Kg of MLCAPE late
Monday and early Tuesday evening with effective deep layer shear
approaching 20 kt. A few thunderstorms could be strong with gusty
winds if instability is on the higher end of guidance, but the main
risk of severe weather will remain to our north where shear and
instability is expected to be maximized.

The surface cold front is expected to be across western Kentucky
near the Ohio River by 0z Tuesday and this will move into our area
by late Monday night or early Tuesday morning with additional
periods of rain and thunderstorms along and ahead of this front. PW
values will be between 1.9 and 2.2 inches late Monday and Monday
night, so heavy rain rates will be a possibility with the stronger
thunderstorms and result in localized flash flooding.

The front moves east of the area on Tuesday with decreasing PoPs
from west to east. A few rain showers may linger across the
mountains on Tuesday afternoon with some weak orographic enhancement
and shallow post frontal moisture. Drier air and high pressure moves
in Tuesday night and Wednesday with dry weather dominating through
the end of the week. NAEFS forecast anomalies show 850mb
temperatures being around the 1st percentile of climatology on
Wednesday which is a strong signal for below normal temperatures.
For this reason, expect temperatures to be near 10 to 15 degrees
below normal on Wednesday. Overnight temperatures will also be about
10 to 15 degrees below normal with the dry airmass in place.
Temperatures rebound closer to normal by the end of the week as the
airmass begins to moderate and upper ridging increases across the
south/central parts of the country.


Chattanooga Airport, TN             87  73  85  70 /  30  30  70  60
Knoxville McGhee Tyson Airport, TN  87  73  83  68 /  30  40  80  70
Oak Ridge, TN                       87  72  82  67 /  40  40  80  80
Tri Cities Airport, TN              88  70  81  65 /  40  40  80  70




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