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

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FXUS64 KMRX 200854

Area Forecast Discussion
National Weather Service Morristown TN
354 AM EST Fri Jan 20 2017

.SHORT TERM /Today and Tonight/...
A negatively tilting upper-trough over the central Plains has
pushed a weak cold front and a broad area of moderate to locally
heavy showers over the eastern Tennessee Valley. The last of this
activity is currently exiting the Cumberland Plateau and is moving
into the I-75 corridor of the central/southern Valleys as of 0830Z.
Over the next 3-4 hours, this activity will spread NE across the
region, before exiting into NC/VA after 12-13Z.

Drier air will quickly shift into the region today as an upper-
level ridge axis shifts into the area by midday. Low stratus will
be slow to dissipate this morning, thanks to residual moisture
remaining trapped in the boundary layer. However, by 18z, drier air
will begin to help create some breaks in the clouds over much of
the Valley. This heating, along with some southerly winds will
help to push highs well into the mid to upper 60s in most spots. A
partly cloudy sky will linger through the evening and most of the
night, before another round of clouds increase late tonight ahead
of an approaching warm front from the SW. Another round of showers
is possible across the far south late tonight, but most of the
shower and thunderstorm activity will hold off until late Saturday

.LONG TERM /Saturday through Thursday/...
An active weekend is shaping up in the weather department across
the Southern Appalachians. Saturday should start off dry, but
clouds will increase throughout the morning hours as gulf moisture
begins to stream into the area. By afternoon, showers are likely
across much of the area with PWAT values increasing to near 1.0
inch. Enough instability will be in place across the southern half
of the forecast area to spark some afternoon thunderstorms. There
is a chance that a few storms could strengthen and become severe,
especially during the late afternoon and evening hours as a warm
front approaches the area and shear increases. Model soundings at
KCHA show a backed wind profile at the surface, strong 0-1 km speed
shear, good directional shear in the 0-3 km layer (indicative by
the looped hodograph depicted on the 00z GFS run). This shear,
combined with a NE advancing warm front could result in a very
isolated tornado threat across the S. Plateau/Valley Saturday
afternoon/evening. Will make a mention in the HWO.

An upper level closed low will rotate into the southeast US on
Sunday, bringing another chance for thunderstorms and heavy rain. At
this point, the center of the low is progged to cross to our
southeast. However, we will need to keep a close eye on this track.
If the center of the low shifts just slightly further north, this
would put portions of our forecast area in position for another
round of strong to severe storms Sunday night. Rain chances will
continue into Monday night as the low tracks across the Carolinas
and continues to sling moisture back into our area. Weak ridging
builds in for Tuesday into Wednesday, bringing a brief period of
drier conditions. From here, model solutions diverge, but the
general consensus is another cold front will bring some showers as
it pushes through the region Wednesday into Thursday. Have carried
widespread slight chance to chance PoPs for this period.

For most of the extended period, mild temperatures will prevail,
with highs in the 50s and 60s. Cooler air may finally return to the
area for the second half of next week following the
Wednesday/Thursday frontal passage.


Chattanooga Airport, TN             69  54  69  55 /  20  20  70  80
Knoxville McGhee Tyson Airport, TN  66  54  68  52 /  30  10  60  70
Oak Ridge, TN                       66  54  67  52 /  30  10  60  70
Tri Cities Airport, TN              65  49  65  50 /  50  10  40  60




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