Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
FXUS64 KMRX 300754
Area Forecast Discussion
National Weather Service Morristown TN
354 AM EDT Thu Mar 30 2017
.Short Term (Today)...Warm southerly winds will increase low level
moisture and convective instability across the region, ahead of an
approaching storm system that will impact the area tonight. Expect
showers and perhaps a few thunderstorms to develop and move into the
Plateau and southern valley in the afternoon, although the more
widespread activity will not arrive until tonight. As winds increase
today, strong mountain wave winds will develop during the late
afternoon and continue overnight.
.LONG TERM (Tonight through Wednesday)...A negative upper trough
will move across the Ohio and Tennessee Valleys tonight and early
Friday morning. A series of jet streaks exiting the upper trough
will produce divergence aloft over the region late today through
early Friday morning. These circulation around this jets will
enhance the fronto-genetic forcing overnight.
Models show the airmass becoming moderately unstable with MLCAPES
of 1000-1500 J/Kg with Hail CAPEs of 150-300 J/kg. Shear/SR
Helicity does become quite strong with favorable values for
rotating updrafts with incoming storms. LCL heights lower
overnight as well. Models show a 850mb jet of 40-50kts overnight. Given
these parameters, isolated tornadoes are a concern with the main
threat being damaging winds up to 60 mph and hail of 0.5 to 1
SPC has placed essentially the entire area under a slight risk of
severe thundestorms, even though the western/southern half of the
area seems to have the greatest threat.
Given the low-level jet and favorable thermodynamic profile,
strong winds are expected across the mountains and foothills for
tonight. Have issued a wind advisory for these locations.
For Friday, after early more showers (thunder northeast), models
show plenty of boundary layer moisture remaining keep the area
under mostly cloudy sky. Enough low-level instability to keep
chance showers going, especially for the orographic lift areas.
For this weekend, upper and surface ridging will produce a dry and
warm Saturday and Sunday.
Next strong upper trough will move into the area for early next
week. This system also has strong upper jet forcing with potential
of widespread showers and scattered storms.
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 78 56 71 49 / 40 80 20 0
Knoxville McGhee Tyson Airport, TN 79 55 67 47 / 10 80 60 10
Oak Ridge, TN 79 55 68 46 / 10 90 50 10
Tri Cities Airport, TN 73 54 67 44 / 10 90 70 20
TN...Wind Advisory from 5 PM this afternoon to 8 AM EDT Friday for
Blount Smoky Mountains-Cocke Smoky Mountains-Johnson-Sevier
Smoky Mountains-Southeast Carter-Southeast Greene-Southeast