Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Nashville Tennessee
715 PM CST Friday Dec 19 2014
00z ohx sounding shows atmosphere across middle Tennessee remains
fairly dry with a precipitable water of 0.49 inches...although column has
moistened somewhat since 12z. Radar imagery shows a large area of
rain across central MS/al...but surface observation indicate no precipitation is
reaching the ground north of a Tupelo to Huntsville line due to
drier atmosphere up this way. In addition...all latest 12z/18z
model guidance including the European model (ecmwf)/GFS/NAM/hrrr keeps majority of
measurable precipitation south and east of the middle state tonight.
Thus have gone ahead and lowered probability of precipitation significantly with only
slight chance north and chance probability of precipitation south/plateau. Forecast
soundings indicate any precipitation that falls would likely start as or
transition to snow quickly...but will keep rain/snow mix mention
for the evening hours and over southern zones after midnight.
Cannot completely rule out some very light snow accums in the
upper Cumberland overnight but looks very unlikely at this point.
Tweaked low temperatures and dewpoints up slightly over northern areas
due to latest observation and cloud cover...but rest of forecast looks OK
at this time.
Previous discussion... /issued 620 PM CST Friday Dec 19 2014/
Update...for 00z aviation forecast
system down along Gulf Coast will will spread rain northward tonight
with middle state on northern fringe...not confident we are going to
see much over north half especially at Clarksville and Nashville.
Latest laps soundings along with a quick glance at the 00z ohx
radiosonde observation showing quite a bit of dry air in lower troposphere that will
need to moisten up before precipitation will hit the ground. Taking into
account wet bulbing think profile will cool down below zero
celsius except in boundary layer and near surface where temperatures will
likely hover around freezing. This said we may not see any precipitation
at Clarksville or Nashville with Crossville having the better
chance of seeing a light rain and snow mix 06z. System exits
quickly after 12z Saturday.