Scientific Forecaster Discussion
fxus64 kohx 251119
Area forecast discussion
National Weather Service Nashville Tennessee
619 am CDT Thu may 25 2017
for 12z aviation discussion.
Upper closed low continues to churn overhead and provide enough
lift for some isolated showers this morning. Models have some
backside showers moving into the northeast zones this morning as
the upper low moves to the northeast. A welcomed drier period will
move in for Friday as shortwave ridging moves in behind the upper
low. This weekend, however, looks to be wet with strong to severe
thunderstorms possible Saturday and Sunday.
Looking at Saturday, models have shortwave activity over the Ohio
River valley and a cold front moving southward from the Great
Plains. The GFS and NAM are roughly lining up, while the European model (ecmwf) and
Canadian are providing different solutions. They are much more
wet over the mid state but have been trending drier little by
little with each New Run. Looking at model soundings, the GFS and
NAM look to be quite dry around the area Saturday due to a
substantial cap in the afternoon preventing any convection from
tapping the large amounts of MUCAPE around 2000-3500 j/kg. The 00z
European model (ecmwf) did come in drier than the previous run, so its possible
that it will line up more with the GFS/NAM solution. If that
occurs, Saturday will be mainly dry with the convection mainly
staying north of the area.
Saturday night into Sunday morning looks to have a line of
convection moving in from the northwest with the initial shortwave
activity aloft. These storms look to have severe potential with
MUCAPE between 1000-2000 j/kg depending on which model you look at,
and 0-6km shear values around 40 to 50 knots. The atmosphere will
remain in the warm sector thanks to the cold front being further
to the northwest and moving through the area later in the
overnight hours Sunday into Monday morning, so MUCAPE values look
to climb again on Sunday. Shear values will remain high as well,
so another round of severe storms may be possible during the
afternoon and even into the overnight hours Monday morning ahead
of the cold front.
Models have slowed down a bit, so showers may be lingering around
Monday morning and early afternoon. After that, solutions begin to
differ a bit with isolated to scattered chances for convection
during the week, depending on the model. A series of upper troughs
pass through the Great Lakes region, and look to try to drag a few
boundaries southward toward the area, so mainly went with
consensus for pops next week for now. As of right now, nothing
substantial stands out between the models, so there will be some
dry periods mixed in with some afternoon precip potential during
the work week next week.
12z taf discussion.
Mainly VFR conditions today, but there will be a couple of hours
of MVFR cigs at all 3 terminals this morning as the backside of
this current system affects the mid-state. Confidence on timing
of reduced categories is low due to the cloud shield skimming all
3 terminals, so there could be an up and down morning before all 3
terminals clear out late this afternoon.
Winds will pick up this morning as westerly gusts of 20-23 kts
blow across all of middle Tennessee. Winds will relax as we approach 00z