Scientific Forecaster Discussion
fxus64 kohx 261100
Area forecast discussion
National Weather Service Nashville Tennessee
600 am CDT Fri may 26 2017
for 12z aviation discussion.
Quiet night so far across the mid state as upper ridging builds
into the area. This will keep the region dry today before The
Rounds of showers and thunderstorms this weekend. Models have not
changed very much from yesterday's solutions, and continue to show
a decent cap in place on Saturday during the day with 2 rounds of
showers and thunderstorms possible Saturday night, another round
during the day Sunday, and the last round with the cold front
Sunday night into Monday morning.
A few models such as the European model (ecmwf) are showing some precip along the
Kentucky/Tennessee border Saturday morning, but the GFS shows dry conditions.
The NAM looks to split those solutions and keeps the activity just
north of the area. With the instability and shear in place, will
not rule out some strong to severe storms Saturday morning should
models get on board with the early morning convection. Looking at
all model solutions, Saturday afternoon consensus has been to
mainly to stay dry with the substantial cap in place, however
potential exists for a few showers and thunderstorms to develop
before better chances arrive from the northwest in the evening.
The GFS has now started to show a few storms in the afternoon
Saturday per quantitative precipitation forecast output, and the afternoon cap that was showing up
on yesterday's runs has weakened enough that some showers and
storms may pop up in the late afternoon. Also some short term
models are showing some quantitative precipitation forecast as well along the Tennessee/Kentucky border as
early as 21z. However, model consensus is to have ongoing
convection from Kentucky to move into the region during the evening
Saturday from the northwest and progress through the mid state
during the late evening/overnight hours. MUCAPE values are around
1000-2500 j/kg, with 0-6km shear values around 40-50 knots. Model
soundings are showing strong mid level lapse rates early in the
event, so large hail will be a threat, but the main threat looks
to be damaging winds with the strong shear values and large cape.
Tornado threat appears low attm with poor hodographs, weak low
level shear, as well as weak low level helicity. The NAM is the
most bullish with low level shear, but for now is the only model
showing strong low level signals supporting isolated tornadoes.
Precipitable water values are high for most model soundings, and with the
potential for a few waves of precip/training of stronger storms,
flooding will also be a threat into Sunday morning.
Models have different solutions for the daytime Sunday, however
agree on having scattered precip chances across the area. Better
chances will arrive ahead of the front late Sunday through Monday
mid day. Potential does exist for some strong to severe storms
during the day with models hinting at some shortwave activity
aloft Sunday mid day, especially on the GFS. The mid state will
still be in the warm sector with the warm front far north of the
area, so plenty of instability and shear will be in place should
stronger convection get going in the afternoon. The better threat
will be with the front, however, which looks to start to move into
the northwest just before 06z Monday. Cape does look to fall off
overnight as the front moves through the area, so best threat of
severe storms will be during the evening and early overnight hours
just ahead of the front for the northwest half of the area.
Showers and storms will continue overnight as the front moves
through the mid state, and looks to be completely through the area
by the afternoon Monday. Therefore, showers and storms will be
possible for the southeast half of the area through the early
afternoon on Memorial Day.
Even though the upper trough lingers over the Great Lakes Tuesday,
most of the precip will remain to the north, so kept the area dry.
Next chance of precip will be on Wednesday and Thursday as both
the GFS and European model (ecmwf) put some quantitative precipitation forecast over the area. Upper level
solutions are different, however, so just have slight chance in
for now. Models try to line up for the remainder of the week even
though upper level solutions are slightly off, so have chance pops
in from later on Thursday through Saturday morning.
12z taf discussion.
VFR. Scattered/broken low/mid level clouds expected at times.
Light south winds will increase and become gusty out of the
southwest later this morning at all airports.