Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Louisville Kentucky
104 PM EDT Fri Jul 25 2014
..updated aviation discussion...
issued at 1034 am EDT Fri Jul 25 2014
Areas of fog are starting to mix out across the southeastern part of
the County Warning Area. However, expansive fog/low stratus continues over much of
southeastern and eastern Kentucky. Partly to mostly sunny skies were
noted across southern Indiana and central Kentucky this morning. We
will see some high cirrus blowoff from upstream convection across
eastern Iowa and NE Missouri. This convection is still moving off to
the southeast, however, latest model simulations still have this
complex dying off before reaching our region. The high level cirrus
may impact afternoon temperatures across our northwest and western
sections this afternoon. Afternoon highs in the lower to middle 80s
still look attainable at this time.
Short term (now through saturday)...
issued at 257 am EDT Fri Jul 25 2014
High pressure moving from the Ohio Valley to the mid-Atlantic coast
will keep our skies mostly clear and our winds light today and
tonight. We'll be a little warmer today than we were yesterday, with
highs in the lower and middle 80s, but dew points will still only
be in the 55 to 60 degree range so we should still be able to enjoy
a comfortable Summer afternoon. Lows tonight will be in the 60s.
On Saturday a cold front will begin to approach from the northwest.
Thunderstorms will be ongoing from Friday night into Saturday to our
north from Illinois through Indiana to Ohio. Down here, sounding
progs show capping and a fair amount of dry air in the profile, so
any storm activity in the lmk County Warning Area is expected to remain scattered.
The best chance for storms will be north of I-64 towards Saturday
Heat and humidity will return on Saturday with afternoon highs
around 90 and heat index readings in the mid 90s.
Long term (saturday night through thursday)...
issued at 334 am EDT Fri Jul 25 2014
Saturday night through Sunday night:
An active start to the long-term period as thunderstorm activity
lights up across southern Indiana and into northern Kentucky
overnight Saturday. Starting from the top down, height falls will
begin across the region ahead of a well-advertised Stout upper
trough digging down from Canada and the Great Lakes. Mid-level lapse
rates will be decent in the overnight period, exceeding 6.5 degrees
c/km and both 0-3km and 0-6km shear will be on the increase with
35-40+ kts., Particularly across southern Indiana. Closer to the
surface, low pressure initially over the plains states will have the
ability to ride the periphery of exiting high pressure, eventually
phasing with a low digging down from the Great Lakes, thanks to the
approaching trough. A cold front associated with the low will be
crossing the forecast area by late Sunday but its slow approach will
provide aid as a lifting mechanism. Looking at the total atmosphere,
pwats are depicted by the 00z GFS as flirting with the 2 inch mark,
which is close to 2 Standard deviations above climo. Last but
certainly not least, there will be instability to work with in the
overnight period as low-level MUCAPE surpasses 1000 j/kg, again
concentrated over the northern portions of the forecast area. Bottom
line: combining the ingredients for copious amounts of moisture,
good instability, and lifting, there is a good chance of seeing an
mesoscale convective system develop Saturday night and track across southern in and northern
Kentucky before dying out as it loses these key features for continued
maintenance. The primary threats with any stronger storms that
develop late Saturday through early Sunday will be heavy to locally
torrential rainfall and strong to possibly severe winds. While the
rain will certainly be welcome for many, runoff and quick hitting
downpours, along with the potential for training, could produce some
issues. Stay tuned as the time approaches and finer details come
For Sunday, thunderstorm chances look to continue with the focus
shifting from the north to the east as the day progresses. A bit
less confident in the details as it will likely depend on any early
morning activity and remnant boundaries and cloud cover. Regardless,
chances for storms will continue ahead of the front, currently
looking to cross central Kentucky late Sunday.
Temperatures will be rather warm overnight Saturday, ranging from
the low to mid 70s but actually not too far from normal for this
time of year. Highs on Sunday are currently forecast to range from
the upper 80s in the north to the mid 90s in the south but cloud
cover and precip could throw a wrench into this.
Monday through Thursday night:
Once the upper-level trough takes hold of the Ohio Valley, a
significant airmass change will take place, allowing for much cooler
than normal temperatures and clearing skies dominating much of next
week. However, with lower-level moisture looking to linger around
Monday and potentially even into early Tuesday, can not rule out
showers from developing, particularly in the Bluegrass region. This
pattern looks to be similar to what was experienced last week with
the lingering low clouds and light precip. From Tuesday Onward, high
pressure will be settling in, bringing a rather pleasant weather
regime in the middle of next week. Look for temperatures to struggle
to reach 80 Monday through Wednesday, and possibly exceeding that
mark on Thursday. Lows will respond accordingly, ranging from the
mid to upper 50s Monday night and Tuesday night, then near or
slightly above 60 degrees on subsequent nights.
Aviation (18z taf update)...
issued at 103 PM EDT Fri Jul 25 2014
High pressure drifting eastward out of the Ohio Valley will continue
to keep winds at the terminals light and variable this afternoon.
Some scattered cu along with some high level cirrus from convection
to the northwest will drift through the region this afternoon.
However, this will not affect aviation activities. Light winds and
VFR conditions are expected during the overnight period and through
much of the day on Saturday.