Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 281031
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
631 AM EDT Tue Oct 28 2014
...Updated Aviation Discussion...
Issued at 630 AM EDT Tue Oct 28 2014
Band of showers with embedded thunderstorms is tracking east
toward the region a couple of hours than previously forecast, so
have adjusted POPs for the morning hours. Otherwise, no
significant changes at this point.
.SHORT TERM (Now through Wednesday)...
Issued at 300 AM EDT Tue Oct 28 2014
...Strong Thunderstorms Possible This Afternoon Across Central
and Eastern Kentucky...
Early morning water vapor imagery combined with 500 mb heights shows
an upper level low across the northern Plains with a shortwave trough
extending through the mid-Mississippi River Valley. Downstream
ridging exists across the Ohio River Valley. At the surface, strong
southwesterly flow continues with mild late October temperatures.
Plenty of high clouds spilling over the region with the cold front
stretched back from near Milwaukee to St. Louis. Showers and
thunderstorms are ongoing with this front.
28.00z guidance in excellent agreement showing this band of
precipitation to cross the region west to east today, beginning in
the late morning hours across southern Indiana, then reaching
central and southern Kentucky by early afternoon, and finally making
a push into the Bluegrass and Cumberland regions mid to late
afternoon. Looking at the hi-res models, most are in similar
agreement with the deterministic models. Overall, confidence is
high that locations will get a 3-6 hour period of showers as the
front passes. Precipitation chances were increased to 90-100 percent.
Main forecast challenge and impact to the public is with the
strong/severe thunderstorm potential. As the main mid/upper level
energy advances eastward, the deep layer shear environment looks to
increase to nearly 40 kts, depicted by the NAM. The better shear
environment lies across northern and eastern KY and further
northeast, tied closer to the main upper level forcing. Shear
profiles are unidirectional as the flow from the surface to 6 km is
largely southwesterly. With sufficient daytime heating /highs in the
middle 70s/ MUCAPE is progged to be between 500-1000 J/kg. Forecast
soundings show the instability profile to be skinny as lapse rates
are not overly impressive. If cloud cover becomes extensive ahead of
the front, limiting daytime heating, then instability may be limited
which could really hamper the strength of the storms. Nonetheless,
the combination of the shear environment, marginal instability and
the passage during peak heating supports the possibility for strong
thunderstorms east of I-65 and especially for the Bluegrass region.
Loosely organized multicells / bowing line segments make damaging
winds the main impact. The timing looks to be early afternoon to
late afternoon, as the loss of daytime heating should weaken storms
as they lift to the east/northeast.
Cold air advection takes over in the wake of the frontal passage as
850 mb temperatures fall to around +1C by Wednesday afternoon. Lows
tonight will be noticeably cooler /15 to nearly 20 degree change/
and highs on Wednesday look to only top out around 60, or around 5
degrees below late October normals, despite a sunny to mostly sunny
.LONG TERM (Wednesday Night through Monday)...
Issued at 315 AM EDT Tue Oct 28 2014
...Frost/Freeze Potential Increasing for this Weekend...
We`ll start the long term period in a cool zonal flow on Wed
night/Thurs leading to dry conditions and temps slightly below
normal. We should start the day Thurs in the upper 30s and lower
40s with highs reaching the mid 50s to around 60 Thurs afternoon.
Thurs night we`ll see a quick hitting weak upper level trough which
looks to bring a small chance for a shower to the area. A more
potent upper trough or some models depict an upper low will dive
into the Ohio Valley for Fri bringing another small chance for rain
and noticeably colder air. The 0Z ECMWF is the strongest with this
upper low, QPF, and cold air surge. Will consider it an outlier for
now, but can`t completely rule out a stronger soln. Did decrease
high temps for Friday a bit going off of a compromise between model
solns. As a result, forecast high temps for Friday are currently in
the mid to upper 50s but confidence is low.
Frost and perhaps a freeze is looking likely for the weekend as a
cold Canadian high dives into the Ohio Valley. Fri night/Sat
morning we`ll be under strong CAA which should help drive temps down
below freezing. The sfc high will become more centered over the
Ohio Valley Sat night/Sun morning lending to good rad cooling and
likelihood of temps falling below the freezing mark. Have forecast
temps both Sat and Sun mornings in the upper 20s and lower 30s.
Portions of the region stand a good chance at a killing freeze this
weekend. Sat high temps will be limited to the upper 40s and lower
The forecast will remain dry Sat through the first part of Monday
with sfc high pressure in control and upper level ridging moving
into the Midwest. We will see a warm up as the ridge moves in. Sun
high temps should reach the low to mid 50s. As return flow
increases Monday, we`ll see a bigger warm up into the low to mid 60s.
The next front looks to arrive Mon night or Tuesday bringing showers
and possibly some storms to the area.
.AVIATION (12Z TAF Update)...
Updated at 628 AM EDT Tue Oct 28 2014
LLWS threat will subside by 12z, especially since surface winds have
remained up around 10kts this morning and will increase as mixing
picks up. Otherwise, plan on band of showers with embedded
thunderstorms to march east toward the TAF sites later this morning
and afternoon. Timing wise, band is arriving a bit faster than
previously forecast, so bumped up arrival groups. Also, plenty of
lightning observed upstream and with instability remaining in place
or increasing today, have added thunder mention to all TAF sites.
There are some MVFR ceilings and visibility restrictions occurring as
well, so have included a tempo group for the period most likely to
see those restrictions.
Precipitation looks to end west to east closer to 00z, first at SDF
then likely lingering at BWG and LEX early evening. Winds will
become westerly and then northwesterly toward the end of the TAF
period as cold air advection takes over in the wake of the frontal
passage. Broken ceilings will scatter out before midnight.