Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 011742
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
142 PM EDT Wed Jul 1 2015
Issued at 142 PM EDT Wed Jul 1 2015
Showers, with a few embedded rumbles of thunder, have developed and
have been crossing the region over the past few hours. There are
several potential triggers for additional convection in the warm,
muggy atmosphere this afternoon including an east-west surface
boundary draped from southern Ohio to central Illinois, differential
heating boundaries as debris canopy clouds from the overnight MCS
thin, and a weak upper level disturbance near Paducah affect the
area. One can also detect general mesoscale circulation in radar
data with the activity currently over southern Indiana and also the
activity that has crossed south central Kentucky.
Though there is instability available, it appears that the main
threat with storms will be locally torrential rain rather than
widespread severe. Lebanon-Springfield Airport reported 1/4SM in a
very heavy downpour as storms moved through that location earlier.
Mesoanalysis shows PWATs pooling to two inches west of I-65. Local
interactions between storms and their outflows will help to produce
any stronger storms, which would be capable of gusty winds as the
.SHORT TERM (Now through Thursday)...
Issued at 305 AM EDT Wed Jul 1 2015
Northwest flow aloft continues to allow disturbances to cross the
region, sparking enhanced storm threats. One such system is over
eastern NE and forcing new storms to form now over western Missouri.
Another is over central North Dakota. Expect the first system to
take a turn southward into Arkansas, whereas the second system
should move to Indiana/Ohio later this afternoon. At the same time,
a healthy slug of moisture will surge in from the west today. Thus
expecting another round of thunderstorms to develop, starting by
late this morning in our southwest and into the rest of the region
by late this afternoon.
That moisture will linger with us for the next few days, so rain
chances will be good each day. A stalled frontal boundary in the
region will provide the focus for storm development each day, as
well as further disturbances in the flow aloft. The primary focus
for rains in this set of models is over our southwest, which
according to RFC flash flood guidance can handle the most rain. Thus
decided against a flash flood watch for now. Cannot rule out one
going out soon, as the focus right now for the long term period
shifts northward, into areas that have seen a little more rain of
With the initial round of storms today, especially any that form on
the leading edge of that surge, we may see some stronger cores with
hail as wet bulb zeroes start out below 10 kft, just ahead of the
moist surge. That threat should end quickly with the increased
moisture and warmer air coming in though. After that think the
threat for severe weather ends and we will have to deal more with
heavy rain in the storms.
The increased moisture will mean diurnal temperatures having a
smaller range, and highs below normal.
.LONG TERM (Thursday night through Tuesday)...
Issued at 303 AM EDT Wed Jul 01 2015
Thursday Night - Friday Night...
Shallow NW flow at the base of an eastern CONUS trough will rule the
upper pattern to end the work week. Meanwhile, a surface boundary
looks to be stalled across central KY. Deeper moisture should pool
into the area both along the boundary, and ahead of disturbance
dropping through the flow over the upper Midwest. This disturbance
then passes Friday night. This will result in scattered to numerous
showers and storms, with locally heavy rainfall possible in the high
precipitable water airmass. Best focus looks to be across central
and southern KY along and south of the boundary. Lows Thursday night
will be in the mid and upper 60s, with highs on Friday in the upper
70s to around 80. Lows on Friday night will again be in the mid and
Saturday - Sunday Night...
The main trough axis looks to shift NE through the weekend, however
a secondary weak upper low will meander from the southern Plains to
the mid Mississippi River Valley. Meanwhile, stalled frontal
boundary looks to remain near our southern CWA. This should continue
to allow for iso-scattered coverage of showers and storms, mainly
each afternoon/evening. Will likely try to hit more on the diurnal
minimum through the overnight weekend hours, resulting in lower
chance. Main focus continues to be across KY, with southern IN
possibly staying completely dry. Temperatures should continue to be
around 80 and into the lower 80s for highs. Lows should remain
mostly in the upper 60s.
Monday - Tuesday...
Flat upper ridging from the southern CONUS looks to pump up a bit to
start the new work week. This will shift the main belt of westerlies
furthern north across the upper Midwest and lower Great Lakes,
however a weak reflection of the surface boundary may still hang
around our CWA. Think coverage of showers and storms will be mainly
in the widely scatttered to scattered range (30-50%) given less
influence from individual disturbances passing through the flow.
We`ll see an increase and heat/humidity with the ridging becoming
more established so continued to reflect this with warmer highs more
solidly into the 80s, and lows around the 70 mark.
.AVIATION (18Z TAF Update)...
Issued at 102 PM EDT Wed Jul 1 2015
Given various mesoscale boundaries, upper level disturbances, a
surface front, and an approaching low pressure system, shower and
thunderstorm chances will be with us throughout the TAF period. In
the TAFs, rather than having 24-36 hours of VCTS, attempted to
indicate the most likely times for thunder this afternoon in the
unstable atmosphere, and late tonight as possible redevelopment to
our northwest moves in. Kept VCSH for the rest of the time to convey
the thought of pervasive convection chances.
Synoptic scale winds will generally come in from the southwest
around 5 to 10 knots, though may become chaotic and stronger in