Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/16/21
Area Forecast Discussion
National Weather Service Louisville KY
929 PM EDT Thu Jul 15 2021
Issued at 929 PM EDT Thu Jul 15 2021
Convection has diminished considerably in the last hour across much
of the region. Only remnant activity is is over our far northern
counties of southern Indiana where residual outflow dominated
showers continue to press east. These showers should continue to
diminish due to the loss of instability and subsequent stabilization
of the boundary layer.
In general, we expect a lull in the precipitation over the region
for the next several hour. After midnight, convection will probably
re-enter our northwest CWA as ongoing convection out across central
MO/IL works east southeast.
Current forecast has this well in hand for the overnight period.
Will be making just a few tweaks and adjustments to the grids and
have an updated forecast package out by 945 PM EDT.
Issued at 538 PM EDT Thu Jul 15 2021
Couple of areas of strong convection continue to push eastward
across central Kentucky this afternoon. First batch was located up
over the eastern Bluegrass region (Harrison/Bourbon/Nicholas
counties). These storms remain sub-severe with wind gusts of 30-35
MPH, heavy rainfall, and frequent lightning. Earlier storms moved
through this region and these storms trained over it. For that
reason, we have small Flood Advisory in place for the next few
hours. Most likely will see some minor impacts with this rainfall
with creeks and streams going to bankfull along with poor drainage
areas flooding. As seen in recent days, much of this runoff will
drain off fairly quick after the storms move out of the area.
Localized rainfall rates of 1-2 in/hr will be possible.
Second area of storms seems to be on the increase. These storms
were located from near Lawrenceburg and extend southward to near
Campbellsville. Storms are moving through an environment of 2000-
2500 J/Kg of MLCAPE. A small corridor of 900-1000 J/Kg of DCAPE is
just downstream of this activity. Effective shear remains very weak
with values of less than 20kts. Nonetheless, robust updrafts keep
ongoing feeding off the localized area of instability here. Current
thinking is that strongest storms will remain on the north end of
this cluster and will affect portions of Anderson/Mercer/Washington
Counties over the next hour. Should the storms hold together, they
could affect the Lexington Metro. However, earlier convective
activity may have eliminated a bit of the instability over that way.
Main threats with the Anderson/Washington/Mercer activity will be
wind gusts of 30-40 MPH, heavy rainfall, frequent lightning, and a
small risk of sub-severe hail. A special weather statement is in
effect for this cluster of storms, but will continue to monitor
trends over the next hour.
.Short Term...(This evening through Friday)
Issued at 310 PM EDT Thu Jul 15 2021
Regional radar mosaic shows very isolated showers popping up across
the region as sfc temperatures exceed convective temperatures. KY
Mesonet obs show temps mostly in the upper 80s, and the SDF heat
island in full effect with 91F so far. Model soundings seem to have
a good handle on current conditions compared to latest AMDAR
sounding data from SDF, which continues to show a strong 600mb
inversion overhead. Expect this mid-level warm layer to persist
though this afternoon and evening, but should eventually erode by
the overnight hours.
For the rest of this afternoon, expect to continue to see isolated
shallow showers. Will keep a low chance PoP in before 00z for the
entire CWA, but most folks will stay dry. Could have a few rumbles
of thunder mixed in, but the inversion should be enough to cap tall
vertical cloud growth.
For tonight, upper shortwave trough currently across Kansas will
shift eastward across Missouri, resulting in the southeastern US
ridge to weaken and push further east. A secondary sfc low will
develop across Missouri by tomorrow morning and track to the NE
along the I-70 corridor. As a result, tightening low level pressure
gradient will develop a LLJ, with 850mb winds expected to be 20-
35kts. As the SW LLJ noses into our region, scattered convection
will be moving in from Illinois ahead of the slow moving sfc frontal
boundary tonight and into tomorrow.
SPC holds a Day 2 Marginal Risk across our northern half of the CWA
for tomorrow, which seems well placed. CAMs are hinting at some
possible organized convection tomorrow afternoon and evening, most
likely across souther IN under the 850mb jet core. Temperatures
should breach ConvT again, with highs primarily in the upper 80s and
low 90s. Instability could reach 1000-2000 J/kg of MLCAPE during
peak daytime heating, and effective bulk shear values between 20-
30kts. With PWATs also expected to be 2.10+", torrential rain rates
with any training or slow moving storms would create some localized
flash flooding hazards. Organized convection could also pose a
threat of damaging winds and frequent lightning.
.Long Term...(Friday night through Thursday)
Issued at 240 PM EDT Thu Jul 15 2021
Friday Evening through Sunday...By Friday evening, the surface
boundary will be stretched SW-NE across central IL/IN and into the
lower Great Lakes with ongoing convection out ahead of the boundary,
affecting our area in southern Indiana and central KY. The OH
Valley`s position between Atlantic ridging and the upper trough will
result in deep SW flow with PWATs around 2.00 inches. GEFS/GFS IVT
continues to advertise moisture maxima remaining to our north, but
model soundings continue to show saturated columns with tall, skinny
CAPE profiles and high RH throughout the low to mid levels. Expect
to see some efficient rainfall with this activity with localized
flooding concerns being the main hazard of concern given parallel
nature of steering flow to boundary positioning. Mitigating factors
will include dry antecedent conditions and progressive nature of
individual cells. Will just have to watch for training. And given
the weak shear and moderate to high CAPE, expect low-end severe
chances with pulse storm modes most likely. Diurnal enhancements
will result in most rainfall accumulation taking place Friday
evening and again Saturday afternoon. And as the boundary drops
south through central KY on Sunday, expect to see lower PoPs across
Monday and beyond...Models continue to show Omega Block over the
western and central CONUS, which will place the OH Valley under NW
flow. Expect mostly dry conditions throughout this period.
Thickness values slowly increase through the week so expect high
temps in the mid 80s to increase to upper 80s by Thursday.
.Aviation...(00Z TAF Issuance)
Issued at 730 PM EDT Thu Jul 15 2021
VFR conditions will remain into this evening.
Models are showing some showers along a surface trough ahead of the
front starting around 6Z at HNB and sinking southeast to LEX around
11Z. BWG should not be affected by these showers overnight. Most of
tomorrow should remain dry until later tomorrow evening when the
surface front pushes southward and along with it, a line of showers
and storms. Timing confidence on this is low, so PROB30s are not
mentioned in this TAF cycle.