Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/10/21
Area Forecast Discussion
National Weather Service Louisville KY
911 PM EDT Mon Aug 9 2021
.Forecast Update...
Issued at 911 PM EDT Mon Aug 9 2021
Earlier storms have dissipated with the setting of the sun and
increasing convective inhibition. There are a few factors in play
that suggest we could still see some widely scattered shower and
thunderstorm redevelopment overnight, including a possible small
disturbance that sparked convection in the St Louis area earlier and
is heading eastward...possible outflow from severe convection to our
north if it can push far enough south...and a modest increase in the
low level jet and MUCAPE above a stable surface layer. The current
forecast accounts for this possibility.
&&
.Short Term...(This evening through Tuesday)
Issued at 306 PM EDT Mon Aug 9 2021
Current radar shows a line of storms pushing east of our CWA with
scattered showers and storms redeveloping behind it. Earlier
convection has severely limited afternoon heating for southern
Indiana and a large portion of central KY. As a result, a well
defined temperature gradient can be observed via KY Mesonet
observations with southern KY reporting in the upper 80s to low 90s
and central KY in the low 70s. So far, convection has remained sub-
severe with the highest wind gusts in the 30-35mph range associated
with the aforementioned line of storms.
Moving into the late afternoon and early evening hours, convective
debris will continue to have stabilizing effect over much of the
CWA. Focus going forward will be on southern KY where heating has
occurred unabated. Latest mesoanalysis also confirms southern KY as
having the most instability with CAPE values upwards of 3500 J/kg
with a sharp gradient dropping values northward into central KY.
Shear values remain weak, so continue to think pulse storms with
locally strong gusts and torrential heavy rain as the main concerns.
AMDAR soundings out of SDF and BNA also reveal near moist adiabatic
lapse rates in the mid levels. Overall, expect scattered showers and
thunderstorms to continue through sunset with the strongest storm
potential across southern KY.
Hi-res models do hint at some isolated showers during the overnight
hours as the upper trough slowly exits the region. Lows will remain
mild in the low 70s.
The area will see another chance of diurnally induced afternoon
showers and storms as the area remains under SW flow in a warm,
moist environment characterized by large CAPE (3000 J/kg) and weak
shear (<20kt) resulting in pulse storms with heavy rain potential.
Soundings show some pockets of dry air aloft throughout the
afternoon that have bumped DCAPE values up to around 1000 J/kg
roughly along and north of the OH River. As a result, SPC has
included portions of north central KY and southern Indiana within a
Slight Risk for wind potential.
Highs tomorrow will reach into the upper 80s to low 90s. Dew points
in the mid 70s will result in oppressive heat indices in the upper
90s and low 100s, especially across our western counties. These
values do not warrant a Heat Advisory at this time for our area, but
will continue to monitor the potential.
.Long Term...(Tuesday night through Monday)
Issued at 305 PM EDT Mon Aug 9 2021
Warm and unsettled summer pattern looks to continue through the end
of the week before a cold front moving through brings somewhat
cooler and drier weather for the end of the period. The area will
remain in relatively weak quasi-zonal flow aloft as the main belt of
westerlies stays well to our north with the base of a broad upper
level trough sinking across the northern-tier of the CONUS. In the
lower-levels, expansive area of high pressure will be anchored over
the Southeast CONUS. This will help to keep us in deep southwesterly
flow through a majority of the period with warm, moist air being
pumped into the region. Daily chances of scattered showers and
storms will be possible in this setup, with the highest PoPs
occurring Friday into Saturday as a surface cold front approaches and
drops south through the area. Model soundings indicate afternoon
environments each day will be characterized by moderate to strong
instability, high PWATs (generally between 1.75-2.0 inches) and weak
shear. As such, expect locally gusty winds, torrential rainfall and
frequent lightning to be the main threats within any stronger storms.
Before the cold front moves through for the weekend, hot
temperatures will also continue to be a main focus of the forecast
as highs top out in the lower to mid 90s Wednesday - Friday. Heat
indices will approach 100 degrees each day, with areas along and
west of I-65 standing the best chance of seeing 100-105 heat
indices. Overnight lows will not offer much in the way of relief
either as low temperatures remain in the lower to mid 70s.
For the weekend, expect drier air to begin filtering in from the
north as high pressure builds in across the Great Lakes and OH
Valley region, with dewpoints dropping into the lower to mid 60s.
Similarly, afternoon temperatures will drop near/slightly below
climatological normals, topping out in the mid to upper 80s Saturday
and Sunday. May see some lingering PoPs mainly over the southern
portion of the area into the weekend as the frontal boundary looks
to stall out across the TN Valley, although there is low confidence
in exact positioning of the front at this time.
&&
.Aviation...(00Z TAF Issuance)
Issued at 732 PM EDT Mon Aug 9 2021
IMPACTS:
-Brief period of MVFR CIG around LEX to start the forecast
-Mainly VFR this evening into overnight
-Chc. of isolated rain/storms from SDF/LEX overnight
-Chc. of isolated/scattered storms tomorrow afternoon
DISCUSSION: Satellite imagery as well as radar continue to show
improving conditions across our forecast area this evening.
Lingering MVFR at LEX as of writing the discussion so decided to
keep this around for the first hour of the forecast. Rest of the
overnight looks like VFR conditions for TAF sites. The only concern
overnight is the possible development of storms from SDF to LEX
between 07-09z. Few of the Hi-res models pick up on this scattered
activity north and along I-64 east of I-65. Went with vicinity
thunder for LEX/SDF.
Winds will increase tomorrow out of the southwest around 10kt with
possible gusts to near 18kt. We are also anticipating another
afternoon and evening of isolated to scattered showers/storms. These
could once again produce MVFR/IFR conditions in and around the
storms as gusty winds and heavy rain are the main threat with any
activity tomorrow.
CONFIDENCE:
Low confidence on storm development for SDF/LEX overnight. Medium
confidence on development of storms tomorrow afternoon.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Update...13
Short Term...CG
Long Term...JML
Aviation...BTN
With the busy first 36 hours or so, previous forecast discussion
will remain unchanged.
KMD
Wednesday through Sunday...
Continued warm and humid conditions with afternoon heat index
values possibly surpassing 100F are expected on Wednesday and
Thursday. The environment looks to become quite capped on
Wednesday as WAA quickly commences behind Tuesday night`s
potential convection. With weak deep-layer cyclonic flow still
influencing the area and the expected conditionally unstable
airmass, will maintain chance PoPs through the day Wednesday. A
weak boundary/wave embedded in the broader mid- level flow will
trigger potential convection Wednesday, with low chances of
thunderstorms continuing into Thursday with a slightly drier and
weakly capped profile.
Cooler and less-humid conditions will arrive on Friday and
continue through the upcoming weekend as high pressure builds into
the area from the north.
Kluber
&&
.AVIATION...
For the 00Z TAFs...
652 PM CDT
The concerns for the Chicago area airports include:
* TSRA this evening for the Chicago metro terminals
* Threat for a round of TSRA with wind Tuesday afternoon with
higher confidence in evening TSRA
Thunderstorms with a history of rotation and tornadoes now over
the far northwest suburbs will be monitored closely for impacts to
ORD and DPA. Current trajectory of the two storms of interest
would bring the brunt of them north of MDW, though can`t rule out
southward progression. On Tuesday, looking at another day of gusty
south- southwest winds with questions on how much capping there
is. A few high resolution models bring a linear complex of gusty
TS through the area in the early to mid afternoon and can`t rule
out this scenario. Confidence is currently highest in evening TS,
which also could have strong and gusty winds. For now, opted for a
PROB30 for the afternoon potential and prevailing TS on Tuesday
evening.
Castro
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-
ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-
ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108...noon
Tuesday to 7 PM Tuesday.
IN...Heat Advisory...INZ001-INZ002-INZ010-INZ011-INZ019...noon
Tuesday to 7 PM Tuesday.
LM...None.
&&
$$
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