Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/01/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 934 PM EDT Wed May 31 2023

.Forecast Update...
Issued at 934 PM EDT Wed May 31 2023

We will add patchy fog tonight for portions of central Indiana. It
is most likely where it rained this afternoon resulting in moist
ground, and particularly in low-lying/sheltered areas where
radiative processes will be maximized once remnant convective clouds
diminish. Cold pools cooled temperatures more rapidly than would`ve
otherwise happened in the background environment giving a head start
on the radiative cooling process tonight. We will also adjust hourly
temperatures to account for this, though it`s difficult in these
scenarios after isolated/scattered convection to convey much spatial
detail. Some areas were not influenced by convective outflow and the
original temperature forecast is still good. Thus, some temperature
error over the next several hours can be expected for some areas.
Otherwise, as cold pools become less of an issue, wind should become
more uniformly east-southeasterly and light given MSLP pattern.
Other forecast elements look fine.

&&

.Short Term...(This evening through Thursday)
Issued at 127 PM EDT Wed May 31 2023

Cumulus continues to build across central Indiana this afternoon as
the boundary layer destabilizes. Temperatures have risen into the
mid 80s with dew points sitting around 60 degrees. This has led to
SBCAPE values between 1500-2000 J/Kg with mid-level dry air leading
to a few pockets of 800-1000 J/kg DCAPE. The first blips on radar
are noted near Bloomington, and convective initiation is expected
to begin shortly across the remainder of the CWA. Storms are
expected to be widely scattered, and focused on areas of mesoscale
convergence. Some hints of this can be seen via convergent
convective rolls on satellite, especially across central portions of
the area.

ACARS soundings out of IND show little to almost no vertical shear.
In fact, sfc-6km bulk shear is only 9kts. As such, little storm-
scale organization is expected. Convective elements will be pulse-
like in nature, growing quickly in the unstable environment before
collapsing in upon themselves. Enough DCAPE exists that some briefly
gusty winds are possible within any of these collapsing
thunderstorms. Cell motion will generally be the mean wind which
will be out of the south to south-southeast today. Should any
outflow boundaries or cold pools become established, then some
additional storms may preferentially fire up along them. CAPE
centered upon the hail growth zone (-10 to -30c) may allow for some
small hail in the more robust cells. The lack of shear / fast flow
aloft will limit hydrometeors size sorting and preclude the risk for
large hail. Therefore, severe weather is not expected this
afternoon.

Given the pulse-like nature of today`s convection, rapid
stabilization near and after sunset will lead to any lingering
storms quickly diminishing. Dry conditions are expected into tonight
with some residual mid-level cloud cover / convective debris. Even
this should diminish with time during the overnight. Broad ridging
and associated surface high pressure to our northeast will lead to
generally southerly flow at the surface through tonight. Some drier
air may begin to work its way in by Thursday morning as flow gains
an increasing easterly component.

Overnight lows should stay warm, with readings dropping into the low
to mid 60s for most locations. With dew points in the 60s as well
along with light winds, it should feel a little muggy compared to
the previous few nights. Some patchy fog is not out of the question
near river valleys and places that received any rainfall.

Pop up shower and thunderstorm chances are possible once again on
Thursday, but slightly drier air advecting from the east should
reduce chances and coverage compared to today. The best chance of
seeing one of these would be in the western half of our CWA where
lingering moisture may be present. Temperatures should climb to near
90 increasing subsidence and drier air raise convective temps and
increase mixing depth.

&&

.Long Term...(Thursday night through Wednesday)
Issued at 239 PM EDT Wed May 31 2023

Thursday Night Through Sunday.

Generally dry and quiet conditions are expected for the late week
and weekend with only small chances for pulse thunderstorms during
peak heating. A broad and weak ridge of high pressure will be in
place by through the early weekend as a low pressure system slowly
sinks in from the northeast. The center of the ridge will gradually
be moving to the west early weekend as a response to the approaching
low which will allow for a return to the northeasterly surface winds
and a gradual drop in afternoon dewpoints

This will create slightly elevated fire weather conditions with
afternoon minRH around 20-25 percent although the winds will be
light enough to limit the overall threat. With the arrival of drier
air, coverage of afternoon showers and storms will also gradually
lessen into the weekend with PWATs near the 25th percentile and a
PBL of almost 10kft on Saturday. This dry airmass and plenty of
sunshine will also allow for a continuation of 90 degree days
through Saturday.

Monday Through Wednesday.

The pattern tries to change early next week as the upper level flow
becomes more northerly as the aforementioned low pressure system
begins to move back to the east. Gulf moisture remains locked to the
far southern states with dry air and little to no precipitation
chances. A reprieve from the heat looks likely though with the more
northerly surface flow advecting cooler air into the area which
should keep temperatures limited to the low 80s by Wednesday.

&&

.Aviation...(00Z TAF Issuance)
Issued at 650 PM EDT Wed May 31 2023

Impacts:

* No noteworthy impacts

Discussion:

Convective outflow remains as convection continues to weaken. With
time, the broader flow will influence the winds and light uniformly
southeasterly winds are expected through the night and into
tomorrow. Patchy fog is possible, especially where rain occurred and
cooled the environment, but current expectations are for it to be
localized and only a low probability to impact TAF sites.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

Update...BRB
Short Term...Eckhoff
Long Term...White
Aviation...BRB



Area Forecast Discussion

National Weather Service Louisville KY

 950 PM EDT Wed May 31 2023

.Forecast Update...
Issued at 950 PM EDT Wed May 31 2023

The last bit of showers are finally exiting our CWA at this hour,
which are located down in Simpson and Logan County and quickly
dissipating. The only main tweak needed to the forecast was to
expand mention of patchy fog a bit more across central KY for the
pre-dawn hours tomorrow. Give the stagnant winds tonight, mild temps
in the 60s, and some partial skycover clearing, we should see some
patchy fog develop where rain occurred earlier this afternoon and
evening. Main time frame for fog will be between 08-12z tomorrow
morning. Otherwise, the rest of the forecast is on track for the
overnight.

&&

.Short Term...(This afternoon through tonight)
Issued at 252 PM EDT Wed May 31 2023

Synopsis...A weak mesoscale convergence zone has settled in the
western half of the forecast area amid recurving flow at the edge of
the surface high over the Northeast and gravity wave action moving
north-to-south from previous convection over the central Plains. By
tomorrow, the mid-level ridge and associated surface high will start
retrograding to the Great Lakes which in turn will advect a lower PW
airmass through the Bluegrass. Temperatures will stay above average.

This Afternoon...Satellite imagery already shows an agitated cumulus
field over the region with some mixed-phase clouds trying to break
through the freezing level. Latest SDF ACARS is validating SBCAPE
between 1000-1500 j/kg, steep low-level shear, and a disorganized
vertical wind profile characterized by weak shear. Therefore, the
forecast reasoning is unchanged as the main convective mode today
will be short-lived cellular convection with the main weather
hazards being heavy rainfall, lightning, and sub-severe gusty winds.
The best convective coverage is expected along and west of I-65
(more isolated elsewhere) between 20-01Z.

Tonight....The diurnally-driven showers and storms will be declining
after sunset, although a few lingering low-topped, highly-efficient
showers might linger close to 1/2Z. Rest of the night will feature
quite weather, clearing skies, and lowering temperatures as lows
drop to the low 60s. HREF guidance and cross-over temperatures are
indicating a possibility of fog after 1/6Z with the most likely
areas being the ones that receive rainfall this afternoon and river
valleys to the south and southeast.

Thursday...Isolated to widely scattered convection will develop once
again, but the spatial coverage will be more restricted to the
westernmost part of the CWA as dry air filters from the east. Also,
the HREF model suite is indicating an earlier convective initiation
time, so the official forecast is reflecting the best window for
showers/storms between mid-morning and early afternoon with activity
pushing out to the east after 1/21Z. Furthermore, slightly similar
environmental conditions will promote the same convective mode as
today; however, dry-air entrainment could further limit initiation.

.Long Term...(Thursday through Tuesday)
Issued at 235 PM EDT Wed May 31 2023

Typical early summer weather is expected for most of the forecast
period as modest sfc and upper ridging remain largely in control.
Friday and Saturday look "hot and dusty" with a light and subtly
downslope easterly flow. These will be the two hottest days, with a
better than 50-50 chance of reaching 90 degrees for the first time
this season. Fri-Sat will also be the two driest days for most, with
no mention of precip even though a very isolated afternoon pop-up
can`t be completely ruled out.

We won`t be as well capped Sunday or Monday as a closed upper low
retrogrades SSW from Quebec to the mid-Atlantic coast. Confidence in
the finer details remains limited, but for now we will carry a
diurnal ~20% POP each day. Increasing cloud cover and the slightly
weaker ridging will limit max temps a bit, but we will still be
above normal.

Tue-Wed look a little more unsettled with vort lobes pinwheeling
around the closed low and trying to push a backdoor cold front into
the Ohio Valley. Look for slightly greater T-storm coverage and
further moderation in daily max temps.

&&

.Aviation...(00Z TAF Issuance)
Issued at 720 PM EDT Wed May 31 2023

Isolated showers and outflow boundaries are still ongoing at the
issuance of this TAF package, though overall coverage has been
diminishing within the last hour or so. Cloud debris from earlier
storms may linger into tonight, though VFR conditions are
anticipated for most of the TAF period. Patchy fog appears possible
in the predawn hours tomorrow, especially in areas that received
rain today. Included brief periods of 6SM vis at BWG/HNB/LEX for BR
tomorrow morning, but confidence on seeing impacts below VFR are low
at this time. Otherwise, tomorrow should feature much of the same,
with afternoon diurnal cu and isolated to scattered showers and
storms.


&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Update...CJP
Short Term...ALL
Long Term...RAS
Aviation...CJP