Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/17/22

Area Forecast Discussion...UPDATED

National Weather Service Indianapolis IN

 1122 PM EDT Sat Jul 16 2022

.Mesoscale Update...
Issued at 1122 PM EDT Sat Jul 16 2022

A cluster of thunderstorms has developed over east-central Illinois
into west-central Indiana. A couple of cells initially reached
intensity sufficient for small hail up to penny size, but such
intensity has been brief. The best chance of strong to possibly
severe wind gusts would be if a more robust cold pool can form and a
more organized cluster or line segment evolved. We are watching for
signs of more organized cold pool development with the most intense
cells in Vigo County, which could then sustain a strong wind threat
eastward across portions of central Indiana. Otherwise, brief small
hail and gusty winds can be expected with the stronger convective
cores, and frequent lightning will be the primary convective hazard.
Individual cells should move eastward at around 25 mph. If a more
organized cold pool system develops, preferential development along
the cold pool flanks where the modest low-level jet interacts may
cause a slight rightward (southward) deviation.

&&

.Forecast Update...
Issued at 855 PM EDT Sat Jul 16 2022

Shallow convection has been noted for the couple of hours across the
northwest portion of central Indiana. This has mostly been suppressed
by dry subsident capping layer evident on ACARS aircraft sounding
from Indianapolis. However, as midlevel height falls occur signaling
increased large scale ascent, convection will more readily be
able to grow and sustain. Its greatest concentration at least
initially should be near and north of a stalled weakly baroclinic
surface front which is now just northwest of Williamsport. The last
couple of radar volumes show deeper convection just east of Fowler
and just north of Williamsport. The trend toward more successful
convective attempts and an increase in coverage and intensity should
continue into late evening and overnight. Further south, we can
see weak echos and towering cumulus just west of the NWS
Indianapolis office, but these may still struggle to
develop/organize for the next couple of hours at least.

Kinematic and thermodynamic environments are not particularly
supportive of severe storms, as described in the previous mesoscale
discussion. Nevertheless, remaining instability over a still
somewhat mixed PBL could support strong wind gusts. Steep theta-e
lapse rates could subsequently support fairly robust cold pool
development when/if more intense and numerous convection can
develop. Clusters would would move east-southeastward at around
20-30 mph but may tend to propagate rightward as modest low-level
jet and associated surge of higher moisture/theta-e strengthens.
The spatial details are still uncertain with regards of how much
upstream convection can form in Illinois and how the convective
evolution will occur. But, a more concentrated convective cluster
in central Illinois would be central Indiana`s best chance of more
widespread convection toward and just after midnight. Otherwise,
as the main compact shortwave trough (now over Minnesota)
approaches early Sunday, more widespread showers and thunderstorms
are likely.

A quick look at the latest CAM QPF and HREF probability match
mean seem to signal highest amounts across southern Indiana into
Sunday. This is conditional on placement of mesoscale features
and upscale evolution in Missouri tonight, however, and some shift
in heavier amounts is possible. Deep tropospheric moisture,
mesoscale forcing, and duration of this event could lead to
localized flooding, despite anomalously dry conditions and 3-hr
flash flood guidance roughly from 2.50-3.50 inches. We will look
at this closer tonight and provide more details.

&&

.Short Term...(This evening through Sunday night)
Issued at 259 PM EDT Sat Jul 16 2022

A surface low associated with an upper trough is slowly moving
across Illinois and will approach central Indiana this evening.
Current visible satellite imagery shows little cloud cover over
central IL/IN. This has allowed for moderate instability to build
through the day with sunny skies warming temperatures to near 90.
Increased daytime mixing due to plentiful sunshine has also led to
20-25mph wind gusts. Expect these winds to diminish as the boundary
layer stabilizes this evening. Improving dynamics along with
increasing moisture will allow for scattered showers and
thunderstorms to develop this evening.

An isolated strong storm cannot be ruled out, but the main hazard
through the short term period will be the flood threat. Forecast
soundings show high freezing levels, deep saturation, and moist
adiabatic lapse rates late tonight through overnight Sunday. This
along with PWAT values exceeding 2.0in. may lead to localized
flooding with storms that produce high rainfall rates.

Weak mean flow may aid in the flood risk as storm motions will be
rather slow. Although effective bulk shear less than 25kts will
create an adverse environment for severe weather on Sunday.
Furthermore, weak instability due to poor lapse rates should limit
the potential for severe weather. Thunder is less likely tomorrow
due to weak instability, but a few thunderstorms are still possible.

Expect below average highs tomorrow with rain and extensive cloud
cover in place. Meanwhile, lows will be above average as high
surface moisture and cloud cover limit overnight cooling.

&&

.Long Term...(Monday through Saturday)
Issued at 259 PM EDT Sat Jul 16 2022

An upper trough will slowly exit the area on Monday. Before it does
and drier air moves in, some showers and perhaps a thunderstorm will
remain possible. Temperatures will be near average for mid-July.

Some drier air long with surface high pressure will move in on
Tuesday, keeping the area dry. As the upper high to the southwest
tries to nudge into the area, high temperatures will return to
around 90 degrees.

On Wednesday, an upper level low will move into the Upper Great
Lakes region. At the surface, a cold front will move through central
Indiana. Forcing will remain mainly north of the area, closer to the
upper system. In addition, deep moisture will be lacking. Thus, feel
any chances for rain will be small. Warm advection ahead of the
front will bring highs in the lower 90s.

High pressure will then return for Thursday into Saturday, providing
dry conditions for much of that period. The upper high will begin to
drift farther east toward the area, and this will bring highs in the
lower and middle 90s by Friday and Saturday.

A few showers or thunderstorms may pop up by Saturday in the heat,
but with the upper high getting closer, confidence for any rain is
lower than average.

&&

.Aviation...(06Z TAF Issuance)
Issued at 1049 PM EDT Sat Jul 16 2022

IMPACTS:

* Some wind direction variability through the night, especially near
  thunderstorms.

* Showers and thunderstorms will increase in coverage through the
  night.

* MVFR ceilings developing early Sunday morning; low probability of
  IFR.

Discussion:

Showers and thunderstorms will expand across the area overnight.
Some timing refinements via amendments may be needed depeding on
trends. Showers and a few thunderstorms will continue through much
of the day Sunday. Mesoscale boundaries from convection, and
potential mesohighs may alter wind direction some, causing
variability from time to time especially early in the TAF period.

Convergent low-level flow and extensive moisture late tonight and
especially Sunday morning will support MVFR stratus. There is a low
potential for this to at least briefly be IFR and potentially last
periodically into afternoon. Improving conditions are likely toward
the end of the TAF period.


&&

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

$$

Mesoscale...BRB
Update...BRB
Short Term...Melo
Long Term...50
Aviation...BRB