000
FXUS63 KIWX 091734
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
134 PM EDT Tue Apr 9 2024

.KEY MESSAGES...

- Showers and a thunderstorm will be possible this afternoon
  into the evening east of I-69.

- A wet, active pattern returns through the end of the week. A
  slight chance for rain/storms Tuesday night then a much more
  widespread, substantial chance for rain/storms Wednesday
  afternoon through Friday morning.

- 1.5 to 2 inches of rain is possible in many locations
  Wednesday afternoon through Friday morning, which will likely
  reinvigorate river and stream flooding again late in the week

- Saturday appears to be the drier of the two weekend days.

&&

.DISCUSSION...
Issued at 259 AM EDT Tue Apr 9 2024

A baroclinic zone is reinvigorated today as warm air advection
occurs on the eastward side of the boundary to start the day. Cold
advection takes over as the boundary slides eastward through the
morning. At 18z models indicate the boundary is in the vicinity of I-
69 meaning areas east of it have the greatest chance to see pop
showers or maybe a thunderstorm. The 09.00 HRRR actually holds pop
showers to forming just south of our forecast area. Models still
bring 500 to 1000 J/kg MUCAPE with the moisture plume from the south
finally getting close around 21z to 03z this evening. There is some
model signal for 30 kts of effective shear being available between
the 18 to 00z time frame this afternoon with potentially 6 to 6.5
C/km mid level lapse rates initially available. If showers form
early enough and grow fast enough, maybe there would be a
chance for some hail to form and perhaps some wind threat due to
moisture loading. Would think this trends lower as we reach the
00 to 03z time period and we begin to lose ingredients. 850 mb
temperatures, where mixing heights rise up to, reach around the
mid single digits meaning 70 degree highs will once again be
achievable especially east of I-69.

Surface high pressure behind the baroclinic boundary
potentially influenced by left over cold pool forcing helps
protect the area from precipitation returning overnight, but it
drifts off to the east Wednesday morning opening up a path for
another warm advection wing to return as a surface low develops
on the stalled baroclinic boundary and begins to ride northward
along it. There is some indication that drier air will be
draining southward into the area on Wednesday making initially
arriving rain difficult to reach the ground, but could see rain
begin to reach the ground during the afternoon or evening time
frame as the boundary layer moistens. Slightly lower mixing
heights provide slightly cooler high temperatures for Wednesday
with mid to upper 60s more likely as precipitation begins to
arrive.

As we head towards Wednesday afternoon and night, a trough that
helped to push the aformentioned upper low in south-central Canada
northward previously traverses across the southern CONUS, collects
pooled moisture in the southeast vicinity of TX and draws it
towards the area as a neutrally to potentially negatively
tilted trough develops. Interesting to see similar trends to
recently forming low pressure systems where the short term/high
res guidance takes the storm track still east of I-69, but the
ECMWF and GFS take the storm track more towards Lake MI. The GFS
was first to catch this correctly verifying trend with the last
storm, but this one appears to be more surface based with the
baroclinic boundary involved, which may play more of a role this
time (Maybe the Maddox synoptic pattern type heavy rain
idealized case?). Something that will be interesting to follow
along and watch. PWATs for this system reach 2 to 3 SDs above
normal along with a moist column combined with ample large
ascent and favorable jet dynamics will create a favorable
environment for moderate to heavy rain. QPF is highest and
reaches between 1.5 and 2 inches west of IN-15 on the GFS/ECMWF
which would be opposite of where we had most of our recent river
flood warnings issued. This is as opposed to what the NAM
shows, which is actually along I-69, closer to where our more
recent river flood warnings were issued, but still 1.5 to 2
inches of output. Some convective element could be realized with
a warm sector moving through on Thursday along with 100 to 500
J/kg of MUCAPE and as much as 30 kts of effective shear. Of
course the speed of the low through the area could affect how
much instability we get into the area and raise or lower that
and therefore the event`s intensity. This amount of rainfall, in
the right location, could reinvigorate area rivers.
Additionally, runoff may be more efficient this time with a
more moist ground allowing less permeation into the ground.
Lastly, shallow mixing may be able to limit some of the
potential for gusty winds on Thursday, but 25 to 40 mph wind
gusts will be possible as the low pressure system deepens.

Cold rain likely takes over as northwest flow ensues on the
northwest side of the eastward moving upper low allowing for
scattered light to moderate showers through the day. As such,
expect a cooling trend from Wednesday`s 60 degree highs to
Friday`s 50 degree highs. Once, again strong wind gusts to 30 to
40 mph will be possible should stronger mixing be realized.

This all departs Friday night into Saturday morning as the large
scale trough moves eastward and surface high pressure noses in along
with mid level ridging. A warm advection pattern will allow a
warming trend with highs achieving 70 degrees once again on
Sunday behind the passing warm front. Perhaps a few scattered
showers could be had as long as adequate saturation is
available. Will retain slight chance PoPs a result. A cold front
moves through in the afternoon and so will hold onto chance
PoPs then.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 126 PM EDT Tue Apr 9 2024

Few weather concerns during this TAF cycle. A cold front is
nearly bisecting Indiana from northeast to southwest this
afternoon. Clouds are streaming in to the northeast along this
feature and there is a non-zero chance of a pop-up south
primarily south of KFWA. Coverage looks to be sparse. Wind will
gradually veer through the TAF period.
 &&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Roller
AVIATION...Brown