178
FXUS63 KIWX 271915
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
315 PM EDT Sat Apr 27 2024

.KEY MESSAGES...

- Showers and thunderstorms will be possible this afternoon and
  tonight with heavy rain that could lead to flooding as well as
  strong gusty winds being the main threat.

- Additional chances for showers and thunderstorms occur Sunday
  night through Monday night and again mid to late week next
  week.

- Temperatures remain in the 70s Sunday into the next week with
  80s possible in southern areas Sunday and Thursday.

&&

.DISCUSSION...
Issued at 309 PM EDT Sat Apr 27 2024

An upper low pressure system continues to move northeast into
Eastern Canada from the Western Great Lakes today and tonight.
Meanwhile, the low level jet allows for a moisture stream to arrive
north of a US-24 line with an instability axis of around 1000 J/kg
MUCAPE just slight farther north as it resides north of a line from
Monticello to Hillsdale. DCAPE above 900 J/kg does look to work into
similar axis as the instability axis with more like 700+ J/kg south
of there. Given how little forcing is available, showers will be
more scattered with forcing more relegated to areas of surface
convergence and/or upper divergence. An area of these ingredients
materializes between this evening and around midnight and moves into
the aforementioned instability axis area. Before then, much of the
showers are being models as moving through areas south of that
Monticello to Hillsdale line, which would likely point to their lack
of severity. However, once we get to perhaps 22z, but probably more
like after 00z, high res models start producing storms in the
northern area. The issue by that point is the DCAPE and to a large
extent the MUCAPE has shifted northward. So if the timing is right,
perhaps there`s a strong storm that forms, but still don`t have
confidence that that`s the case. On the other hand, could see a
flood scenario where training of storms occurs in this moisture
axis especially if we are able to get an outflow boundary to
come in as well as some upper divergence to help focus storms.
HREF has PMM QPF totals 1 to 3 inches or so in this area, which
is slightly north of where the higher precip has been across our
south and west across the last 7 days.

For Sunday, the rain axis has shifted so that areas north of US-6
have the greatest chance to see any rain as that is where the
surface warm front appears to draped. There are splotches of shear
and instability to work with west of IN-15 and north of US-6 in the
morning time frame and north of US-6 during the afternoon. Perhaps a
strong storm could be had during that time. Otherwise, areas south
of that will struggle to receive rainfall with the lack of forcing.
We`ll have to wait until later Sunday night and into Monday morning
for the next chance for rain as the cold front shifts eastward. Even
still, much of the low level convergence appears to dissipate on the
ECMWF and the GFS loses much of the omega across the area. With it
being a cold front, still thinking this is much more of a chance to
maybe likely PoP scenario than a likely to categorical PoP scenario.
Meaning there will be breaks in the showers as opposed to being
widespread and we`ve also lost much of the instability so the most
these showers will be is light to moderate rain. One thing of note
is that the moisture axis stalls over our east Monday afternoon and
it appears instability may be around ahead of the thermal boundary
along with some shear. There may be a wind threat with storms that
form then. That looks to swing out of the area overnight Monday
night with Tuesday remaining dry.

As our second low pressure system, which helped push the front
through Monday into Tuesday, moves into Central Canada, yet another
area of low pressure follows it into Central Canada and that pushes
a cold front into the area later Tuesday night. The forcing for it
is diminishing so while a few thunderstorms are possible, the
column looks much drier restricting coverage. There is some
instability being forced to its south and east as it progresses
through the area Wednesday, but if it moves through too fast it
could be out of the area before storms are able to fire then.
Have retained some slight chance PoPs for this chance for
showers/storms. The waters become a little bit more muddied for
the end of the week as far as timing goes, but a trough in the
west and ridge in southeast would point to continued
precipitation chances with waves pushing off the Plains having a
chance to tap into Gulf moisture out ahead of a baroclinic
zone.

Temperatures through this period all look to be able to reach the
70s for highs with Sunday and mid to late week next week having a
chance to see 80s for highs. It trends cooler for next weekend
behind a wave of low pressure.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1235 PM EDT Sat Apr 27 2024

Strong broad southwesterly low level flow will continue through
the remainder of the afternoon with some gusts to 35 knots at
times. This southwest low level flow has maintained a moist low
level air mass across the area which will allow for weak to
moderate surface based instability through early evening. The
limiting factor, at least through early evening, for more
substantial shower/storm coverage is lack of a clear
focusing/forcing mechanism. Expecting a stronger uptick on
shower/storm coverage later this evening into the overnight
hours as low jet ramps up. Moisture convergence with the low
level jet and potential interaction from leftover outflow
boundaries from convection may allow for period of regeneration
of thunderstorms and some training of storms potential during
the overnight hours. Forcing mechanisms in terms of low/mid
level moisture convergence looks to maximize from northeast
Illinois into northwest Indiana, and thus have hit
shower/embedded thunderstorm potential a bit harder for KSBN
overnight into early Sunday. Mainly VFR conditions expected
this period, although any stronger showers and storms will have
temporary vsby/cigs restrictions. Have also included a brief
LLWS mention at KFWA to account for northward migration of the
low level jet.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for LMZ043-
     046.

&&

$$

DISCUSSION...Roller
AVIATION...Marsili