-- Discussion containing changed information from previous version are highlighted. --
481
FXUS63 KIWX 252222
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
622 PM EDT Sat May 25 2024

.KEY MESSAGES...

- Showers and thunderstorms expected Sunday afternoon and night.
  Damaging wind, hail and flooding will all be possible with
  tornadoes possible with any evening storms that form.

- Lingering showers/embedded thunder may impact activities on
  Memorial Day through Wednesday.

- Dry weather looks to follow for late this week.

- Hazardous swimming conditions for Lake Michigan beaches in La
  Porte County in Indiana and Berrien County in Michigan
  Memorial Day through Wednesday.

&&

.DISCUSSION...
Issued at 253 PM EDT Sat May 25 2024

Saturday starts with a phased Pacific and Subtropical jet across the
southwestern US within a Western CONUS trough and a Northern Plains
upper low. All this is west of a departing trough in the Northeast
CONUS. Pushing play on the model physics causes the Northern Plains
upper low to push farther northeast into Canada and opening up an
opportunity for coupled jets to form a surface low pressure system
across the Central/Southern Plains this evening. Closer to home, a
cold front pushed eastward this morning and is in the I-69 corridor
this afternoon. With the moisture axis having just departed, the
strongest convective ingredients will be in our east and
lingering/dissipating instability east of I-69, but minimal shear
may allow for a pop shower/storm this afternoon before it departs.
Will carry slight PoPs there to cover that possibility. Behind the
cold front, expect clearing clouds as dry air temporarily moves in.

Moving forward to Sunday`s severe weather chance, the aforementioned
Western CONUS trough, shifts eastward carrying the developing
aformentioned surface low towards the forecast area Sunday. 8am
Sunday morning, the moisture axis is south of the forecast area due
to Saturday`s cold FROPA, but lifts northward in conjunction with an
arriving 40 kt low level jet just to our west. As a warm front lifts
northeastward, the 12z HRRR indicates thunderstorms will be along
it, but how strong it will be is in question. Expect 60F degree dew
points to begin pushing in with 850 mb dew points also achieving
mid teens Celsius readings. Temperatures will begin rising into
the 70s tomorrow morning with 80 degrees possible south of
US-30. This combination of heat and humidity will allow for 500
to 1000 J/kg of MUCAPE and 900 J/kg of DCAPE. These ingredients
lead to more of a marginal severe setup with wind being the
primary hazard, but hail also not ruled out. At 2pm Sunday,
effective shear of 30 kts have just reached our west, which is
just behind the warm front. This begs the question about if we
can get clouds to scatter out behind the warm front. Should
there be enough insolation, there could be a chance to force a
second round of severe weather starting around 8pm and continue
until after midnight. Should clouds break, instability
approaches 1500-2000 J/kg of CAPE, mid level lapse rates
approach 7 C/km along with 8 to 9 C/km low level lapse rates,
effective shear reaches 45 to 55 kts by 00z and low level
turning in hodographs and effective helicity surpasses 200 m2/s2
allowing for all severe hazards to be on the table. Flooding
could also become an issue with training storms in a moist
environment. Storm motions appear fast enough to keep things
progressive, which could negatively impact QPF totals. An
initial guess on when things would dissipate would be between 2
and 4 am. The cold front doesn`t look to move through until
Monday morning, but instability drops off Sunday night with mid
level lapse rates dropping to 6 C/km by 2am. Of course, another
wrinkle in this is that models have been too slow with the
arrival of recent thunderstorm events so this could be pushed
earlier and that would also affect instability recovery windows.

For Monday, subtle ridging and mid level height rises indicate a
break in the action will be possible behind the departing cold
front. Negative theta-e advection will be drying out the moisture
column allowing dew points to fall into the 50s and highs only
achieve the upper 60s to low 70s. A Pacific shortwave is
directed towards the region for Monday evening with these
antecedant conditions. Instability appears to be at or below 500
J/kg for thunderstorms so rain will be the likely outcome, but
embedded, non- severe thunderstorms will be possible. Rounding
this carousel of shortwaves, the vorticity from the original
central Canadian upper low rounds the base of the trough towards
the area for Tuesday. Dew points are still relatively dry, in
the 50s, but the ECMWF still forms 1500 J/kg of MUCAPE (GFS is
more like 500 J/kg) so perhaps a thunderstorm or 2 could be had
with that given scattered cloud cover at best, but thunderstorms
appear marginally severe, at best.

Meanwhile, on Monday, a cold front ejecting off of southeast Asia
starts a chain of cyclonic wave breaks later Sunday/Sunday
night across the North Pacific that invigorates a strong ridge
across the Western CONUS Monday night into Tuesday. Rain is
finally out of the area on Wednesday as this ridging arrives and
provides a reprieve of dry weather until at least Saturday. Mid
60s to low 70s highs on Wednesday slowly trend warmer, reaching
the low 80s across a few of our southern counties on Saturday.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
-- Changed Discussion --
Issued at 622 PM EDT Sat May 25 2024

Light winds and mainly clear skies are expected tonight with sfc
ridging in control. Strong warm front and associated moist
advection looks to send an arcing line of convection east-
northeast through northern Indiana during the early-mid
afternoon hours on Sunday. Added a tempo TSRA/IFR group in the
18-20z window given relatively high confidence, though
refinements in timing will likely be needed in future issuances.
-- End Changed Discussion --

&&

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

&&

$$

DISCUSSION...Roller
AVIATION...Brown/Steinwedel