506
FXUS63 KIWX 040859
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
459 AM EDT Sat May 4 2024

.KEY MESSAGES...

- Active weather pattern for this week, with chances for showers
  and storms every day. The best chances will be Tuesday into
  Thursday when a stronger low pressure system moves through the
  area. A few strong to severe storms are possible Tuesday
  afternoon into Wednesday, but confidence is low at this time.

- Temperatures linger in the 70s and low 80s through most of the
  week, except Sunday when highs north of US 24 will be in the
  50s and 60s, coldest near Lake Michigan. Next weekend lows
  will be in the 60s.

&&

.DISCUSSION...
Issued at 458 AM EDT Sat May 4 2024

Mostly dry today as a weak surface high lingers in place, with mid
level ridging breaking down somewhat late this afternoon thanks to
an approaching trough. There is a stationary front settled just to
the southeast of our CWA, oriented from roughly southern Ontario
southwest towards Lima, OH and down into Saint Louis, MO. This will
be a focus for shower activity, maybe a few storms, into the
afternoon-with the best chances after 18z as we build up some
instability. Going by the NAM, it looks like we`ll have around 500-
1000 J/kg of sfc based CAPE by 21z largely east of I 69 (more like
200-500 J/kg west), in addition to weak moisture advection from the
southeast and mid level lapse rates of around 7 C/km. We have a
subsidence inversion to overcome and weak forcing overall, but felt
20-30 percent pops were warranted for the east. Luckily the bulk
effective shear for the afternoon time period is less than 20 knots,
so if any storms develop, don`t expect much in the way of severe
weather. Otherwise, expect partly to mostly sunny skies with
increasing clouds towards the evening. Highs will be in the 70s.

Late this afternoon into tonight, a surface low and mid level trough
will move through, bringing better chances for rain and some storms
that dwindle with eastward progression. SPC Day 1 outlook has all of
our area in general thunder, with the marginal risk for severe
weather to the west of our CWA associated with the system, where
wind shear is more on the order of 25-35 knots and the cold front is
moving through during more favorable time of day. For us, the shear
weakens to about 20-30 knots, with waning instability-so while I
have higher pops west tonight (40-60 percent) I dropped them off to
20-35 percent further east with lesser chances for thunder. Severe
weather is not expected at this time. Lows will be in the 50s and
60s, warmest inland from Lake Michigan.

Isolated/scattered showers & storms will persist east of I 69
through Sunday evening-largely associated with the slowly exiting
cold front. Again, minimal shear with around 500-1000 J/kg of sfc
based CAPE by Sunday afternoon in the east warrants 20-30 percent
pops, however, severe weather is unlikely. Highs will be in the 50s
and 60s north of US 24 (coldest near Lake MI) and the low to mid 70s
south. Otherwise, expect partly to mostly sunny skies.

For most areas, Sunday night into late Monday night will be dry
thanks to an amplifying mid level ridge and an expansive surface
high sprawling over the Great Lakes. A low pressure system
approaching from the southwest Monday afternoon and evening will
bring increasing chances for showers and maybe a few thunderstorms
south of US 24, but confidence is low (it could miss us to the south
all together). Highs will be in the upper 60s and low to mid 70s.

Tuesday into Wednesday will be the best shot at more significant
precipitation and even thunderstorm chances. An upper level low
dives into the north central CONUS and develops a surface low
somewhere over IA/MO/KS Tuesday afternoon, lifting it through the
Great Lakes as it deepens. The low is forecast to reach southern
Ontario roughly Wednesday evening. The warm front moves through
Tuesday, followed by the cold front on Tue Night/Wed Am, with decent
moisture transport out ahead of the low. Kept the 50-90 percent
chances Tuesday into Tuesday night, with thunderstorms likely. I
suspect that we have potential for severe weather if this pans out
as the models currently suggest, with 40-65 knots of bulk effective
shear and 500-1500 J/kg surface based cape by Tuesday
afternoon/evening. At this time, we are in the 15 percent for the
western half of the CWA for the Day 4 SPC outlook, and think it`s
definitely worth monitoring.

The upper low over the central CONUS will gradually migrate eastward
into the Great Lakes by Friday afternoon, lingering through the
weekend and bringing additional chances for showers and storms,
particularly Thursday. A secondary low develops behind the Tue/Wed
system in much the same location, drifting over the forecast area
through the day and bringing potentially heavy rain-but too far
out to add much detail at this point (we are in the WPC
Excessive Rainfall Outlook Marginal Category for Wed/Thu).
Temperatures linger in the 70s and low 80s until the weekend,
when we cool into the 60s for highs (40s and 50s for lows).

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1230 AM EDT Sat May 4 2024

Lingering boundary layer will likely allow a high MVFR to low VFR
stratocu deck to settle in over KFWA through much of the forecast
period. Drier air has worked into KSBN where lesser diurnal cu
coverage is anticipated mid morning into the afternoon. Models do
try to generate isolated showers in the vicinity of KFWA later
this afternoon as weak surface based buoyancy develops on the
western fringe of a stalled OH trough. However, point chances
are too low for a mention in the TAF at this time. A sfc trough
does approach KSBN toward the end of the period (3-6z Sun) with
non-zero chances for decaying showers/iso storms. May opt to
add in at least a VCSH with the 12z issuance if this signal
persists.

&&

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

&&

$$

DISCUSSION...MCD
AVIATION...Steinwedel