540
FXUS63 KIWX 261836
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
236 PM EDT Sat Apr 26 2025

.KEY MESSAGES...

- Low temperatures tonight into Sunday morning drop into the
  30s. Frost will be possible in areas mainly west of US-31 and
  north of US-6. Temperatures then trend warmer through Tuesday.

- Thunderstorms possible across the area early Tuesday morning through
  early Wednesday morning. Storms may become strong to severe,
  especially Tuesday afternoon/evening. Still considerable
  uncertainty on the details at this time.

- After a brief reprieve, rain quickly returns to the area mid
  to late week with thunderstorms also possible at times.

&&

.DISCUSSION...
Issued at 232 PM EDT Sat Apr 26 2025

A trough swung through Michigan this morning allowing northwest
winds to come into the area and keep us cooler today. Low clouds
broke up midday into the early afternoon allowing temperatures to
reach the 50s to low 60s today. With clouds breaking up today and
winds becoming light to calm by after midnight, temperatures will
have a good chance to drop into the 30s tonight allowing for a
chance for frost. METRo model shows road temps taking their time to
reach the upper 30s despite having air temperatures reaching the
upper 30s during the evening. The other issue is clouds may try to
arrive during the overnight, which would slow down any radiational
cooling that may have taken place. It still looks like the area most
conducive to frost would be west of US-31 and north of US-6. Even
the warmest of the models (the low res models including the
GFS/ECMWF and the NBM as well as high res models like the RAP and
HREF) have some frost formation in this area. Even though
uncertainty remains, still think the threat is high enough to send
out a frost advisory to cover these areas. Will keep the advisory
from Pulaski, Fulton, southern Kos, Whitley, Dekalb, and Williams
where a combination of factors including warm ground, high clouds
(generally west), and low to no residence time of 30 degree
temps is expected to keep widespread frost at bay. Have
retained patchy frost in the weather grids in a few of these
locations where outlying areas could still see frost.

Surface high pressure pushes through Sunday morning and south winds
become more prevalent across the area midday into the afternoon.
This allows temperatures to trend warmer: from the 50s and low 60s
today to everywhere surpassing 60 degrees on Sunday and surpassing
70 degrees to potentially reaching 80 in our southwest on Monday.
Mixing heights increase during the day and a low level jet edges
into our west later afternoon Monday allowing breezes between 20
and 30 mph to pick up.

A warm front looks to push through during Monday evening allowing 60
degree dew points to creep in on Tuesday. At least elevated
instability and 7 C/km mid level lapse rates reside across the area
Monday night and even the believable (speed-wise) ECMWF model
brings precipitation through late Monday night and Tuesday
morning and then brings the front into our NW at 18z leaving
just south of US-24 to taste the better warm sector airmass on
Tuesday. Given these times of rain, still noting plenty of
uncertainty with how severe this chance for thunderstorms gets
on Tuesday. There`s some question with how much the mid level
lapse rates get washed out Monday night and Tuesday, which would
impede the ceiling for the hail threat. Sufficient effective
shear (>30 kts) looks to arrive as early as Monday night and
continue into Tuesday out ahead of the cold front. Effective
helicity still looks strong enough so that this threat cannot be
removed yet. Boundary-parallel flow would likely allow for
training storms and introduce a flood threat with anomalous
PWATs. Boundary orientation makes discrete cells look a little
less possible in our area. Even still, all threats look
possible, we`re gonna need to get enough instability to form and
the timing of the pieces to line up to get this severe threat
to be realized.

The aforementioned surface high pressure slows down along the
western Atlantic and this helps to slow down the cold front just to
our south Tuesday night into early Wednesday. For later Wednesday,
we`ll begin to see a sheared out developing upper low captured by
the next trough and carried northward so that chances for rain
return and continue through late week. We`ll also have anomalous
PWATs as the low pressure system passes (probably Thursday). Some
thunder will also be possible (maybe south of US-24) Thursday
afternoon. Given this increased moisture and repeated rain chances,
the flood threat would be increased if they are realized.

A return to quieter weather is expected for next weekend as
another trough pushes through the north and brings in a cooler
and drier airmass.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1215 PM EDT Sat Apr 26 2025

MVFR stratocu already showing signs of scattering/lifting as of
16z with a full mixout to VFR by mid afternoon at the latest.
Northerly winds will continue to gust up to near 20 knots
otherwise this afternoon before high pressure builds in with
light winds and mainly clear skies tonight into Sunday morning.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Frost Advisory from 2 AM EDT /1 AM CDT/ to 8 AM EDT /7 AM CDT/
     Sunday for INZ005>008-012-014-103-104-116-203-204.
OH...None.
MI...Frost Advisory from 2 AM to 8 AM EDT Sunday for MIZ078>081-177-
     277.
MARINE...Small Craft Advisory until 11 PM EDT this evening for LMZ043-
     046.

&&

$$

DISCUSSION...Roller
AVIATION...Steinwedel