569
FXUS63 KIWX 080737
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
337 AM EDT Mon Jul 8 2024

.KEY MESSAGES...

- Chances for showers and thunderstorms increase for NW IN/SW
  Lower Michigan today into tonight mainly west of I-69.

- Remnants of tropical system Beryl will bring showers and
  thunderstorms to the area Tuesday afternoon through Thursday
  with heavy rain at times.

- Warmest conditions this forecast period expected on Monday
  (mid 80s to around 90), and possibly again next weekend.

&&

.DISCUSSION...
Issued at 333 AM EDT Mon Jul 8 2024

A mid level trough continues to be centered across the Northern
Plains with its eastern periphery traversing through the Lake MI-
adjacent counties of MI and IN. As of this writing, there`s still
plenty of disagreement on handling of the weak shortwaves moving
through this area. Some high res guidance wants to bring showers
through this morning whereas others hold things off until this
afternoon and evening when a stronger shortwave moves into the
northwestern Great Lakes and grazes our northern and western zones.
Have a little more confidence in carrying PoPs this afternoon and
evening with the better forcing, but also because better instability
is able to build in west of I-69. Even still will cap PoPs at low
end chance still with us being far enough south of the forcing in
some model solutions. As this area of vorticity advances eastward,
expect the forcing to wash out and for the instability to wane
beyond sunset so PoPs will diminish to slight chance overnight,
never reaching the I-69 corridor. There appears to be some residual
outflow boundary from the overnight activity that may serve as
forcing for showers and storms that could initialize Tuesday morning
as the sun comes up and instability begins to develop. The ECMWF
increases sfc dew points Tuesday morning and that will make the
atmospheric column more conducive to lift as the remnants of Beryl
reach Arkansas and upper divergence (outflow) and moisture streams
northward from it. As such, will allow chance PoPs to blossom and
extend outward along a line from Grissom to Hillsdale. Highs today
look to achieve the upper 80s in most places to around 90
degrees east of I-69. Highs Tuesday will be a little cooler as
Beryl approaches with increased cloudiness, only achieving the
upper 70s to mid 80s.

As we head into Tuesday night, a ECMWF/NAM camp seems to bring
better low level moisture into the area associated with the remnants
of Beryl. 850 mb dew points increase to around 15C in these models,
but sfc dew points drop below 70F. At the same time, this is also
when the better large scale ascent makes it into the area and starts
squeezing out this influx of moisture. A slight southward shift of
the low pressure center in recent model runs has shifted
precipitation totals slightly southward back to the US-24/I-69
corridor. Models have come into better agreement when compared to
yesterday at this time, but there`s still some chance for shifting
of rainfall axis up until probably Monday night/Tuesday. A
statistical glance at the guidance (Model Certainty tool) for FWA
indicates a 25th percentile around 1.6" whereas a 75th percentile
resides around 2.15", which is right around where WPC`s storm total
qpf winds up. Fort Wayne was already 2 inches below normal for June
and is 0.5" below normal for July so there is some ground to make up
before the ground can become saturated. It will likely require
vigorous rain rates or stalled/training cells and this system does
appear to be fairly progressive in nature on the GFS/ECMWF models so
that`s not in its favor. Given the cloudiness and the location of
the low pressure center, we`re likely also too far west to see any
significant convective cells in a warm sector so that`ll keep
rainfall totals down as well. Have the most confidence in saying
some low-lying and normally flood prone areas could see standing
water as a result of this time period. The coolest highs of this
period will be observed on Wednesday with the most cloudiness and
likely the heaviest rain observed, only achieving the mid 70s
to around 80 degrees.

This system begins to depart Thursday as the trough still stalled to
our west since today finally pushes the system`s energy east.
Vorticity within the base of the nearby trough and developing
instability will at least require slight chance PoPs Thursday with
the greatest chance during the afternoon. Mid level height rises
take over behind Beryl and surface high pressure comes in so am
skeptical of anything higher than slight chance PoPs for Thursday.
The trough stalls out overhead through the weekend into next week so
will at least keep a token slight chance PoP around during the
afternoon Saturday within the diurnally forced instability.
Temperatures look to slowly trend warmer, towards 90 degrees by the
weekend or next Monday as the ridge that was in the west slowly
trends eastward.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 128 AM EDT Mon Jul 8 2024

Low level moisture will continue to slowly increase this period
but conditions will likely remain VFR. Another weak shortwave
rippling through the Great Lakes may touch off some late
afternoon/evening storms near KSBN again on Monday. Confidence
in timing is very low given poor forcing but 21-03Z appears most
likely for now. Much lower chances at KFWA given drier low
levels and further displacement from weak forcing. Winds will
remain light through the period.

&&

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

&&

$$

DISCUSSION...Roller
AVIATION...AGD