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000
FXUS63 KIWX 252328
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
728 PM EDT Thu Apr 25 2024

.KEY MESSAGES...

- Much warmer temperatures this weekend with highs around 80.

- Periodic chances for rain and a few storms, particularly Friday
night and Monday.

- The risk of severe weather is low at this time.

&&

.DISCUSSION...
Issued at 315 PM EDT Thu Apr 25 2024

On the heels of a freeze warning and frost advisory from this
morning and with the shifted pattern for tonight, a good
question to posit is if we return to frost conditions again
tonight. Well, as opposed to being in the trough with various
areas of mid level vorticity to support high clouds last night,
tonight will have mid level ridging around with NAM and GFS
bufkit soundings indicating decoupling is possible. This is in
frost formation`s favor, however, increasing gradient is not. As
an upper level low pressure system lifts northeast out of the
Southern Plains, the gradient starts tightening after 6z from
west to east and a low level jet approaches by 12z Friday. This
also may be able to spread some high clouds in west of US-31 to
also stunt any remaining cooling after 6z there. Temperatures
could also crater not too long after sunset with the dry air
around. With these thoughts in mind, have hoisted a frost
advisory to cover areas generally north of US-30 and east of
US-31.

Moving forward, for Friday, a warm front encroaches on the area
spreading moisture into the area. PWATs between 1.25 and 1.5 inches
which is 1 to 3 SDs above climatological norms help indicate the
moisture to be tapped into. Surface convergence arrives during the
afternoon especially for areas along and south of US-30 and then
continues moving northeastward through 6z. While some embedded
thunder may be possible as this front passes through, much of the
instability will stay to our west through 12z Saturday. Given this
and the fact that the better moisture still hasn`t arrived yet, QPF
totals stay below 0.5 inch and taper off quickly southeast of our
2nd tier of counties away from Lake MI.

For Saturday, more instability looks to be able to work into areas
west of I-69 with the best instability looking to be in the
aforementioned lake-adjacent counties. West of I-69, better columnar
moisture looks to move in with surface dew points surpassing 60
degrees and 850 mb dew points surpassing 10C. However, we lose the
better forcing between 12 and 18z with it going northeast of the
area so would expect coverage of rainfall to decrease unless we
can get an outflow boundary to move through. If we can get some
thunderstorms to form, it looks like there`ll be around 30 kts
of effective shear to work with. SPC has those aforementioned
lake-adjacent counties covered with a marginal chance of severe
weather for Saturday. The shear would make damaging wind the
most likely outcome from severe storms, but perhaps a tornado
with SRH around 200 m2/s2 and sub- 1000m LCLs, as well as a few
sporadic reports of hail with 6 to 7 C/km mid level lapse rates
attempting to move in, but that moist low levels may remove that
possibility.

Moving forward, for Saturday night, the moisture axis shifts from
along our western counties to along and north of US-6 by Sunday
morning, which would allow for a break for much of the forecast area
from rain, especially those south of US-6. Now, there is still some
700 to 1500 J/kg of MUCAPE to work with on the ECMWF model Sunday so
if there is a lingering boundary, perhaps we could tap into that for
some storms then. We`ll have to wait for a better chance for rain
along an area of upper divergence as it swings through ahead of the
main cold front late Sunday night/Monday. This area of moisture does
look to stall out overhead and may be able to have some instability
to work with. The GFS has an axis of 30 kts of effective shear east
of I-69 during the afternoon so perhaps some severe weather could be
had as well.

All told, through these successive rainfall events from later
Friday into Tuesday morning, the NBM doesn`t have more than 10
to 20 percent chance of 1 inch in 24 hours. Would think these
percentages might be a little higher should convective rain be
added to the equation. That helps to draw a picture for how
little rain we get with the main limiting factor being the
forcing.

While the GFS forms what appears to be convective rain with sporadic
weak vort maxes moving through in the mid level flow, think that the
next best chance for rain holds off until the Tuesday night through
Wednesday time frame as another cold front moves through. With the
speed of the front, perhaps a few thunderstorms could form early
afternoon south of US-24 Wednesday as long as clouds break up to
allow instability to form.

Temperatures during this forecast period trend warmer from today`s
50s to tomorrow 60s to around 70 degrees. Then from Saturday through
the end of the forecast period, 70s for highs will be in play. No
threat for additional frost occurrences is forecast.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 728 PM EDT Thu Apr 25 2024

VFR conditions will dominate through most, if not all, of the
period as high pressure retains control. A warm front will begin
to edge north late in the period with some indications of rain
trying to take shape near after 21Z Fri mainly at KSBN. Models
have not been consistent on this with a fair amount of dry air
to work through before anything reaches the ground. While some
rain may impact KSBN, vsbys are unlikely to be impacted and cigs
will remain VFR through at least 00Z. As a result, have left any
mention of precip out for now and relegate the addition of any
impacts to later forecasts and especially later periods.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Frost Advisory from midnight tonight to 9 AM EDT Friday for
     INZ005>009-017-018-025>027-116-216.
OH...Frost Advisory from midnight tonight to 9 AM EDT Friday for
     OHZ001-002-004-005-015-016-024-025.
MI...Frost Advisory from midnight tonight to 9 AM EDT Friday for
     MIZ078>081.
MARINE...None.

&&

$$

DISCUSSION...Roller
AVIATION...Fisher