IWX issues Area Forecast Discussion (AFD) at Apr 30, 1:30 PM EDT
626
FXUS63 KIWX 301730
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
130 PM EDT Wed Apr 30 2025
.KEY MESSAGES...
- Widespread rain returns tonight into Thursday and showers
will persist through Friday night.
- There is a low risk of severe weather late Thursday afternoon
into Thursday evening for areas along and south of highway
24.
- Cooler and drier weather is expected over the weekend.
&&
.DISCUSSION...
Issued at 303 AM EDT Wed Apr 30 2025
Brief surge of postfrontal negative theta-e advection overnight
has resulted in a 30 degree drop in surface dewpoints and will
maintain tranquil weather through most of today. SSW flow ramps up
once again by late today though as upper low currently seen pivoting
through the southwest CONUS begins to eject NE. The initial
(elevated) isentropic ascent is not particularly impressive. 300K
analysis shows just a brief period of modest cross-isobar flow that
will be intersecting a very dry and stable ambient airmass. A few
very light showers are possible in our W/SW zones during the late
afternoon but by and large expect most locations to remain dry. Late
day WAA will help push highs into the mid/upper 60s despite cool
start this AM and increasing clouds PM.
Much better chances for rain arrive overnight as the surface warm
front strengthens and lifts northward into our area. Much stronger
and deeper isentropic upglide noted by late tonight as the nocturnal
LLJ ramps up with approaching shortwave. This initial shortwave
arriving late tonight is not the primary trough/vort max ejecting
out of the Southwest but rather a convectively-modified shortwave
associated with the remnants of convection developing over the
Ozarks later today. This leads to some increased uncertainty in the
exact placement of heaviest rain which some hi-res CAM's suggest may
pass just to our northwest. This uncertainty is already reflected
well in inherited grids with highest PoP's and QPF in our NW zones
and have generally kept that trend. Do think even our SE zones have
a chance of at least SCT showers late tonight into Thu morning.
Thu will feature the best rain chances for most of the area.
Southern stream shortwave zips NE as another potent northern stream
trough dives SE into the region. This leads to a prolonged period of
moist SW flow and broad isentropic ascent. It won't be an all-day
soaker but most locations are likely to see at least some rain at
some point during the day. Initial cold front passes Thu evening and
there is some potential for better instability to build in our E/SE
zones and support a chance for a few strong storms as suggested by
the 00Z NAM. There will be a lot of prefrontal clouds/precip though
and surface dewpoints may struggle to get much above 60F. Will
certainly keep an eye on this period but the severe risk appears low
in our area at this point (especially north of US-24).
With the secondary trough digging SE, precip chances will linger
into Fri night with a prolonged period of cyclonic low level flow
until main trough axis finally passes Sat morning. Better moisture
will be steadily pushed E/SE though and any showers will remain on
the SCT side. Left in a slight chance thunder mention given cold
temps aloft (below -20C at 500mb) but severe weather is not
expected. Cooler weather also returns briefly with this trough.
Anticipated highs in the 50s on Sat and lows touching 40F both Fri
and Sat night.
No significant changes to NBM initialization in the extended though
did maintain a dry forecast for now...supported by vast majority of
ensemble guidance. It should be noted deterministic ECMWF still has
a cutoff upper low over our region during this period which would
bring a persistent low chance for rain.
&&
.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 129 PM EDT Wed Apr 30 2025
Dew points fell down into the 30s last night into this morning and
this will allow some time before rain arrives at the terminals.
It'll likely take until later tonight to begin to get lowered flight
conditions, likely into MVFR, but perhaps a few hours dipping into
IFR. Wind-wise, east southeast winds today become southerly
Wednesday morning with gusts picking up by that time as a low level
jet moves into the area.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...AGD
AVIATION...Roller
Source: IWX issues Area Forecast Discussion (AFD) at Apr 30, 1:30 PM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202504301730-KIWX-FXUS63-AFDIWX)
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