Office: IND
FXUS63 KIND 301043
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
Issued by National Weather Service Northern Indiana
643 AM EDT Wed Apr 30 2025
.KEY MESSAGES...
- Rain chances return later today into this evening from south to
north. Scattered thunderstorms also possible later this
afternoon into tonight.
- An isolated strong to severe thunderstorm is possible late this
afternoon into this evening.
- Rain and embedded thunderstorms also expected on Thursday with
some severe weather risk again Thursday afternoon into the
evening hours.
&&
.SHORT TERM (Today and tonight)...
Issued at 325 AM EDT Wed Apr 30 2025
Light winds and clear skies this morning under the influence of high
pressure over the upper Great Lakes has set the stage for areas of
dense fog, primarily across the southern half of the area where rainfall
was maximized yesterday and ample shallow moisture is trapped beneath
a nocturnal inversion. This fog will mix out in typical diurnal fashion
after daybreak as boundary layer mixing ramps up and the inversion
is mixed out.
An upper level low will shift from the southwestern CONUS into the
southern Plains/lower Mississippi valley today into tonight, allowing
developing surface low pressure to strengthen as it swings from the
Plains into the Midwest tonight, bringing yesterday's cold front back
northward as a warm front.
Potential for an MCV to move into the region from upstream convection
ongoing this morning as the warm front pushes northward is driving
a reasonable day one marginal risk for southern portions of central
Indiana today. These sorts of setups can be sneaky severe weather
producers, though uncertainty remains as to the degree of destabilization
that will occur ahead of time. Will need to keep an eye through the
day on insolation and degree of low level moisture return into
the area, as this will drive any potential severe threat this
afternoon into this evening. If destabilization is strong enough
this afternoon to produce thunderstorms, organized convection
should be a good bet given good deep layer shear, and CAMs do show
some evidence of low level profiles which may be conducive to
rotation.
Outside of the severe threat, precipitation chances will be ramping
up through the day into tonight as the warm front pushes northward
and kinematic support increases owing to the aforementioned upper
low. Even if severe weather does not materialize, deep moisture
and strong tropospheric flow will produce embedded thunderstorms
in broader showers, which may be heavy at times tonight with
precipitable water values in excess of the climatological 90th
percentile.
Temperatures should push back into the 70s across much of the area
today with the front returning northward, and lows tonight are unlikely
to drop much more than into the 60s with central Indiana remaining
solidly in the warm sector of the surface low.
&&
.LONG TERM (Thursday through Tuesday)...
Issued at 325 AM EDT Wed Apr 30 2025
Unsettled conditions continue with additional opportunities for
showers and thunderstorms as we wrap up the work week with a cold front
moving across the Thursday night followed by a trailing upper level
low and associated surface trough on Friday. High pressure will
build in for the weekend with an amplified and blocky upper level
pattern developing across the country by early next week. There
remains the possibility that the upper trough passing through the
Ohio Valley during the first part of the weekend closes off into a
low to our east into early next week. This would delay the
arrival of ridging and warmer air by a few days and could cause a
wet and unsettled pattern to linger but confidence is low in this
solution coming to pass. The more consistent idea remains that
ridging aloft and at the surface will become the dominant features
across the region and bring a return to warm and dry weather by
early next week.
Thursday through Friday
The warm front should be fully north of the forecast area by Thursday
morning as low pressure lifts into north central Illinois. The low
will strengthen as it tracks into the Great Lakes by the afternoon with
a noted increase in 850mb flow late day immediately ahead of the approaching
cold front into the afternoon. MLCAPEs between 1500-2000 j/kg along
with an increase in storm relative helicity levels within the near
surface layer support the potential for better organized convection
ahead of the front with model soundings hinting at some directional
shear present within the boundary layer as well. The potential for
severe weather focused during the afternoon and evening has increased
across much of the forecast area with damaging winds as the primary
concern. Showers will diminish Thursday night as the cold front moves
off to the east.
An upper wave will pivot across the area Friday afternoon with a trailing
surface trough in the areas as well. With model soundings showing steepening
lapse rates and weak instability developing underneath the mid level
cold pool...there is potential for scattered convection during peak heating
in the afternoon and early evening. The combination of the freezing
level falling back to near the 700mb level with instability elevated
through the column does support the potential for small hail within
any stronger cells that can develop.
Friday Night through Tuesday
As mentioned above...there remains a bit of model uncertainty with
respect to the upper trough as it departs off to the east over the
weekend. The more plausible scenario at this point is a more progressive
and weaker feature moving off to our east...ensuring the expansion
of high pressure at the surface that will set the stage for a dry weekend
with mainly clear skies. This will also enable the arrival of ridging
aloft by late Sunday into the first half of next week...bringing an extended
period of dry weather and progressively warmer temperatures.
Saturday will be the coolest day of the extended with low and mid 60s
common for highs. Temperatures will rise from that point as southerly
flow takes over on the back side of the surface high...with highs
back to near 80 by Tuesday and continuing for much of the rest of
next week.
&&
.AVIATION (12Z TAF Issuance)...
Issued at 636 AM EDT Wed Apr 30 2025
Impacts:
- Showers and a few thunderstorms possible late today into tonight
Discussion:
Cloud cover will increase today as stalled boundary begins to lift
back northward as warm front. VFR conditions are expected, though
some restrictions may occur off and on in precipitation
Showers and a few thunderstorms will be possible, particularly later in
the day into tonight as the front moves back into the area and upper
level support increases. PROB30 groups will be utilized focused around
the most likely timing for thunder threats.
Winds will become more easterly with time into the daytime hours, continuing
to veer with time as the boundary moves northward. Sustained
winds will likely be 10KT or less much of the period.
$$
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...Nield
LONG TERM...Ryan
AVIATION...Nield
Office: IWX
FXUS63 KIWX 301040
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
640 AM 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 /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 640 AM EDT Wed Apr 30 2025
Brief return of very dry/stable air mass will ensure VFR
conditions through this evening. Overnight, warm/moist air
advection will ramp back up as a warm front lifts through the
area. A few light showers are possible prior to 06Z but the most
widespread and impactful precip is not expected until after 06Z
when the LLJ ramps up. MVFR ceilings are likely though exact
onset time is still uncertain. Isolated thunderstorms will also
be possible during the time but will leave out any mention for
now given low confidence.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...AGD
AVIATION...AGD
