195
FXUS63 KIND 230144
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
944 PM EDT Sat Jun 22 2024

.KEY MESSAGES...

- Some showers and storms overnight into Sunday. Isolated strong to
  severe storms possible.
- Tuesday likely to be warmest day of the week.
- More thunderstorms possible Tuesday into Wednesday, with one or
  more rounds of strong to severe storms possible, though uncertain.
- A brief respite from heat and humidity late in the week.

&&

.FORECAST UPDATE...
Issued at 942 PM EDT Sat Jun 22 2024

Following the third consecutive day to reach 92F at Indianapolis...
generally scattered mid-level cloud continues to steadily cross the
region this evening along the southern portion of a rather broad and
strengthening baroclinic system currently crossing the Great Lakes.
Associated slowly-approaching cool front and weak low-level jet will
combine to promote scattered convection, currently over the
southeastern third of Iowa, across Illinois tonight and into the
Upper Wabash Valley by 08Z.

Latest CAMs appear a bit fast and perhaps generous with coverage of
storms, but imagine flux of better deep moisture into this cluster
could bring a couple stronger storms into the CWA`s northwestern
zones during pre-dawn hours...with isolated marginally strong/severe
winds possible.  Suspect at least widely scattered showers and
weakening cells to cross region towards dawn.

Southwesterly surface winds gusting around 20 MPH amid the passing
wave will help to push dewpoints into the upper 60s, holding
overnight minimums to the low 70s.  Rainfall expectations are mainly
light, with the potential for 0.50-1.00 inch for Crawfordsville and
points north/ west, especially for locations caught under the few
stronger cells.

&&

.SHORT TERM (This evening through Sunday)...
Issued at 305 PM EDT Sat Jun 22 2024

The persistent mid-upper ridge is dampening quickly, but since we`re
on the northwest side with enhanced southwesterly flow, 2-m
temperatures are hot this afternoon (~+7 degree anomalies for mid-
late June). With an upstream shortwave trough, the MSLP pattern has
shifted and is providing a stronger breeze. This has kept wet bulb
globe temperatures in the moderate category.

As the aforementioned shortwave trough approaches, it will nudge a
stationary front southward resulting in a diurnal blow-up of
convection concentrated over Iowa. This is modeled to grow upscale
and propagate into Illinois this evening. Despite it being on the
southern periphery of stronger westerlies aloft, modest low-level
jet will encourage east-southeastward propagation into Indiana late
tonight. Although we will be approaching a diurnal minimum, a band
of richer moisture through a deep layer will contribute to modest
instability late into the night. This should support continued east-
southeastward movement through our area during the morning, albeit
in a weakened state. Intensity trends should mean only a low
probability of strong to locally damaging winds across our northwest
counties later tonight.

The temperature forecast tomorrow has a higher degree of uncertainty
than usual due to a substantial model spread (up to around 10
degrees of spread). This appears to be due to 1. remnant clouds from
convection early and/or remnant PBL moisture, 2. over mixing and
warm bias in ECMWF. We nudged lower to avoid the ECMWF, and
generally near the mean of most other model guidance.

Gradual infiltration of drier air mass and convergence displaced to
the south by peak surface heating should preclude additional
convection, once morning remnants moves out.

&&

.LONG TERM (Sunday night through Saturday)...
Issued at 305 PM EDT Sat Jun 22 2024

Continued warmth is expected throughout much of the long term
forecast, with at least one day of widespread 90s expected Tuesday.
The saving grace will be that some relief from the recent stifling
humidity is expected on Monday, with slightly more sustained lower
dewpoints late in the week.

Additionally, a couple of opportunities for thunderstorms are
expected, with some potential for organized severe thunderstorms
late Tuesday into Wednesday, though uncertainty remains significant
given guidance discrepancies and daily dependencies of convection on
the influences of prior days` activity.

The work week will begin with some slightly lower heat and humidity,
and dry weather under the influence of surface high pressure.

As we move into Tuesday and Wednesday, convection is likely to
develop to our northwest along the tail end of a boundary extending
from low pressure well to then north in a background environment of
ample deep layer shear and strong to extreme instability within a
prefrontal theta-e axis. This activity is likely to rapidly grow
upscale into one or more QLCSs, then move steadily along the
instability gradient late Tuesday into Wednesday. This is not unlike
the traditional "ridge rider" scenario we often see around this time
of year into the depth of the warm season, though there will be some
contribution from frontal forcing as the boundary sags further south
as well. However, if severe storms are to occur in central Indiana,
it will be most likely be cold pool driven given far weaker deep
layer shear this far south, with damaging winds the primary threat.

Diurnal timing is not ideal, though late night severe is frequently
seen this time of year via the aforementioned thermodynamically-
driven scenarios. Additionally, reintensification or redevelopment
of strong to severe storms will be possible Wednesday along the
front or boundaries from prior convection, though degree of
destabilization is more in question given the impacts of this prior
activity on insolation and low level moisture advection.

Overall, Tuesday into Wednesday will merit close monitoring for one
or two windows of severe threat, primarily due to damaging wind
potential, along with some heavy rain/localized flooding threat
given fairly significant precipitable water values. Experimental
machine learning guidance continues to support this potential.

The latter portion of the work week will offer some relief in the
form of quiet weather, slightly lower temps, and significantly lower
dewpoints as high pressure traverses the region, though this may be
short-lived as guidance indicates potential for the southwestern
ridge to push back eastward and additional convective potential
along the periphery as we get into next weekend, though model
differences are significant with respect to ridge amplitude and
location, and thus relatively low chances are forecast for the
moment.

Tuesday appears likely to be the hottest day of the week, though
guidance clustering, as well as recent and longer-term NBM biases
suggest the blend highs are a few degrees too warm. These were
adjusted accordingly. Additionally, multiple potential influences
from low level moisture, mixing potential, and convective influences
present several ways that may impact ability to reach the hotter NBM
numbers. The remainder of the week looks to see temps near to
slightly above normal for the time of year.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 734 PM EDT Sat Jun 22 2024

Impacts:
 - Showers and generally low probability of thunder after 07Z tonight
 - 2-4 hours of MVFR stratus Sunday morning, passing from NW to SE
 - Southwest winds tonight gusting 18-20KT at KIND/KLAF after
   04Z... with winds at all terminals veering to NW by 23Z Sunday

Discussion:

VFR conditions to prevail through at least 10Z tonight across
central Indiana as surface low pressure strengthens while tracking
from near the Quad Cities eastward across the Great Lakes. Mid-
level clouds to slowly increase this evening ahead of weakening
convection that will track across Indiana to the east-southeast
after midnight...with some thunder possible, especially at KLAF.
Otherwise rain showers may impact TAF sites for a few hours within
the 08-13Z period.

MVFR stratus should follow convection within the 11-17Z window,
albeit with lower confidence.  Winds mainly sustained at 8-12KT
through the TAF period, with gusts to 18-20KT at KIND/KLAF after
midnight tonight...flow to veer to westerly by 16Z Sunday, and to
northwest by 23Z.

&&

.IND WATCHES/WARNINGS/ADVISORIES...None.
&&

$$

UPDATE...AGM
SHORT TERM...BRB
LONG TERM...Nield
AVIATION...AGM