401
FXUS63 KIND 011616
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1216 PM EDT Mon Jul 1 2024

.KEY MESSAGES...

- Continued cool with low humidity today
- Heat and humidity returns on Tuesday and continues through
  Friday
- Rain and thunderstorm chances Wednesday onward

&&

.FORECAST UPDATE...

- Sunny and Pleasant this afternoon

Surface analysis late this morning shows strong high pressure in
place over MI. Cool and dry easterly flow was in place over Central
Indiana. GOES16 shows clear skies across Central Indiana, and dew
points were mainly in the 50s. Aloft, water vapor imagery showed
strong ridging in place over the plains states. This was resulting
in NW flow aloft and subsidence over Indiana.

ACARS soundings this morning show a very dry column with a sharp mid
level inversion that will prevent any CU formation. Little overall
change is expected through the day with this profile. Thus a mostly
sunny sky will be expected as the high drifts to the eastern Great
Lakes by this evening. The dry and easterly flow today will result
in weak cold air advection today. However this should just result in
persistence type highs, in the upper 70s. Overall, ongoing forecast
remains in good shape.

&&

.SHORT TERM (Today and tonight)...
Issued at 220 AM EDT Mon Jul 1 2024

Mid-upper level ridge axis will remain west of Indiana today and
winds will veer to easterly as the whole pattern progresses. This
synoptic configuration will support one more day of relatively cool
temperatures and low humidity. Periodic cirrus may be observed as
high-level moisture crests the ridge. With a reasonable model spread
on temperatures, a blended approach is acceptable. An increase at
most locations by a degree or two compared to yesterday is expected.

Radiative conditions will still be reasonably good for anomalously
cool temperatures tonight, and have adjusted to raw and high
resolution models that fall between about the 10th and 90th
percentile. Low to mid 50s for minimums.

&&

.LONG TERM (Tuesday through Sunday)...
Issued at 220 AM EDT Mon Jul 1 2024

The synoptic scale pattern through the upcoming week won`t be too
different than the last few weeks, with low-amplitude progressive
shortwave troughs periodically passing. These may trend slightly
more amplified than we`ve seen recently, but we`ll still be on
the southern periphery of stronger westerlies aloft resulting in
marginal shear and overall weak forcing for each precipitation
event.

As we saw yesterday, it`s difficult to accurately convey precision
of convective timing and intensity in these type of patterns. One
diurnal convective uptick can augment the upper flow pattern and
influence mesoscale features in the subsequent diurnal maximum,
essentially resulting in a domino effect causing model
predictability to deteriorate with time. The good news is that the
deterministic and ensemble suite of model guidance is in
generally good agreement on individual shortwave trough timing and
periods of stronger forcing for ascent in our region (albeit
relatively weak as explained above).

A lead wave that passes to our north early Tuesday and hastens the
return of rich subtropical moisture to the higher latitudes, though
still positioned to our west. Convection spawn by this wave should
be relegated to the northern Great Lakes. Also, as the ridge axis
passes, warm plume will advect in causing temperatures to return to
about normal for early July (mid 80s).

Later Tuesday, a more amplified shortwave trough and attendant
surface cyclone and front will encourage convection centered on Iowa
and Wisconsin. Longevity should be limited by narrow rich moisture
plume seen in IVT and PWAT anomalies, and weak flow/shear south
of subgeostrophic speed maxima over Michigan. Nevertheless, some
weak convection or convective debris will probably reach central
Indiana late Tuesday night into early Wednesday.

On Wednesday, the broader shortwave trough over Ontario and slightly
dampening Southeast ridge will result in an east-west placement of a
weakly baroclinic front across central Indiana. Veered flow and a
connection to rich subtropical moisture, combined with diurnal
destabilization and frontal forcing should result in scattered to
numerous thunderstorms. Stronger westerlies aloft remain to the
north but there may be just enough shear for weakly organized multi-
cell clusters, and a thermodynamic environment that could favor at
least localized severe wind gusts. In a reasonable worst case
scenario, more organized short line segments would be capable of
some more sustained strong to damaging wind gusts.

Thursday (July 4th) is where mesoscale uncertainties increase
considerably. At the synoptic scale, multi-model ensemble mean
shows continued weakening Southeast ridge and an upstream trough,
which should result in the synoptic boundary still being present
somewhere in our region. It could be shunted south if previous day
convection is robust enough, refocusing diurnal convection closer
to the Ohio River or into Kentucky. There could also be one or
more MCS/MCVs to focus renewed more concentrated convective
development somewhere across the region. Thus, our approach for
now is an ensemble based mean precipitation probability approach
which is fairly broad and accounts for a variety of mesoscale
scenarios. It`s worth noting though that our partners in media and
emergency management should communicate a potentially active day
with regards to thunderstorms, and associated hazards including
lightning and strong wind gusts being the primary threats.

Friday may be a little more synoptically-driven with a closing
midlevel low to our north, probably focusing most of the convection
east of our area into Ohio. There is some uncertainty on this as
ensemble spread grows larger at this time range. This could give a
modest reprieve from humidity and lower thunderstorm chances into
next weekend.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1216 PM EDT Mon Jul 1 2024

Impacts:

- VFR Conditions expected.

Discussion:

Surface high pressure moving across the Great Lakes will continue to
provide a dry easterly flow to Central Indiana. Forecast soundings
remain dry through the period under the influence of this high
pressure system. Winds will become a bit more southerly as the high
reaches the eastern Great Lakes on Tuesday.

&&

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

$$

UPDATE...Puma
SHORT TERM...BRB
LONG TERM...BRB
AVIATION...Puma