971
FXUS63 KIND 231856
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
256 PM EDT Thu May 23 2024

.KEY MESSAGES...

- Scattered to numerous showers with some storms south, but dry
  north today

- Rain and t-storms possible on Friday, and likely on Sunday...
  with strong/severe storms possible both days

- Temperatures expected to return to near normal next week

&&

.FORECAST UPDATE...
Issued at 916 AM EDT Thu May 23 2024

The stationary boundary has begun to weaken with broader southerly
flow overtaking the Ohio Valley ahead of another shortwave. This has
allowed for moisture to return northward, providing lift and showers
across the southern half of central Indiana. A few of these showers
have tall enough tops for occasional lightning, but a majority
should remain lightning free.

Later this afternoon, destabilization should allow for more coverage
of thunderstorms, although still remaining over southern Indiana.

&&

.SHORT TERM (Today and tonight)...
Issued at 307 AM EDT Thu May 23 2024

Early this morning, a front was across southern Indiana. Aloft,
central Indiana remained under southwest flow. A few showers and
isolated storms have developed across southern Illinois.

A couple of pieces of upper energy will move through the southwest
upper flow and produce lift over the surface front. Decent moisture
south of the surface front isn`t that far away from the area, so the
lift will continue to be able to tap into that.

Farther north, drier air along with weak surface high pressure will
remain in place. This will limit how far any rain can get from the
southern forcing.

Given the above, will go with high end chance category to low end
likely PoPs across the southern forecast area. PoPs will be lower to
the north, with dry conditions not too far north of I-70. There will
likely be a relative lull in the PoPs late morning into early
afternoon between the rounds of upper energy.

Best instability will remain south of central Indiana today, but
wouldn`t rule out a brief strong storm in the extreme southern
portions of the area this afternoon.

With clouds and rain around, highs will be around 80 in the south.
Meanwhile, deeper in the slightly cooler and drier airmass but with
more sunshine, highs in the north will also be around 80.

Forcing from the last upper wave may linger into the evening hours,
so will keep some low PoPs south and southeast then. Afterward, a
brief period of upper ridging will provide dry conditions.

There may be some stratus/fog development overnight tonight, as low
level moisture returns in light southerly flow as the surface high
exits to the east. The rain that falls today could amplify this
moisture. At the moment conditions do not look favorable for
widespread dense fog though. Will continue to monitor.

Lows will be in the lower 60s.

&&

.LONG TERM (Friday through Wednesday)...
Issued at 307 AM EDT Thu May 23 2024

Friday through Sunday...

Our recent zonal, yet disturbed pattern will continue through the
weekend with embedded waves promoting showers/thunderstorms amid
rather humid southerly flow both Friday-Friday night...and again
Sunday-Sunday night, with weak ridging on Saturday providing a more
pleasant day in between.  Friday`s threat will be amid a weak warm
frontal zone type pattern with RW/TRW expected to arrive from the
southwest during the afternoon before rain chances peak during the
evening and linger overnight.  Timing of stronger storms may be
bimodal, with ample afternoon instability over the region`s western
half...before CAPE returns overnight over mainly southwestern zones.
Less confidence in the conditional daytime potential where both
lapse rates and wind shear are expected to be less impressive.
Overnight storms may, however, have 200-300 m2/s2 of 0-3 km storm
relative helicity to utilize west of I-65.  Rainfall amounts should
be mainly under 0.50 inches, with over 1.00 inch under most intense
cells along the Wabash Valley.  The overall marginal severe threat
would include all potential hazards, with winds and hail the
greatest concerns.

Mostly sunny with light northwesterly breezes on Saturday which
might actually bring mid-50s dewpoints by late day to northern
counties.  Sunday will then sport the greatest rain chances of the
long term, with a couple negatively tilted vort maxes, ahead of
approaching surface low pressure, progged to return rain chances for
about 18-24 hours to any specific location.  Widespread showers and
scattered thunderstorms are possible through afternoon and evening
hours with a general 1.00-2.00 rainfall potential following the
usual gradient with greatest precipitation likely south/west of
Bloomington.  Strong to severe storms are certainly on the table for
Sunday with a 1000-3000 J/kg CAPE gradient possibly aligned over the
CWA during afternoon and evening hours...which may be coupled with
locally high afternoon lapse rates and/or briefly impressive
helicity values along arriving vort maxs...all under 40-60KT of bulk
shear.  Still not the greatest confidence in strong/severe storms
with several potential limiting factors ranging from better moisture
being slower to return Sunday, considerable cloudiness squelching
instability, and perhaps upstream storms to our south zapping or
thermodynamic potential.  This outlook, along with Friday`s, will
continue to be monitored through further updates.

Monday through Wednesday...

The generally disturbed pattern should continue into the next work
week as the H500 flow over west-central North America becomes more
amplified...with an upper ridge building from the Rockies into the
Canadian High Plains, before advancing eastward towards the Upper
Midwest by the end of the long term.  Fairly good model agreement in
downstream short waves, one crossing the Missouri Valley Monday and
a second trying to plunge from the Canadian Plains to the Upper
Midwest around Tuesday...phasing/dumb-belling together over the
Great Lakes by Wednesday.  Lingering surface low pressure near
Indiana should be re-organized by the approaching southern trough...
before deepening while occluding near the southern Great Lakes. This
circulation should then slowly work east during the mid-week, while
the combined trough sags and drags across the northern Midwest as
long-awaited cold (or more practically lower-humidity-) air
advection begins to arrive from Canada.

All points considered, potential for organized, if not heavy
rainfall exists during Monday-Monday night...before further
opportunity for lighter/stratiform rains under low ceilings through
at least Tuesday and potentially longer as the combined trough
swings near the CWA.  The arrival time of Monday`s rain/convective
threat will be dependent on exactly when and where arriving upper
level dynamics catch up with lower level thermodynamics.  Guidance
is suggesting at least briefly heavy rain is possible Monday
somewhere within the IL/IN realm...under what may be impressive
lapse rates along a strong instability gradient.  Strong t-storms
could also be on the table, especially if the short wave were to
negatively tilt on arrival.

Better deep moisture should push east of the region around Monday
night ahead of the slowly departing system.  The early springtime
type pattern of WNW flow under the passing trough should be at times
brisk from the accompanying gradient.  Readings next week should be
overall near normal, with lows in the 50s returning by the mid-week.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 256 PM EDT Thu May 23 2024

Impacts:

- Scattered showers and isolated storms at southern sites today
  and this evening

Discussion:

Generally VFR conditions are expected. A few showers or
thunderstorms are possible at the southern sites this evening,
especially KBMG.

Will have to watch for some fog or stratus development overnight
tonight, but confidence is not high enough to include at this time.

&&

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

$$

UPDATE...Updike
SHORT TERM...50
LONG TERM...AGM
AVIATION...Updike