385
FXUS63 KIND 042301
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
701 PM EDT Sat May 4 2024

.KEY MESSAGES...

- Isolated to scattered showers and thunderstorms into tonight.
  Severe storms are not expected.

- Isolated flooding threat Monday.

- Growing confidence in the potential for a few rounds of severe
  thunderstorms Tuesday through Wednesday.

&&

.SHORT TERM (This evening through Sunday)...
Issued at 258 PM EDT Sat May 4 2024

The low cloud deck has slowly given way over the last few hours as
boundary layer mixing has commenced. Much of the forecast area is
now enjoying a mix of sun and cu with a noted min in the cu field
extending from Carroll County south into Putnam and Hendricks
Counties and indicative of remnant subsidence and a stable layer
courtesy of the high pressure ridge that moved off to the northeast
earlier. 18Z temperatures ranged from the low 70s in eastern
counties to near 80 in the Wabash Valley.

Rest of This Afternoon and Tonight

Messy pattern lingers across the Ohio Valley this afternoon with a
trailing axis of moisture in the wake of the weak low over western
Ohio. Stagnant wind flow has been unable to completely mix out the
low level moisture and with a subtle instability axis present across
southeast Indiana...have continued to see isolated convection pulse
up generally east of a Muncie-Shelbyville-Bedford line. These cells
will remain confined to mainly eastern portions of the forecast area
over the next few hours producing brief heavier rainfall and a few
lightning strikes as they pop up and down in an environment with
virtually no shear or forcing aloft. Convection will be dependent on
available instability which is likely to tick upwards a bit as we
approach peak heating late this afternoon.

Further west across the forecast area...the atmosphere is more
stable and will remain so into the early evening hours as the axis
of residual dry air and subsidence pivots east. Focus will turn to
scattered convection associated with a cold front approaching the
mid Mississippi Valley currently. Expect convective coverage and
intensity to increase over the next few hours as it crosses into
Illinois and interacts with an axis of moderate instability. The
storms will approach the Wabash Valley by mid evening in a steadily
weakening state as they move into a more stable environment. May
continues to see a few rumbles of thunder as the convection shifts
into the forecast area but will see a gradual decrease in coverage
tonight to just isolated showers after 06-07Z.

Sunday

Low clouds will again expand across much of the forecast area in the
predawn hours as the air dries aloft and low level moisture becomes
trapped beneath a shallow inversion. While the clouds should mix out
quicker on Sunday than they did earlier today with stronger winds
present...it will likely be late morning before stratus begins to
diminish setting up a nice afternoon with a mix of sun and clouds.
It will be noticeably drier than today as high pressure shifts into
the region and stronger subsidence is advected into the region from
the north. This will be a temporary reprieve from the unsettled
weather pattern which will return in earnest by early Monday with
the back end of the front set to pass through central Indiana
tonight returning north as a warm front. More on this and the
expected multiple opportunities for severe weather Tuesday and
Wednesday in the Long Term section below.

Temps...despite the arrival of drier air in the post-frontal
environment by early Sunday...the expansion of low clouds will keep
temperatures from falling much lower than the upper 50s and lower
60s. Dry air and northerly flow will keep temperatures slightly
cooler Sunday but still very pleasant for early May. Expect low to
mid 70s for much of the forecast area.

&&

.LONG TERM (Sunday night through Saturday)...
Issued at 258 PM EDT Sat May 4 2024

Our primary forecast challenge in the long range is severe weather
potential in the Tuesday and Wednesday timeframe. Occasional non-
severe showers and thunderstorms are possible Sunday into Monday.
Heavy rainfall potential exists through the period as well.

SYNOPTIC OVERVIEW

A trough moving ashore over the Pacific Northwest today is set to
become our feature of interest over the next several days. Before
that system arrives, a subtle mid-level wave developing over Texas
will lift northeast tomorrow towards Indiana. Occasional showers and
thunderstorms are possible, especially Monday morning as the core of
the wave passes by. Weak flow aloft will preclude an organized
severe threat. However, models show nearly moist adiabatic thermal
profiles with deep moisture. Large LCL freezing level spread
signifies that rainfall production could be quite efficient. A few
locally heavy downpours are possible within any deeper convection
that manages to form. Confidence is low regarding flood potential,
as large-scale lift associated with the wave is weak and may be
displaced to our south. Recent trends in guidance have taken this
system a bit further south since yesterday.

Turning our attention back to the western trough, guidance has it
ejecting into the Plains Monday afternoon. A prolonged period of
southerly flow has allowed a rather broad and buoyant warm sector to
take hold ahead of the trough. Instability will not be in short
supply going forward. Additionally, the trough flattens considerably
as it heads eastward which will allow a fast quasi-zonal jet streak
to impinge on the broad warm sector. Vort maxes embedded in the
faster flow should provide larger-scale lift to help initiate
convection ahead of the primary trough axis. Monday`s threat is well
to our west, mainly over the Great Plains. However, the trough
pushes east just enough to bring severe potential to our region by
Tuesday and Wednesday.

Beyond that, the trough wraps up and departs to our east leaving us
with cooler and drier northwesterly flow.

FORECAST CONFIDENCE

Confidence in the evolution of the larger-scale pattern is good.
Ensembles are in agreement regarding the position and timing of the
western trough. However, models differ with respect to the embedded
vort maxes and waves. Since these features may be the primary
drivers of severe weather potential...confidence decreases a bit.
Exact timing and location for the best severe weather chances cannot
yet be pinpointed.

However, our confidence in severe weather over the Midwest and Ohio
River Valley is increasing. The synoptic-scale pattern is quite
favorable for organized convection (large amounts of moisture,
instability, and shear). Additionally, CSU machine learning and CIPS
analogs are honing in on our region for severe weather Tuesday and
Wednesday. They paint a rather broad area, however, and as mentioned
above the exact location will need to be refined with time. Still,
the potential exists, and is increasing, that multiple rounds of
potentially severe storms affect the region next week.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 701 PM EDT Sat May 4 2024

Impacts:

-MVFR to briefly IFR cigs 04Z to 17Z
-MVFR vsbys due to rain 02Z to 07Z
-Wind shift from west to north after 06Z

Discussion:

Cloud cover will gradually increase after 00Z with the arrival of
rain at HUF and LAF around 02Z and IND and BMG around 04Z. TSRA is
not expected, but a few rumbles are possible.  MVFR cigs will then
prevail through 17Z with brief IFR at HUF and LAF towards 12Z. Winds
will generally be light and variable through the TAF period with a
predominately west direction becoming more northerly after 06Z.

&&

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

$$

SHORT TERM...Ryan
LONG TERM...Eckhoff
AVIATION...White