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000
FXUS63 KIND 230701
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
301 AM EDT Tue Apr 23 2024

.KEY MESSAGES...

- Afternoon/evening rain expected. Total QPF under a half inch.

- Cooler mid-week, with some frost possible Wednesday night for
North Central Indiana

- Active pattern returns Friday into next week with above normal
temperatures and numerous storm chances

&&

.SHORT TERM (Today and tonight)...
Issued at 301 AM EDT Tue Apr 23 2024

Latest surface analysis shows a surface low located over Northern
Lake Superior with a front extending southwest toward another
surface wave across the Front Range in Colorado. Energy from that
wave rides along the front as it slowly pushes southeastward through
Indiana this afternoon and evening increasing rainfall coverage and
intensity. Latest hi-res guidance continues to slow down the front
and arrival of rain across the region, so have continued the trend
in the forecast. Latest satelitte and radar imagery show scattered
areas of clouds and showers along the front associated with an upper
level wave along the Kansas/Nebraska Border. Expect this activity to
continue its eastward progression through the day, expanding in
coverage along the front. Although latest sounding and ACARs data
from around the Midwest shows a very dry profile in the lowest 5 km
of the atmosphere. In fact, latest observations still show dew point
depressions of 20-25 degrees across Indiana and points west. With
such a dry low and mid level profile, it is going to take a while
for the column to saturate and for precip to reach the ground. This
adds to the confidence in a later start time for rainfall across
Indiana. QPF values are likely a bit overdone as well as guidance is
likely not handling the very dry antecedent conditions very well.
While rainfall amounts were already forecasted to be under a half
inch, it is likely that most areas will see around a third of an
inch or less.

With all that said, best forcing for ascent and saturation through
the column arrives during the 19-22z timeframe this afternoon with
the arrival of the mid level energy riding along the front. This can
easily be seen in 850mb maps as the low level jet ramps up to 30-40
kts. Forecast soundings by 18Z show good saturation in the mid and
upper levels across the area with pwats around 1 inch. Recent
guidance does keep the boundary layer fairly dry as low level
moisture advection will likely be lagging as much of the deep Gulf
moisture is blocked from pushing north due to a strong area of high
pressure and associated subsidence across the Gulf Coast. While
forcing seems quite favorable for precip, moisture is somewhat
limited. Thus a light rain is expected. So we are looking at high
confidence, low amount type rain event. Furthermore, forecast
soundings fail to show much instability, so any thunder will be
minimal to none.

With a drier atmosphere and later arrival of rainfall, bumped highs
up across the region several degrees into the mid to upper 60s for
South Central Indiana and lower 60s for North Central Indiana.
Despite increasing clouds, greater boundary layer heating today will
allow for greater mixing to occur resulting in winds in the low
level jet and drier air being brought down to the surface. Winds may
gust upwards of 20-30 kts at times this afternoon ahead of the
approaching front. This may promote even drier air also mixing down
to the surface ahead of the rainfall, further working to keep
rainfall amounts fairly light.

&&

.LONG TERM (Wednesday through Monday)...
Issued at 301 AM EDT Tue Apr 23 2024

On Wednesday, cold advection in the wake of departing shortwave
trough will overspread the central part of the state. This will
moderate readily given the degree of diabatic surface heating this
time of year. However, a subsequent minor shortwave perturbation
looks to be enough to cause lingering stratus across roughly the
northeastern half of the state. This could result in a 10-12 degree
temperature gradient across central Indiana. Temperature forecast
uncertainty is above average.

By Thursday pronounced ridging will be building into the Mississippi
Valley with a shortwave trough emerging onto the Plains.
Temperatures moderate some but the warm front and associated warm
advection-driven precipitation hold west until Friday.

Temperatures should be warmer Friday with pronounced warm advection
in response to aforementioned Plains mid-latitude system, although
this may be offset some by clouds and precipitation. It appears as
of now, precipitation would be most likely the latter half of the
day, though this timing may need to be adjusted. Precipitation
should mostly be from a northwest to southeast oriented warm frontal
rain band with some embedded convection/thunder given the presence
of weak instability.

Models show a weakening of this shortwave trough and a track holding
stronger height falls/forcing to our northwest. Nevertheless, its
warm conveyor belt and associated broad/strong IVT signal will be
positioned over Indiana late Friday into early Saturday and support
precipitation during that time. The track and life stage of the
cyclone by then will mean steeper midlevel lapse rates will be
displaced from the warm conveyor belt and so this should limit
intense convection and severe potential. Also, this pattern will
support cold advection holding to the northwest without a push into
Indiana, so temperatures will remain warm through the weekend and
into early next week.

A more classic frontal band scenario with greater instability looks
to arrive late Sunday or Monday with the next shortwave trough. This
looks to take a similar path as the previous, but is
broader/stronger with greater forcing and steeper midlevel lapse
rates. Thus, a more robust QPF signal and a better chance of severe
storms. This is supported by a broad relatively low probability CSU
machine learning signal.

For the Day 8-14 period, early indications are for ridging and
anomalous warmth over the east and positive precipitation anomalies
staying to our west. There is too much chaos in the ensembles to
identify a specific impact, but given the overall synoptic pattern
indicated some convective hazard risk may exist during this period.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 822 PM EDT Mon Apr 22 2024

Impacts:

- LLWS late tonight at LAF. May periodically impact other sites as
well

- Rain to move through tomorrow, lowering ceilings and
visibilities to MVFR with it

- SW  to W winds tomorrow will be sustained near 15 kts with gusts
up to 30 kts

Discussion:

VFR conditions will persist through the night and into tomorrow
morning ahead of an approaching system that will brings rain, MVFR
conditions, and breezy winds. High clouds ahead of this system have
already started to move into the area. Rain and MVFR conditions will
arrive from the NW tomorrow, reaching LAF near mid-morning and the
other TAF sites by early to mid afternoon.

There will be a threat for LLWS from 06-12z that is mostly expected
to impact LAF but can not rule out that it impacts the other sites
periodically during that timeframe. Winds overnight will be from the
SW near 7-10 kts. Sustained speeds will increase to near 15 kts in
the morning with gusts up to 30 kts possible through much of the
day. Wind direction will become more westerly by the end of the TAF
period.


&&

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

$$

SHORT TERM...CM
LONG TERM...BRB
AVIATION...KF