Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 231243

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


- 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


Issued at 841 AM EDT Tue Apr 23 2024

- Increasing Clouds with afternoon Rain

Surface analysis late this morning shows low pressure over Lake
Superior and a second area of low pressure was in place over SW OK.
A cold front across WI, IA and NE KS connected these two lows. Broad
and elongated high pressure was found across the east coast.  This
was resulting in southerly flow across Central Indiana, however the
high pressure system was effectively blocking moist gulf flow from
reaching the Ohio Valley.

Aloft, a moderate short wave was found over MN and SW Ontario, with
a trough axis extending SW across SD. This was resulting in moderate
westerly flow aloft across Indiana. This short wave was being
influence by the broader cyclonic flow across northeast North
America as a deep upper low was anchored near Hudson Bay.

GOES16 shows abundant cloud cover ahead of the frontal boundary,
pushing toward Central Indiana. An area of rain was found over NE MO
and western IL, pushing east. Dew points across central Indiana
remained quite dry, in the middle 30s, resulting in current dew
point depressions of 15-20F.

The upper short wave over the northern plains is expected to pivot a
trough axis southeast across Central Indiana this afternoon before
exiting this evening. The associated cold front is expected to
slowly advance southeast and elongate somewhat this afternoon. HRRR
suggests advection of the clouds and precipitation to west to reach
much of Central Indiana through the afternoon hours. Forecast
soundings also show a brief period of column saturation late in the
afternoon. This seems reasonable considering the dry lower levels
and large dew point depressions. Thus will try and focus highest
pops during the mid to late afternoon hours, when this best moisture
is suggested to arrive. Given the expected increasing cloud cover
and rain arrival, highs around 60 will be expected, with low to
mid 60s south.


.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 IVs 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 (12Z TAF Issuance)...
Issued at 631 AM EDT Tue Apr 23 2024


- LLWS through around 18z

- Rain moving in this afternoon and evening, periods of MVFR cigs
and vis

- SW  to W winds increasing after sunrise to 12to 18 kts with gusts
up to 30 kts


VFR conditions persist early this morning across all of Central
Indiana. A front will slowly push southeast through the state later
today bringing a period of rain with winds shifting from southerly
to westerly into the evening. Latest guidance continues to push back
the timing of the rainfall arrival, so have kept the TAFs more
optimistic for much of the day. Expect conditions to begin
deteriorating around late morning to early afternoon for KLAF, then
after 20z for KHUF, KIND, and KBMG. MVFR cigs and cigs expected at
times during the rain, however conditions should become VFR again
during the 00-06z timeframe. Very slight chance of an isolated
lightning strike along and south of I-70 later this evening, but
confidence in that occurring is too low to mention it in the TAF.

There will be a threat for LLWS through around 18z. Latest ACARS
soundings does indicate a strengthening southwesterly low level jet
overhead; however winds at the surface have not responded due to a
low level inversion. Once mixing begins later this morning, stronger
winds will mix down to the surface. Winds early this morning are
from the SW near 7-10 kts. Sustained speeds will increase to near 15
kts after sunrise 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.




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