Severe Thunderstorm Warning 61, NWS Indianapolis, IN

Area Forecast Discussion
National Weather Service Indianapolis IN
924 PM EDT Thu Apr 18 2024

.KEY MESSAGES...

- Severe storms and are possible through the early overnight and
  locally heavy rain is possible through daybreak.

- Cooler but dry Friday through Monday. Some frost potential mainly
  north Sunday morning, more widespread frost possible Monday
  morning.

- Increasing rain chances next Tuesday, low chance for thunderstorms

&&

.FORECAST UPDATE...
Issued at 923 PM EDT Thu Apr 18 2024

Latest radar loop was showing a broken line of strong to severe
thunderstorms moving east and southeast across east central Illinois
with individual cells moving northeast around 30 mph. These storms
were within a SW-NE oriented instability axis with SB CAPE to 1500+
J/kg. Further west, CAPEs were only around 500 J/kg, over the lower
Wabash Valley, where the Severe Thunderstorm Watch extended to. HRRR
has had a good handle on this broken line of convection and moves it
over central Indiana 02z-06z. The combination of low level
convergence from frontal boundaries and a surface low tracking
through, moisture transport, instability and 30 to 40 knot deep
shear has lead to some upstream damage over the LSX, ILX and PAH
forecast areas.

CAMS in good agreement the squall line will gradually weaken as it
moves into the more stable air in place across east central and
southeastern parts of central Indiana. That said, the Watch
currently runs through 3 AM over parts of the lower Wabash Valley.

Radar was showing additional convection further northwest across
west central Illinois. This convection should roll across central
Indiana overnight with instability waning, not be a course for
concern regarding severe weather.

Upstream 6 hour MRMS QPE was showing a few localized areas of an
inch or so to 2 inches or so, but otherwise, don't atnicipate to
many water concerns in addition to the ongoing river flooding.

Wind gusts will approach 25 mph and turn to the northwest overnight
in the wake of the cold front. The gusty winds and cloud cover will
temper the cold advection and should keep temperatures to no lower
than middle 40s to lower 50s by daybreak.

&&

.SHORT TERM (This evening through Friday)...
Issued at 317 PM EDT Thu Apr 18 2024

It's another day of above normal temperatures and a conditional
threat for severe weather. Satellite shows high clouds currently
over central Indiana while surface observations show temperatures
warming into the 70s and dew points creeping higher over the SW
counties.

Thunderstorms will move in this evening, likely entering the state
between 8 and 10 pm and tracking eastward through the overnight
hours. The storms in question are currently over Missouri as of this
afternoon. As they approach, winds will start to increase to
around 10-15 mph with non-thunderstorm gusts possible through the
night. Withe the severe threat, confidence remains low given the
conditional nature. The latest CAMs show that variables may not
line up quite right, but if they do damaging winds will be the
main threat while an isolated tornado and isolated hail can't be
ruled out. Isolated flooding may also be a concern as up to an
inch of rain will be possible as the line of storms moves through
a region that already has a pretty saturated ground.

The best threat for severe weather will be over the SW counties
where the best instability and moisture content will be. As the
storms reach the area, CAPE of 500 to 1000 J/kg are expected,
especially over those SW counties, but looks to drop to less than
500 J/kg over the following few hours. However, latest CAMs are
showing less than impressive shear and helicity over the area and
the surface low driving this system looks to lift as it reaches
central Indiana. Lapse rates of 7 C/km may still be around when the
line arrives but confidence is low and it seems more likely that
those will have dropped off beforehand.

The line of storms and the cold front causing them are expected to
move out of the forecast area by sunrise or shortly after. Highs
tomorrow will be lower and closer to normal, reaching only the mid
50s to low 60s. Otherwise, nice weather is expected for the day
tomorrow with only partly cloudy skies remaining.

&&

.LONG TERM (Friday night through Thursday)...
Issued at 317 PM EDT Thu Apr 18 2024

Friday night through Monday...

Quiet weather conditions are expected for several days as surface
high pressure remains dominant over the region. Aloft, guidance
shows a few upper level impulses traversing the region which could
help to keep clouds around at times over the weekend. A weak LLJ
associated with an upper disturbance moving through Saturday will
likely help promote breezy conditions. Gusts up to 25 mph are
possible during the day.

Expect temperatures to trend cooler heading into the weekend due to
cold air advection. Lows dropping into the 30s both Saturday/Sunday
night combined with relatively light winds could support the
potential for frost. There is higher confidence in frost Sunday
night into Monday morning at this time since guidance shows much
less cloud cover. Greater cloud cover from an upper level impulse
Saturday night leads to higher uncertainty. Highs are generally
going to range from the low 50s to near 60F over the weekend before
warming up early next week.

Monday night onward...

Rain chances return late Monday night into Tuesday as a shortwave
trough and associated low pressure system move across the Great
Lakes Region. Return flow ahead of the approaching system should
allow for temperatures to continue moderating. Sufficient moisture
return combined with increasing dynamics supports likely POPs on
Tuesday. The system is likely going to move out Tuesday night. Cold
air advection and surface high pressure building in behind the
departing low will allow for quiet weather conditions to return
briefly before another system approaches late next week.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 616 PM EDT Thu Apr 18 2024

Impacts:

- Showers and thunderstorms moving in 00Z-02Z and ending 09z-11z

- MVFR and briefly worse flying conditions will accompany the
  convection and MVFR or worse will likely hang around a few
  hours after the convection moves out

- Damaging winds to 50 knots possible in the stronger cells

- Winds will shift to NW, in the wake of the front, with gusts to
near 25 knots, after 05z-15z

Discussion:

Showers and thunderstorms, with the leading edge likely linear, will
sweep across central Indiana late this evening into the overnight.
Deteriorating flying conditions will accompany the convection and
low ceilings will hang around a few hours after frontal passage.

Damaging winds are possible mainly with the leading line and later
winds will turn northwest and gust to near 25 knots behind the cold
front.

&&

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

UPDATE...MK
SHORT TERM...KF
LONG TERM...Melo
AVIATION...MK

Hazardous Weather Outlook...UPDATED
National Weather Service Indianapolis IN
940 PM EDT Thu Apr 18 2024

INZ021-028>031-035>049-051>057-060>065-067>072-191000-
Carroll-Warren-Tippecanoe-Clinton-Howard-Fountain-Montgomery-
Boone-Tipton-Hamilton-Madison-Delaware-Randolph-Vermillion-Parke-
Putnam-Hendricks-Marion-Hancock-Henry-Vigo-Clay-Owen-Morgan-
Johnson-Shelby-Rush-Sullivan-Greene-Monroe-Brown-Bartholomew-
Decatur-Knox-Daviess-Martin-Lawrence-Jackson-Jennings-
940 PM EDT Thu Apr 18 2024

This Hazardous Weather Outlook is for Central Indiana.

.DAY ONE...Tonight.

Weather hazards expected...

  Elevated hail risk.
  Elevated thunderstorm wind damage risk.
  Elevated lightning risk.

DISCUSSION...

Scattered to numerous thunderstorms are expected this evening and
into tonight. Severe storms are possible with damaging winds as
the primary hazard. A lower risk for large hail, localized
flooding, and tornadoes also exists. Lightning is a hazard with
any thunderstorm.

Storm motion will be to the northeast 30-40 mph.

.DAYS TWO THROUGH SEVEN...Friday through Tuesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is requested this evening into the early
overnight.

&&

This product in graphical format...along with other weather...
hydrological and climate information...at:

http://www.weather.gov/erh/ghwo?wfo=ind
http://www.weather.gov/ind

WFO IND

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