Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 211624
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1224 PM EDT Mon Jun 21 2021

...Updated Aviation Discussion...

.Forecast Update...
Issued at 1020 AM EDT Mon Jun 21 2021

The cold front is bisecting the forecast area from northeast to
southwest this morning with isolated light showers developing.
Humidity levels are already dropping as dewpoints have slipped back
into the low and mid 60s...especially behind the front. 14Z
temperatures were generally in the 70s with lower 80s over the
southeast counties.

The overall forecast is in good shape with a few adjustments based
on current obs and trends. Expect the front to continue moving
southeast through the rest of the day with most convective
development focused along and south of the southern forecast area
border. Have nudged pops back a bit but still likely to see at least
a few showers and storms with the trailing upper trough not swinging
through the area until this evening. Most locations have already
seen their high temperatures for the day. With an abundance of cloud
cover and cold advection commencing with the frontal passage...
expect steady if not slowly falling temps through the 70s into the
evening. Winds will veer to northwest and remain gusty.

Zone and grid updates out.

&&

.Short Term...(Today through Tuesday)
Issued at 231 AM EDT Mon Jun 21 2021

The convective allowing models are consistent in weakening and
breaking up the potent central Illinois convection as it reaches
west central Indiana after 07z this morning. That said, deep layer
bulk shear increasing to around 40 knots, mixed layer CAPEs 1000 to
2000 J/kg and approaching cold front and sharp upper trough support
the convection holding together a bit more than the CAMs suggest and
therefore keeping high PoPs in. Best combo of shear, instability and
forcing is in good alignment with the SPC Day1 Slight Risk over
areas north of and parallel to Interstate 70. Curved hodographs
support a brief window before daybreak for isolated tornadoes,
otherwise damaging winds main severe threat.

Due to saturated grounds and precipitable water 1.75 to 2 inches,
there will be a concern for localized flooding, especially over
south central sections that saw so much rain Friday night.

BY 12z, best coverage should be over areas south of Interstate 70 as
the cold front should be moving into that area and will be south of
the forecast area by 18z. Instability will be waning as well, so
threat of severe weather will be next to nil after 12z. Will keep
PoPs going through the afternoon and evening though with the trough
yet to move through. by 06z Tuesday, the front should be through and
much drier and cooler air will be ushered in for Tuesday.

With plenty of convective related clouds around, and the front
moving through early, temperatures will likely only reach the 70s
this afternoon, except for perhaps mid day highs around 80 south of
Bloomington.

Very dry column Tuesday combined with subsidence from surface high
pressure over the Ohio Valley will result in sunny skies and well
below normal temperatures. Based on low level thermals, afternoon
highs will only reach the lower to middle 70s and with dew points
only in the middle 40s, it will be similar to a typical mid May or
late September day.

&&

.Long Term...(Tuesday night through Sunday)
Issued at 315 AM EDT Mon Jun 21 2021

Quite cool and crisp conditions will start the period, as surface
high pressure over the Mid-West brings another mostly clear and calm
overnight with readings dropping to the low-mid 50s across central
Indiana early Wednesday.  A small embedded wave within the mid-level
cyclonic flow may spread scattered clouds across the region Tuesday
night-Wednesday, but the antecedent very dry column will prevent
any measurable rain.  Otherwise, following few changes in latest
guidance, a slow-paced return to typical early summer will follow
Wednesday and Thursday...with increasing southerly breezes bringing
dewpoints back into the upper 60s.

Chances of showers and at least a few thunderstorms will then follow
in the Thursday night to Sunday timeframe...as the upper trough
approaching the Mid-West is locked in place from the central Plains
to the western Great Lakes courtesy an amplifying ridge over the NW
US / SW Canada.  The associated stationary front to our west will
allow deep Gulf moisture to advect over Indiana, will PWATs
occasionally surpassing 2.00", especially south of I-70. Uncertainty
is introduced by potential surface cyclogenesis along the boundary
in the Friday-Saturday period...which would likely increase forcing
over much of the region...and perhaps even pull the front eastward
towards Ohio by the end of the weekend, as several ensembles
suggest. Nonetheless given low confidence in this feature, kept
at least chance POPs through Sunday.

Despite the humid summery feel, temperatures should be no higher
than normal values through the late week/weekend, as the more-
amplified upper levels prevent much of the southwestern ridge from
building into Indiana...and considerable cloudiness/rains keep
readings moderated.

&&

.Aviation...(18Z TAF Issuance)
Issued at 1224 PM EDT Mon Jun 21 2021

IMPACTS:

- Isolated to scattered showers this afternoon...most likely to
impact KBMG
- Northwest winds gusting to 20-25kts through early evening
- Other than perhaps a brief drop to MVFR ceilings early this
afternoon...VFR conditions expected.

DISCUSSION: The cold front has passed through all of the terminals
early this afternoon but lower stratocu remains along with a few
showers. As drier air slowly advects into the region from the
northwest...should see ceilings gradually lift with scattered
showers diminishing by late day.

High pressure will build into the region overnight as the front
moves away to the southeast. Skies will become mostly clear early
Tuesday. May see scattered diurnal cu develop by early afternoon
Tuesday. Winds will be from the N/NW overnight and Tuesday at 10kts
or less.

&&

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

&&

$$

Update...Ryan
Short Term...MK
Long Term...AGM
Aviation...Ryan


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