Area Forecast Discussion
Issued by NWS Indianapolis, IN

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461
FXUS63 KIND 222220
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
620 PM EDT Thu Apr 22 2021

...Updated Aviation Discussion...

.Forecast Update...
Issued at 618 PM EDT Thu Apr 22 2021

Concerns about widespread frost potential late tonight,
especially over the eastern zones, given current dewpoints in the
20s and winds diminishing after dark with surface high pressure
centered over the Ohio Valley. Latest short term model data
suggest lows may be a little lower than what is currently forecast.

Based on above, will be issuing a Frost Advisory for the eastern
zones for late tonight into Friday morning. Thickening cloud cover
arriving from the west late tonight should help to minimize
widespread frost potential farther west.

&&

.Short Term...(This evening through Friday night)
Issued at 144 PM EDT Thu Apr 22 2021

Satellite imagery this afternoon shows scattered diurnal Cu
across the area. High pressure and subsidence at the surface have
moved in and are keeping much of the lift out of central Indiana
while just off to the east there have been scattered snow mixed
showers. Paired with the eastward shift of the surface high,
ridging aloft starting to move in later today will end the CAA and
winds will shift from westerly to southerly overnight. Despite
this southerly shift, overnight lows are still expected to drop
down to the mid 30s. With these temperatures, patchy frost will be
possible. Skies are expected to briefly clear out this evening to
early tonight, but clouds will move back in from the SW late
tonight which should help to minimize widespread frost impacts and
will refrain from issuing any headlines at this time.

A low pressure system will begin to move out of the Plains states
and a warm front will spread into the area on Friday night. Precip
with this system has slowed a bit from previous runs, so only
maintained a slight chance along the western border just before 0z.
Isentropic lift moves in slowly before then but saturation pressure
deficits indicate the air is too dry initially for precip. With
clouds arriving later and precip arriving later along with the warm
advection in place during the day Friday, should see highs in the
upper 50s to lower 60s.

The dry column will saturate during the course of the overnight
Friday night, and forcing will increase as low pressure moves
northeast out of the plains toward Indiana. Temperatures should be
warm enough for precip to fall as rain. PoPs will increase from NW
to SE as the system moves in. Lack of instability means no thunder
is expected, but given the good forcing with the low expect to see
rain in at least the western and probably central counties before
Saturday morning.

&&

.Long Term...(Saturday through Thursday)
Issued at 310 PM EDT Thu Apr 22 2021

Two confident periods for rain chances in the long term. One on
Saturday and the other focusing on the Wed/Thu time period. Some
spread in the model solutions for timing of that last system, but
the blended guidance`s best focus, that is the highest 6-hourly rain
chances, for our region is for Wed. after and evening period.

The first system is an inverted surface trough stretching north from
a low pressure center over AR Saturday morning. Precipitation likely
will be ongoing at the start of this period and then tapering off by
the end of the day from west to east. Rainfall totals likely will
be around a half inch. Narrow north/south oriented high pressure
will move in from the west and provide for a dry Sunday, though a
zonal flow aloft will allow for some mid and high clouds to stream
in from the west.

The next work week starts as a couple of low pressure systems move
through the Central Plains and head well north of our area. The
pressure gradient over Indiana will tighten up, with winds picking
up from the south...flippling the script on our wintry weather
period and bringing us anomalously warmer weather by midweek. Look
for highs around 80 on Tuesday. Temperatures Wed. will depend on
timing of those rain chances mentioned above. Also, the time of
day that systems moves in would have an impact on us seeing
stronger thunderstorms. For now will just mention a rumble of
thunder chance with the likely rain chances.

&&

.Aviation...(230000Z TAF Issuance)
Issued at 618 PM EDT Thu Apr 22 2021

IMPACTS:
- Lingering surface gusts 18-20 kts from 260-280 degrees will end
with sunset.

DISCUSSION: Any lingering surface gusts are expected to end with
sunset, as mixing diminishes.

Otherwise, surface high pressure over the Ohio Valley, coupled with
a dry lower level air mass, will result in no significant low cloud,
unrestricted visibility, and light winds tonight.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 1 AM to 9 AM EDT Friday for INZ040>042-048-
049-056-057-064-065-072.

&&

$$

Update...JAS
Short Term...CP/KH
Long Term...WFO LMK
Aviation...JAS



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