Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 260746
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
346 AM EDT Mon Oct 26 2020

.UPDATE...
The SYNOPSIS...NEAR TERM...SHORT TERM
and LONG TERM Sections have been updated below.

&&

.SYNOPSIS...
Issued at 340 AM EDT Mon Oct 26 2020

This week will involve multiple rounds of precipitation, as
central Indiana is placed within a trough like pattern. First
chance for widespread showers will be this evening and tonight.
Followed by another widespread rain event Wednesday night and
Thursday. Temperatures look to remain cool with highs in the 50s
most days. This weekend looks much more pleasant, as a pattern
shift places upper level ridging over central Indiana. Expectation
for Saturday and Sunday are for dry weather along with highs near
60.


&&

.NEAR TERM /Today and Tonight/...

Issued at 340 AM EDT Mon Oct 26 2020

For today, a robust upper level jet along with a plume of moisture
within strong southerly gulf flow will initiate showers west of
Indiana. These showers will gradually move in as the moisture axis
moves eastward. Chances for showers will start in the late
morning, but greatest chances will be during the late afternoon
through the night time hours when large scale lift within
diffluence aloft is strongest. The peak source of lift, along
with highest PWAT values look to remain south of central Indiana.
Although, prolonged periods of rain this this evening and tonight
should allow for total rain amounts between 0.25 and 0.5 inches
over southern central Indiana.

The boundary will remain well south of central Indiana, keeping the
region within a cooler sector. Consistent overcast skies and a moist
boundary layer will help suppress temperatures as well. Expect highs
to be in the low 50s across most of the region. Some locals to the
south where stronger WAA will be ongoing could reach 55. The
persistent cloud cover should also help keep winds light with a
primary surface wind out of the north.

&&

.SHORT TERM /Tuesday through Wednesday Night/...

Issued at 340 AM EDT Mon Oct 26 2020

By Tuesday morning, the upper level jet axis should be well east of
central Indiana, and along with it the large scale lift. Some
showers could still hang around for parts Tuesday morning over
southern portions of central Indiana, until moisture levels drop
in the afternoon. With the upper level jet south and east of the
region, central Indiana will be placed with suppressed heights and
cyclonic flow. The is a recipe for continued cloud cover, but a
few breaks are possible in the afternoon. Again, afternoon high
will be cool with highs near 50.

For Wednesday, the upper level pattern will alter slightly so that
southerly flow will return. Moderate WAA out ahead of a deep trough
should help increase tempertures. Expectations are for highs to
approach 60. An increase in moisture should lead to continued cloud
development. However, increased vertical motion should help break up
the clouds leading to mostly cloudy conditions. Most of Wednesday
looks dry as a surface feature and greatest lift stays south.
Although, any movement north of the boundary would place southern
portions of central Indiana in a more optimal shower development
zone.

By Wednesday night however, vertical motion will increase and
with a gulf moisture reaching central Indiana, consistent shower
development is likely. Models vary greatly on the heaviest axis of
rainfall, but precipitation amounts greater than 2 inches are
possible where deformation occurs. Northern portions of central
Indiana should be far enough away from a likely deformation zone
to get higher the rainfall rates. Continued updates will focus on
the trends this moisture axis as the low pressure system develops.


&&

.LONG TERM /Thursday through Monday/...

Issued at 340 AM EDT Mon Oct 26 2020

The remnants of Zeta will interact with a cutoff upper level low to
maintain a wet and active weather pattern to begin the extended on
Thursday before cool and dry weather develops Friday into the
upcoming weekend.

Zeta will make landfall on the northern Gulf coast late Wednesday
and lift northeast into the Tennessee Valley on Thursday as it
becomes heavily influenced by a deep cutoff low aloft tracking east
from the southern Plains. A deep plume of tropical moisture will
advect north into the region late Wednesday into Thursday as first
the remnant low from Zeta passes by to the south followed by a
secondary surface wave associated with the upper low late Thursday.
Models continue to oscillate on just how much and how quickly the
two surface waves will interact which will determine the eventual
intensity of the system as it tracks through the Tennessee and lower
Ohio Valleys. The intensity of the surface waves will also likely
set up a modest temperature gradient across the area Thursday...from
the lower and mid 50s north to the mid 60s in the far south.

Regardless of system phasing...widespread rain will be ongoing
across the forecast area at the beginning of the extended Thursday
morning with a wet day expected for the region. There remains some
question as to how much rainfall will occur across central Indiana
but confidence is growing on a period of soaking rains Wednesday
night into Thursday with the potential for some localized flooding
likely focused over the southern half of the forecast area. While
the deeper moisture plume will be shunted off to the east of the
region Thursday afternoon...a mid level deformation will lag
enabling rain to continue well into Thursday night until the upper
low can pass. At this point...it does appear that 1 to 2 inches of
rain is possible through early Friday with locally higher amounts.

Once the system passes...high pressure will build into the Ohio
Valley Friday setting the stage for a much quieter weather pattern
through next weekend. A weak but dry cold front may bring a subtle
increase in clouds Sunday...otherwise cool and dry weather is
expected. Highs mainly in the 50s are expected Friday through Sunday
with a few spots warming to around 60 over the weekend. Lows in the
30s to low 40s will be common.

&&

.AVIATION /Discussion for 260600z TAF issuance/...

Issued at 1138 PM EDT Sun Oct 25 2020

IMPACTS: MVFR conditions are expected through the period, with
potential for a drop to IFR around or after 0z.

DISCUSSION: Scattered sprinkles are possible for the next couple
of hours but should not diminish visibilities much if at all.
Rain moves in from the southwest during the afternoon/evening.

CONFIDENCE: High confidence in MVFR or lower through 18z. High
confidence in rain showers moving in over the sites by around 21z.
Medium confidence in IFR ceilings after 0z Tuesday.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS...Updike
NEAR TERM...Updike
SHORT TERM...Updike
LONG TERM....Ryan
AVIATION...CP


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