Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 222100
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
400 PM EST Thu Feb 22 2018

.UPDATE...

The Synopsis, Near Term, Short Term, and Hydrology sections have
been updated below.

&&

.SYNOPSIS...
Issued at 400 PM EST Thu Feb 22 2018

Persistent frontal zone that has been in the region for the past
several days will continue to influence the area, lifting back
northward again as another wave of low pressure moves along it
late tonight into Friday, producing another round of rainfall. A
brief break will follow with only chances for rain south Friday
afternoon and evening, followed by another more substantial low
pressure system late Friday night into Saturday night, bringing
another round of potentially significant rainfall. This rain will
likely exacerbate ongoing flooding on area waterways and may
produce flood problems in other areas as well. Will carry a flood
watch beginning this evening through Saturday night from Indy
metro southward as a result.

&&

.NEAR TERM /Tonight/...
Issued at 400 PM EST Thu Feb 22 2018

Expect another round of rainfall mainly late tonight as another
impulse pushes northeast along the quasistationary front that has
been in the region for the last several days. Convective indices
suggest thunder is at least an outside threat late tonight across
the southern half of the area, and will carry a slight chance
there.

This round of rainfall may amount to as much as an inch to an inch
and a half in spots.

Consensus temperatures seemed reasonable with minor tweaks. Warm
advection ongoing through the night will prevent temperatures from
dropping much from afternoon highs, and surface wetbulb progs with
widespread rainfall expected also agree relatively well with
consensus.

&&

.SHORT TERM /Friday through Sunday/...
Issued at 400 PM EST Thu Feb 22 2018

Focus then shifts particularly to late Friday night into Saturday
night. Will have to carry at least some chances Friday afternoon
and evening across the south, but the next substantial round of
rainfall will come during that aforementioned time frame. A more
substantial low pressure system will begin to wrap up over the
Plains as the western upper level trough finally begins to push
eastward. This round of significant rainfall will again be focused
mainly across the central and southern portions of the area, with
the southern half of the area again seeing the highest totals. See
the hydrology section below for more.

Thunder will be a threat again, mainly Saturday afternoon and
evening, and day 3 convective outlook brings a marginal severe
risk into our south which is reasonable given the low level
dynamic environment, although as is often the case this time of
year, degree of destabilization will be the limiting factor.

Precipitation will come to a close late Saturday night and Sunday
looks to be a dry day in the wake of the cold front.

Consensus temperatures were generally in the ballpark with minor
tweaks, although I suspect Sunday max temps will need to come down
as model consensus forms around frontal passage time - may see
only minor warming during the day with cold advection ongoing.

&&

.LONG TERM /Sunday Night through Thursday/...
Issued at 224 PM EST Thu Feb 22 2018

Dry weather is expected Sunday night through Tuesday. Late Tuesday
night moisture begins to arrive as the high pressure moves out of
our area. Models have pops returning as a warm front moves in from
the SW. The ECMWF shows several short waves arriving Tuesday night
through Wednesday night providing forcing for rain along with the
warm front which is reflected in the pops in the middle of next
week.

Thursday, a cold front will move into central Indiana bringing
more chances for rain... mainly early in the day.

Given the warm air advection, above normal temperatures are
expected much of the week.

&&

.AVIATION /Discussion for the 221800Z Tafs/...
Issued at 1244 PM EST Thu Feb 22 2018

MVFR/VFR CIGS across the area will deteriorate to IFR or worse
tonight.

Models show a short wave arriving from the southwest late tonight
along with a low pressure system pushing through the Mississippi
Valley. The warm and moist SW flow aloft will continue to provide
ample moisture for showers tonight. Models show best moisture
arriving after 06Z as deep moisture arrives and remains over the
forecast column through the night and pas 12Z Fri as the upper
support passes. Time heights and forecast soundings suggest low
CIGS...below 1000kft through the overnight hours into Friday
morning...suggesting IFR through much of Friday morning.

As the dynamics depart on Friday Morning...precip should come to
an end as models suggest dry air arriving within the column by
18Z. However forecast soundings continue to suggest trapped lower
level moisture and a return to VFR CIGS.


&&

.HYDROLOGY...
Issued at 400 PM EST Thu Feb 22 2018

River flooding is ongoing or developing across much of central
Indiana, and recent precipitation analyses show even areas that
were not as significantly impacted by precipitation earlier this
week have still received 2 to 4 inches in the last 7 days, with
another 2-3 inches and possibly higher expected by 12Z Sunday.

Precipitable water values tonight and again Friday night into
Saturday night will at times approach climatological maximum for
the time of year, with this significant rainfall occurring over an
already waterlogged environment.

Thus, given these factors, have chosen to post a flood watch for
areas from Indy metro southward where rainfall in excess of 2
inches appears likely through Saturday night.

&&

.IND WATCHES/WARNINGS/ADVISORIES...

Flood Watch from 10 PM EST this evening through Sunday morning
for INZ045>049-051>057-060>065-067>072.

&&

$$

SYNOPSIS...Nield
NEAR TERM...Nield
SHORT TERM...Nield
LONG TERM...KH/JP
AVIATION...JP
HYDROLOGY...Nield



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