Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 221038
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
538 AM EST Thu Feb 22 2018

.UPDATE...
The AVIATION Section has been updated below.

&&

.SYNOPSIS...
Issued at 415 AM EST Thu Feb 22 2018

Several upper waves of low pressure will lift northeast across
central Indiana late this week and this weekend. In addition, a
quasi-stationary front will meander over the Ohio Valley and
tropical moisture will continue to flow over the area. Finally, a
sharp upper trough will move over the Great Lakes late in the
weekend. This will force a cold front over central Indiana. The
combination of all these factors will bring several rounds of
widespread rains to the area through Saturday night. More flooding
will result, especially along area rivers and streams.

After that, high pressure will provide a brief dry period through
next Tuesday, but another frontal system will bring more chances of
rain in by the middle of next week.

Look for slightly above normal temperatures today with well above
normal temperatures by Friday.

&&

.NEAR TERM /Today/...
Issued at 415 AM EST Thu Feb 22 2018

The main focus for today will be rainfall trends and any impacts
from a wintry mix over areas north of Noblesville.

Radar loop overnight was showing heavy rainfall training over
western Tennessee and northern Kentucky to the north of a warm
front, in the vicinity of a low level jet and within the right rear
entrance region of the upper jet. To the north of the heavy rain,
radar was showing areas of moderate rain over central Indiana.

With surface temperatures holding in the middle and upper 30s,
pulled the Winter Weather Advisory for our far northern counties, as
impact of any mix should be minimal. Meanwhile, models, radar trends
and High Resolution Rapid Refresh were strongly suggesting the
widespread rains would be diminishing in coverage from west to east
this morning before briefly ending this afternoon and evening.
Confidence is good in this trend.

Low level northeast and then east winds should keep from rising much
today. Only slightly above normal blend highs look good.

&&

.SHORT TERM /Tonight through Saturday night/...
Issued at 415 AM EST Thu Feb 22 2018

Widespread rain and flooding will be the main concerns for the late
week and weekend.

Models are in good agreement that a Tennessee Valley front will lift
north and become quasi-stationary over the Ohio Valley. In the
meantime several upper waves of low pressure will lift northeast
across central Indiana in the fast southwest flow aloft and tropical
flow will persist. Finally, a negatively-tilted trough will pivot
over the Great Lakes Saturday night and Sunday and push a cold front
through central Indiana. In addition, nocturnal low level jets will
be in play overnight tonight, Friday night and again Saturday night.
Precipitable water amounts will be around 300 percent of normal at
times, and especially Saturday night, and mainly along and south of
Interstate 70. Finally, the area will be within the right rear
quadrant of a strong upper Great Lakes upper jet. The synoptic
factors along with the deep moisture will result in widespread rain,
overnight tonight and Friday morning and Friday night through
Saturday night. Went with Categorical POPs overnight tonight and
Early Friday and again Friday night through Saturday night.

A Flood Watch will likely be needed in the next 12 to 24 hours for
areas mainly near and south of Interstate 70. Could see up to an
additional three inches of rain there through the weekend with inch
to an inch and a half additional north.

Good confidence in well above normal temperatures by Friday as low
level flow shifts back to the south.

&&

.LONG TERM /Sunday through Wednesday/...
Issued at 257 AM EST Thu Feb 22 2018

A much deserved break from the active weather regime of late will
dominate much of the extended as high pressure builds in behind
the departing front on Sunday.

Rain will be east of the forecast area by daybreak Sunday with
deep subsidence poised to overspread the region as the
aforementioned high builds into the Ohio Valley. The highly
amplified flow regime aloft across the country will relax as well
with the deeper moisture fetch shifting well south of the region.

Return flow will develop by midweek as the high drifts away to the
east. While differences exist with strength and track of the
developing surface wave amongst the extended models at this early
stage...consensus growing on low pressure tracking into the
region out of the central Plains Wednesday and Thursday bringing
rain into the forecast area.

Temperatures will remain mild with 50s quite common for highs
through the period as we wrap up February.

&&

.AVIATION /Discussion for 221200Z TAF Issuance/...
Issued at 538 AM EST Thu Feb 22 2018

Subtle improvements in ceilings later today before widespread
sub-IFR conditions return tonight.

The back edge of the steadier rain is moving through central
Indiana early this morning with pockets of lighter rain extending
back into central and southern Illinois. Will highlight the
potential for scattered light showers this morning with a VCSH
mention at all terminals through midday. Ceilings may hover near
IFR levels through the morning but the arrival of drier air aloft
should enable ceilings to rise this afternoon. Model soundings
show moisture remaining trapped beneath an inversion all day so
expect the primary ceiling to linger around 2kft into the evening.

Deeper moisture will advect into the region tonight ahead of a
surface wave riding along a frontal boundary set to track into the
region early Friday. High confidence in ceilings tumbling back to
sub-IFR levels mainly after 06Z as steadier rainfall returns into
central Indiana. Visibilities will drop as well to 2-3SM with
higher rainfall rates.

E/NE winds at 10-15kts will continue throughout the day
today...shifting to SE and diminishing below 10kts tonight and
early Friday. The arrival of a low level jet Friday morning will
bring an increasing threat for low level wind shear.

&&

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

&&

$$

SYNOPSIS...MK
NEAR TERM...MK
SHORT TERM...MK
LONG TERM....Ryan
AVIATION...Ryan



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