Area Forecast Discussion
Issued by NWS Indianapolis, IN

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626
FXUS63 KIND 200834
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
334 AM EST Tue Feb 20 2018

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

&&

.SYNOPSIS...
Issued at 330 AM EST Tue Feb 20 2018

A cold front will drop southeast across central Indiana overnight
tonight. The front will interact with copious amounts of moisture and
result in widespread rain, heavy at times through tonight. Another
front and waves in southwest flow will bring more rain to the area
through the weekend. Some mixed precipitation is also possible
mostly north of Interstate 70 Wednesday and Wednesday night.

Record high temperatures are possible today, and above normal
temperatures are expected the next seven days.

&&

.NEAR TERM /Today and Tonight/...

Issued at 330 AM EST Tue Feb 20 2018

Heavy rain and flooding will be the main concern today.

Models in good agreement that a cold front will drop southeast
across central Indiana overnight into Wednesday morning. In
addition, numerous impulses will move across the area in fast
southwest flow. The front will interact with max precipitable water
values for this time of year. Central Indiana will also be in the
right rear quadrant of a strong upper jet over the upper Midwest.
The result will be widespread rain showers. Heavy rain will be
possible, especially in any embedded convection. Models suggest,
northwest sections will continue to see the best chance of rain
today. The rain will then spread southeast overnight and should be
south of the area Wednesday morning.

Blend QPF amounts of 1.75 to 2.5 inches extended from Vermillion to
Boone to Tipton counties and northward. After coordinating with
adjacent offices, expanded the Flood Watch to include all these
counties starting 00z this evening and culminating 12z Wednesday.

In addition to the rain, south and southwest winds gusting to 30 mph
will result in record or near record daily highs per the blend.

Confidence is high in heavy rain potential along with the very mild
temperatures.

&&

.SHORT TERM /Wednesday through Thursday night/...

Issued at 330 AM EST Tue Feb 20 2018

Models are in fair agreement in the overall synoptic pattern through
the short term and so a blend is accepted. The main focus for
Wednesday and Wednesday night is the possibility of mixed
precipitation over northern sections in the wake of the cold front
but in persistent southwest flow aloft with embedded short waves.
Model soundings due support some freezing rain, sleet or snow over
the north, mainly late morning Wednesday and Wednesday night.
However, with the warm ground, do not think there will be much or
any impact. With the front south of the area, there will be a sharp
NW-SE POP gradient Wednesday afternoon and night per the blend as
southern sections will be close enough to any waves lifting along
the front to justify high pops there.

After a relative lull, the widespread showers will return Thursday
night as another front sets up northwest of the area and high
pressure shifts to the east.

With the persistent eastern upper ridge, good confidence in above
normal blend temperatures.


&&

.LONG TERM /Friday through Monday/...
Issued at 300 AM EST Tue Feb 20 2018

The wet and active pattern will continue through much of the
weekend with the weather finally settling down late Sunday into
Monday as the amplified upper flow regime finally relaxes and high
pressure builds into the region.

Solid model consensus for Friday and Saturday with the frontal
boundary lifting back north across the region as multiple surface
waves track along it. This will provide a renewed threat for
rain...heavy at times...and flooding when adding the expected
rainfall over the next few days prior to the extended period.
After some drying on Thursday with the front off to the
south...the initial wave of moisture will arrive early Friday and
linger through the day. A brief respite Friday evening will be
followed by a secondary wave late Friday night into Saturday as
the frontal boundary lifts into the northern half of the forecast
area. This will bring an additional round of rain with embedded
thunder as elevated instability lifts into the region.

The final surface wave is poised to swing through the area
Saturday night into Sunday morning. The op GFS deviates from the
consensus at this point by sending up a rapidly intensifying
surface low into the Great Lakes. Most of the model data including
the bulk of the ensemble members favor a less wrapped up wave
that tracks along the boundary across the region Saturday night.
Even with this solution...the final surface wave will bring a
third round of moderate to heavy rain with a convective component
along and ahead of the cold front.

Potential for an additional 2 to 4 inches of rain with locally
higher amounts from Friday through early Sunday with precip water
values once again rising to climatological maxes for late
February. Taking into account expected rainfall through
Thursday this will only exacerbate flooding concerns into the
weekend...especially for rivers and streams...and in lowland and
poor drainage areas.

Once the front shifts east during the day Sunday...drier weather
will finally arrive as high pressure builds into the Ohio Valley
and the amplified upper level pattern across the country this week
relaxes back to more of a quasizonal regime. Highs Friday and
Saturday have the potential to rise into the 60s once again south
of wherever the front eventually lays out. Behind the system
Sunday and Monday...temperatures will remain mild with highs
ranging from the upper 40s into the 50s.

&&

.AVIATION /Discussion for the 200900Z TAF Update/...
Issued at 300 AM EST Tue Feb 20 2018

Pulling back on any precip mention at all terminals except KLAF
for the rest of the overnight. Still appears the next surge of
moisture will bring increased rainfall coverage to the northwest
half of central Indiana by mid morning...potentially impacting
KHUF and KIND.

06Z discussion follows.

VFR much of the period. MVFR will be possible at HUF and
especially LAF.

Rain showers will be present at or near LAF much of the period,
and may overspread the other sites later in the period.

Winds and wind shear will be of impact during this period, with
gusts at times ranging from 23-34KT, generally from 190-210.
Sustained winds will be 9-18KT.

Low level winds around 2kft will be as strong as 45-55KT, and will
carry wind shear at all sites.

Visibilities will occasionally be impacted by rain and fog, and
will be MVFR at times, particularly at LAF.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Wednesday morning for INZ021-028>031-035>038-
043-044.

&&

$$

SYNOPSIS...Koch
NEAR TERM...Koch
SHORT TERM...Koch
LONG TERM....Ryan
AVIATION...Nield/Ryan



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