Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 201922
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
222 PM EST Tue Feb 20 2018

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

&&

.SYNOPSIS...
Issued at 222 PM EST Tue Feb 20 2018

A cold front will sag southward across Central Indiana
tonight...spreading rain showers across the state as it passes.
High pressure will then build across northern Indiana on
Wednesday as the departing cold front stalls across Kentucky.

Meanwhile...warm southwest flow aloft will continue to allow moist
tropical air to surge into the Ohio Valley. This will result in
daily chances for rain across Indiana for the rest of the week.
Flooding threats will continue through the week with the expected
rainfall.

Look for temperatures to remain above normals the next several
days.

&&

.NEAR TERM /Tonight/...

Issued at 222 PM EST Tue Feb 20 2018

Surface analysis early this afternoon shows strong low pressure in
place across the Great Lakes with a strong cold front stretching
from SE Wisconsin across Central Illinois to Central Missouri.
Water Vapor imagery shows the story today. A deep trough was found
across the western United States...resulting in a sharp SW flow
across the Mississippi and Ohio River Valleys. Water Vapor shows
the plume of tropical moisture streaming across the Illinois and
Indiana from the tropics. Radar shows showers continuing to stream
across NW Indiana and Central Illinois.

GFS and NAM suggest the cold front to the west will sag southeast
across Central Indiana overnight. Again...favorable conditions
remain in place for precip. Tropical flow aloft...excellent lower
level convergence. A warm and relatively humid air mass ahead of
the front. Forecast soundings show a saturated column arriving by
09Z with Pwats near 1.32. Time height sections show excellent
saturation within the mid and lower levels. 305K GFS Isentropic
surface shows a surge of mixing ratios over 6 g/kg tonight ahead
of the front. Thus 100 pops tonight appear reasonable. Given the
expected progression of the front...will hold off on extending the
flood watch for now...but given possible rain amounts of over
0.50 inches...isolated nuisance flooding cannot be ruled out.
Given the expected cold air advection yet ongoing rain in the wake
of the front...will trend lows very close to the forecast builder
blend.

&&

.SHORT TERM /Wednesday through Friday/...

Issued at 222 PM EST Tue Feb 20 2018

For much of Wednesday the GFS and NAM suggest the cold front sags
to Kentucky...taking the bulk of the precipitation with it.
However...aloft the strong...SW tropical flow continues to stream
into the Ohio Valley. Yet another short wave embedded within the
flow is suggested to pass across Central Indiana...mainly late in
the day toward evening. Time heights show good lift aloft...yet
some dry air within the lowest levels as high pressure build
across Wisconsin and the Great Lakes. Thus best chances for precip
should be across the southern parts of Central Indiana on
Wednesday...closer to the lingering front...with lesser chances to
the north where more dry air will have settled in. Will trend pops
in this manner.

On Wednesday night another the GFS and NAm suggest another short
wave approaching Central Indiana with the stalled cold front
across Kentucky. Again excellent saturation will be found within
the lower levels as suggested by the forecast soundings. Again
will trend pops at or above the forecast builder values...mainly
across points across southern Central Indiana...closer to the
stalled front.

THE GFS suggests a break in upper forcing in Thursday with little
in the way of dynamics passing at that time. However the warm and
moist southwest flow continues across Indiana aloft. Meanwhile at
the surface...High pressure moving across the Great Lakes will
begin to drift east of Indiana...which will begin to allow return
flow to begin for Friday. Will only keep some minimal precip
chances across the area on Thursday with little in the way of
dynamics and only the departing short wave early in the day
providing forcing. By late in the day and into Thursday
evening...dry air appears to intrude into the column.

Yet another short wave looks to arrive on Late Thursday Night and
Into Friday. Forecast soundings show deep saturation by Friday
Morning with pwats suggested near 1.20 inches again. Meanwhile the
stalled front over Kentucky begins to return northward as a warm
front...providing yet another focusing mechanism. Thus will again
trend toward very high pops on late thursday night into Friday.

Overall will stick close to the forecast builder blend on temps.

&&

.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 201800Z TAFS/...
Issued at 1132 AM EST Tue Feb 20 2018

Area of rain and embedded lightning strikes expected to affect
mainly the KLAF terminal through the afternoon hours, based on
short term model guidance. Precipitation may tend to diminish
temporarily later this afternoon in that area. IFR visibility
restrictions expected in the heavier precipitation areas.

A cold front is expected to move into the western zones by late
this evening, so more organized showers, along with possibly some
embedded lightning strikes, expected to affect the KHUF/KLAF areas
after 210300Z. This front may reach the KIND vicinity by 222200Z.

Otherwise, outside of precipitation areas, ceilings generally
above 050 this afternoon, dropping to near 030-035 after dark.
Surface winds 190-210 degrees with frequent gusts 30-34 kts this
afternoon will diminish towards sunset. Threat for low level wind
shear will develop after dark, given a low level jet around 55
kts overhead. Wind shift to 320-350 degrees probable in the
210300Z-222200Z time frame at KLAF/KHUF.


&&

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

&&

$$

SYNOPSIS...Puma
NEAR TERM...Puma
SHORT TERM...Puma
LONG TERM....Ryan
AVIATION...JAS



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