Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 290216
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1016 PM EDT Fri Apr 28 2017

.UPDATE...
The NEAR TERM and AVIATION Sections have been updated below.

&&

.SYNOPSIS...
Issued at 154 PM EDT Fri Apr 28 2017

A warm front will lift north across central Indiana on Saturday.
Then, a cold front will sweep through from the west Sunday night.
Record moisture for this time of year combined with the fronts,
upper level support and instability will result in numerous strong
thunderstorms through the weekend with a potential of heavy rain and
flooding. After a brief break, more showery weather is possible for
the middle of next week.

After a muggy weekend, cooler weather will follow next week.

&&

.NEAR TERM /Overnight and Saturday/...
Issued at 1016 PM EDT Fri Apr 28 2017

Only minor changes needed for the evening update. Initial round of
convection has moved on into Ohio with a new area of storms along a
warm front currently pushing into south central Indiana from the
southwest. This activity should migrate across the southeast third
of the forecast area over the next several hours with additional
strong to severe storms. Will maintain the severe thunderstorm watch
in its current state as a result and monitor for any adjustments
over the next hour or two. Think the primary focus for strongest
storms should be in an axis from Washington E/NE through Seymour and
North Vernon as warm front resides just south of the forecast area.

As the front takes a more substantial shift north late tonight...
expect convection to push back further to the north up to near I-70.
Considering rainfall already from earlier storms...bumped the Flash
Flood Watch north another row or two of counties to encompass most
areas south of I-70.

Left temps alone overnight but would not be surprised to see rising
temps over the south late with readings well into the mid and even
upper 60s by daybreak.

Previous discussion follows.

Latest water vapor imagery was showing an upper circulation over
eastern Utah and western Colorado within a broader Rockies trough.
Meanwhile, a warm front was developing over the Tennessee Valley.

Main focus late this afternoon and tonight will be on heavy rain and
flooding. Very good setup for heavy rain with record precipitable
water values, an advancing warm front and a strong upper jet over
the Great Lakes. Best focus for convergence will be over south
central Indiana near the nose of a 40-50 knot low level jet and in
exit region of 130 knot 250 millibar jet. Frontal forcing combined
with strong isentropic lift on the 305K level, precipitable values
to over 1.75 inches and CAPE to over 1000 j/kg will result in
widespread thunderstorms. The combination of shear and instability
will also support severe storms, especially over our southwestern
counties, where SPC has us in a Day 1 Enhanced Risk. Slight and
Marginal Risks extend further to the north over the county warning
area. Can not rule out isolated tornadoes, mainly south of
Bloomington, otherwise, large hail and damaging winds will be the
main threat. Threat should continue through Midnight or possibly
later.

With such good combination of synoptic forcing, moisture transport,
instability, slow moving front and upper jet dynamics, should see
numerous storms over south central Indiana late this afternoon
through tonight and could see enough for flash flooding. Thus, after
coordinating with adjacent offices, went with a Flash Flood Watch
from Sullivan to Decatur counties and south through noon Saturday.
More flooding concerns are possible if not likely the remainder of
the weekend. So, stay tuned to further updates.

The thunderstorm coverage and intensity may lull a little bit
Saturday morning as the front lifts slowly northward and the low
level jet subsides. However, by afternoon, the best chances for
thunderstorms will shift to our northwestern counties, which will
also be closer to a 45 knot plus jet moving in from the Ozarks. In
addition, model instabilities are much higher Saturday afternoon
then this afternoon and evening. Thus, more severe weather is
possible Saturday afternoon and evening. SPC has a Day 2 Slight Risk
over all of central Indiana for Saturday and Saturday night.
Damaging winds and large hail will be the main threats, but isolated
tornadoes can not be ruled out.
LONG TERM
With southerly flow and clouds around, temperatures will not fall
much tonight. All but the far north should likely to be in the warm
sector by Saturday afternoon, so should see a strong southeast to
northwest gradient and highs close to a MOS blend in the mid 60s far
north to lower 80s south.

&&

.SHORT TERM /Saturday night through Monday/...
Issued at 154 PM EDT Fri Apr 28 2017

Main focus will continue to be on heavy rain, including flooding and
severe weather through the weekend.

Low level jet continues to point across areas northwest of
Indianapolis Saturday night. So, will continue with high pops there.
This area may need to be in a Flash Flood Watch soon, but prefer to
see how south central Indiana fares this evening first. Needless to
say, heavy rain and flooding will be hit hard in the Hazardous
Weather Outlook and Weather Story.

Areas southeast of Indianapolis should see a little lull Saturday
night and evening as they will be further away from the front.
Finally, strengthening Rockies low will move into the southern
Plains Sunday morning and then northern Missouri by 12z Monday. As
it does, an associated cold front will sweep through central Indiana
Sunday night and bring with it more widespread thunderstorms with
more heavy rain and possibly severe weather. Things will finally
improve Monday when only scattered lighter showers are possible in
the wake of the cold front.

Accepted the Mild MOS blend temperatures this weekend the southerly
flow and dew point advection.

&&

.LONG TERM /Monday Night Through Friday/...
Issued at 209 PM EDT Fri Apr 28 2017

Models are close enough that the model blend initialization
was accepted.

Cool conditions with frequent chances for rain will be the rule next
week. While one upper system will exit the area Monday night, models
try and develop another during the week. As usual, models don`t
quite agree on timing or location. Thus confidence is low in rain
timing and location so see no reason to change the model
initialization.

&&

.AVIATION /Discussion for 290300Z TAF Update/...
Issued at 1016 PM EDT Fri Apr 28 2017

Making a few adjustments primarily to ceilings...otherwise no
changes. 00Z discussion follows.

Poor flying conditions expected overnight and for much of the day
Saturday.

A warm front located over southern Indiana this evening will
continue to lift slowly north through the region overnight and
into Saturday. Multiple rounds of convection are likely to impact
the terminals through Saturday morning as waves aloft track along
the northward moving boundary. Expect ceilings to tumble to IFR or
worse overnight with potential for visibility restrictions within
rain and storms. Surface flow should largely remain anywhere from
E/NE to SE through daybreak Saturday as the warm front remains
south of Interstate 70.

The front will shift north by late day Saturday with surface flow
veering to S/SE as a result. More widespread rain and storms will
impact the terminals during the first half of the day with
convection much more scattered during the afternoon as the
boundary surges north. Lower ceilings however are likely to linger
for much of the day with perhaps some scattering of the deck by
late day.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Saturday morning for INZ043>045-051>057-
060>065-067>072.

&&

$$

SYNOPSIS...MK
NEAR TERM...MK/Ryan
SHORT TERM...MK
LONG TERM....50
AVIATION...Ryan


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