Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 172306
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
706 PM EDT Thu May 17 2018

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

&&

.SYNOPSIS...
Issued at 358 PM EDT Thu May 17 2018

Unsettled weather will return to the Ohio Valley through early next
week as a frontal boundary returns north from the Tennessee Valley
and interacts with a slow moving upper level low pressure system.
Rain and storms will be possible daily through Tuesday. High
pressure will then build in for the middle of next week with drier
weather. With the exception of cooler temperatures mainly in the 70s
Friday...well above normal highs in the 80s will be common for the
weekend into next week.

&&

.NEAR TERM /Tonight/...
Issued at 358 PM EDT Thu May 17 2018

Pleasant afternoon ongoing as much of the region remains under the
influence of high pressure centered over the Great Lakes. Easterly
flow around the high pressure continuing to advect drier air across
much of the forecast area this afternoon. 19Z temperatures were
generally in the upper 70s and lower 80s.

The primary focus for the rest of the afternoon into tonight is the
return of deeper moisture into the region from the southeast in
response to an approaching upper low over Missouri and the frontal
boundary drifting back north out of the Tennessee Valley. The
potential for scattered showers and perhaps a few rumbles of thunder
will increase from the south tonight.

Convection so far this afternoon has been drifting W/SW across
southern Ohio and northern Kentucky within an area of higher precip
water values and better instability. Modest moisture advecting into
southern counties over the next several hours does support at least
a threat for isolated convection south of I-70 and especially south
of a Sullivan-Bloomington-Greensburg line. Cannot entirely rule out
a storm or two as weak instability exists but overall...am not that
impressed in thunder potential late today into the overnight.

General trend via the HRRR and HREF at scattered showers shifting
north after midnight to the I-70 corridor and points north as
moisture continues to advect into the region ahead of the upper low.
Overall model consensus pops are far too high and continuing to
overdo rainfall coverage. Cannot justify much higher than 30-40 pops
at best . While rainfall coverage will increase...still anticipate
relatively spotty coverage to the convection overnight...especially
with a persistent easterly flow in the low levels.

Temps...utilized a model blend for lows overnight ranging from the
upper 50s north to the mid 60s over the far south. Cloud cover and
showers will keep temperatures warmer in general that Wednesday
night.

&&

.SHORT TERM /Friday through Sunday/...
Issued at 358 PM EDT Thu May 17 2018

Forecast challenges remain focused on daily rainfall and convective
threats as the aforementioned upper low passes through the Ohio
Valley and the pesky frontal boundary returns north into the region.

The upper low will slowly track across the Ohio Valley through early
Saturday before eventually getting picked up by the northern stream
jet over Ontario and Quebec over the weekend. This feature will
provide the overall broad but weak forcing aloft to contribute to an
abundance of cloud cover and scattered showers on Friday and Friday
night. In addition...the frontal boundary will return north into the
region as the strong high pressure lifts out into New England on
Friday. Several weak surface wave traversing the boundary will also
contribute to the increase in rainfall coverage...especially Friday
afternoon and night.

Initial scattered showers focused more over the northern half of the
forecast are Friday morning should diminish to a lull in activity
midday before more substantial coverage of showers and a few storms
expands north from Kentucky late day in tandem with a surface wave
along the northward moving frontal boundary. CAMs capturing this
thinking well and have trended highest pops south of I-70 for the
afternoon and evening. The presence of clouds will limit instability
levels substantially and outside of embedded thunder during the
afternoon and evening...expect the primary impact will be locally
heavy rainfall under slow moving convection.  With that being
said...the overall flood threat remains low with the antecedent dry
soils present over the area currently.

The best rainfall coverage should shift to the eastern half of the
forecast area Saturday as the upper low opens up and lifts out to
the northeast. Better heating and instability present Saturday
supports a better potential for thunderstorms but again coverage
will be scattered at best. The frontal boundary is likely to return
to a position somewhere across the northern half of Indiana Saturday
night into Sunday in response to low pressure lifting northeast out
of the central Plains. This will bring a return to a warmer and more
humid airmass for central Indiana for the second half of the
weekend. Subtle waves traversing the boundary are likely to kick
out6 across the region Sunday and while overall confidence in the
details is low...this setup would support scattered convective
development within the warm and unstable airmass across the region
Sunday.

Temps...clouds and rain will keep temperatures down on Friday with
Indy remaining below 80 for the first time in 10 days. Trended towards
the warmer MAVMOS with highs in the upper 60s to mid 70s. Highs will
recover Saturday into the lower and mid 80s for most...with a return
to summer conditions Sunday as many locations are likely to warm
into the upper 80s. The warmer MAVMOS was again largely preferred
for weekend highs. An overall model blend worked fine for lows
through the period in the 60s.

&&

.LONG TERM (Sunday night through Thursday)...
Issued at 205 PM EDT Thu May 17 2018

There is a lot of forecast uncertainty through Tuesday. Forecast
confidence is higher Wednesday and Thursday.

The European model and GFS differ in their handling of a frontal
boundary early in the period. Which is right, if either, will have a
big impact on both temperatures and rain chances. Even using the
consensus, temperature errors could exceed 5 degrees and today`s
POPs may need adjustment by 30 percent.

Forecast confidence increases midweek. The models agree dry high
pressure will enter our area. Potential temperature errors are 3
degrees or less. Potential POP errors are mostly 10 percent or
less.

&&

.AVIATION /Discussion for 180000z TAF issuance/...

Issued at 700 PM EDT Thu May 17 2018

VFR at the sites to start with easterly component winds of 8 to 12
kts. Gusts at the sites up to around 20 kts may continue for the
next hour but should drop off pretty quickly so did not include
them. Scattered showers across southeastern Indiana could possibly
impact KBMG over the next few hours but not confident enough of
them hitting that site to include beyond a VCSH mention there.
Think the other sites should remain dry through the night.
Sometime after 12z Friday could see ceilings drop to MVFR and
showers move into the sites. Some IFR will be possible Friday late
morning/early afternoon as well.

&&

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

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan
SHORT TERM...Ryan
LONG TERM....JK
AVIATION...CP



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