Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 190412
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1212 AM EDT Wed Jul 19 2017

.SYNOPSIS...
Issued at 1159 PM EDT Tue Jul 18 2017

High pressure will continue to provide mainly dry and clear
conditions tonight. A weak front will bring a low chance for
showers and thunderstorms on Wednesday. Lows tonight will drop
into the 60s, with highs on Wednesday well into the 80s. Thursday
through Sunday will feature humid conditions and periodic chances
for showers and thunderstorms.

&&

.UPDATE...
Issued at 755 PM EDT Tue Jul 18 2017

Remnants from very weak sfc trough/low level convergent axis
persist this afternoon across extreme southeast portions of the
forecast in Lima vicinity. Combination of diurnal heating/weak to
moderate sfc based instability pocket has been sufficient for a
few isolated showers across Allen county Ohio. These isolated
showers should be highly diurnally driven and no change to going
forecast with silent PoPs after 01Z. A few showers may try to move
into far west/northwest portions of the area toward daybreak as
weak mid level trough passes through early morning, but this
trough should start outrunning better upstream instability and
slight chance PoPs from previous forecast will be maintained.
Otherwise, quiet conditions tonight with perhaps some low end
patchy fog potential, but this potential appears to be even more
minimal than last night and will continue to omit from forecast at
this time.

&&

.SHORT TERM...(This Evening through Wednesday)
Issued at 301 PM EDT Tue Jul 18 2017

A weak low level trough/instability axis may continue to spark a
few isolated showers mainly south of US 24 in nw OH this
afternoon. Dry/warm otherwise late this afternoon into this
evening with stable theta-e minimum still in place from MI sw into
nw IN/ne IL.

An Upper Midwest disturbance will top a building Plains upper ridge
through the Northern Great Lakes tonight. Associated weak height
falls will aid in folding upstream theta-e ridge and convective
outflow boundary into the local area later tonight into Thursday.
Lacking forcing/flow with mid level heights on the rise precludes
anything higher than a slight chance PoP along this boundary even
as boundary layer moisture/instability increases. Increasingly
hot/humid otherwise on Wednesday with highs well into the 80s and
afternoon sfc dewpoints up near 70.

&&

.LONG TERM...(Wednesday Night through Tuesday)
Issued at 301 PM EDT Tue Jul 18 2017

Thursday through Sunday will feature periodic chances for
rain/storms and humid conditions with the area located in a
precarious position on the northeast fringe of a mid-summer
ridge. Several convectively aided/induced waves in quasi-zonal
westerly flow overtop this stout ridge will help focus mesoscale
convective systems ese through the Upper Midwest/Great Lakes near
an oscillating frontal boundary. Moisture/instability parameters
will also become increasingly impressive with time near this
convectively reinforced boundary which could pose a heavy
rain/flooding threat at any time (best chances Thursday night
through Saturday). As expected this time of year shear/flow should
for the most part be on the marginal side for more organized
severe weather. However, if any MCS becomes better established
with a cold pool a severe threat (more than just isolated
wind/hail) could materialize. Confidence in timing/strength of
these low magnitude features, and where frontal boundaries
(modulated by convection) will end up in any one period, remain
low any more than a day in advance. As a result have capped PoPs
in these periods at 40/50 percent. Otherwise...heat indices may
reach 95-100F during each afternoon south of the convective
outflow/cloud debris.

The latest guidance continues to suggest drier and slightly
cooler/less humid wx by early next week as troughing into the Great
Lakes finally forces active boundary and deep moisture south of the
region.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
Issued at 1158 PM EDT Tue Jul 18 2017

A large upper ridge will build toward the mid Mississippi Valley
this period as weak disturbances track over the top of the ridge
and move into the Upper Great Lake region. Convection this evening
over IL associated with one of these weak systems was moving into
much more stable air and is expected to dissipate overnight and
not reach the terminals. There could be some regeneration over
northern Indiana with daytime heating later today, but given the
stable mid level lapse rates and some large scale subsidence on
the northeast fringe of the upper ridge, have kept thunder out of
TAFs. It appears activity will be too isolated to include in TAFs
at this time.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

UPDATE...Marsili/Skipper
SYNOPSIS...Steinwedel
SHORT TERM...Steinwedel
LONG TERM...Steinwedel
AVIATION...Skipper


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