Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 191730

Area Forecast Discussion
National Weather Service Northern Indiana
130 PM EDT Wed Jul 19 2017

Issued at 111 PM EDT Wed Jul 19 2017

Hot and humid weather will persist as an upper level ridge builds
across the Mid Mississippi Valley. Furthermore, an impulse will
slide across the region and may set off a shower or thunderstorm
before sunset this afternoon. Thereafter, a weak front along with
weak upper level disturbances will bring a chances for storms
from tonight through Saturday. The first instance of this will
come early Thursday morning. Highs will be near 90 the rest of the
week with lows around 70 to 75. Afternoon heat indices will
mainly be in the 90s the next 4 days.


.SHORT TERM...(Today and Tonight)
Issued at 302 AM EDT Wed Jul 19 2017

Convective complex moving across southern WI decaying as it moves
eastward out over lake Michigan and away from instability axis
and better flow/forcing. IR imagery showing warming and lowering
of cloud tops over the past couple hours with any new cells
regenerating/backbuilding to the west where better influx of low
level moisture and mid level flow exists...but even those are
fading fast. CAMs continue this downward trend toward daybreak and
current grids have good handle as just slight chance of lingering
shower/storm in far NW this morning. Potential of remnant
boundary from this convection may linger in vicinity and combine
with diurnal instability to generate a pulse storm or two but
lacking any type of organized flow these should be sparse and
short lived. Any lingering high clouds expected to erode quickly
this morning and lead to a hot and humid day as temperatures
expected in the upper 80s to around 90 with dewpoints rising to
around 70. 95kt upper jet streaming up over plains ridge will be
positioned this afternoon to favor MCS development similar to last
night. Difference tonight will be better flow and forcing should
have more well developed complex rolling toward our far NW by
early Thursday morning and will therefore maintain POPs here after
midnight. Otherwise warm and muggy with lows around 70.


.LONG TERM...(Thursday through Tuesday)
Issued at 302 AM EDT Wed Jul 19 2017

Remnants of nocturnal MCS mentioned in short term expected to be
in play across the northern CWA Thursday morning. Chances for
storms spreads south by Thursday afternoon as leftover outflow
boundary once again combines with diurnal instability. Large scale
pattern remains rather stagnant through Saturday bringing
multiple rounds of storms to the region as our area remains on NE
edge of plains ridge allowing short wave impulses riding along
the ridge to turn E/SE toward us. Timing and placement of each MCS
to be modulated by the previous one as quasi-stationary surface
boundary is continually convectively modified by these systems. So
while confidence in the occurrence of each MCS remains high...the
mesoscale dominant nature of this pattern yields low confidence
in the predictability in any one particular forecast
period...making it prudent to continue to avoid mention of likely
POPs in this time range. Hot and humid conditions will continue
through Saturday with highs upper 80s to around 90 and heat
indices reaching the mid to upper 90s in some areas. A break from
this pattern expected to come beginning of next week. Upper low in
eastern Pacific just off British Columbia coast will come onshore
and move along the US/Canadian border and dig into the great
lakes region by Monday and carve out longwave trough over the
region as surface frontal boundary pushes south into the Ohio
valley. Cooler and less humid air behind front as high pressure
builds into the region.


.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
Issued at 111 PM EDT Wed Jul 19 2017

An area of high pressure will be slowly pushing east today
allowing the terminals to have light northwesterly winds changing
to more southerly winds by the end of the forecast period. In
addition, little shear, but plenty of instability will allow a few
showers and possibly a thunderstorm or two to fire this afternoon
across the forecast area. Most of these storms are expected to be
non-severe with gusty winds and possibly small hail being the
impacts and may even miss the TAF sites altogether. Next,
especially if the TAF sites do actually receive precipitation
from showers and storms that fire this afternoon, but also with
lighter winds and enough breaks in the clouds, we`ll introduce the
possibility of BR with MVFR VIS. The other thing that would
impact this process would be if the potential convective system
tracks into the region from the northwest earlier than forecast.
The current forecast timing of this system would come into SBN in
the morning and then later in the day for FWA, meaning FWA may be
more affected by VIS restrictions in the morning than SBN. Have
gone with VCSH at SBN for 21z this afternoon as well as for
Thursday morning since the chance for precipitation this afternoon
is low at SBN and storms have a chance to die out before hitting
SBN Thursday morning.





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