Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 151950

Area Forecast Discussion
National Weather Service Northern Indiana
350 PM EDT Fri Sep 15 2017

Issued at 347 PM EDT Fri Sep 15 2017

Quiet weather will persist through the first part of the weekend
as a ridge of high pressure is slow to depart to the east. Warm
conditions can be expected through the weekend with high
temperatures in the lower to mid 80s for Saturday and Sunday. A
weak frontal boundary will approach the region later Sunday into
Monday resulting in a chance of showers and isolated
thunderstorms. High temperatures will only be slightly cooler on
Monday as the frontal boundary stalls across the area, ranging
from the upper 70s to lower 80s.


.SHORT TERM...(This Evening through Saturday)
Issued at 347 PM EDT Fri Sep 15 2017

Quiet weather is expected through the short term period. The upper
level trough that affected the area over the past few days has
worked well east of the area this afternoon, although a sheared
vort max digging across western periphery of this trough has aided
in greater afternoon cu coverage across far northeast
Indiana/northwest Ohio. Otherwise for tonight, persistence
forecast utilized. Low level anticyclone will make a slight
eastward shift, allowing for some very subtle increase in
southerly low level flow, particularly across western portions of
the forecast area. With weaker flow across the east, cannot
discount some patchy shallow fog development across extreme
northeast Indiana/northwest Ohio late tonight/early Saturday
morning. Expecting progressively less impacts from past few
mornings on Saturday, with more localized nature to fog and low
confidence in any patchy dense fog. May also need to watch western
portions of the forecast area for some patchy low clouds
developing later tonight via weak low level warm/moist advection,
but confidence is low and maintained mostly clear mention.

Low level thermal moderation will be relatively minor into Saturday
as advective pattern remains weak across southern Great Lakes and
Ohio Valley. However, good deal of insolation and slight moderation
in air mass should add another 3 to 5 degrees to highs from
today`s readings, generally in the lower 80s, with some mid 80s
possible across the far west/southwest.


.LONG TERM...(Saturday Night through Friday)
Issued at 347 PM EDT Fri Sep 15 2017

By Saturday evening, a strong upper level trough across Great Basin
region will begin to lift northeast across the northern High Plains.
A strong southwesterly low level jet will initially be situated from
southern Plains to the Corn Belt, and will gradually veer more
westerly by Sunday morning as this trough reaches southern Canada.
Shower and storm chances remain of somewhat low confidence Sunday
afternoon as strongest forcing remains well divorced from trailing
frontal boundary eventually dropping across the southern Great Lakes
Sunday night. Some favorable factors for shower chances Sunday will
be expectation of a pre-frontal moisture axis advecting into the
area with broad low level pre-frontal confluent flow. It is also
possible some remnant smaller scale convective enhanced vort could
be propagating through the flow from overnight upstream
convection. Maintained consistency with the previous forecast in
low-mid chance PoPs. Kept an iso thunder mention going, but mid
level lapse rates appear to be relatively meager.

Cool frontal boundary will hang up across the mid MS Valley and Ohio
Valley region late Sunday night into Monday. Rain chances will
remain low late Sunday night into Monday with lack of forcing. Some
uptick in shower/iso storm chances is anticipated for Monday
night/early Tuesday as guidance depicts slightly better synoptic
short wave advecting into the area via upper level southwest flow.
Some weak upper jet coupling also noted per GFS during this
period, which supports mid to high chance PoPs for this period.

The next significant Pacific upper trough will eventually allow axis
of slightly stronger low level southerly flow to shift across the
area some time in the mid week time frame, although trend in
medium range models has been toward maintenance of longwave
ridging across southern Great Lakes/Ohio Valley as the series of
Pacific waves only temporarily dampen this ridge. Given synoptic
pattern of periodic warm advection/isentropic lift episodes, and
potential of smaller scale southwest flow waves to interact with
baroclinic zone across the region, unfortunately had to maintain
broadbrush chance PoPs for much of the long term period.
Temperatures in this pattern should run above normal and summer-
like generally from the upper 70s to mid 80s.


.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 126 PM EDT Fri Sep 15 2017

VFR conditions will continue this afternoon helped along by
diurnal processes. Heading into tonight, models show the potential
for more MVFR BR especially at FWA with a marginal cross-over
temp, a little bit drier sfc moisture and stronger than light
winds at SBN. In addition, southwest winds to start the afternoon
will be able to slightly back towards southeast as a nearby high
pressure system slowly moves away from the region.




SHORT TERM...Marsili
LONG TERM...Marsili

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