636
fxus63 kiwx 190033
afdiwx
area forecast discussion
national weather service northern indiana
833 pm edt tue aug 18 2026
.key messages...
- the next chance of rain arrives tonight and persists through
wednesday.
- severe weather is not expected but a few strong storms may be
possible in far nw in/sw mi late this evening into the early
overnight. the primary threat is brief heavy downpours and
wind gusts to 50 mph. while brief higher rain rates are
possible, rainfall amounts are not expected to be heavy
tonight.
- after pleasant conditions thursday and friday, more light rain
is expected on saturday.
&&
.update...
issued at 830 pm edt tue aug 18 2026
broad pre-frontal confluence and low-mid level theta-e advection
have allowed a band of showers and storms to form along a modest
mlcape axis. this instability axis from eastern iowa into
southeast wisconsin should build southeast into sw lower
mi/northwest indiana through 04z. instability may become
slightly elevated through time progressing through late evening.
this leads to some question as to maintenance of stronger 50-60
mph gusts currently being observed with this line across se
wisconsin. a 50-60 knot speed max at 500 mb is progressing
through a low amplitude upper trough across the southern great
lakes tonight with plenty of low level and deep layer shear to
sustain this convection through at least lower michigan/far
northern indiana, at least partially compensating for more
marginal instability. there also could be some mcv-type feature
forming on northern periphery of this convection across se
wisconsin that could help sustain storms through 05z-06z. based
on current trends, did increase pops to categorical across the
northwest with expectation that some temporal window exists late
evening/early overnight for 40-50 mph gusts across sw lower
michigan/northwest indiana, with a gradual weakening with
east/southeast extent overnight as some boundary layer
destablization occurs and better mlcape axis gets pinched off
to the west. in addition to the potential of gusty winds, some
brief heavy rainfall is expected that could lead to some
localized ponding. however, overall progressive should keep
rainfall amounts in check most locations. it is possible some
localized 1+" inch amounts could be realized across far nw
indiana/sw lower michigan.
&&
.discussion...
issued at 206 pm edt tue aug 18 2026
not a lot of wholesale changes to this forecast period. cool
front currently sitting over southcentral mi and orientated to
the southwest into central il still on schedule to begin pushing
southeastward into the area this evening. looks like after 6 pm
edt chances for some light showers increase out ahead of the
incoming frontal boundary for our far northwestern parts of the
cwa before some scattered thunderstorms along the front push in
shortly afterwards and continues to move southeastward through
the area overnight into wednesday. forecasted instability,
mainly elevated, with values less than 1000 j/kg coupled with
decent shear values ahead of and along the front with values
around 70-80 kts, and surface dew points currently in the 60s
across the area. expectation in this environment with the later
diurnal timing that some of the storms may become strong but
would trend weaker through the evening as the front
southeastward.
on wednesday, depending on the exact position of the frontal
boundary, which at this time will most likely be over our far
south/southeastern parts of the cwa. which if this does pan out
then there will be afternoon slight chances of showers and
storms mainly for the southern half of the cwa with the close
proximity of the frontal boundary to provide a bit of lift.
however, severe storms are not expected with most of the area to
the north of the boundary with a less than ideal environment
especially with a drier airmass pushing in from the north in the
wake of the front by wednesday afternoon and evening. zonal flow
aloft across the region will bring slightly cooler temperatures
across the area into friday with highs in the upper 70s
expected. fairly nice weather with comfortable conditions will
be in place for thursday and friday before another cool front
associated with a trough dropping southeastward into the great
lakes arrives late friday and into saturday increasing chances
once again for showers and storms and before pushing quickly
eastward.
by sunday, ridging over the central conus then begins to
build northward into the region bringing another period of dry
weather and a slight warming trend into next week with highs
back into the low 80s.
&&
.aviation /00z tafs through 00z thursday/...
issued at 725 pm edt tue aug 18 2026
pre-frontal confluence and a broad, low amplitude mid/upper
level trough have allowed a band of showers and storms to
develop this evening across southern wisconsin. these storms are
developing along a 1000-1500 j/kg mlcape axis. through time the
better low level theta-e advection should become pinched off
across the corn belt region, with instability axis dropping
across the southern great lakes in a more moderate form late
this evening into the early overnight. despite the limited
instability, an upper jet streak nosing across the southern
great lakes this evening will provide ample shear to keep some
convective organization going with this line as it enters
northwest indiana after 03z. the general expectation is for a
brief period of storms at ksbn in the 03z-05z with some gusts to
30 to 35 knots possible with the storms. given stronger upper
forcing lags well back to the nw across the dakotas/northern mn,
some question as to the longevity into kfwa overnight and will
continue for now with prob30 mention given lesser elevated
instability.
associated frontal boundary will become a bit more diffuse and
slow moving into wednesday but could trigger some additional
showers/isolated storms at kfwa in the afternoon. confidence in
frontal placement and availability instability is lon the low
side, so will limit mention to prob30 shra at this forecast
distance. will maintain mention of mvfr conditions late tonight
in vicinity of the front, particularly at ksbn, although
confidence is on the lower side in terms of duration. any mvfr
cigs should improve late morning with diurnal mixing.
&&
.iwx watches/warnings/advisories...
in...none.
oh...none.
mi...none.
marine...none.
&&
$$
update...marsili
discussion...andersen
aviation...marsili