Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 211735

Area Forecast Discussion
National Weather Service Northern Indiana
135 PM EDT Fri Jul 21 2017

Issued at 1146 AM EDT Fri Jul 21 2017

Hot, humid, and party cloudy conditions are expected this
afternoon with highs into the upper 80s. Storms are expected to
develop across Minnesota and Wisconsin and track towards the area
tonight into Saturday morning bringing increased chances for
strong to possibly severe storms and heavy rainfall to parts of
the area. Conditions Sunday into early next week will then trend
drier and less humid.


Issued at 1012 AM EDT Fri Jul 21 2017

Did a quick update this morning for the forecast-overall-no major
changes. Just cleaned up the pops a little bit-trimmed them back a
little bit based on current radar observations. Kept any
precipitation chances for the remainder of the morning confined to
areas far south of US 30. In the afternoon there is still
uncertainty as to how things along our surface boundary and the
associated instability axis/moisture transport that runs roughly
from IA/IL to southern IN. Have some slight chance/chance pops in
the far west as we get into the later afternoon given the potential
for any convection along that boundary to go rouge and impact those
areas...but confidence is lower and may trim them back further if
need be. Most of the high res model guidance keeps things focused
along our southern boundary for this afternoon and even into early
evening...and it looks pretty isolated/scattered at best. Subsidence
from the upper level ridging and behind this mornings convection
will probably keep things limited. Otherwise, the main threat for
heavy rain/localized flooding potential and even a few severe wind
gusts north of US 30 tonight looks on track-but will highly depend
on how things go today.

It will be interesting to see how much of the cloud cover we can get
rid of today, and how high temperatures will rise. Given the
stagnant, hot, and muggy conditions-heat will be the main concern
today, with highs still forecast into the mid-upper 80`s, with some
locations even seeing 90. Some areas could see heat indices
approaching near 100 degrees (mainly the far southwest)-so if
working outdoors take frequent breaks, and make sure you are
hydrated. As of right now, we`re still dealing with the convective
debris/clouds, but temps re already into the mid-upper 70`s in
some locations.


.SHORT TERM...(Today and Tonight)
Issued at 400 AM EDT Fri Jul 21 2017

Complex near term as 2 clusters of storms to monitor, first one
taking aim at SW parts of the area over the next couple of hours
and second one upstream in eastern Iowa. Past few runs of HRRR has
initialized fairly decent in handling of both areas of convection
with even some indications of uptick in intensity/coverage as the
first area moves into the western CWA. Some concern that this
area could become somewhat more organized as it rides gradient of
2000 J/KG of SBCAPE and mid level lapse rates over 7 C/KM. IR
cloud tops have been also cooling with overall looks of a bowing
segment trying to take shape. Updated grids earlier to nudge pops
up higher and somewhat further north to handle northward
propagation of initial cells. Thinking locations from LaPorte
county south and east into Grant county have the best shot of
seeing some measurable rainfall and storms through 12Z with a slow
weakening trend thereafter. 25 to 30 kt low level jet appears to
be feeding into back of the first line, keeping moisture feed
intact and aiding somewhat in increased forward movement. Threat
of locally gusty winds or small hail does exist, but greater
concern may be rainfall with PWATs 2" or slightly more.
Introducing at least a small window of categorical pops in SW
areas next couple of hours and monitor trends.

2nd complex/MCV appears to be following right behind the first one
with a east to slightly southeast trend. Not sure how long it will
survive or impacts to SW locations so will allow pops to linger into
mid morning before drying things out as boundary will likely be at
least temporarily pushed south into central Indiana. How fast the
boundary works back north and it`s it moves back north will depend
on amount/timing of clearing north of it and increasing low level
flow which may be delayed until tonight. NAM takes the front the
furthest north well into Michigan, but is discounted as it has no
clue on current convection and thus starts too far north. Front will
likely reside somewhere near or just into southern counties towards
00Z and then try to move northward as complex of storms takes shape
across the eastern Dakotas/Minnesota and eventually drops southeast.
Frontal location will dictate to some extent how far south this will
track and as a result not ready to make major changes to pops
overnight. Not a big fan of categorical pops in far N areas later
tonight, but enough signals points towards maintaining it, but not
bringing any further south for the moment even though could easily
be argued for locations north of route 30.


.LONG TERM...(Saturday through Thursday)
Issued at 400 AM EDT Fri Jul 21 2017

Frontal boundary responsible for the periods of active weather
across the region will finally be pushed south of the area by Sunday
as upper level trough briefly digs into the Great Lakes. How much
convection may occur with the passage of the front and arrival of
the wave remains somewhat dependent on evolution of convection
tonight into Sat morning. Frontal timing late afternoon into evening
would normally be favorable, but amount of heating and subsequent
destabilization will depend on track/timing of expected MCS tonight.
Upper level wave will have a bit more punch than recent ones which
may help overcome potential impacts of clouds. Will maintain higher
pops north Sat AM for potential impacts of overnight MCS tracking
across at least the northern half of the area. Beyond that can`t
justify anymore than chc pops this far out with no confidence in
model evolution.

Cooler and less humid air will start to arrive on Sunday, with main
push coming Sun night into Monday when temperatures drop below
normal. Upper level flow quickly flattens out and then builds
slightly allowing temps to head back towards normal levels again.
Forecast should remain dry until late in the period when next wave
ripples through the flow and brings at least a chance for
showers/storms back to the area.


.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 135 PM EDT Fri Jul 21 2017

This afternoon into early this evening will continue to feature
VFR/mainly dry conditions north of a quasi-stationary front. This
front lifts back north tonight in concert with a MCV/convective
complex approaching from near the IA/MN border. Moist/unstable
inflow into this complex should be sufficient to maintain this
convective complex through northern IN from nw to se later this
evening into early Saturday morning, though guidance does continue
to differ a little with respect to timing given questions on what
mesoscale feature becomes the main driver. Favor the quicker
timing offered by the HRRR at this time with strong winds/IFR
conditions possible for a time. Trailing outflow could then
continue to force additional rain/storm activity and restrictions
beyond 8/9z, though confidence beyond this point is low.




LONG TERM...Fisher

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