Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 211040

Area Forecast Discussion
National Weather Service Northern Indiana
640 AM EDT Fri Jul 21 2017

Issued at 400 AM EDT Fri Jul 21 2017

Early morning thunderstorms south of a Laporte to Marion line will
exit shortly after sunrise. Clearing will slowly take place
through the day, especially across northeast sections of the area
by this afternoon. High temperatures will quickly jump into the
middle to upper 80s where clearing occurs. A few spots may reach
90 if enough sunshine is realized. 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.


Issued at 607 AM EDT Fri Jul 21 2017

Grid update to extend categorical pops further SE for a few hours
as convective complex charging much further SE than expected. No
concerns for severe weather as wind gust have been in the 30 to 40
mph range. MCV working southeast right behind the area of rain and
storms stirring up some increased thunderstorms activity that may
remain just south of the area. Interestingly enough, despite the
passage of the MCV and what would normally be a lull in precip a
narrow broken line of storms has developed from eastern Iowa back
into SE South Dakota where frontal boundary was surging back
north. Not sure what if any impacts this may have further down
stream, especially the activity in eastern Iowa. Still keeping
with a downward trend in pops into the morning.

Last change made was a few hours of patchy fog in the NE where
mostly clear skies and low temp/dewpoint depression has allowed
for some pockets of fog, locally dense at times.


.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 12Z TAFS through 12Z Saturday Morning)
Issued at 636 AM EDT Fri Jul 21 2017

Convective complex did move just south of terminals and should be
far enough south of KFWA at issuance to preclude any VCTS in 12z
TAF. Some broken MVFR clouds may linger a few hours this morning
but should see transition to VFR. Winds will be light and variable
this morning but become more southeast to south but still below 10
knots. Uncertainty lingers tonight with convective development and
movement of thunderstorm complex. Added a VCTS at KSBN for now as
guidance favors the far north overnight but still not a lot of
continuity in models with respect to timing and track.




LONG TERM...Fisher

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