Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 201409

Area Forecast Discussion
National Weather Service Northern Indiana
1009 AM EDT Sun May 20 2018

Issued at 316 AM EDT Sun May 20 2018

Several rounds of showers and thunderstorms will be possible into
Monday as a frontal boundary remains in the region. Locally heavy
rain is possible along with a small risk of strong storms Sunday
afternoon and evening along and south of Route 24. Dry and warmer
weather returns for the middle of the work week.


Issued at 1008 AM EDT Sun May 20 2018

Some changes to forecast may be warranted, especially across N/NW
areas based on radar as well as HRRR. 2 areas of showers/embedded
storms, 1 over N IL/S WI and the other S IL were working east.
HRRR suggests that these 2 areas will come together and at least
attempt to move across the forecast area, albeit likely in a
weakening state as loss of LLJ occurs. Current grids have slgt chc
to chc pops and will let them ride for the next hour or so to
monitor trends.

HRRR also suggests that a small cluster of stg-possibly severe
storms could develop south of US-24 and then propagate SE towards
better instability. Given remnants of above noted convection and
possible MCV scenario is at least plausible. Again previous shift
had some low pops which will work for the time being.


.SHORT TERM...(Today and Tonight)
Issued at 316 AM EDT Sun May 20 2018

Sizable uncertainty remains in the forecast concerning convective
chances later this morning and tonight. Complexity of the
forecast stems from the convective influences of ongoing
convection across the central US. Convection over lower WI and
northern IL may be able to sneak in our northern zones towards
daybreak since as it is closest to the limited upper level
dynamics. Have retained low end POPs for the morning hours mainly
for the northwestern zones.

Weak upper level ridging should win out during the day to keep any
convective activity limited to a few isolated showers. As we move
into the early afternoon hours, the shortwave which initiated
storms across the Southern Great Plains overnight will be nearing
the area. This should be enough to initiate convection along
I-70. There is great uncertainty if this convection will be far
enough north for strong to marginally severe storms to impact the
area. If the convection develops further north (possibly along
Route 24) than where CAMs are currently showing them, then we
could see organized storms. But if the CAMs are correct with the
further south positioning (along I-70) then the area would be
stuck underneath the rain shield.


.LONG TERM...(Monday through Saturday)
Issued at 316 AM EDT Sun May 20 2018

Storms are still expected for the start of the work week. Some
lingering storms from the previous night are possible Monday
morning. Models show a slight lull in activity around midday
before the next round of storms develop during the late
evening/overnight hours. The second round of storms could have
the ability to become organized with 1000 - 1500 J/kg of MLCAPE
and deep layer shear of 40kt. The best chance for organized
convection is the southern counties of the CWA (primarily along
and south of Route 24). As time progresses, surface wind flow
becomes very weak and thus storms will become cold pool dominated
as they lift northeast. Early on both hail and damaging wind gusts
would be the primary hazards, but damaging wind gusts would be
the primary hazard later in the night. PWATs remain in the 1.5"
range throughout this round of convection keep the possibility of
period of moderate to heavy rainfall.

A few lingering storms across western Ohio should clear out
during the early parts of the day on Tuesday. This will start our
dry period which is expected to last into the latter parts of the
work week. Our next chance of storms are on the horizon at the end
of this forecast cycle (Friday/Saturday).


.AVIATION...(For the 12Z TAFS through 12Z Monday Morning)
Issued at 639 AM EDT Sun May 20 2018

Light north to northeast flow continued over northern Indiana on
the north side of a stationary front. Widespread postfrontal
conditions have become IFR over far southern Lower Michigan into
northern Indiana. Given the latest obs & trends combined with
conditional climatology, have delayed improvement of IFR
conditions at the terminals. Much uncertainty concerning the
timing and development of convection this afternoon and evening.
For now, have mention of thunder after 00Z, but this timing may
need to be adjusted. There is a good chance an expanding meso
convective complex near St. Louis early this morning will bring
showers and storms into northern Indiana.





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