Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 201924

Area Forecast Discussion
National Weather Service Northern Indiana
324 PM EDT Sun May 20 2018

Issued at 320 PM EDT Sun May 20 2018

Showers and thunderstorms will move in from Illinois towards
Monday morning and work east across the area. Additional showers
and thunderstorms will be possible Monday afternoon and evening
with a threat for severe storms existing mainly south of Route
24. Drier weather will arrive Tuesday and continue into Thursday
with highs climbing to near or above 80.


.SHORT TERM...(This Evening through Monday Night)
Issued at 320 PM EDT Sun May 20 2018

Rather drastic changes made to forecast for Monday into Monday
evening as models finally keying in on MCS to move across the area
Monday morning.

Before that, we are watching the departure of an area of showers
across the far N/NE in association with a weak wave. Additional
light showers were moving along the US-24 corridor in association
with a weak mcv riding axis of limited instability. Some of the CAMs
still try to develop isolated storms but looking less likely so slgt
chc pop held onto in far south into evening.

Focus then shifts to expected convective develop upstream across
Missouri and Iowa this evening, eventually propagating northeast
towards the region and growing upscale in coverage and to some
extent intensity as it moves into Illinois late tonight. Models
generally agreeing on MCS working across most if not all areas
Monday morning, arriving somewhere around 12Z Mon in the west or sw
and then translating rapidly NE. Threat should be confined to heavy
rain and maybe locally gusty winds but a few CAMs (namely 12Z NMM)
develop a rather pronounced line of storms that races into the area
with over 1000 J/KG MUCAPE feeding in ahead of it. After extensive
coordination with surrounding offices pops were ramped up to
categorical by Monday morning and transitioning across the area in
the AM. Will need to watch trends for any severe potential, but
think greater concern will end up in afternoon. Low pressure moves
northeast across NW areas, influx of higher instability will edge
into S/SE areas mainly south of US-24 but could see some potential
further north. SWODY2 has introduced a slgt risk in this area which
is on track given plenty of instability, 30 to 40 kts of shear and
proximity of sfc low. Chances for precip will linger into Monday
evening, mainly SE areas as cold front sweeps across. Minor
adjustments to pops.


.LONG TERM...(Tuesday through Sunday)
Issued at 320 PM EDT Sun May 20 2018

Increasing 500 mb heights (582-585 dm) will bring a fair amount of
sunshine and period of dry weather through Thursday with above
normal temps.

Closed upper low over Nevada on Tuesday will eject northeast into
the northern Plains and then work east, amplifying as it heads for
the northern Great Lakes. Shower chances will likely increase into
the weekend, but exact timing remains uncertain with model
differences in strength and timing of the wave. Forecast will remain
muddled with slgt chc to chc pops into Sunday.


.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
Issued at 111 PM EDT Sun May 20 2018

Low level inversion associated with broad easterly low level flow
will continue to promote IFR/MVFR cigs for a few more hours into
this afternoon before some continued gradual diurnal improvement.
Axis of warm advection/low level fgen has been sufficient for some
elevated showers across northwest Indiana, and a period of rain
showers at KSBN. More vigorous convection later this afternoon
should remain south of KFWA where strong instability gradient
will reside, and where influences from MCV type forcing may result
in isolated-scattered thunderstorm development across
central/east-central Indiana. Otherwise, mainly dry conditions
expected this evening with next concern very late tonight into
Monday morning as larger scale convective system moves into the
region. Confidence in widespread rain/embedded storms in the
morning is beginning to increase, and will include prevailing rain
shower Monday morning. Some elevated thunder will likely be a
concern but with timing uncertainties, will cover this forecast
cycle with VCTS. After some expected improvement of IFR/MVFR
conditions, deteriorating conditions are expected again later
tonight into Monday morning due to diurnal effects with easterly
flow, and then impacts from precipitation. Additional scattered
thunderstorms are possible Monday afternoon/early evening.




LONG TERM...Fisher

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