Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 201037

Area Forecast Discussion
National Weather Service Northern Indiana
637 AM EDT Sat May 20 2017

Issued at 500 AM EDT Sat May 20 2017

Low pressure over the southern Plains will move slowly northeast
into the upper Great Lakes this weekend causing showers and
thunderstorms at times across our area through Sunday morning,
with best chances late today through tonight. High pressure will
build then into the area later in the day Sunday providing dry
weather which should then continue through Monday night.
Temperatures over the next few days will be falling below normal
early next week.


.SHORT TERM...(Today through Sunday)
Issued at 456 AM EDT Sat May 20 2017

An upper low will move from the High Plains into the Upper
Midwest by Sunday morning. Ahead of this system, a warm front from
southeast Missouri extending along the Ohio River will move
north. Showers and storms will increase across the area later
today into tonight. An initial meso convective vortex over
northeast Illinois early this morning will move northeast and
spread a few showers and possibly a storm into northwest Indiana
around daybreak. A second system will move northeast and help
shower and storm chances increase as the front moves north later
today as very moist air spreads north. Precipitable water values
of 1.7 inch per GFS will top the average climate maxes for this
time of year. There is the potential for severe weather later
today and tonight as surface based instability increases and may
possibly top 3000 J/Kg if the surface warm front moves into the
southern part of the forecast area. The instability combined with
low level shear will favor the chance for severe storms. Rainfall
amounts are expected to range from around an inch to an inch and a
half by late Sunday night.


.LONG TERM...(Sunday through Friday)
Issued at 456 AM EDT Sat May 20 2017

Sunday night through Friday... An amplifying upstream ridge will
cause a broad upper level trof to develop and deepen through the
middle of the upcoming week. Another round of rain is expected as an
upper level disturbance moves south out of Canada and deepens the
main trof. Chilly air behind the next system will cause high
temperatures to struggle to reach 60 Wednesday.


.AVIATION...(For the 12Z TAFS through 12Z Sunday Morning)
Issued at 625 AM EDT Sat May 20 2017

Unsettled pattern for this aviation forecast cycle with showers
and thunderstorms expected today/tonight. The other forecast
challenge will be trying to resolve duration of any IFR cigs

Thunderstorm complex across southwest/western Illinois should tend
to diminish in intensity as it lifts northeastward over the next
several hours, but expecting scattered to numerous
showers/isolated storms to spread northward across northern
Indiana later this morning/early afternoon as low level warm/moist
advection increases downstream of convectively enhanced vort max.
At least brief IFR cigs appear likely this morning, with eventual
transition to 2-3k ft MVFR cigs this afternoon and to eventual VFR
later this afternoon at KFWA as low level warm front begins to
push northward.

Thunderstorms are expected to redevelop across northern/eastern
Illinois late afternoon/early evening as upper diffluence begins
to increase downstream of Plains upper trough. Future forecasts
will likely need to include TS at some point for both terminals,
but at this forecast distance will limit mention to VCTS. LLWS may
also need to be considered for a brief time tonight. Otherwise,
east winds to continue today north of sfc warm front, with
strongest gusts into the 20 to 25 knot range expected at KSBN
where sfc pressure falls migrating across western Great Lakes may
provide some enhancement in the midday period.


LM...Small Craft Advisory until 4 PM EDT this afternoon for LMZ043-



SHORT TERM...Skipper
LONG TERM...Skipper

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