Area Forecast Discussion
Issued by NWS Chicago, IL

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446
FXUS63 KLOT 291940
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
240 PM CDT Sat Apr 29 2017

.SHORT TERM...
237 PM CDT

Through Tonight...

Overall, will continue the flash flood watch as heavy rain is
possible this evening. The precip doesn`t look like it will evolve
as I imagined yesterday, but we are still looking at a lot of rain
over the next 48 hours that will result in river flooding and
some areal flooding.

The surface low is forming over Texas and its warm front lies from
central Missouri through central Indiana.  The front will lift over
our far southern counties by Sunday morning.  Showers have blossomed
nicely across the forecast area, and it seems like the majority of
convective activity will occur south of I-80 especially where rain
has briefly ended.  Still have at least a slight chance of
thunderstorms across the region though as embedded thunder is
possible.

Followed the HRRR and NAMNest guidance that feature a line of
convective showers/storms forming from Rockford south over the next
couple of hours and then marching east. This convective line should
produce the most precip tonight and raised QPF values slightly. Have
0.5 to 1.0 inches of rain between 00 and 06Z Sunday. However, we
could see a break in precip or just light showers/drizzle after the
line. Lowered precip chances to likely behind the line because I did
not have enough confidence to go with straight drizzle.  Lowered QPF
using a blend of the previous forecast and GFS between 06 and 12Z
Sunday.

Temperatures are also a bit tricky. Temps will continue to fall over
the northwestern half of the CWA while temps will warm over the
southeast CWA.  That temp trend should continue into this evening.
Then temps over the northwest will hold steady or warm slightly in
the low 40s.  Temps over the southeast will also hold steady around
50 or in the low 50s.

JEE

&&

.LONG TERM...
343 AM CDT

Monday through Friday...

The large upper low and the attendant surface low will continue
gradually shift towards the Upper Great Lakes on Monday into
Monday night. Rap around moisture will likely result in some
additional light showers over the area on Monday before ending
Monday evening as the storm system finally shifts out of the
region. It appears that much of the extended period will be mainly
dry, though another storm system could try to produce
precipitation in the area around mid week. But at this time we
have maintained a primarily dry forecast. Otherwise expect
temperatures to be on the cool side, mainly in the lower 60s.

KJB

&&

.AVIATION...
For the 18Z TAFs...

Showers have reached all of the terminals and will persist through
the majority of the forecast period. Could hear a few rumbles of
thunder at the eastern terminals in the late aftn and early
evening. Have medium confidence in thunder occurring and low
confidence in coverage and location. Gusty northeast winds also
continue and cigs will fall to IFR late this aftn. Thinking cigs
will stay above LIFR although some models suggest LIFR will occur.
Showers diminish to sprinkles late this evening, but another round
of showers is expected Sunday morning. Thunderstorms may also
occur in the afternoon, but have concerns about how much energy
will be available for storms. East winds at arnd 15 kt are
expected Sunday.

JEE

&&

.MARINE...
237 PM CDT

Headlines...Will go with a gale warning for the south half and
nearshore waters this afternoon through most of tonight. While gales
will subside, small craft conditions will likely continue through
Sunday. Gales are then expected over the northern half of the lake
Sunday afternoon and night, and upgraded the previous gale watch to
a warning.

A weak high is over western Ontario and the western Great Lakes
while a low is forming over Texas.  The tightened pressure gradient
will keep northeast winds at 30 kt and they will increase to 35 kt
gales over the south half late this afternoon.  Both the low over
Texas and the high over Ontario will lift north through Monday and
gales will form over the northern half of the lake Sunday afternoon.

The low will pass over the western Great Lakes Monday night and
reach Quebec Tuesday.  The low`s cold front swings through late
Monday night/early Tuesday morning. Southwest to west winds may
increase to gales over the southern half Monday night into Tuesday.
High pressure moves over the lake Wednesday and then shifts
southeast of the lake late in the week.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flash Flood Watch...ILZ014-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039...7 PM Saturday to 7 AM Monday.

IN...Flash Flood Watch...INZ001-INZ002-INZ010-INZ011-INZ019...7 PM
     Saturday to 7 AM Monday.

LM...Gale Warning...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 until 4 AM Sunday.

     Small Craft Advisory...nearshore waters
     until 4 PM Saturday.

     Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM Sunday to 4 PM Sunday.

&&

$$

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