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Area Forecast Discussion (AFD)

Issued by Chicago, IL (LOT)

FXUS63 KLOT 172322

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
622 PM CDT Mon Jun 17 2019

156 PM CDT

Through Tuesday night...

High pressure expected to be situated across the region for much 
of the period, with mainly dry conditions persisting. Any 
showers/thunderstorm developing along surface trough/front to the 
south this afternoon and evening will likely remain to the south. 
Additional showers/thunderstorms expected to develop along 
approaching surface trough over IA and southwest WI on Tuesday. 
Once again, this precip will likely stay just to the 
west/northwest of the CWA. Additional development expected to 
remain focused on this feature, but expect this axis to begin 
drifting into parts of northern IL Tuesday night. Thunder will be 
possible, however, instability is not looking overly high at this 
time. Some potential for some clearing skies this afternoon, but 
think cloudy skies will continue to be the trend into tonight and 
Tuesday. With the cloudy skies likely lingering on Tuesday, did 
lower high temps. If cloud cover holds on longer, temps will need 
to be lowered even more. Did add fog for tonight into Tuesday 
morning, as the pattern doesn't really look to change too much. 
Similar coverage is possible, and will once again need to monitor 
for the possibility of dense fog.



236 PM CDT

Wednesday through Monday...

Guidance is in fairly good agreement on shortwave trough rippling
through the zonal flow and across the region Wednesday. Most
models depict some amplification of this wave as it moves across
the region, probably due in part to some convective enhancement.
While there has been some variability in the track of this
feature, the 1200 UTC guidance suite would continue to favor our
southern CWA for the heavier rain/better rain chances. If the more
southerly track of the wave verifies, then the warm sector with
the better instability and attendant severe threat would likely be
south of our area as well.

Should see a break in the precip Thursday and probably much of the
day Friday as well, before we potentially end up in a more active
weather regime over the weekend. Medium range guidance continues
to show a long wave trough digging into the western CONUS with
ridging over the southeastern U.S. which would place our area on
the potentially active north/northwest periphery of the ridge.

Several days of moisture return with flow originating from the
southern Gulf of Mexico and northwest Caribbean should provide 
for ample fuel for storms and when combined with stronger flow 
aloft on the flanks of the ridge certainly looks favorable for 
severe weather somewhere in the Midwest and middle/upper 
Mississippi Valley region. Could potentially see several waves of 
showers and storms Friday night through the weekend, which if it 
were to hit same areas repeatedly would raise the specter for 
flooding concerns as well. Still many days out and placement of 
the boundary and better chances of storms will undoubtedly be 
dictated by convection, so confidence on the precise details is 
low, but chances are there for strong-severe storms as well as 
heavy rainfall/flooding. 

- Izzi


For the 00Z TAFs...

622 PM...Primary forecast concern this period is low clouds/fog 
developing this evening and continuing through mid/late Tuesday 

Cigs have lifted to mvfr for all areas except the immediate lake
shore areas including gyy. Fog over the lake is expected to drift
inland this evening with vis under 1sm expected most of the night
at gyy. Cig trends this evening are a bit uncertain and additional
scattering is possible away from the lake. However...lower cigs 
are expected to slowly spread inland from the lake this evening
and lower overnight. Ifr cigs are possible at ord/mdw and for now
have just added tempo mention but trends will need to be
monitored. Fog trends are also uncertain. There may be some dense
fog especially near the lake and south of the terminals though
there are some signals for vis in the 1-2sm across northeast IL
and added lower vis with the tempo.

Northeast winds under 10kts will become light and variable this
evening and then turn back east/northeast under 10kts for the
Chicago terminals Tuesday. Winds are expected to become light
westerly further west including at rfd on Tuesday. cms


LM...Dense Fog Advisory...nearshore waters until 10 AM Tuesday.