Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS63 KLOT 222340
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
640 PM CDT Sun Jul 22 2018

.SHORT TERM...
145 PM CDT

Through Monday...

Aside from a few thunderstorms yet late this afternoon, mainly 
south of I-80, no significant weather is expected during the 
period.

The remnants of the upper low will continue to reside just to our
east across the IN and OH state line into Monday. This will
continue to support a northerly wind across the area on Monday,
though winds will likely shift northeasterly off the lake in the
afternoon as a lake breeze shifts inland. 

While some cloud cover will likely continue Monday over
northwestern IN, it appears partly cloudy skies will prevail
elsewhere. This should allow temperatures to warm back into the
lower 80s across most areas. There is a very small chance for a
few isolated showers across mainly eastern sections of the area 
on Monday, but confidence on this is too low to include a mention 
at this time. 
KJB

&&

.LONG TERM...
211 PM CDT

Monday night through Sunday...

Overview...Relatively quiet extended period expected. Temperatures 
being above average but dip to near to below average by mid to late 
week. No significant rain is expected.

High pressure continues to build over the Midwest through Wednesday. 
Guidance suggests showers may form over northern IL Tuesday, but I 
cannot identify a clear source of forcing, so I removed precip 
chances from the forecast. I also raised high temps into the mid-
upper 80s Tuesday and Wednesday. Lake side cooling is possible 
both days. 

An upper level trough brings slightly cooler air to the region mid 
to late week with highs around 80. Despite periods of slight chance 
to chance of precipitation, I have low confidence in measurable 
precip through the extended.

JEE

&&

.AVIATION...
For the 00Z TAFs...

Concerns with the aviation forecast through Monday are: 

- North-northeast winds becoming north-northwest by daybreak
  Monday, then becoming northeast again by or during early Monday
  afternoon

- Potential for the departing MVFR ceilings early this evening to
  return Monday, along with a slight chance for a stray shower

Influence of the broad low centered over the eastern Great Lakes
continues with northerly winds and spokes of moisture rotating 
over the area. The north-northeast winds will ease in speed by 
mid- evening and start inching back to the north-northwest. A lake
breeze, or at least a "flop" to northeast due to marine layer 
influence, is likely on Monday. Confidence in timing is medium. 
Speeds will be quite a bit less overall on Monday, but still 
likely to be 10+ kt frequently.

Current MVFR clouds over far northeast Illinois and far northwest
Indiana that are partially marine-induced are likely to depart by
01Z per satellite trends. Later tonight, broken VFR clouds look
as if they may return and there is potential in the morning for 
more of an MVFR deck to develop over the lake and possibly spread 
inland. Confidence in this at ORD and MDW is low, as is 
confidence in isolated showers, though they are possible.

MTF

&&

.MARINE...
211 PM CDT

Did not make any changes to the Small Craft Advisory as waves will 
subside this evening. There is a chance that waves may subside 
slower than expected, and if that occurs, the Small Craft Advisory 
will have to be extended into tonight.

10-20 kt northeast to north winds diminish Monday as the pressure 
gradient weakens over the lake. Weak and variable winds become 
northwest to west 10-20 kt behind a cold front Wednesday. Winds 
diminish and vary in direction late this week.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement...ILZ006-ILZ014 until 10 PM Sunday.

IN...Beach Hazards Statement...INZ001-INZ002 until 10 PM Sunday.

LM...Small Craft Advisory...nearshore waters 
     until 10 PM Sunday.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

National Weather Service Glossary of Abbreviations