Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS63 KLOT 162008
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
308 PM CDT Wed Oct 16 2019

.SHORT TERM...
230 PM CDT

Through Thursday...

The region remains under cyclonic flow, as the large upper level 
low slowly spins across the Great Lakes. In this pattern, 
persistent cloud cover is still in place, with northwest winds 
still gusting to 30-35 mph. As the previous forecast noted, there 
have been some holes in the stratus this afternoon, that I think 
may become larger this afternoon into the evening. Daytime mixing 
likely allowing some drier air aloft to filter down and help erode
some of the cloud cover, with this possibly continuing this 
afternoon. Additionally, there looks to be some diurnal component 
to the cloud cover, with some additional scattering going into 
this evening appearing possible. If this stratus doen't completely
erode, upstream mid/high clouds noted on Satellite imagery will 
move overhead and provide cloudy skies this evening. This 
moisture does look to remain fairly progressive though, with some
clearing across north central possibly occurring late tonight 
into Thursday morning. Meanwhile, northwest winds will continue 
but will see speeds/gusts diminish this evening. Under at least 
partly cloudy skies and lighter winds tonight, do think some 
locations across north central IL will see lows in the mid/upper 
30s. With this potential setup, did add patchy frost to the 
forecast. WAA really ramps up on Thursday with temps rising to the
mid/upper 30s, with lighter winds and sunnier conditions 
expected.

Rodriguez

&&

.LONG TERM...
308 PM CDT

Thursday Night through Wednesday...

By Thursday night, upper ridging will begin to build across the 
Mississippi Valley while a long wave trough digs into the western 
CONUS, bringing the pattern chance toward more warmer conditions for 
the local area.  In general, there is good agreement in the various 
models in lifting short wave energy out of the western trough and 
across the area Saturday.  Latest guidance is indicating a bit 
higher QPF/PoPs and have increased PoPs generally to likely, tied to 
the timing of the enhanced forcing of the mid-level short wave and 
the associated cold frontal passage.  Showers will be likely with a 
slight chance of thunderstorms during the daytime hours. With a 
more Pacific air mass spreading across the region in the wake of the 
front, generally looking for near to slightly above normal temps 
this weekend into next week.  With a relatively warm, moist air mass 
in place, the next system expected to impact the region early next 
week will bring the potential for another round of showers and 
thunderstorms for late Sunday night through Tuesday. 

&&

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

VFR ceilings and northwest winds/gusts in place early this 
afternoon, and this looks to remain for much of the forecast
period. Have observed these ceilings rise over the last several
hours, with this trend continuing this afternoon into the early
evening. Some scattering of the current stratus deck in place
might occur later today, but with upstream mid/high clouds
expected to move overhead later this evening. Gusts well in the 20
kt range will persist this afternoon, but will continue to observe
a diminishing trend before gusts end completely this evening.

Rodriguez

&&

.MARINE...
242 AM CDT

Northwesterly gales will develop early this morning, with peak
speeds/gusts this morning around 35 kt for the Illinois nearshore
and around 40 kt for the Indiana nearshore. The northwest gales 
will ease by about mid day today for the Illinois nearshore and 
likely by sunset for the Indiana nearshore. Waves will build to 10
to 14 ft along the Indiana nearshore by mid day today, particularly
from Burns Harbor to Michigan City. Hazardous waves for small craft
will linger through late tonight for the Illinois nearshore and 
through mid to late Thursday afternoon for the Indiana nearshore.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Lakeshore Flood Advisory...INZ002 until 9 PM Wednesday.

LM...Small Craft Advisory...IL nearshore waters until 4 AM Thursday.

     Gale Warning...IN nearshore waters until 7 PM Wednesday.

&&

$$

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

National Weather Service Glossary of Abbreviations