|National Weather Service Forecast for:
Issued by: National Weather Service Chicago, IL
|Updated: 8:17 pm CST Feb 23, 2017
|Lo 40 °F⇑
||Hi 61 °F
||Lo 27 °F
||Hi 32 °F
||Lo 22 °F
||Hi 42 °F
||Lo 29 °F
||Hi 47 °F
||Lo 36 °F
Hazardous Weather Outlook
|Showers likely and possibly a thunderstorm before 2am, then a chance of showers and thunderstorms after 2am. Cloudy, with a temperature rising to around 55 by 3am. East northeast wind 10 to 15 mph becoming south after midnight. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.
|A 50 percent chance of showers and thunderstorms. Some of the storms could be severe. Mostly cloudy, with a high near 61. South wind 10 to 15 mph, with gusts as high as 30 mph.
|A slight chance of rain before 11pm, then a slight chance of rain and snow between 11pm and midnight, then a chance of snow after midnight. Mostly cloudy, with a low around 27. Breezy, with a west southwest wind 15 to 20 mph, with gusts as high as 30 mph. Chance of precipitation is 50%.
|A 40 percent chance of snow before noon. Mostly cloudy, with a high near 32. Breezy, with a west wind 15 to 20 mph, with gusts as high as 30 mph.
|Partly cloudy, with a low around 22. West northwest wind 5 to 15 mph becoming southwest after midnight. Winds could gust as high as 20 mph.
|A 20 percent chance of rain after noon. Partly sunny, with a high near 42.
|A chance of rain and snow before midnight, then a slight chance of snow. Mostly cloudy, with a low around 29. Chance of precipitation is 30%.
|Partly sunny, with a high near 47.
|A chance of rain before midnight, then a chance of rain and snow. Mostly cloudy, with a low around 36.
|A chance of rain. Mostly cloudy, with a high near 55.
|Rain likely. Mostly cloudy, with a low around 38.
|A chance of rain. Partly sunny, with a high near 47.
|Partly cloudy, with a low around 26.
|A slight chance of rain. Mostly sunny, with a high near 40.
Forecast from NOAA-NWS
for Peotone IL.
FXUS63 KLOT 240244
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
844 PM CST Thu Feb 23 2017
844 PM CST
Primary change to going forecast this evening was to sharpen up
the temperature gradient across the area tomorrow. Strong warm
front is looking increasingly likely to make it as far north as
about I-80, with areas north of the front likely to see low
clouds, fog, drizzle, and occasional showers with stiff northeast
winds likely to hold temps in the upper 30s or lower 40s. GFS and
NAM have been consistent their past few runs with this, though
RAP and HRRR are a bit more gung-ho on bringing the front a bit
farther north, especially given the tendency for the cold lake to
retard northward advancing warm fronts this time of year.
To the south of the boundary temperatures should climb well into
the 60s with 70 not out of the question far south if the sun
breaks out. Big question convectively for tomorrow is how far west
will initiation occur. Impressive EML advecting into the area
should provide for a strong capping inversion that will take some
work to overcome, though strong forcing and heating in the warm
sector should eventually cause cap to break, just a matter of
whether it is over our eastern CWA or just to our east. Unusually
strong instability for this time of is progged tomorrow with very
strong shear as well, leading to the potential for supercells and
damaging wind producing line segments. At this distance, too hard
to say exactly where initiation will take place, so no changes
made to that aspect of the forecast this evening.
Continued isentropic ascent tonight should lead to continued
development of scattered showers and eventually some thunderstorms
too as steeper lapse rates advect north and lead to increasing
elevated instability. Overall, forecast for tonight appears to be
in good shape. Did add some fog to the forecast for late tonight
and especially Friday morning north of the warm front, where some
locally dense fog could form, especially north of the warm front
close to the surface low.
230 PM CST
Tonight through Friday...
Several forecast concerns through the short term period, including
large north-south temperature gradient, locally heavy rainfall,
timing/extent of thunderstorms, and the potential for severe
weather Friday afternoon across the southeastern parts of the cwa.
Deepening surface low pressure was over far southwestern Kansas
this afternoon, with a nearly stationary frontal boundary
extending northeast into central IL and IN. This low is expected
to propagate to near far southern Lake Michigan by mid-afternoon
Friday, in response to a strong mid-level short wave ejecting from
the central Rockies. Isentropic upglide was already developing
into the region this afternoon, as indicated by rain spreading
into western IL per regional radar mosaic. Increasing south winds
above the warm frontal inversion into this evening will support
strengthening moisture transport, and an increase the coverage
and intensity of showers/rain. Guidance focuses the greatest pops
and rainfall amounts generally along/north of the I-88 corridor
across northern IL, with high-res members eventually shifting
focus mainly across and north of the IL/WI border area early
Friday morning. Forecast soundings depict precipitable water
values approaching 1.00" late tonight, with blended guidance QPF
of 0.75-0.95 inches north of I-88 indicated through Friday.
Thunderstorm potential appears fairly high for late February, with
a plume of steep mid-level lapse rates (700-500 mb >7.5 C/km)
atop 40-50 kt southwest low-level jet late this evening into early
Friday morning. Forecast soundings depict anywhere from 150-450
J/kg of elevated mucape which should support embedded thunder
especially across the aforementioned area overnight.
The surface low is progged to be over far northeast MO/western IL
near Quincy by 12Z Friday, with general model agreement in taking
it across the southern parts of the Chicago metro/far southern
Lake Michigan during the mid-late afternoon hours. With the mid-
level dry slot spreading across the cwa from the southwest during
the afternoon, the focus for surface-based thunderstorm
development is across the southeast parts of the cwa, especially
east of I-55 and along/south of I-80 (with much of the high res
CAM guidance highlighting areas from I-57 east). SPC has
appropriately tightened up the western part of the day 2 slight
risk a little further east of their previous outlook. WRF and GFS
soundings indicate fairly substantial capping around 750 mb,
though large scale height falls associated with ascent with
approaching mid-level wave, divergent left exit region of upper
jet and surface cold front should be enough to force a narrow
band of convection along/just ahead of the front during the
afternoon. While mlcapes are fairly week (
NWS LOT Office Area Forecast Discussion