Area Forecast Discussion
Issued by NWS Chicago, IL
FXUS63 KLOT 162039
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
239 PM CST Mon Jan 16 2017
235 PM CST
The low over the Kansas/Missouri border will move over northern IL
late tonight/early Tuesday morning. Soggy conditions will continue
through that time. The good news is temperatures will remain above
freezing through tonight so no additional freezing rain or ice is
expected. Rain continues through the night with periods of moderate
rain possible. An additional 0.5 to 1.0 inch of rain is expected
through tonight with higher totals north of I-80. Forecast soundings
also feature a little elevated instability so a few isolated,
embedded thunderstorms are possible this evening. While an isolated
storm may occur anywhere across the forecast area, the best chance
is along and south of I-80. Convection/thunderstorms may result in
locally higher rainfall amounts.
Dense fog will likely continue south of the current rainfall
(Livingston and Kankakee counties south and all of northwest
Indiana) through this afternoon when steadier rain arrives. I have
medium confidence in how dense fog will be tonight. The abundance
of moisture will likely result in around 1 to 2 mile visibility, but
periods of drizzle may bring visibilities down to less than a mile.
Decided to go with widespread fog, but no mention of dense fog
tonight due to low confidence.
235 PM CST
Tuesday through Monday...
High impact weather chances are presently low in the extended
with a pattern atypical for January. Precipitation type looks to
remain mainly if not entirely rain during the latter part of the
week and weekend. While certainly an above normal temperature
pattern for January will strengthen, do have concerns on how far
above normal, especially near the lake front where they could be a
stiff onshore component at times, or much of, later this week and
through next weekend.
The surface low by Tuesday morning is expected to be in southwest
Michigan with gradually increasing northwest surface flow. Early
morning fog, some of it possibly dense, should ease from west to
east across the area. Scattered early morning showers also should
depart east with this system, but clouds will stick around with
high confidence. Temperatures will likely be well into the 40s
across northwest Indiana at daybreak, but as the system warm
sector moves east, temperatures there will cool, and elsewhere
likely hold steady.
A northern stream upper short wave disturbance will move east into
Wisconsin tomorrow afternoon and likely tap some of the moisture
left in the wake of the preceding, deeper system. Convective
allowing guidance with solutions that far do indicate isolated to
scattered showers across Wisconsin and northern Illinois during
the late afternoon shifting southeast into the early evening. Have
nudged up pops a tad during that time frame. The column will be
cooling, with a small chance for some brief wet snow before
With fairly quick height rises late Tuesday night into early
Wednesday, a scattering of the persistent clouds is expected.
Temperatures will gradually moderate on southwest to south winds
Wednesday and then Thursday, with 40s for highs likely areawide.
A large blocking upper ridge across eastern NOAM, with heights
near record across eastern Canada, will keep systems from an
active Pacific jet slowing as they move into the middle of the
country. Not only will they slow, they look likely to occlude,
keeping precipitation influence potentially minimal over our area,
or at least slowing chances. Do have the chances for rain lifting
north late Thursday night and Friday with a first system. Have
higher chances with the next system predicted by 12Z global models
to move into the Ohio River Valley one week from now. Confidence
in this system and timing is very low.
The forecast 925mb temperatures are well above normal, especially
by Friday into the weekend. Given the multiple systems over the
plains, at the surface an east wind is presently forecast, and at
times fairly stiffly. Given water temperatures in the lower 30s,
lake adjacent counties including downtown Chicago would remain
quite a bit cooler than inland locations that have a good
potential for low 50s one or both days this weekend.
For the 18Z TAFs...
Rain will continue through tonight. The low over Kansas will move
over the region late tonight/early Tuesday morning. As such,
ceilings will remain very low at LIFR. Visibility is not as
straight forward. 1SM vsby is expected through this afternoon, but
vsby may drop to less than a mile after midnight. Have medium
confidence in how low vsby will go overnight as the models may be
confusing the very low ceilings with fog.
Isolated embedded thunderstorms are possible late this evening.
Have low confidence in how many thunderstorms there will be and
exactly where they will form. Rain may also taper off to drizzle
after midnight which could also lower vsby.
Winds become northwest to southwest behind the low Tuesday
morning. The drier west winds will help raise vsby to VFR in the
morning. However, guidance suggests cigs will struggle to rise so
kept them in the IFR range. Another upper level wave approaches
Tuesday afternoon, and it may kick off scattered showers, so kept
VCSH in the TAFs through Tuesday afternoon.
235 PM CST
Fog will continue to be a problem into Tuesday morning across the
southern part of the lake, especially the far south. Webcam
visibility and reports indicate near 1/2SM visibility, and have a
marine fog advisory now issued. There will be times when rain
showers abate some of the fog, especially this evening. However
there is a good possibility of the visibility dropping again
Otherwise, this evening will see an increase in easterly winds
across the southern part of the lake. There could be a period
north of Chicago where winds and more so waves briefly reach Small
Craft Advisory criteria, but it should be short lasting. As the
low center moves over and past the lake, winds will turn northerly
across the entire lake, dissipating the fog. Winds turn southwest
on Wednesday and last into Thursday. Confidence in the wind
forecast Friday into the weekend is low, as trends are now
indicating more of an east to northwest wind given multiple slow-
moving low pressures to the southwest of the area.
IL...Dense Fog Advisory...ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 6 PM
IN...Dense Fog Advisory...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 6
LM...Dense Fog Advisory...NEARSHORE WATERS
UNTIL 9 AM Tuesday.
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