Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 222001

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
201 PM CST Wed Feb 22 2017

336 AM CST

Through tonight...

The main concerns initially today will be with regards to the
dense fog across the area, and how quickly it will burn off this
morning. Visibilities thus far this morning have been very low in
some of this fog, with KRFD reporting down to 1/16th of a mile.
The main area that has been spared this dense fog thus far, aside
from the immediate Chicago area, has been over my southeastern
counties, where cloud cover has helped reduce the extent of the
fog. This may change, however, in the next couple hours as some of
the higher clouds shift out of this area. This could result in
the need to expand the current fog advisory for these areas
through mid morning. We will continue to monitor the latest
conditions to see if this will be needed. Otherwise, expect a
gradual improvement in the fog by mid to late morning.

The main story then becomes the potential to have another very
warm day across the region today. I did not make any big changes
to temperatures yet today, other than to lower them by a degree or
two. However, these record breaking temperatures into the lower
70s will largely depend on how quickly with burn off this fog and
low clouds, if it takes longer than currently anticipated, our
temperature forecast may end up being a bit too warm.




Friday night through Wednesday...

201 pm...Main forecast concerns include much colder air this
weekend with the potential for snow Saturday morning...and then
another storm system Tuesday/Wednesday next week.

By Friday evening...the bulk of the thunderstorm activity is
expected to be east of the cwa with some lingering showers
possible...mainly in the eastern cwa. Colder air will be spreading
into the cwa and its likely there will be a lull in the precip as
the dry slot moves across the area. By Saturday morning...the
main shot of colder air will arrive and with it a period of light
snow or snow showers is expected and likely across most of the
area. But the best chance of any accumulation appears to remain
across far northern IL and confidence as to how much may
accumulate is fairly low from this distance. The ground will be
warm and what snow does accumulate may end up just on elevated and
grassy surfaces. However...did bump pops up some and with the qpf
amounts approaching a tenth of an inch in the far north...snow
amounts near an inch are possible...again low confidence with
amounts diminishing to just a few tenths between I-88 and I-80.
This activity should be ending by early afternoon but be replaced
with strong/gusty northwest winds. Still some differences with
regard to the pressure pattern/surface low location but gusts into
the 30-35 mph are certainly possible.

A ridge of high pressure will move across the area Saturday night
with winds turning back southerly on Sunday and then a weaker
system moves from the central plains Sunday to the Ohio Valley
Monday. Bulk of the qpf with this system remains mainly south of
the cwa. If precip does materialize in the southern might
hold off until after sunset Sunday evening and by then precip
type could be a mix of rain/snow changing to all wet snow. Still
quite a bit of uncertainty from this distance.

Another weak high passes across the area Monday afternoon/evening
and then the next system arrives Tuesday with still quite a bit of
uncertainty as to how this system evolves. Low pressure is likely
to develop over the central plains Tuesday and move northeast
across the western lakes Tuesday night into Wednesday. This should
keep precip mainly rain across the area as the warm front lifts
north across the area Tuesday but given the low confidence...large
changes will be possible over the next few days though best chance
of precip currently appears to be in the Tuesday afternoon/evening
time period. Another period of colder temps then looks possible
behind this system Wednesday into Thursday. cms



A highly anomalous warm stretch that has already broke daily
records will continue to threaten records this week, including the
all time February warm records for any time of the month on
Wednesday. Here are daily records.

Chicago:                         Rockford:
      High:      High Min:       High:      High Min:
2/22: 68 (1922)  52 (1930)       61 (1922)  48 (1930)

All-time February Record Highs:
Chicago:  75  2/27/1976
Rockford: 70  2/25/2000

For more, including consecutive days of such warmth this time of
year, please see our web top news headline.


For the 18Z TAFs...

Visibility and ceilings continue to slowly improve late this
morning into the afternoon. Once ceilings scatter out by early
this afternoon, expect winds to increase with gusts into the high
teens to low 20 kt range. Winds should taper again after sunset.
Confidence in timing and magnitude of ceilings and visibility late
this evening and overnight is low. Fog is expected to redevelop
for some areas over the region and could possibly become dense
once again. A weak cold front will push across the region late
tonight turning winds to the northwest and then eventually
swinging around to the northeast tomorrow morning.




201 pm...Areas of dense fog extend across much of the open waters
of Lake Michigan this afternoon. A cold front will move south
across the lake tonight and this should end the fog threat across
at least the northern portions of the lake but dense fog may
persist into the overnight hours tonight across the southern parts
of Lake trends will need to be monitored this

Low pressure will move across northern portions of the lake this
evening with a trailing cold front moving south across the lake
which will shift winds northeasterly and these winds will increase
to 30 kts on Thursday as low pressure over the central plains
moves northeast to the western lakes by Friday night. Winds are
expected to increase to low end gales Thursday night as the low
approaches and the gradient tightens. Once the low moves east of
the lake Saturday...a period of northwest gales will be possible
Saturday into Saturday evening. cms


LM...Dense Fog Advisory...LMZ777-LMZ779 UNTIL 9 PM Wednesday.

     Gale Watch...LMZ777-LMZ779...MIDNIGHT Friday TO 9 AM Friday.




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