Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 161220

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
620 AM CST Thu Feb 16 2017

245 AM CST

Through Friday...

Winter will be in the rear view mirror beginning today, at least
for the coming week. Deep cutoff upper level low pressure over New
England will move very little today and even on Friday. Weak
shortwave energy in the northwest flow behind the low will steer
higher clouds southeastward through the area through tonight,
occasionally more opaque. High surface pressure will shift east
today opening the door to warm advection from the west. A broad
low pressure trough will extend through the plains which will
maintain and east component to the winds, and therefore highs in
our inland western zones should get close to the 50 mark while it
should still be on the cooler side (upper 30s) near the lake.

April then arrives on Friday. Upper ridging behind the low will
move overhead on Friday and will make for a near cloudless day.
NAM/GFS/EC all move the warm front to at least the WI border and
lakefront areas. Low level wind progs also depict 10-15 kt in the
boundary layer and above which would typically be enough to get it
through and keep a lake breeze at bay, but being an early season
event we could still see some onshore component along the IL
lakeshore, and given there is a weakness in the surface pressure
field over far northeast Illinois/southeast Wisconsin. Mixing
will be shallow so we won`t realize the full 850 temperature
warming, but the thermal ridge will move right overhead on deep
wsw flow and mid 50s to low 60s seem a decent bet area wide. If
the NAM/EC play out, records for both Chicago (137 year record set
in 1880 of 60) and Rockford (59 in 1981) would be in jeopardy.



242 AM CST

Saturday through Wednesday...

Saturday is an interesting day in that we have the potential for a
record warm day, but some caveats at play. We will be starting off
with low temperatures early Saturday above normal highs for this
time of year. We will get missed by a weakening low across the
Ohio valley and a more compact system near Lake Superior. Both of
these features, especially the southern one,  could affect the
area with some clouds, but the northern wave will send a cold
front to the area. We should be able to warm quickly initially
ahead of the front giving many areas as warm or an even warmer day
than Friday, but northeast Illinois stands the chance of a
significant cool down in the afternoon if the winds fully flop
over to NE as the high-res NAM suggests.

The front will wash out on Sunday, with 850/925 temperature
recoveries returning quickly. It seems another warm day for most
areas, but another concern for onshore winds closer to the lake
and portions of the Chicago metro area. Still looks like a nice
day with the upper ridge rebuilding.

A secondary warm frontal surge will ensure Sunday night into
Monday but this one brings a bit more moisture with it, entering
concerns about clouds. It will still be mild on Monday as
dewpoints head up into the upper 40s northeast to lower 50s south,
so in spite of the clouds it highs will still be in the 50s and
60s. EC/GFS hold upper ridging in place. The GEM in the extended
blend and even the GFS paint some very light QPF with the warm
front Monday morning, and therefore we carry some very low pops
for this feature, though there could be a period of lower clouds
which could keep temps in check a bit farther north. Better
chances for rain will be tied to a cold front embedded in the
a weakening upper stream wave. With the system appearing to weaken
in current guidance (this has been the trend but some wavering
still as to its strength), precip will be along the front and it
may not end up being a whole lot for our area, thus the muted
chance pops for now. A more significant storm system for the
plains/midwest may be out in model future land beyond this time



427 AM CST

We will be heading into an unseasonably warm stretch of weather with
near to possibly record breaking warmth at times. Here are some
statistics on daily records, and consecutive days of 50+, 60+ degrees.


Chicago:                         Rockford:
      High:      High Min:       High:      High Min:
2/17: 60 (1880)  42 (1890)       59 (1981)  39 (1961)
2/18: 62 (1981)  45 (1981)       58 (1981)  38 (1997)
2/19: 65 (1930)  51 (1994)       63 (1930)  42 (1994)
2/20: 64 (1930)  49 (1930)       61 (1983)  46 (1930)
2/21: 67 (1930)  47 (1930)       64 (1930)  42 (1930)


Chicago:                         Rockford:
Longest in February              Longest in February
8 days: 2/22-29/2000             8 days: 2/22-29/2000
        2/18-25/1930                     2/18-25/1930
7 days: 2/22-28/1998             5 days: 2/23-28/1998
6 days: 2/24-29/1976                     2/16-20/1981
        2/11-16/1882                     2/25-29/1932
5 days: 2/19-23/1943             4 days: 2/12-15/1984
        2/25-29/1932                     2/24-27/1976
        2/9-13/1876                      2/21-24/1927

Longest in Meteorological Winter
12 days: 12/14-25/1877           8 days: 2/22-29/2000


Chicago:                         Rockford:
Longest in February              Longest in February
4 days: 2/24-27/1976             3 days: 2/19-21/1930
3 days: 2/19-21/1930                     2/23-25/1930
                                 2 days: 2/25-26/2000

Longest in Meteorological Winter
5 days: 12/2-6/1998              3 days: 2/19-21/1930



For the 12Z TAFs...

Light and variable northeast to southeast winds will be in place
early this morning but will become predominantly more SSE/SE
through the morning as winds speeds increase ahead of an
approaching warm front and should remain there throughout the day.
The warm front is not expected to bring any precipitation to the
area and is expected to slow over northern Illinois late this
evening and overnight. Winds should drop off again within the
frontal trough and may become variable at times overnight. Cannot
rule out some patchy fog developing by early tomorrow morning
within the light flow but probability is too low to include in the
TAF at the moment. The front should push north of the area later
Friday morning with southwest winds moving in behind the front.
Skies will remain VFR throughout the period.



300 AM CST

Winds are expected to continue to diminish this morning as high
pressure builds across the western Great Lakes. A small craft
advisory will be allowed to expire this morning and should leave
our waters headline free for several days. Winds will eventually
turn southerly this afternoon as the ridge axis shifts east of
Lake Michigan and south to southwest flow will prevail through
midday Saturday. Low pressure moving east across northern Ontario
Saturday will drag a weak cold front across Lake Michigan Saturday
causing winds to veer to the west. With unseasonably mild
temperature in place, lake breezes are not out of the question in
the coming days, though Saturday may have the best chance for
winds to turn onshore, especially across southern Lake Michigan
where winds are weakest. Weather is expected to become more active
next week as a series of lows move across the region, though
timing and track details still need to be worked out.






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