Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 181751

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1151 AM CST Sat Feb 18 2017

1005 AM CST

Another record warm and sunny mid-February day is unfolding as

The 925mb temperatures observed on area 12Z raobs this morning
were again at daily record territory of 12C-13C. While this proxy
for today`s top of the mixed layer will not be warming like
yesterday, the warmer starting point than yesterday provides 10
a.m. temperatures a tad above 24 hours ago. Highs should then fall
out similar, with mid 60s and some spotty upper 60s expected
east, after a little nudge up on the going forecast temperatures.

The forecast lake breeze timing and inland impingement has not
been changed, with it mainly occurring near the shore during mid-
afternoon and easing its way inland after 3-4 pm, potentially
quite slowly before fading early this evening. The wind speed
behind the wind shift looks to be light, and this would keep
marine layer induced cooling from reaching too substantial of a
rate, including in downtown Chicago, where forecast temperatures
are expected to dip into the upper 40s by 6 pm.



254 AM CST

Through tonight...

Another spring like day is expected with temperatures well above
normal.  A weak cold front currently over eastern Iowa will pass
over the region today. Winds will become light out of the northwest
behind the front. 925 mb temps will be cooler than yesterday, but
low to mid 60s seem reasonable for highs across the area today. we
will once again make a run at record high temps, and see the climate
section below for more details.

A lake breeze may form this afternoon but expecting it to stay on
the immediate lake shore. If it does come on-shore, it should be
after we reach our high temps for the day.

Calm winds and clear skies overnight will help temps fall into the
30s tonight.



254 AM CST

Sunday through Friday...

Sunday will be much like today except for a more potent lake breeze.
High temps away from the lake will be in the low to mid 60s, but the
lake breeze will keep lakeside temps in the mid 40s to around 50. I
think the record high temps at ORD and RFD will not be broken Sunday.

The next low pushes over the plains Sunday night, and its warm front
lifts north over the region.  High temps Monday will be in the 60s
with upper 60s possible south of I-80. On-shore flow will keep temps
along the lake in the 50s.  The low continues to Hudson Bay by
Tuesday night, and its cold front sweeps through Monday into
Tuesday.  The GFS has the fastest frontal passage compared to other
models. Therefore have a chance of rain Monday afternoon through
Tuesday. There is a bit of elevated CAPE Monday afternoon and night
so have a slight chance of thunderstorms. Confidence is medium in
thunderstorms occurring and coverage.

Highs in the upper 50s to low 60s continue mid week with drier
conditions thanks to zonal flow aloft.  The next low impacts the
region Thursday afternoon through Saturday morning.  Models are
rather consistent with the strength and path of the low with a 982
mb surface low over southwest WI/northeast IA Friday afternoon.
Precip chances increase Thursday night as the low organizes to our
east. Thunderstorms are probable with a deepening low in the
vicinity. Gusty southerly winds are also possible Friday.

The surface low continues northeast, and colder air associated with
the trough aloft spreads across the region Friday night. Lows Friday
night will be around or below freezing, and lingering precip may
transition to snow on the backside of the low.

In a very spring-like fashion, high temps are forecast to go from
the 50s Friday to the 30s Saturday.



1145 AM CST

An unseasonably warm stretch that has already broke daily records
on Friday February 17th and Saturday February 18th will continue,
with potential for more breaking of records. Here are statistics
on daily records.

Chicago:                         Rockford:
      High:      High Min:       High:      High Min:
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)

For more, including February warmth on consecutive days, see our
web top news headline or Public Information Statement.



For the 18Z TAFs...

The only forecast items of interest with the TAFs are wind
direction and speed.

West to northwest winds will continue this afternoon and will
keep an expected lake breeze from moving quickly inland. It is
possible ORD and MDW briefly flop light northeast between 00Z and
03Z, but the speeds should be less than 7 kt if that occurs.

A high pressure ridge will be directly over the area Sunday
morning and then move slowly east. This will favor a southeast
wind, which will become more easterly or northeasterly at Chicago
area airports thanks to a lake component and likely a true lake
breeze. Confidence in specific timing of this lake breeze passage
is low-medium, with confidence in speeds around 8 kt being



120 AM CST

Southwesterly winds of 15 to 25 KT currently ongoing over the
lake, will ease today as a weak cold frontal boundary shifts over
the lake early today setting up light westerly flow. A surface
ridge of high pressure will build over the Upper Midwest through
the day, and this feature could allow wind speeds to ease enough
this afternoon over southern Lake Michigan to allow for lake
breeze development with light onshore winds over southern Lake
Michigan. Winds should then shift back southeasterly by late
Sunday as the surface ridge moves east and an area of low pressure
sets up over the Plains. While wind speeds will likely initially
remain light out of the southeast on Sunday, speeds should be on
the increase into Monday as the Plains low shifts northward into
into south central Canada. South-Southeasterly winds of 25 to 30
KT look probable Monday and Monday night. Winds then will turn
southwesterly and weaken following the passage of another cold
front. Later in the week there are signs that a significant storm
system could tack aim on the region. This could result in a period
of strong winds Friday into Saturday of next week.






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