Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 062323

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
523 PM CST Sat Mar 6 2021

235 PM CST

Through Sunday night...

Another quiet weather day across the region under abundant
sunshine with generally light winds. A surface ridge axis
extending southward into north-central Illinois this afternoon
will drift east of the area by Sunday morning. Light/calm winds
under mostly clear skies and a dry airmass will support min temps
in the upper teens to low 20s where snow pack remains and mainly
the mid 20s elsewhere. Given the lack of any significant
visibility restrictions last night and decent daytime mixing of
dew points into mid 20s today, any shallow fog risk over the
snowpack tonight should be fairly low. However, hazy conditions
will likely be common across the area by daybreak Sunday.

WAA will commence on Sunday as low-level winds increase and
become S/SSE across the area through the day. With low-level
moisture return lagging, temps over bare ground will likely rise
into the mid 50s. The main limiting factor on temps is the
potential for a thicker shield of upper-level clouds ahead of a
modest upper jet streak to move over the area in the afternoon. If
the cirrus is fairly transparent or show limited coverage, 60F is
not out of the question for some locations south of the
Kankakee/Illinois River in Illinois.

S to SW winds remaining around 10-15 mph Sunday night will keep
temps above freezing across the area, which should significantly
aid in commencing the eradication of the remaining snowpack across
north-central Illinois over the next several days.



300 PM CST

Monday through Saturday...

The warm up really gets into full gear the beginning of the work
week as persistent southerly flow ushers in a period of well
above normal temperatures with highs in the 60s Monday through
Wednesday likely. In fact, Tuesday night we could see record
breaking warm min temps. See the climate section below for more
details. Will also have to keep an eye on record highs Tuesday
and Wednesday if temperatures over perform.

Monday will probably be the nicest of the three days to spend
outside with Tuesday and Wednesday looking especially breezy. Highs
top out in the lower to mid 60s areawide including our typically
cooler spots near the lakeshore. Tuesday the surface pressure
gradient begins to tighten as a quick moving disturbance ejects
off the Rockies and moves overhead. Depending on when this
arrives, associated increased cloudiness could impact how warm we
get in the afternoon somewhat, but mid 60s look like a good bet

As we head into Wednesday there is increasing uncertainty in the
finer details with the approach of surface low from the Midwest
and an associated warm front lifting across the area. This could
provide us with the chance for a few spotty showers into Wednesday
afternoon. Am a bit lower confidence on this occurring, however.
If we are able to stay well capped, this could help push
temperatures even warmer, with a 70 degree reading somewhere in
the area certainly within the realm of possibilities. This would
also likely act to decrease dewpoints locally and increase surface
wind gusts even more than the 30-40 mph gusts currently forecast,
and thus resulting in an increased potential fire weather threat.
Will continue to monitor this period over the coming days.

By Wednesday evening/night the cold front will begin to sag south
into the local the area bringing the potential for heavy rain
showers and even a few embedded thunderstorms, beginning a
prolonged period of precipitation somewhere across the forecast
area through Thursday, and potentially longer depending on where
the boundary ultimately stalls out.

Beyond Thursday, however, guidance begins to diverge even more with
the placement of the surface boundary as it stalls out. WPC does
have a broad area of 1-2+" of QPF across northern Illinois
Wednesday through Saturday. Depending on how far south the
boundary sags, we could see a bit of mixed precip Friday into
Saturday in areas that end up on the cold side of the front.



300 PM CST

Very mild air mass will be over the region Monday through
Wednesday. This could set the stage for record high minimum
temperatures to be threatened or broken on Tuesday and Wednesday.

Tuesday March 9th
Record High Min for Rockford: 46 in 2016
Forecast Low: Lower 40s

Wednesday March 10th
Record High Min for Chicago: 52 in 1876
Record High Min for Rockford: 44 in 2010
Forecast Low: Lower 50s for both Chicago and Rockford



For the 00Z TAFs...

Aviation Forecast Concerns:

* South-southeast winds gradually increase Sunday afternoon into
  Sunday evening, becoming more south-southwest Sunday night. Some
  potential for a period of LLWS conditions Sunday night, just
  beyond the current TAF period.

Surface high pressure ridge persists from central WI into central
IL late this afternoon. A couple of mesoscale influences on the
surface wind field appear to be the cooler temps over lingering
snow cover across north central IL (producing a NNW wind direction
of the colder snowpack into largely snow-free northeast IL) and a
lake breeze producing east-northeast winds across northeast IL.
Both of these circulations should decay with sunset and cooling
temps, with the weak surface pressure gradient in the vicinity of
the surface ridge supporting generally light/variable or calm
winds overnight.

The surface ridge axis is expected to move off to the east of the
terminals early Sunday morning, allowing a light southeast wind to
develop to start the day. Surface pressure falls to our west and
into the upper Midwest should result in winds gradually increasing
and veering more south-southeast by afternoon. A subtle warm
frontal boundary should lift across the area Sunday evening,
shifting winds a bit more south-southwest and maintaining speeds
around 10 kts (perhaps with a few gusts). In addition, southwest
winds above the boundary layer are progged to increase into the
40-45 kt range by around 06Z, which will likely produce a period
of LLWS conditions through early Monday morning.

Can`t rule out a little MVFR-VFR light fog where snow cover
lingers across parts of north central IL late tonight and early
Sunday morning. Of the terminals, KRFD would be the main location
to potentially see this, though better potential for actual vis
restrictions are likely limited to rural areas south/west of KRFD.
Cloud-wise, generally clear conditions are expected overnight
before VFR high clouds increase into Sunday afternoon. Some lower
level moisture may support some lower VFR clouds in the 3500-4500
foot layer during the afternoon per model forecast soundings.





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