Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 050119

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
819 PM CDT Sun Jun 4 2023

Issued at 818 PM CDT Sun Jun 4 2023

Smoke from wildfires in Quebec will continue to degrade air quality
and result in hazy skies through at least Monday. Otherwise, it`ll
be warm and dry to kick off the work week, with chances for
precipitation arriving late Tuesday into Wednesday with a back door
cold front. Higher precipitation probabilities will arrive this
weekend as a trough digs into the Great Lakes.


Issued at 818 PM CDT Sun Jun 4 2023

Dry conditions will prevail the remainder of the night as daytime
instability wanes with sunset and showers and storms off to our
west begin to diminish. Temperatures are on track to fall into the
50s overnight under mostly clear but hazy skies.



Issued at 229 PM CDT Sun Jun 4 2023

<<<<<<< Key Messages >>>>>>>

1. Smoke-driven air quality concerns through at least Monday

2. Temperatures trending less warm

3. Chance for showers Tuesday-Wednesday
   Better opportunity this weekend

Lest anyone beguile you into believing the atmosphere is not a
dynamic fluid, take a look at water vapor satellite imagery, which
reveals east-southeast flow overspreading central Illinois on the
west side of high pressure centered across southern Lower
Michigan/northern Indiana. Visible satellite shows lofted wildfire
smoke continues to flow into our area from the east. Fortunately,
the highest particulate concentrations are aloft, though (1)
visibility reductions at multiple observing sites and (2) PM2.5
particulate concentrations in the unhealthy category for sensitive
groups from Illinois EPA both confirm some of this is near the sfc,
where HRRR and RAP smoke suggest concentrations will increase this
evening as the atmosphere decouples and particulates become trapped
beneath the near sfc inversion. (PM2.5 are inhalable particulates
that are less then 2.5um -- for perspective, a strand of human hair
is ~70 um -- in diameter and in this case are emanating from
wildfire smoke.) HRRR suggests an even more significant increase in
near sfc smoke concentration tomorrow morning east of I-57, but
since the wildfires responsible are way up in Quebec this trajectory
is not going to be perfect. The greatest concern with this would be
air quality deterioration (southern Wisconsin and northeast Illinois
have experienced unhealthy -- and not just for sensitive groups --
air quality much of the day already), the latest information for
which you can find at The smoke, however, may also lower
temperatures tomorrow, as these particulates generally mitigate
receipt of shortwave (solar) radiation but remain largely
transparent to longwave (from earth`s sfc) radiation. It takes quite
a robust concentration to have this effect, though; our highs may
ultimately be just a degree or two cooler than NBM`s deterministic
forecast which has been doing well the past several days.

Otherwise, it`ll be pleasant and less warm with highs in the low to
mid 80s through midweek -- possibly (~30% chance, per NBM) even in
the 70s on Wednesday and/or Thursday in our northeast when >60% of
the LREF brings 850mb temps to sub 12 degC on the western edge of
the expanding upper trough centered across the northeast CONUS. When
the backdoor cold front with this system arrives late Tuesday-
Wednesday, it`ll bring some chance for showers and perhaps even
thunderstorms as a layer of elevated moisture and instability
arrives from the west-northwest. NBM now has 20-30% PoPs during this
time frame (highest in the southwest), which may need to be adjusted
up further eventually given ~40% of the LREF (CMCE+GEFS+EPS) now has
measurable precip falling across central Illinois.

Cluster analysis suggests agreement among the long range guidance in
north to northwest 500mb flow continuing through the weekend, with
varying degrees of sub-normal 500mb heights over Illinois across
individual clusters -- anywhere from 25-50m below climatological
normal in the least troughy cluster (dominated by the GEFS) to 100-
150m below normal in the troughiest two clusters (dominated by the
CMCE). The raw ensemble would suggest a 60-80% chance for measurable
precip this weekend, while the calibrated and bias-corrected NBM is
a little more pessimistic with only 50-60% PoPs by late Saturday.
NBM does suggest, however, that there is a 35-50% chance for more
than 0.5 inches of rain by the time the upcoming weekend is through,
implying that this precip, being convectively-driven, could be quite
heavy -- at least in spots. Nonetheless, the chances appear quite
low (<10%) that we`ll receive enough to climb out of our precip
deficit, which at this point is 2 to 4 inches!



.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 628 PM CDT Sun Jun 4 2023

High pressure will remain anchored over the Great Lakes providing
light NE flow and primarily VFR conditions through the period.
Some smoke from Canadian wildfires may occasionally drop vsby to
MVFR this evening and during the day Monday.




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