325
FXUS63 KLOT 081117
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
517 AM CST Fri Nov 8 2024

.KEY MESSAGES...

- Patchy fog possible this morning, mainly in areas outside of
  the Chicago metro.

- Brief period of showers Saturday evening into early Sunday
  morning followed by breezy winds Sunday afternoon.

- Another storm system may result in another period rain around
  mid-week.

&&

.DISCUSSION...
Issued at 239 AM CST Fri Nov 8 2024

Through Saturday:

Clear skies overnight have allowed surface temperatures to cool
to or near the surface dew points at most of our ASOS/AWOS
sites away from the heart of the Chicago metro early this
morning. Considering this and the fact that we still have several
hours of darkness to go, we will probably see some fog develop
before sunrise. That said, low-level flow appears that it may
remain elevated just enough in this relatively dry air mass to
prevent widespread dense fog from developing, and forecast
guidance on the whole is not particularly excited about that
possibility as well, so thinking that we`ll likely be able to get
by without a Dense Fog Advisory. Still, at least patchy dense fog
development cannot be ruled out, so we`ll have to continue to
monitor observational trends over the next few hours.

Tranquil weather conditions are otherwise expected today with
surface high pressure in the region. High temperatures
overperformed model guidance by a few degrees yesterday, and
would expect a similar story to play out today in the same air
mass with the passing cirrus not likely to inhibit solar
insolation as much as the HRRR and RAP, among other models,
would suggest. Thus, have nudged forecast high temperatures
upwards a smidge with most of our forecast area likely to see
highs reach or eclipse the 60 degree mark. The mostly clear
skies should then afford us another seasonably cool night with
low temperatures in the low-mid 40s favored across much of the
Chicago metro and mid-upper 30s favored elsewhere.

Upper-level cloud cover will be on the increase going into
Saturday as a closed-off upper-level low slides eastward across
the central Plains. These clouds should thicken up enough to
keep Saturday`s daytime temperatures a few degrees cooler than
what they should be today. While the cloud deck may grow deep
enough for attempts at hydrometeor production to get going as
the leading flank of mid-level vorticity glides overhead
Saturday afternoon, a sub-500 mb wedge of dry air will likely
prevent any raindrops from reaching the ground until after
sunset.

Ogorek


Saturday Night through Thursday:

Overall, the long term period remains seasonably mild, with
only a couple brief chances for primarily light rain. The first
shot of rain will be right at the start of the period, namely
Saturday night into at least early Sunday morning. The main
feature of interest supporting this period of rain is the slow
moving mid/upper low that is expected to shift out across the
front range of the Colorado Rockies into this evening. As it
does, surface low pressure is expected to quickly consolidate
and become occluded under the main upper low across the Central
Plains into Saturday. An accompanying occluded frontal boundary
will then sweep eastward across our area Saturday night as the
vertically stacked system tracks into the Upper Midwest.

Our best shot of rain comes with the arrival of the frontal
boundary Saturday evening/night. This looks to be a fairly short
period of rain (~6 hours), however, as a mid-level dry slot is
expected to quickly punch northeastward into the area following
the surface frontal passage. This should thus result in a quick
west to east ending of the rain either late Saturday night or
early Sunday morning. Some additional low chances (15-35%) for
light showers will continue Sunday afternoon, with the best
chances being near the WI state line and points northward as the
main system tracks into the western Great Lakes. With no real
push of colder air into the area on the back side of this system
conditions on Sunday will remain mild (highs in the upper
50s/low 60s), albeit with breezy west winds.

Dry and quiet weather is expected in the wake of this system
for Monday and Tuesday before our next shot of rain comes with
another approaching weather system during the mid-week period
(Wednesday into Thursday). However, model and ensemble guidance
still continue to display a large amount of spread with the
actual timing and overall evolution of this mid-week system.
With this in mind, I did not make any changes to the NBM chance
POPS (30-50%), though they are admittedly likely too broad
brushed from Wednesday into Thursday.

KJB

&&

.AVIATION /12Z TAFS THROUGH 18Z SATURDAY/...
Issued at 517 AM CST Fri Nov 8 2024

There are no significant aviation weather concerns through the
period.

Light west winds through daybreak will turn northwesterly by
mid-morning, then northeasterly later this afternoon. Winds
then become east-southeasterly in the 10-15 kt range late
tonight into Saturday morning. Otherwise, expect VFR conditions
through the period, with mainly some patchy high clouds
increasing later today into this evening. Once winds turn east
off the lake late tonight, some patchy MVFR cloud bases can`t
be ruled out.

KJB/Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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