Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/04/24

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 531 PM CST Sat Feb 3 2024

.KEY MESSAGES...

- Patchy fog and low clouds may redevelop overnight

- Unseasonably warm temperatures will continue next week, with
  near-record warmth possible Wednesday and Thursday

- The next chance of precipitation will arrive in the Thursday
  to Friday timeframe

- A pattern change with colder temperatures is expected toward
  the middle of February

&&

.DISCUSSION...
Issued at 121 PM CST Sat Feb 3 2024

Through Monday Night

The morning stratus deck that spread into far northeastern
Illinois hit a wall and continues to erode, which will give way
to partly cloudy to mostly sunny skies areawide by late
afternoon. Tonight, model guidance again suggests low clouds and
pockets of fog will rapidly redevelop, though confidence is a
recurrence tonight is lower than the previous nights since
inversion heights continue to crash (recent AMDAR soundings from
ORD/MDW show the base of the inversion is now a mere 1000 ft
AGL). To cover our bases, our forecast will advertise partly
cloudy skies and patchy fog overnight keeping in mind neither
may be as widespread as the past few nights.

Barring any widespread stratus at daybreak, tomorrow looks pleasant
with mostly sunny skies and highs in the mid to upper 40s. A weak
upper-level shortwave will dive south across Michigan and may
provide enough forcing to generate another stratus deck during
the afternoon and evening. However, with inversion heights being
even lower than they are today, it`s entirely possible we
remain completely sunny. For now, opted to maintain partly
cloudy skies all the way through tomorrow night.

The forecast Monday and Tuesday is fairly straight-forward with
surface ridging promoting light winds and partly cloudy to mostly
sunny skies. Highs will be in the mid to upper 40s and lows will be
in the upper 20s to lower 30s. The upper-level pattern will undergo
a substantial change Wendesday onward with deep troughing becoming
established across the western US and ridging to the east. As a
result, deep southwesterly flow will materialize across the
Mississippi River Valley and usher in unseasonably (to near
record) warmth. Highs Wednesday and Thursday are expected to
climb into the low to mid 50s, with readings as high as the
lower 60s entirely possible (particularly on Thursday).
Overnight lows will be in the mid to upper 40s which is
remarkable for early February. Using our forecast high and low
temperatures, the average temperature through the first 9 days
of February may easily end up as the warmest on record for both
Chicago and Rockford.

Chances for rain (and even a thunderstorm) will increase in the
Thursday to Friday timeframe as a weak cold front moves through
the area. The system appears fairly progressive suggesting
overall rainfall amounts should be light (chances for rain
totals >0.33" through Saturday morning are only around 33%)
thereby mitigating hydrologic concerns.

Borchardt

Week 2 and beyond (February 10th onward):

While the first 9-10 days of February may be one of the warmest if
not the warmest on record, a mid month pattern change after
February 10th to a colder (seasonable or colder) and at least
somewhat active pattern is favored.

The passage of the aforementioned cold front toward the end of
next week will be the first signs of the impending pattern
change. Toward and after Valentine`s Day, mid and upper level
ridging will develop and establish itself near the west coast
and extend up to or just north of Alaska. The western ridging is
known as a +PNA (positive Pacific North American)
teleconnections pattern, and the ridging near Alaska is known as
a -EPO (negative East Pacific Oscillation). In response to the
upstream mid and upper level ridging (think a rise or bump in
the jet stream), downstream troughing (think of a dip or buckle
in the jet stream) will develop and establish over central and
eastern North America. Meanwhile, high latitude blocking in the
Arctic and North Atlantic (generally near Greenland) is expected
to develop, leading a -AO (negative Arctic Oscillation) and
-NAO (negative North Atlantic Oscillation) teleconnections.

As troughing develops across the central and eastern US and
ridging manifests to the west and over Greenland, a seasonably
cold mass from interior Canada should discharge into the Midwest
and potentially get "locked" in place. Meanwhile, depending on
the exact positioning and amplitude of western ridging, an
active El Nino subtropical jet (STJ) may continue to cut
underneath the ridging and feature associated disturbances
tracking eastward toward the Lower Great Lakes. Taken together,
the return of seasonably cold or colder air masses should bring
an attendant return of more regular occurrences of
precipitation to the general region, including the wintry
variety, during the 2nd half of February. Stay tuned!

Castro

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 530 PM CST Sat Feb 3 2024

Main aviation concerns through the TAF period:

- Potential for IFR/MVFR conditions early Sunday morning, but
  confidence is low

A swath of stratus clouds that provided BKN009 at KORD is
traveling west. Timed out arrival at KRFD between 01Z and 03Z;
therefore added a TEMPO to account for a brief period of MVFR
cigs.

Otherwise, mostly VFR conditions through much of the TAF period.
However, there is a non-zero chance for IFR/MVFR conditions to
develop, although guidance provides little confidence. Patchy
fog is possible mainly for areas west of the city early Sunday
morning. The TAF was updated to hint at the best possible time
should something develop, but until a clearer signal develops,
the TAFs were left as VFR. Otherwise, winds out of the east to
northeast up to 10 knots for Sunday.

DK

&&

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

&&

$$

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