Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 280647
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
147 AM CDT Thu Mar 28 2024

.KEY MESSAGES...

- Periods of storms are forecast Friday evening through early next
  week. Severe potential will be low (up to around 5%) Friday
  night, but appears to increase Sunday into Monday.

- There is a 30-50% chance for freezing temperatures north of I-72
  Tuesday night, with slightly lower chances Wednesday night.
  Precautions might be needed to protect tender vegetation once
  again.

&&

.DISCUSSION...
Issued at 133 AM CDT Thu Mar 28 2024

Water vapor satellite shows an upper trough, whose axis roughly
bisects IL at 145am, slowly migrating eastward across the Upper
Great Lakes. Deterministic and ensemble guidance agrees that as
this shifts eastward today and ridging expands into the Midwest
behind it, 850mb temps will rise to 2-3 degC by late afternoon
when, despite some pesky mid-level clouds, sfc temps should have
no trouble warming well into the 50s (perhaps 60 SW of a Macomb to
Robinson line). The CAMs suggest a piece of mid level energy will
then pass across the northern portion of the ILX CWA, producing
some virga and perhaps even an isolated sprinkle north of I-72
this evening, and fostering an increase in low level moisture with
HREF mean suggesting mid to upper 30s dewpoints area-wide by late
evening. This will thus mark the first of several nights where
sub freezing temps are not expected, and in fact forecast lows in
the mid 30s to low 40s could even be too low given (1) the
aforementioned evening cloud cover, and (2) increasing mid-high
clouds ahead of the next shortwave closer to sunrise tomorrow.

South-southwest winds will strengthen tomorrow for increasing warm
advection which will add about 10 degrees, perhaps a little more, to
our peak readings today. NBM even suggests a 50-60% chance highs
reach or surpass 70 degF south of I-74, which seems plausible if we
mix a little deeper than currently forecast. Precip chances increase
Friday evening, when steepening mid level lapse rates (NAM is as
aggressive as -8 to -8.5 C/km) associated with an incoming EML
foster 500-1000 J/kg MUCAPE across our west/northwest where the
ECMWF suggests thunderstorms develop between 7-11pm. These storms
will translate east-southeast across a portion of central IL
overnight and into Saturday morning, with some redevelopment
across areas mainly east of I-57 Saturday afternoon with the cold
front. Given the steep lapse rates, can`t completely rule out a
marginally severe instance of hail, but the threat seems quite low
(at up to only around 5% from CSU MLP).

Saturday evening into Sunday, the cold front will stall and then
lift gradually back northward as a warm-pseudostationary front with
strengthening warm advection ahead of a low brewing across the Great
Plains. The forecast remains a bit murky Sunday into Monday, as the
deterministic models are each slightly different in how far north
they take the warm front, and have different timing in shortwaves
generating convection as they ripple eastward along it. At this
point, it appears likely that for areas south of I-74 there will be
at least one - and possibly several - rounds of storms those two
days, though the northward extent of robust moisture sufficient for
severe storms is a little ambiguous. The CSU MLP continues to
generate a broad 15% risk for severe storms both Sunday and Monday
area-wide, though LREF joint probs for > 30 kt 0m-500mb shear and >
500 J/kg SBCAPE peak on Monday at around 40-50%, suggesting that may
be the most favored day. We`ll continue to monitor that potential.

Behind the cold front, which some guidance suggests could take until
late Tuesday to completely clear the area, a cooler airmass will
overspread the Midwest and Ohio Valley, though this appears short
lived with only one or perhaps two nights mid next week where
there`s concern for another (hard) freeze. NBM suggests 30-50% (20-
35%) chances for a freeze Tuesday (Wednesday) night north of I-72,
tapering to less than 15% south of I-70. Chances for a hard freeze
are less than 15% area-wide both nights.

Bumgardner

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1057 PM CDT Wed Mar 27 2024

High pressure will result in light winds and VFR conditions
overnight. The high will settle to the south and a warm front will
spread in from the east Thursday afternoon and evening. Southwest
winds will pick up to 10-14 kt within the resulting gradient with
some gusts near 20 kt possible, especially at BMI/CMI. Winds will
diminish again with sunset Thursday evening.

Deubelbeiss

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$


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