Air Resources Laboratory banner image
Air Resources Laboratory web site National Oceanic and Atmospheric Administration (NOAA)

il discuss


Office: DVN
FXUS63 KDVN 281033
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
533 AM CDT Thu Mar 28 2024

...Updated for 12z Aviation...

.KEY MESSAGES...

- Low chance of a rain shower or sprinkle today and tonight

- High confidence of showers and storms Friday night, and again
  early next week

- Wide variety in temperatures early next week due to the precip
  chances

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 239 AM CDT Thu Mar 28 2024

06z surface analysis showed an expansive area of high pressure
covering the Mississippi River Valley and Great Lakes, with a
weak surface cold front stretching from Lake Michigan into
southeast Iowa. Nighttime satellite showed a mid-level cloud
deck stretching from central Iowa into far northwest Illinois,
which was the result of a weak frontal boundary and WAA
occurring along it. Temperatures as of 130 am ranged from 23 in
Dubuque to 36 in Burlington.

The surface high will quickly move south and east of the area
today as ridging builds across the central CONUS. Several weak
areas of 500 hPa CVA ahead of the ridging will track across
area, which will produce mainly mid to high level clouds. A
stray rain shower or sprinkle will be possible, with good
agreement amongst many of the deterministic CAMs. However, this
is low confidence as fcst soundings show plenty of dry air
availible in the low levels that will need to be overcome first.
Have introduced some low chance POPs (< 20%) with this forecast
package for this afternoon and tonight, but expecting most to
remain dry.

Temperatures will be much warmer today with flow out of the south
behind the surface high. Highs will range from the upper 40s along
the Hwy 20 corridor to low 60s in northeast Missouri.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 239 AM CDT Thu Mar 28 2024

Friday through Friday night...

Ridging will centered across the Mississippi River Valley to start
the day, with strong southerly flow at the surface bringing
increasing temperatures and Gulf moisture into the area. Despite
the increasing cloud cover, highs should easily climb into the
upper 50s to mid 60s areawide.

A stronger disturbance embedded in the zonal flow will move into the
area Friday night, and will produce a weak surface low and trailing
cold front as it tracks across Iowa. Increased lift from the surface
low, combined with the increasing Gulf moisture and a strong
LLJ, will lead to widespread showers and storms Friday night
into early Saturday morning. Primary threats will be lightning
and heavy rain with PWATs climbing to around one inch, though
some storms may produce small hail given ample deep layer
shear will be in place.

Saturday...

Daytime Saturday will be dry with lingering showers and storms
exiting the region during the morning. Weak disturbances
persisting in the zonal flow will keep clouds in place, but
temperatures should have no trouble climbing back into the
50s/60s areawide.

Easter Sunday through Tuesday...

The aforementioned cold front will stall and set up shop across north
central Missouri and Illinois on Easter Sunday, and will be the
focus of our attention early next week. Increasing baroclinicity
and strengthening flow against the front from a developing
surface low in eastern Colorado and western Kansas will increase
shower and storm chances across the area, especially nearer to
the front in southeast Iowa, west central Illinois and northeast
Missouri. These chances will persist through Tuesday as the low
will be slow to progress east along the front.

Latest deterministic guidance keeps the warm front south of the
area, which should help keep our severe threat low. Regardless,
rainfall could be heavy as latest NBM probs show medium to high
chances (50-80%) of amounts over one inch along and south of
Interstate 80. Will continue to monitor this period.

Temperatures will be a challenge Sunday and Monday given the precip
chances and warm front position. Current NBM favors a tight north-
south temperature gradient with highs each day ranging from the
upper 40s (Hwy 20) to mid 60s (northeast Missouri and west central
Illinois).

Tuesday night on...

High pressure will follow for mid-week with dry conditions and
warming temperatures expected. Latest NBM favors highs back in the
mid to upper 60s areawide next Thursday with strong ridging
building back across the region.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/
... Issued at 532 AM CDT Thu Mar 28 2024

Weak mid-level front will bring a cloud deck across the area
this morning with a low confidence chance (< 20%) of a rain
shower. Otherwise, expect mainly VFR conditions for the next 24
hours with light westerly winds shifting to the east tonight.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.

&&

$$

SHORT TERM...Speck
LONG TERM...Speck
AVIATION...Speck



Office: LOT FXUS63 KLOT 281110 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 610 AM CDT Thu Mar 28 2024 .KEY MESSAGES... - Warming temperatures through weeks' end - Periods of showers and storms Friday night through the weekend - Another storm system likely to impact the area early next week && .DISCUSSION... Issued at 358 AM CDT Thu Mar 28 2024 Through Friday: Mid-level ridging will continue to build into the southern Great Lakes today allowing temperatures to warm toward more seasonable readings. However, lingering cold temperatures aloft due to an upper low to our north will limit the amount of warming today with highs expected to top out in the upper 40s to mid-50s. In addition, the colder air aloft will also promote some deeper diurnal mixing today which some guidance suggests may pull down drier air and limit the low-level moist advection. While our current forecast does have humidities this afternoon remaining in the 35 to 40 percent range, if dew points are able to mix down this afternoon RH readings could verify lower to around 30% especially across northern IL. Thankfully, winds today should be somewhat light with gusts generally under 20 mph which should limit any fire weather concerns this afternoon. Heading into tonight, a surface baroclinic zone will begin to lift into the area which will likely generate a bit of a north- south temperature gradient with overnight lows. Guidance also continues to show a weak mid-level impulse pivoting atop this baroclinic zone which looks to be sufficient to generate some isolated to widely scattered showers across the southern 1/3 of our forecast area (areas south of the Kankakee River Valley). However, forecast soundings continue to show a decent amount of dry air in the sub-cloud layer which may limit the overall coverage. Therefore, despite a large guidance support for higher POPs, I have decided to maintain the advertised 15 to 20 percent chances for showers this evening through about midnight. Otherwise, expect dry conditions to once again prevail through Friday afternoon with warmer temperatures in the mid-50s to mid-60s. Though onshore winds along the IL lakeshore will keep temperatures notably cooler in the 40s. Friday night through Wednesday... Several periods of active weather will begin to establish across the central CONUS, including our area, Friday night as a broad upper trough moves onshore over southern California and progresses eastward through the early part of next week. The first period of inclement weather for our area is expected Friday night as a modest shortwave passes through the southern Great Lakes and interacts with the aforementioned baroclinic zone which is expected to be stalled across northern IL. As these features interact a weak surface low will develop across eastern Iowa and propagate eastward along the boundary generating a broad area of showers and perhaps thunderstorms as it does so. Given the non-favorable diurnal time, instability over northern IL and northwest IN looks to be somewhat modest at best but still sufficient for at least scattered embedded thunderstorms particularly in the warm sector south of the boundary. As a result, widespread severe weather is not expected. However, there will be a stout 500 mb jet pivoting into the area Friday night which should develop 40 to 50 kts of deep layer shear and possibly allow for some more robust cores to develop. Any storm cores that area able to take advantage of the shear may be able to produce localized instances of small hail and possibly some gusty winds. Additionally, PWATs of 0.75 to 0.90 inches are forecast to advect into the warm sector of this system which may yield some heavier downpours especially with any robust storm cores. Given that soil moistures are above average and the lack of green vegetation yet, runoff from the rain could lead to instances of river and stream rises and result in a concern for localized flooding. Guidance continues to depict that showers and storms should wane Saturday morning as the surface low exits into northern Indiana, but some guidance does redevelop convection in the warm sector Saturday afternoon. Whether or not this warm sector is in our area remains uncertain. A similar story can be told for Sunday as the potential for showers and storms will depend on how far south the baroclinic zone gets shoved in the wake of Saturday morning convection and whether or not it can retreat back into our area prior to storms developing Sunday afternoon. Due to these uncertainties I have decided to maintain the 20 to 30 percent chances for showers in our southern CWA both Saturday and Sunday. Heading into Monday, the aforementioned trough is forecast to be ejecting into the southern plains with a strengthening upper jet aimed at the southern Great Lakes. This broader forcing is expected to be enough to surge the baroclinic zone back north as a new surface low develops somewhere across the Mississippi Valley. However, where this surface low will track once it develops remains very uncertain among guidance members which will play a major role in what impacts we see. While it does appear likely that we will see some additional rainfall from this system, the intensity of said rainfall and whether or not any strong to severe storms develop into our area will be something to monitor over the coming days. Yack && .AVIATION /12Z TAFS THROUGH 18Z FRIDAY/... Issued at 610 AM CDT Thu Mar 28 2024 There are no significant aviation weather concerns through the TAF period. A deck of VFR cigs (around 050) will prevail across the terminals this morning. No precipitation is expected at the terminals. Light southwesterly winds will become a bit breezy/gusty later this morning and afternoon with occasional gusts around 20 kts, perhaps briefly a bit higher late this afternoon prior to sunset. Winds will then become nearly light and variable before trending northeasterly Friday morning. A weak lake breeze will probably turn GYY's winds northeasterly early this evening. Carlaw && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago
Office: ILX FXUS63 KILX 281056 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 556 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 12z TAFs through 12z Friday Morning) Issued at 556 AM CDT Thu Mar 28 2024 WSW winds will increase to 10-14 kt later this morning, gusting to 20 kt during the afternoon and evening, as the pressure gradient tightens between a departing trough and expanding ridge of high pressure. As the atmosphere decouples this evening, winds will ease but ceilings around 050-080 accompanied by virga and isolated sprinkles will move towards the ESE along the I-74 corridor. Bumgardner && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$