il discuss
Office: DVN
FXUS63 KDVN 062251
AFDDVN
Area Forecast Discussion
National Weather Service Quad Cities IA IL
551 PM CDT Mon May 6 2024
...00Z AVIATION UPDATE...
.KEY MESSAGES...
- An organized line of storms is expected to move through the
outlook area late tonight between 1 AM to 7 AM (west to east
through the area). This system will pose a risk for damaging
winds and isolated tornadoes.
- For Tonight: The Storm Prediction Center has a Slight Risk
for severe storms to the south and west of the Quad Cities
with a Marginal Risk covering the rest of the area.
- Isolated storms may redevelop Tuesday afternoon and evening, a
few of which could be strong.
- Scattered showers and storms remain possible on Wednesday
before temperatures cool off late in the week. There is a
Slight Risk for severe storms across the south on Wednesday
with a Marginal Risk to the north.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 245 PM CDT Mon May 6 2024
Tonight into Tuesday Morning
The forecast remains on track with a squall line expected to
track through eastern Iowa, northeast Missouri, and northwest
Illinois late tonight into early Tuesday AM. This complex of
storms will cover a large spatial area so rain chances are high
at 90-100% across the outlook area. The convection will
initially develop across Kansas this afternoon/evening before
growing upscale and tracking to the ENE into Missouri, Iowa, and
Illinois tonight.
Confidence has increased on the line of storms still packing a
punch as it reaches the western to even central counties of the
outlook area. While forecast MLCAPE is on the low side
(250-1000 J/kg), low-level shear is high with 25+ kts in the
lowest 1 km and 30-35 kts for 0-3 km. The strong environmental
shear will help to balance the gust front on the leading edge of
the convection, creating more concentrated lift and enhancing
the potential for stronger storms.
As for timing, the QLCS should reach the western counties
between roughly 1 to 2 AM, central areas (near the Quad Cities)
between 2 - 4 AM, and far eastern counties between 5 - 7 AM.
SPC has expanded the Slight Risk for severe storms to the NE,
now encompassing areas to the south and west of the Quad Cities,
with a Marginal Risk for the rest of the forecast area. The
primary threats are scattered damaging wind gusts around 60 mph,
with a low potential for a few higher gusts over the far
southwest counties. There is also an isolated QLCS tornado
risk (5% within 25 miles of a point), highest in the
aforementioned Slight Risk area.
PWAT values near 1.25" are forecast with strong WAA forcing.
Thus, rainfall on the order of 0.50" to 1" is likely for much of
the area. Scattered showers and isolated storms could develop
mid to late morning on Tuesday behind the departing QLCS, but
these are not anticipated to pose a severe risk at this time.
&&
.LONG TERM /TUESDAY THROUGH MONDAY/...
Issued at 245 PM CDT Mon May 6 2024
The Upper Midwest is forecast to remain under general troughing or
cyclonic flow aloft through the period. Flow aloft will be
southwesterly a 500 MB through Wed/Thurs it becomes more
northwesterly as the current storm system departs. This will allow a
series of troughs and ridges in the northwest to move across the
area into early next week. The trend for chances of showers and
storms continues about every 24 to 36 hours. There will be periods
of quiet weather in between. Timing on rain chances will likely vary
over the next few days. Temperatures are trending below normal
Friday through Sunday.
The long term period begins Tuesday/Tuesday night with a closed 500
MB low over the northern PLains. At the surface, a cold front wiil
move eastward across Iowa and Illinois through 00 UTC on Wednesday.
A decaying MCS will likely be moving across our northwest Illinois
counties at 12 UTC on Tuesday and exiting the area. Models show
skies clearing quickly and do show some instability across the area
ahead of or right behind the front which will lead to the risk of
showers and storms during the afternoon. There could be some
isolated severe storms with CAPE of 500 to 1000 J/KG and about 20
knots of 0 to 6 km shear. The main threats will be hail and damaging
wind gusts. The amount of instability will depend on how quickly
skies clear.
On Wednesday, the closed 500 mb low will transition to an open wave
with a positive tilt as it moves across the area. At the surface, a
low is forecast to lift east northeastward from northwest Missouri
into northeast Illinois or northern Indiana by 12 UTC Wednesday.
This would bring the surface low and warm and cold fronts across the
area during peak heating on Wednesday. SPC has a slight or level 2
out of 5 risk of severe storms on Wednesday for the area along and
south of a Keosauqua to Iowa to Princeton Illinois with a Marginal
or level 1 out of 5 risk for severe storms north of that line.
Current model guidance shows the potentail for a high shear low CAPE
event but it will depend on the track of the surface low and how
much instability moves this far north.
&&
.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 546 PM CDT Mon May 6 2024
A large complex of showers and thunderstorms remains on track to
impact the terminals late tonight, with timing favored between
around 08Z to 12Z. This will lead to periods of MVFR/IFR due to
lower ceilings and reduced visibilities in heavier rain. The
strongest cells could produce wind gusts near 50 kts from the
WSW.
There remains a low chance (20-30%) of a shower or storm
developing Tuesday afternoon ahead of a front across eastern
Iowa. However, latest CAMs are not in agreement on location of
development or timing so have left a mention out of the TAF at
this time.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.
&&
$$
SHORT TERM...Uttech
LONG TERM...Cousins
AVIATION...Speck
Office: LOT
FXUS63 KLOT 062334
AFDLOT
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
634 PM CDT Mon May 6 2024
.KEY MESSAGES...
- Thunderstorms are likely tomorrow morning and may produce
gusty winds and/or small hail.
- A second round of thunderstorms appears probable during the
afternoon, with the highest confidence in storm redevelopment
being east of a Pontiac, IL to Chicago, IL line. A few of
these afternoon storms could become severe with large hail
and damaging winds as the primary hazards.
- Another round of storms may develop late Wednesday, some of
which could be strong to severe, mainly south of I-80 into
central IL/IN.
&&
.DISCUSSION...
Issued at 332 PM CDT Mon May 6 2024
Through Tuesday night:
All eyes are upstream on the central/southern Plains, where a
significant severe weather outbreak is underway and will
continue well into the night. Strong forcing associated with an
ejecting upper-level trough and an attendant cold front at the
surface will promote rapid upscale growth across Kansas and
Nebraska, with the resultant elongated QLCS then expected to
track into Iowa and Missouri late this evening and eventually
into Illinois late overnight. By the time this strongly-forced
line of storms reaches our forecast area, it will likely be
elevated and on a general downward trend in intensity, so
prospects for severe weather in our forecast area with this
early morning QLCS appear to be minimal. Near-surface stability
won't be overly strong, however, and MUCAPE could still be as
high as about 1000 J/kg (highest in our southern counties) as
this line of storms rolls through, so there could still be some
gusty winds and/or small hail with any of the stronger
individual updraft cores within this line.
The remnants of the weakening QLCS should skitter out of our
forecast area from west to east by about 11 AM CDT or so, and
rapid destabilization efforts will begin as soon as it departs.
Cold mid-level temperatures associated with the aforementioned
trough pivoting overhead coupled with strong upper-level forcing
from DPVA and divergence within the left exit region of an
upper-level jet should not have much of a problem with
steepening mid-level lapse rates in the wake of the morning
convection, which is not likely to cause substantial convective
overturning of the troposphere in the first place. Warm/moist
advection will also modestly increase temperatures and dew
points at the surface going into the afternoon, with pockets of
sunshine likely to provide a boost to air temperatures as well.
Taken together, it appears that at least part of our forecast
area will end up realizing 1000+ J/kg of uninhibited MLCAPE
around come the early-mid afternoon, with the greatest degree of
instability (potentially up to 2000 J/kg of MLCAPE) focused
across our southeastern CWA. The aforementioned large-scale
forcing, plus the presence of a low-level jet and isentropic
ascent, thus appears likely to reignite an additional round of
scattered to potentially numerous thunderstorms in at least part
of our forecast area during the afternoon tomorrow, and the
majority of the latest 12Z CAM suite seems to be on board with
this idea.
Wherever instability recovers appreciably by the time the core
of an inbound mid-level vorticity maximum arrives, convection
appears likely to develop, and deep layer shear will be plenty
strong enough to be able to sculpt any mature convection into
supercells, with the largely unidirectional shear profiles
promoting both large hail and damaging downburst winds and the
most likely severe weather hazards. While not particularly
likely, some threat for tornadoes does also appear to exist,
mainly in our far southeastern CWA, where low-level flow looks
like it will be a little more backed than elsewhere. All that
said though, if adequately strong instability is unable to be
realized to balance out the very strong deep layer shear, then
updrafts are likely to be sheared apart by the strong mid- and
upper-level flow and not really be able to get well-organized,
which would greatly limit the overall scope of the severe
weather threat that may be realized. At any rate, the overall
prospects of convective redevelopment and severe weather in our
forecast area tomorrow afternoon appear to be greatest across
our southeastern counties, where the Storm Prediction Center has
delineated a Slight (level 2/5) Risk in their Day 2 Convective
Outlook. Farther northwest in our CWA, confidence in adequate
destabilization occurring in time for convection to develop and
mature is lower, and hence, a Marginal (level 1/5) Risk appears
to more appropriately characterize the overall severe weather
threat there at this time.
After the afternoon convection has departed, there may be one
additional opportunity for isolated to widely scattered
thunderstorms to affect our forecast area in the evening as a
secondary, more subdued vorticity maximum swings into the area
and kick-starts additional convective development to our
northwest. It's possible that this activity could trickle into
our northern CWA near or after sunset and pose some threat for
hail and/or damaging winds, but with gradually waning
instability and sounding profiles looking noticeably drier by
then, confidence in this occurring is relatively low at this
time.
Ogorek
Wednesday through Monday:
In the wake of the Tuesday system the parent mid-upper low will
remain situated over the Central Plains with the core of the
northern stream upper jet directly overhead. Low-level
trajectories from the Gulf of Mexico will allow for a quick
moisture recovery across the Mid-Mississippi Valley on
Wednesday. A semi-coupled upper jet structure will provide
additional synoptic support for widespread thunderstorm
development across this region then spreading east across the
Ohio Valley. The question locally is how far north can this
moist warm sector reach which will impact our severe
thunderstorm potential. Latest trends in 12Z guidance keep the
northern extent to the better instability just south of the
area, confined mainly to central/southern IL/IN and areas along
the Ohio River Valley. However, given the strong dynamics in
play, if better instability can lift into the area, especially
into our southern CWA (along/south of the Kankakee River Valley)
the environment would be supportive of all severe hazards. Will
continue to monitor trends closely.
While the severe threat is more in question, showers and
thunderstorms are expected across the area by Wednesday evening
and overnight. As the surface low occludes and becomes more
elongated, an east-to-west axis of cool wind-whipped rain likely
continues into the day on Thursday, especially along/north of
I-80. The cooler north to northeast winds off the lake in rain
will limit our daytime warming on Thursday to the 50s to lower
60s.
The upper low begins to split, with the western lobe cutting
off over the western CONUS and the eastern lob phasing with a
wave extending across Ontario/Quebec with a northwest flow
pattern setting up, with the next wave diving out of Canada
bringing our next chance for showers an perhaps a few
thunderstorms late Friday into Saturday morning. There are
differences with the handling of the western CONUS cut-off upper
low and resultant upper level pattern though it appears the
pattern remains active with off and on precipitation chances
continuing next week.
Petr
&&
.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 621 PM CDT Mon May 6 2024
Relatively quiet conditions characterized by east to
southeasterly winds of 10-15kt and occasional bouts of SCT to
BKN VFR cloud cover will continue through the first 12 hours of
the TAF.
Toward or just after daybreak, a line of decaying showers and
thunderstorms is expected to move over the terminals from
southwest to northeast. Incoming model guidance appears to
exhibit a very modest slowing trend with the arrival of the
morning activity. For now, opted to shave off the first hour of
the inherited 3-hour TEMPO groups to target the 13-15Z window
in the Chicago terminals, plus or minus one hour at GYY and RFD,
respectively. Once the line fully develops in the Plains
overnight, later TAF packages may offer refinement in the
arrival of the morning activity. With the decaying showers and
storms expected to be rooted above a near-surface stable layer,
confidence is lower than average in whether the morning activity
will be accompanied by a wind shift. For now, felt maintaining
the inherited southwesterly wind shift with gusts to 25kt was a
course of least regret.
Immediately before and after the line of morning showers, MVFR
stratocumulus clouds with bases between 2000 and 2500 feet are
expected to prevail. Chances for a second round of showers and
storms in the vicinity of DPA/ORD/MDW/GYY in the 18-22Z
timeframe appear to be increasing (currently around a 40-50%
chance), though felt it would best to wait one more cycle of
CAM guidance before adjusting the inherited PROB30 groups.
Behind all convective activity tomorrow afternoon,
southwesterly winds will prevail as MVFR cigs erode.
Borchardt
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
Visit us at weather.gov/chicago
Office: ILX
FXUS63 KILX 070112
AFDILX
Area Forecast Discussion...Updated
National Weather Service Lincoln IL
812 PM CDT Mon May 6 2024
.KEY MESSAGES...
- A line of thunderstorms will push through central Illinois late
tonight into Tuesday morning...bringing gusty winds and
downpours, as well as a few tornadoes possible.
- Scattered severe thunderstorms may re-develop Tuesday afternoon
and evening.
- Confidence is growing concerning on a more significant and
widespread severe weather event across much of central and
southeast Illinois Wednesday afternoon/evening.
&&
.UPDATE...
Issued at 810 PM CDT Mon May 6 2024
Line of severe storms is moving across NE/KS this evening and
approaching KS/IA this hour. Latest CAMs suggest this line will
reach the lower Illinois River Valley by around 09/10Z or 400/500 AM
CDT isolated storms popping up ahead of the main line around
08Z/0300 CDT. Given the unfavorable diurnal timing, storms should be
in a weakening trend, but couldn't rule out some strong/severe
storms reaching as far east as central Illinois. Latest RAP suggests
pockets of 1000 J/kg MLCAPE will still be in place as the line
arrives with deep layer shear of around 30kt which would support
a continuing severe threat.
Deubelbeiss
&&
.DISCUSSION...
Issued at 258 PM CDT Mon May 6 2024
While a few showers persist in southeast/east-central IL this
afternoon associated with a shortwave moving ENE up the Ohio Valley,
this activity should gradually diminish this evening as a line of
thunderstorms organizes in the central Plains late this afternoon
and evening and sweep eastward toward central IL. Latest high-res
models are fairly unanimous with this line arriving in far west-
central IL around 2 AM a few hours past peak intensity. MUCAPE
values are forecast to be as high as 2000 J/kg as this line moves
into western MO/IA, down to 1000-1500 entering IL, and 750-1250 as
it exits IL to the east around 9 AM. This instability is also
increasingly likely to be elevated in nature as a stable layer
develops near the surface. Nevertheless, there will be a chance
for scattered severe wind gusts, especially west of the Illinois
River where SPC has denoted a Slight Risk of severe thunderstorms,
likely weakening to more isolated wind gusts as it weakens toward
the I-57 corridor. A few tornadoes could also spin up along the
line, again more likely toward western IL. There will likely be a
lull in precipitation behind this line during the morning hours,
but instability should return fairly quickly during the daytime
hours, as mean surface-based CAPE forecasts increase to 1000-3000
J/Kg (highest southeast of I-70, lower northwest of IL River).
Outflow boundaries left behind from the early morning thunderstorm
line could provide the convergence needed to start storms during
the afternoon. Strong deep-layer shear of 50+ kt should support
another round of severe thunderstorm development, containing large
hail, locally damaging wind gusts, and a few potential tornadoes.
SPC continues a Slight Risk of severe storms from around
Shelbyville to Champaign eastward, and a Marginal Risk for the
remainder of central IL counties. Predominant high-res model
guidance depicts these storms shifting southeastward out of the
area by mid evening.
The closed upper low over the Northern Plains will linger into
Wednesday, with another embedded shortwave likely inducing another
convective system Wednesday. Current model continues to track this
feature into central IL, perhaps a bit earlier with arrival in
central IL Wednesday afternoon. 1500+ J/kg and 50+ kts deep layer
shear continue to be forecast with this feature. SPC has depicted
an Enhanced Risk for severe thunderstorm from near I-72
southward, and a Slight Risk for much of the remaining area to the
north.
Following Wednesday's system, a wavy northwesterly flow aloft sets
up for late week into the weekend, with the large scale trough axis
shifting east of IL. Although occasional precipitation chances can
be expected, amounts would be lighter, instability would be weaker
for a decrease in thunderstorm activity.
Temperatures will remain warm through Wednesday, with highs around
80 Tuesday, and Wednesday, then a strong downtrend can be expected
following Wednesday's cold front, with highs dipping back down to
the 60s north of I-70 Thursday, and mid to upper 60s expected
both Friday and Saturday. Lows into the 40s are forecast for much
of the area each night Thursday night through Saturday night.
Temperatures will begin to trend back upward Sunday into early
next week.
37
&&
.AVIATION... (For the 00z TAFs through 00z Tuesday Evening)
Issued at 646 PM CDT Mon May 6 2024
A line of thunderstorms currently stretching from Nebraska to
Oklahoma will continue to move east overnight, crossing the
central Illinois terminals late tonight. Storms should be in a
decaying phase, but may still be strong producing gusty winds. A
period of MVFR ceilings and briefly IFR ceilings will accompany
the precip tonight. A warm front will lift north across the region
Tuesday morning with SE winds ahead turning SSW behind. A few
spotty showers and storms are possible during the day Tuesday, but
low coverage precludes any mention in the forecast at this time.
Deubelbeiss
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
