Romeoville, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

517
FXUS63 KDVN 160605
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
105 AM CDT Sat May 16 2026

...06z Aviation Update...

.KEY MESSAGES...

- There is an enhanced (level 3 out of 5) risk for severe
  weather late this evening/tonight. Damaging winds (some gusts
  over 70 mph) and a low risk for brief tornadoes will be the
  primary threats.

- Multiple rounds of storms expected through this weekend and
  into early next week. Severe storms are possible each day
  through Tuesday, with low confidence on areal coverage
  Saturday and Sunday.

- Widespread storms likely Sunday night through Monday, with
  increasingly warm and humid conditions.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 231 PM CDT Fri May 15 2026

The "calm before the storm" conditions were seen early this
afternoon with wall to wall sunshine across the CWA and
temperatures in the upper 70s/low 80s. This is thanks in part
to our very strong inversion at 900mb sampled by our 18z
sounding, which has also kept our winds below 20kts today. A
similar sounding was seen upstream at OAX, although much steeper
mid-level lapse rates were seen there. METARs and RAP
mesoanalysis showed the main parent low along the
Manitoba/Ontario border with a boundary extending south to a
surface low in central NE (near KODX), with a subtle warm front
extending eastward towards Des Moines. Just north of this warm front,
some agitated clouds were beginning to form in northwest IA
close to Spencer.

Convective initiation should take place within the next 1-2
hours in northwest IA as MLCIN continues to erode. Storms will
grow upscale through the evening tracking east towards eastern
IA. A favorable environment for severe weather will be in place
with deep layer shear values over 45 kts, steep mid- level lapse
rates, and MLCAPE values over 1500 J/Kg. Latest CAMs all now
suggest this activity becoming more of a QLCS, with damaging
wind becoming the primary threat before they reach our northwest
counties. Several bowing segments will be possible and with 0-3
km shear values around 30-35kts can`t rule out some strong
mesovorts/brief spin-ups tonight. A rather tight DCAPE gradient
with values just over 1000 J/Kg and max theta-e differences in
the 0-3km layer over 25C also support the potential for some 70+
mph gusts possible particularly west of the Quad Cities where
the greater potential for mature/organized convection will exist
and is highlighted by the SPC Enhanced Risk from SPC. Stay
weather aware tonight!

This convection to push east southeast of the CWA after
midnight, quickly diminishing in strength as the BL begins to
stabilize. Overnight lows to drop into the upper 50s/lower 60s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 231 PM CDT Fri May 15 2026

Saturday should be a day of increasing solar insolation
fostering a rebound in highs into the 80s, with another nudge up
in the humidity levels with widespread dew points in the 60s.
Forcing is rather nebulous with some weak height rises depicted
at 500 hPa. But, there is potential by mid to late PM with
strong surface heating to weaken any CIN and trigger widely
scattered storms. Low level shear is quite weak, but 30-40 kt of
0-6km shear and fat CAPE profiles would support a risk for
severe storms perhaps with some supercellular characteristics
capable of large hail and damaging winds. Coverage would appear
to be spotty, and storms could continue beyond sunset. Blended
guidance is quite high with precipitation chances evolving
Saturday night into Sunday AM along/north of I-80 likely
attendant to increasing WAA ahead of a lifting warm front as an
upper trough undergoes amplification across the western CONUS.
Seemingly the signal for the main LLJ core and advection appear
to be aimed further west, and so my confidence on these higher
PoPs is low. Nonetheless, we`ll have a chance for showers and
storms Saturday night into Sunday morning with the warm front
lifting through the region. Thereafter, much of Sunday will be
very summery as we are placed firmly within the warm sector with
highs well into the 80s to possibly near 90 in a few spots and
humid conditions. This could again trigger some widely scattered
late day convection of which could be severe due to the
abundant instability and at least modest shear.

The details in the forecast become murky late in the weekend through
early next week, and severe storm potential will likely hinge some
on previous days convective trends/evolution. That said, synoptically
with the upper trough slowly shifting east placing the region in
strengthening SW flow aloft shuttling embedded disturbances, and a
surface cold front inching closer we have perhaps our best potential
for more widespread storms and increased coverage of strong/severe storms
late in the weekend through early next week. Potential to see another
organized convective complex work through the area Sunday evening/night,
and then how this evolves could play into the timing/location/threat for
severe weather on Monday.

It looks like the cold front will shift through the region on Tuesday
with one last chance for storms. Uncertainty still abounds with
regards to any severe threat Tuesday, which is largely dependent
upon the frontal timing.

Cooler and more seasonable conditions look to settle in mid next
week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1255 AM CDT Sat May 16 2026

Besides the showers and thunderstorms, mainly VFR conditions
will continue for much of the TAF cycle. There may be some MVFR
fog in spots before dawn where the winds go light convergent,
and the overnight convective clusters should be moving east of
the TAF sites after 12z. Rather light south winds on Saturday
with VFR skies, and then there will be the chance for isolated
thunderstorms developing late Saturday afternoon.

&&

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

&&

$$

SHORT TERM...Gross
LONG TERM...Gross
AVIATION...12