Arlington Heights, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

044
FXUS63 KLOT 190518
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1218 AM CDT Fri Jun 19 2026

.KEY MESSAGES...

- An axis of showers may drift across the area Friday evening
  through early Saturday AM (30-40% chance) with isolated
  embedded non-severe storms possible (20% chance).

- A period of heavy rain with embedded thunderstorms is expected
  Sunday which may lead to flooding.

&&

.UPDATE...
Issued at 851 PM CDT Thu Jun 18 2026

Quick update this evening to add some low-coverage (20-30%)
showers across north-central IL. Expectation is that these will
slowly weaken/dissipate over the next couple of hours, with
non-zero but decreasing lightning potential.

A small cluster of showers was approaching western Ogle and
northwest Lee counties as of 830 pm, in association with a low-
amplitude short wave transiting northwest flow and accompanied
by a subtle surface trough/weak cold front. While modest
surface-based instability will diminish with diurnal cooling and
east/southeastward extent, modestly steep (6-6/5 C/km) mid-
level lapse rates may allow these showers to track across the
I-88/I-39 corridors south of Rockford through late evening.
Can`t rule out an occasional lightning strike early, though the
overall lightning trend has been downward. Have noted a few
20-30 mph wind gusts at some of the northwest IL AWOS sites
(Dubuque, Savanna and Freeport), so some brief gusty winds are
possible. Have added some 20-30% pops for this activity for the
evening hours, and will monitor trends to see if they need to be
extended any further east/southeast.

Otherwise, remainder of the forecast appears to be on track with
no other significant changes needed.

Ratzer

&&

.DISCUSSION...
Issued at 302 PM CDT Thu Jun 18 2026

Northwesterly flow across the area in the wake of yesterday`s
strong weather system paired with decent coverage of diurnal
cumulus has helped keep temperatures cooler today with
temperatures in the low to mid 70s across the area. A lake
breeze hugging the lakeshore into Cook County and well inland
across northwest Indiana have held temperatures in the 60s
there. Meanwhile, a few light showers have developed into
portions of southeast Minnesota associated with a weak wave
diving across the Upper Midwest. This may try to sneak in a few
light showers or sprinkles into far northern/northwest Illinois
this evening but have held off on a formal mention in the
gridded forecast with this update given weak forcing amidst an
overall dry airmass.

While winds will remain generally out of the west to northwest
into Friday (away from the lakeshore), lower cloud coverage
should help temperatures warm into the mid-upper 70s across the
area. A weak lake breeze may cool temperatures back into the
upper 60s/lower 70s near the lakeshore in the afternoon. Heading
into the evening hours, a shortwave is forecast to dive
southeast within the broader upper level northwest flow. This
feature may lead to shower and thunderstorm development across
portions of Minnesota and Wisconsin during the day on Friday.
This activity may drift into northern Illinois in a decaying
mode. Some hi-res guidance maintains showers and possible
isolated embedded thunderstorms along an elevated fgen axis
that slides south across the area through the night into early
Saturday morning. Any lingering showers should come to an end
by late morning south of I-80 with temperatures warming into the
upper 70s to lower 80s.

A compact system is expected to eject off the Rockies and move
east across the Central Plains late Saturday into Sunday
bringing a period of inclement weather to the region on Sunday.
There remains model variability in the handling of the
associated surface low, including its strength and exact track,
which will influence which areas are most favored to experience
a longer duration of heavy rainfall and any possible severe
thunderstorm and flooding threats. More northerly solutions
(NAM/ECMWF) would support heavy rainfall across nearly the
entire area, whereas the more southerly solutions (GFS/UKMET),
focus the heavy rain axis south of I-80. The varying solution
tracks may be tied to differences in handling any influence from
an expanding Canadian surface high and the position of closed
mid-upper lows meandering around the southern Hudson Bay/Ontario
region. All in all, Sunday continues to be a day to monitor,
particularly for any flooding concerns (currently a level 1 and
2 out of 4 threat for the local area). If a more northern track
verifies this could lift a marginal severe weather threat north
into portions of the area, mainly south of I-80.

Beyond Sunday we enter a brief dry period as the aforementioned
high pressure expands into the area in the wake of the
departing surface low. Onshore winds will likely keep
temperatures cooler than normal to start the week with highs in
the lower to mid 70s (typically lower 80s in mid-late June).
Temperatures then gradually warm through midweek into the upper
70s, with our next chance of rain returning during the Tuesday
night into Wednesday timeframe as another system dives southeast
within the broader northwest flow pattern.

Petr

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1218 AM CDT Fri Jun 19 2026

There are no significant aviation weather concerns anticipated
through the period.

West-northwest winds will prevail at most terminals through the
period as surface high pressure shifts eastward across the
Lower Missouri Valley today. The only exception to this being at
KGYY, where winds look to turn north-northeasterly off the lake
for a period this afternoon in association with a lake breeze.
It appears unlikely that this lake breeze will shift far enough
inland to impact ORD and MDW. Diurnal mixing of the boundary
layer may result in some gustiness up to near 20 kt this
afternoon, but any gustiness will quickly abate into early this
evening. Otherwise, expect VFR conditions to prevail today.

The next weather impulse will track southeastward into the
western Great Lakes into this evening. As it does, we should see
an increase in VFR cloud cover and a chance (30-50%) for a
period of light showers this evening. Accordingly, I have
maintained the going PROB30 for this at the main Chicago
terminals from 03-06Z this evening, and also added the mention
to the surrounding area terminals. The threat of lightning
continues to look very low with this activity.

KJB

&&

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

&&

$$

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