Joliet, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

419
FXUS63 KLOT 160747
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
247 AM CDT Fri May 16 2025

.KEY MESSAGES...

- A threat of rapid fire spread exists this afternoon due to a
  combination of strong winds and low relative humidity.

- A threat of severe thunderstorms exists late this afternoon
  and early evening (Threat level 1 to 2 out of 5).

&&

.DISCUSSION...
Issued at 247 AM CDT Fri May 16 2025

Through Saturday:

Two primary forecast concerns through early this evening, severe
weather potential and windy, dry conditions for possible wildfires.
Please see the fire weather section below.

Much drier air has spread across western and northern IL with
dewpoints in the upper 40s. The models are in good agreement
with low level moisture surging back north late this afternoon
into early this evening, with dewpoints back into the upper 50s
to possibly lower 60s along and east of I-55. A cold front will
be approaching from the west and scattered thunderstorms are
expected to develop east of I-55. Coverage further north into
the Chicago Metro area is more uncertain with perhaps only
isolated thunderstorms. Strong winds aloft along with ample
instability will allow any storms that develop to quickly become
severe with large hail and damaging winds the main threats.
Given the wind profiles in the soundings, isolated damaging
gusts into the 60-65kt range will be possible.

Before the storms, southwesterly winds will steadily increase
this morning with gusts into the 40-45 mph range expected. There
is a narrow window this afternoon, where gusts could frequently
be at or above 45 mph, which is wind advisory criteria.
Confidence is too low to issue a windy advisory at this time,
but trends will need to be monitored. Gusts will diminish a bit
this evening, into the 25-30 mph range but will remain gusty
through sunset Saturday evening. Another period of higher gusts
in the 35-40 mph is possible as the colder air spreads into the
area late this evening.

Previous forecast included patchy blowing dust for today for the
western cwa and made no changes. There were stripes of heavier
rainfall from the storms Thursday afternoon that will limit this
potential for those areas.

High temperatures today are expected to reach into the middle,
to perhaps upper 80s for most locations. Wind directions may
remain southerly enough to keep temps cooler along the north
lakeshore. Low temps will drop into the lower/mid 50s Saturday
morning. High temps will be cooler on Saturday ranging from mid
60s north to around 70 south. cms


Saturday Night through Thursday:

A sprawling ~1030 mb high will build east across Ontario and the
Hudson Bay on Sunday with mid-level shortwave ridging forecast to
build in across the local forecast area. This high to our north
with send a robust afternoon and evening lake breeze/backdoor
front through the entire region. This will end up holding
lakeside highs in the mid/upper 50s, while inland locales will
likely warm into the 70s prior to the lake breeze push. While
some guidance hints at the potential for some intermittent lower
cloud cover on Sunday, most indications are that any morning
cloud cover should scatter into the afternoon.

On Sunday night into Monday, a sharpening warm frontal zone well
to our south will slowly advance northward into southern Iowa,
northeast Missouri, and southern Illinois. Increasing low-level
warm advection in response to strengthening 925-850 mb
southwesterlies overtopping this frontal zone will lead to the
development of showers and thunderstorms, but given the current
location of the aforementioned boundary and MUCAPE gradient,
most/all of this activity through Sunday night looks to remain
well to our south. Even into the day on Monday any activity
locally currently looks like it should remain isolated to
scattered, with deeper moisture still relegated to our south.
Forecast soundings off the GFS in particular look like they`d be
more supportive of intermittent drizzle/showers as opposed to
thunderstorms.

On Monday night into Tuesday, guidance pushes a modest surface
low (near 1000 mb) towards northern Missouri/southern Iowa as a
robust shortwave pivots across the central plains. During this
time, the northward progress of the returning warm front is
forecast to slow, with the boundary overall becoming
quasistationary across central to downstate Illinois. Isentropic
upglide will increase once again, likely leading to a nocturnal
expansion of showers and storms which-- depending on the
precise location of the stalled front--may begin to push into
our forecast area, particularly south of about I-80.

Thereafter, guidance generally depicts a complex upper pattern
developing, with a series of upper lows/gyres pinwheeling around one
another into the middle of the week. This general evolution will
keep the threat for intermittent periods of rain with embedded
thunderstorms going in the vicinity, at least into Wednesday.
There`s a signal for things to dry out into the end of the week.

Carlaw

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1230 AM CDT Fri May 16 2025

The key aviation weather messages are:

- Increasingly gusty south-southwesterly winds Friday morning
  and afternoon. Some potential for non-thunderstorm winds to
  gust 40+ knots for a brief period during the mid to late
  afternoon.

- Chance for thunderstorms during the late afternoon and early
  evening. Any storms that develop could produce wind gusts in
  excess of 50 knots.

- Winds shifting to the WSW Friday evening and will remain
  gusty, with some potential for 30+ knot gusts through the
  overnight.

VFR conditions with southwesterly winds will prevail tonight.
Winds will increase steadily through Friday morning and into the
afternoon and will become south-southwesterly. During peak
heating, there is some potential for intermittent gusts of 40+
knots at times (roughly during the 20-23z timeframe), although
confidence in persistent gusts this high was not high enough to
introduce higher gusts at this time.

Thunderstorms appear likely to develop late in the afternoon,
although confidence in them directly impacting the terminals
still remains a bit unclear, with the greatest coverage
currently depicted just south. Made no significant alterations
to the inherited PROB30 groups, but consideration for upgrades
to TEMPOs will be needed in future TAF updates if model trends
continue. Any storms that develop will have very high cloud
bases (near 10 kft) and will be capable of producing severe wind
gusts/microbursts.

Winds will shift out of the WSW Friday evening. Another "pop" of
strong winds is possible late in the evening and overnight, and
there is a signal that gusts could be a bit higher than the
current TAFs indicate. MVFR cigs may eventually develop, but
these look to hold off until the very end of the extended
ORD/MDW TAF window or just beyond.

Carlaw

&&

.MARINE...
Issued at 245 AM CDT Fri May 16 2025

Southerly winds are expected to gust to gales to 35 kt this
afternoon for mainly the IL nearshore waters and through Gary
in the IN nearshore. Winds will shift westerly this evening as a
cold front moves across southern Lake Michigan. Winds may
continue to gust to near gale force with and just behind this
cold front. Gusts will then diminish slightly, into the 25-30kt
range which will continue through early Saturday evening. cms

&&

.FIRE WEATHER...
Issued at 245 AM CDT Fri May 16 2025

A fire weather watch remains in effect for all of northeast IL
this afternoon.

Much drier air has spread across western and northern IL and
is expected to remain in place through mid afternoon. Dewpoints
may lower a few more degrees, into the mid 40s and combined with
high temperatures in the middle, to perhaps upper 80s, minimum
relative humidity levels in the 20 to 25 percent range are
possible this afternoon. Southwesterly winds will steadily
increase this morning into this afternoon with gusts into the
40-45 mph range expected this afternoon. This combination of
low relative humidity and strong winds will create the potential
for rapid wildfire spread. A limiting factor is that some areas
received heavier rainfall from the storms Thursday afternoon.

Low level moisture is expected to surge back north late this
afternoon into early this evening, with dewpoints in the upper
50s, perhaps lower 60s, east of I-55. There will also be a
chance of thunderstorms late this afternoon into early this
evening for areas along and east of I-55. The combination of
rising relative humidity levels as well as possible rainfall
will end the wildfire risk by early this evening. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Fire Weather Watch from 10 AM CDT this morning through this
     evening for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039.

IN...None.
LM...Gale Warning from noon today to 10 PM CDT this evening for
     Winthrop Harbor IL to Gary IN.

     Small Craft Advisory from noon today to 10 PM CDT this evening
     for Gary to Burns Harbor IN-Burns Harbor to Michigan City
     IN.

&&

$$

Visit us at weather.gov/chicago