Drought in Illinois, July 1 to 31, 2021

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1229 AM CDT Thu Jul 1 2021

.UPDATE...
915 PM CDT

The moist air mass has one more night of residence in this
consecutive day-night stretch over the area. As such, there
remains the potential for festering or redeveloping brief
convective cells on even the slightest of forcing impetus the
rest of tonight. As the low-levels have stratified though,
outflows have lost their "oomph" so there are less foci for this.

The far southern forecast area will remain one area late this
evening with a composite outflow boundary and a subtle, sheared
short wave gliding east-southeast in the mid-level flow overhead.
Elsewhere to the north, there is a small, gusty convective
cluster approaching the Milwaukee metro that is spurred from a
stronger mid-level wave digging into the central Great Lakes.
Confidence is low on how these cells will behave. They are
working with some more deep layer shear of 35-40 kt and have seen
some regular stronger downdraft signatures on Wisconsin radars.
Could see some of these cells reaching the far northern Chicago
suburbs around 11 pm given MUCAPE > 1,000 J/kg in advance of them,
but likely fading as they move further south than that.

Otherwise for tonight, patchy shallow fog may be realized if the
high clouds can clear. Certainly this time of year is not
climatologically favored, but with the earlier rain and very moist
air mass, it would not take too much. Near the lake front is a
favored area as well with water temperatures in the 50s to lower
60s with continued dew points around 70 and light flow.

MTF

&&

.SHORT TERM...
330 PM CDT

Through Thursday...

An narrow line of showers and thunderstorms continues along the
I-80 corridor this afternoon with a broader area of light showers
that continues across northwest Indiana into east central
Illinois. This activity is going to continue to gradually shift to
the south and east with time through the afternoon and early
evening then diminishing in coverage late this evening. Lack of
notable deep layer shear should limit the severe weather threat,
but given SPC mesoanalysis of DCAPE values to 700 J/kg and the
high PWATs, a few stronger gusts may be possible under any
heavier showers/storms.

These showers have also been very proficient rain makers today
(as they have been the past several days) with 1.5 inches of rain
falling in the Kankakee area in an hour earlier today. The latest
activity has been moving quick enough that any flooding should be
more localized, however, if the motion returns to more easterly
there may be a renewed flooding threat given how much rain has
fallen across portions of the area the past several days. Showers
and a few embedded thunderstorms may linger overnight across the
Kankakee River valley and points south.

A cold front is expected to drop south along the Lake late
tonight into Thursday morning. This will bring a noted uptick in
wind speeds behind it with gusts to 25 to 30 mph expected in areas
near the lakeshore through the day on Thursday. The cooler
northeast winds off the lake will keep temperatures cool for the
Chicago metro area in the 70s. Interior areas may be able to warm
into the low 80s well away from the lake. Model guidance is
suggesting that there may be a layer of fog that moves in
immediately behind the front for Thursday morning. Did not have
enough confidence to add fog into the forecast so will let the
evening shift take another look at it. The strong northeast winds
will result in quickly building waves through the day on Thursday.
Thus have maintained a Beach Hazards statement highlighting the
High Swim risk. Chances for showers and thunderstorms Thursday
have been trending down with some low chances for areas well south
of I-80. A stray shower or two further north are possible,
especially west of the Chicago, can't be entirely ruled out late
morning/early afternoon.

Petr

&&

.LONG TERM...
330 PM CDT

Thursday night through Tuesday...

Concern initially will be dangerous swimming conditions at Lake
Michigan beaches, and then will shift to heat and humidity for
Sunday July 4th. A brief shot of cooler air will be paired with a
brisk northerly winds yielding the high wave action, strong
currents, causing dangerous swimming conditions at Lake Michigan
beaches. No changes were made to the going Beach Hazards Statement,
in effect through Friday night. After lows in the 50s outside of
Chicago tomorrow night, Friday will be very comfortable, ranging
from the mid to upper 70s inland, to near/around 70 lakeside. The
mid-upper trough from which model runs a few to several days ago
gave some concern about getting trapped overhead, now has
consensus agreement in escaping east, with mid-upper ridging
sliding over the region.

The result will be a warming trend, along with increased humidity,
especially on Independence Day, which is now looking decidedly
very warm to hot and pretty humid. Saturday should top out in the
80s area wide, warmest and in the upper 80s near the Wisconsin
border where it's stayed mainly dry. Low level flow aloft and a
fairly weak pressure gradient over the region could enable a lake
breeze to slip inland during Saturday afternoon and cool off
areas near the lake.

On Sunday, the ridging will start overhead and very slowly ease
south, keeping forcing at a minimum and likely resulting in a
mostly dry day. Will have to watch for lake breeze formation
because with upper 80s-lower 90s temps, dew points rising to near
70, and capping eroding, could see some very isolated convection
go on the lake breeze convergence. Kept PoPs sub-mentionable for
now. Otherwise, the main story will be the heat and humidity, with
peak heat indices in the lower to mid 90s. Will definitely be a
day to keep cool (pool, lake, AC) and practice basic heat safety.
Sunday night for fireworks time will be rather muggy with temps
starting in the 80s down into the mid-upper 70s by late evening.
At this time, even if any very isolated convection goes during the
afternoon, it appears we're looking at dry conditions for the mid
to late evening.

Uncertainty increases into next week regarding how quickly more
appreciable convective chances return. Looking at weak west to
northwest mid-level flow as ridging gets flattened out, and warm
and humid and diurnally unstable conditions south of a stalled
front. Could see some drying and stabilization for a time earlier
in the week from a backdoor front northeast wind footprint. The
later work week period could end up most affected by periodic
higher coverage showers and storms as a cold front slowly crosses
the region.

Castro

&&

.AVIATION...
For the 06Z TAFs...

An outflow boundary from convection over Lake Michigan will move
through ORD/MDW/GYY within the first hour of the TAF period with
an abrupt wind shift to the north. An isolated thunderstorm may
occur behind the boundary as well, warranting a continuation of
the inherited VCTS through 07Z to 0730Z or so. Behind the outflow
boundary and isolated thunderstorms, winds will relax and become
light and variable before another front comes off Lake Michigan
between 9-10Z. Fog and low clouds may accompany the secondary
front, so will hold onto the inherited TEMPO for visibility and
ceiling restrictions. Should fog and clouds indeed move over the
terminals, improvement is expected within a few hours of sunrise.
Breezy northeast winds will then become the norm during daylight
hours, with a modest relaxation this evening.

Borchardt

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement...ILZ006-ILZ103-ILZ104...1 PM Thursday
     to 4 AM Saturday.

IN...Beach Hazards Statement...INZ001-INZ002...1 PM Thursday to 4 AM
     Saturday.

LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742...10 AM Thursday to
     7 PM Friday.

     Small Craft Advisory...LMZ743-LMZ744-LMZ745...1 PM Thursday to 7
     PM Friday.

&&

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Hazardous Weather Outlook...UPDATED
National Weather Service Chicago/Romeoville IL
923 PM CDT Wed Jun 30 2021

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-020230-
Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage-
La Salle-Kendall-Grundy-Kankakee-Livingston-Iroquois-Ford-
Northern Cook-Central Cook-Southern Cook-Northern Will-
Southern Will-Eastern Will-Lake IN-Porter-Newton-Jasper-Benton-
923 PM CDT Wed Jun 30 2021 /1023 PM EDT Wed Jun 30 2021/

This Hazardous Weather Outlook is for portions of North Central
Illinois...Northeast Illinois and Northwest Indiana.

.DAY ONE...Rest of Tonight.

Weather hazards expected...

  Limited Thunderstorm Risk.

DISCUSSION...

Isolated non severe thunderstorms are possible.

.DAYS TWO THROUGH SEVEN...Thursday through Monday.

Thursday...
  Limited Thunderstorm Risk.
  High Swim Risk at Lake Michigan beaches.
Friday...
  High Swim Risk at Lake Michigan beaches.
Monday and Tuesday...
  Limited Thunderstorm Risk.

DISCUSSION:

High wave action and strong currents will cause dangerous swimming
conditions at Lake Michigan beaches Thursday through Friday.

.SPOTTER INFORMATION STATEMENT...

  Spotter activation will not be necessary through tonight.

GENERAL STORM MOTION OF THE DAY:

  Moving toward the east southeast at 15 to 25 mph.

LMZ740>745-020230-
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN-
Burns Harbor to Michigan City IN-
923 PM CDT Wed Jun 30 2021

This Hazardous Weather Outlook is for portions of the Illinois
nearshore waters of Lake Michigan and the Indiana nearshore
waters of Lake Michigan.

.DAY ONE...Rest of Tonight.

Weather hazards expected...

  Limited Thunderstorm Risk.

.DAYS TWO THROUGH SEVEN...Thursday through Monday.

Thursday and Friday...
  Hazardous conditions for small craft are likely.
Monday and Tuesday...
  Limited Thunderstorm Risk.

MTF

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