668
FXUS63 KLOT 011117
AFDLOT
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
617 AM CDT Mon Jul 1 2024
.KEY MESSAGES...
- Typical July warmth and humidity through the week with
periodic chances for showers and storms Tuesday through
Friday
&&
.DISCUSSION...
Issued at 308 AM CDT Mon Jul 1 2024
Through Tuesday Night:
Dry and seasonably cool weather is on tap again for today.
Easterly winds off the lake will once again hold temps in the
60s near the lake, but away from the cooling influences of the
lake, the majority of the CWA should climb well into the 70s.
Sunny skies this morning will give way to some increase in high
cloudiness this afternoon. The dry weather and mild temps will
continue most of tonight.
Late tonight into Tuesday attention will turn to a pair of
shortwave troughs. The first, a large trough over the Pacific
Northwest and northern Rockies will move to the east today and
tonight. A surface trough/dryline will develop and sharpen up
today across the northern and central High Plains in response to
the upper trough. Strengthening southerly flow in advance of
this trough will transport higher theta-e air mass northward
across the plains today and tonight.
A second, small and more subtle shortwave trough over the
southern Rockies is forecast to move into the central Plains
tonight and likely be the impetus for a MCS developing across
Nebraska spreading east toward the mid-Mississippi valley by 12z
Tuesday. A few showers could reach our far northwestern CWA
prior to 12z Tuesday, but most of tonight should be precip-free
in our area.
This MCS should be in a weakening phase late tonight and
especially Tuesday morning as it tracks into a drier, more
stable air mass to the east of the Mississippi River and as the
low level jet diurnally weakens and veers tomorrow morning. How
quickly this precip dissipates and how far south it spreads
before it does varies considerably among the various models. The
HRRR is generally farthest south and holds onto lingering
showers and a few storms late into the morning hours Tuesday,
while other guidance barely has any precip south of the IL/WI
border. The ECMWF looks more HRRR-like and for that reason,
opted to bump pops up Tuesday morning north of I-80.
Debris cloudiness and perhaps rain, will likely keep temps
somewhat cooler northern CWA. How much cooler will depend on the
footprint of the potential rain/cloudiness. Opted to nudge temps
down somewhat, but still warmer than the HRRR which holds temps
in the low to mid 70s near the WI border Tuesday afternoon.
Southerly winds Tuesday will advect warmer and more humid air
north into the area, so even a couple/few hours of clearing in
the afternoon could allow for a rapid recovery in temps (and
dewpoints) across our northern CWA.
Showers and thunderstorms are expected to redevelop along the
cold front to our north and west Tuesday afternoon. Those
showers and storms will track east toward our area Tuesday
night, but it appears that they will be in a weakening phase as
they outrun the better synoptic forcing which should remain well
to our north and also encounters a more stable air mass. Still
anticipate this activity to make it into the northwest half of
our CWA where low end categorical pops from the NBM are within
the realm of possibility. Precip chances will decrease with
east and southeast extent across the CWA as this activity is
expected to be weakening as it moves across the area Tuesday
night.
- Izzi
Wednesday through Sunday:
An upper-level trough will be in the process of pivoting into
the eastern Great Lakes on Wednesday as its associated cold
front continues to move southward across northern IL and
northwest IN. Therefore, an area of showers and thunderstorms is
expected to be ongoing along the front Wednesday morning, but
should taper Wednesday afternoon as the front exits to our
south. However, depending on the exact speed of the front there
is the potential for some lingering showers and storms in the
southern 1/3rd of our forecast area into the early hours of
Wednesday evening. Regardless, the better kinematic field should
be removed from the front by Wednesday afternoon which should
keep the threat for any strong to severe thunderstorms low.
Despite the front`s name, temperatures and dew points behind
the front are not expected to be cool in any sense of the word.
In fact, Wednesday afternoon is forecast to be one of the warmer
periods of the week with highs forecast to be in the mid to
upper 80s areawide. Couple these temperatures with dew points
still in the upper 60s to around 70 and conditions look to be in
place for many areas to see peak heat indices in the low to
possibly mid-90s. While these values are nothing uncommon for
this time of year, it will be a day where those sensitive to
heat should use caution.
The aforementioned front is expected to stall somewhere in
south- central IL Wednesday night before lifting back north as a
warm front on Thursday. At the same time, guidance continues to
show a thunderstorm complex developing across the central
Plains Wednesday night and tracking eastward along the frontal
boundary into IL Thursday morning. Depending on how far north
the warm front gets prior to Thursday morning will determine how
much of our area will see thunderstorms for our July 4th
holiday. The latest 00z guidance suite continues to favor a more
southern track with the aforementioned storm complex which may
keep the northern 1/3rd to half of our area (roughly I-80 north)
dry through Thursday afternoon with better coverage of storms
in our southern CWA. However, I will caution that the courser
resolution of long range guidance can struggle with the
mesoscale processes that drive storm complexes and their impacts
on frontal boundaries especially 3+ days out. Thus, recommend
keeping an eye on this period of the forecast for changes as you
work to finalize your July 4th plans.
Regardless of how the daytime hours on Thursday play out,
another cold front is forecast to get pushed into northern IL
Thursday night as an upper-level trough pivots into the Upper
Midwest and Great Lakes. Given that the airmass ahead of the
front will still be warm and humid have no doubts that shower
and storm coverage will increase along the front and persist
into the day on Friday. As the front exits the area Friday
night, a surface high pressure center is expected move into the
Ohio River Valley and southern Great Lakes. This high should
bring the periods of showers and storms to a close as we head
into next weekend, but guidance does continue to depict broad
troughing residing over the Great Lakes through the weekend.
Therefore, there is a chance (albeit low at this time) that some
isolated showers and/or storms could materialize during this
timeframe.
Otherwise, expect temperatures and humidity to remain near
typical July levels with highs in the low to mid-80s and dew
points in the 60s into early next week.
Yack
&&
.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 617 AM CDT Mon Jul 1 2024
Forecast concerns for the terminals...
- Chance for showers and thunderstorms late tonight into Tuesday
morning, especially near RFD
- Breezy south-southeast winds Tuesday afternoon
High pressure overhead today will continue to support VFR
conditions and light winds generally under 10 kts. Wind
directions, however; will become easterly at the Chicago
terminals before turning southeasterly this evening and
overnight. Though, terminals away from Lake Michigan should
favor a more east-southeast direction through this afternoon and
evening.
An upper-level disturbance, currently over the northern Rockies,
will move towards the upper Midwest tonight into Tuesday
generating an area of showers and storms as it does so. While
the current trajectory of this disturbance keeps the better
shower and storm coverage north of the IL-WI line, some showers
and storms are forecast to spill over into northern IL late
tonight into Tuesday morning. Given that low-level moisture will
be a limiting factor, especially with southward extent,
confidence on coverage at the terminals is somewhat low.
Therefore, have decided to maintain dry forecasts for ORD and
MDW for now. However, there is enough of a signal in guidance to
support a PROB30 mention for -SHRA at RFD where confidence is a
bit higher.
Additionally, winds will also begin to increase Tuesday morning
as the system approaches with gusts expected to top out in the
20-25 kt range Tuesday afternoon. Winds should favor a south-
southeast direction on Tuesday, but a brief period of southwest
winds may occur with any storms. Otherwise, expect VFR
conditions to prevail but with increasing cloud cover through
the period.
Yack
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement until 7 AM CDT this morning for ILZ006-
ILZ103-ILZ104.
IN...Beach Hazards Statement until 7 AM CDT this morning for INZ001-
INZ002.
LM...Small Craft Advisory until 7 AM CDT this morning for the IN
nearshore waters.
&&
$$
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