Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1240 PM CDT Sat Oct 5 2024
KEY MESSAGES...
- Low chance for scattered showers and isolated thunderstorms
late tonight, mainly along and north of I-90.
- Elevated fire danger Sunday due to gusty winds and dry
conditions.
- Dry weather continues next week, with above average
temperatures especially mid-late week.
&&
DISCUSSION...
Issued at 316 AM CDT Sat Oct 5 2024
Through Sunday:
The surface high over Lower MI this morning will promote dry
and unseasonably warm conditions for our Saturday as it
progresses east through the day. While there are some mid-level
status clouds over northeast IL and northwest IN this morning,
these clouds are expected to pivot eastward and erode by midday
resulting in mostly to partly sunny skies for this afternoon.
This nearly unabated sunshine in combination with increasing
mid-level warm advection this afternoon will result in high
temperatures topping out in the low to mid-80s today. However,
as the aforementioned high drifts east winds will increase this
afternoon ahead of developing cold front. Therefore, expect
gusts to reach into the 20 to 25 mph range this afternoon.
Heading into tonight, the deepening upper trough, currently
over central MT, will begin to move into the upper Midwest and
northern Great Lakes. At the same time, a cold front will
develop across the central Plains and race east through the
northern IL and northwest IN overnight. While dew points are
expected to increase ahead of the cold front across much of IL,
IA, and WI; precipitation coverage along the front continues to
look rather limited especially with southward extent. The reason
is because of the stout mid-level cap that is forecast to
develop across northern IL and northwest IN which should prevent
any showers or storms from materializing. However, forecast
soundings do continue to show a robust EML plume atop the cap
which could still yield a scattered shower or isolated storm if
the front and trough can lift air parcels up to 5000 ft or more.
That said, have decided to maintain a slight chance (15 to 20%)
of showers and thunderstorms, primarily for areas along and
north of I-90, late tonight through early Sunday morning for
this potential. Regardless, any showers or storms that do
materialize won`t be much in the way of rain producers due to
their fast (upwards of 45 to 50 mph) speeds and the
aforementioned limited moisture.
Aside from the limited shower potential, the cold front will
also generate gusty west-northwest winds in its wake as the
atmosphere mixes into the base of a 50-55 kt low-level jet
overhead. Given the unfavorable diurnal timing, mixing looks to
be limited to under 1000 ft so gusts should generally remain in
the 25 to 35 mph range. However, the potential for slightly
better mixing over the open waters of Lake Michigan looks to
yield a brief period of gale force (35-40 kt) gusts between
midnight and 4 AM local time. Since these gale gusts should be
short duration, am not planning to host a Gale Warning for the
nearshore waters with this forecast package but will mention the
potential for gale force gusts in the nearshore forecast and
Small Craft Advisory.
While winds should briefly ease Sunday morning as the front
exits into northern IN and Lower MI, winds are expected to
quickly rebound as diurnal mixing commences. Therefore, expect
northwest gusts of 20 to 30 mph to persist through Sunday
afternoon. Additionally, dew points are expected to tank behind
the front Sunday morning as much drier air advects into the
area. These lowering dew points will generate minimum RH values
in the 20-30% range Sunday afternoon, especially for areas south
of I-80. The combination of these low humidities, the
antecedent dry conditions, and gusty winds will make for an
elevated fire danger on Sunday. So while the offset between the
highest winds (north of I-80) and lowest RH (south of I-80)
looks to keep conditions just below formal Red Flag criteria,
any burning should be avoided until after winds subside and RH
values improve.
Yack
Sunday Night through Friday:
Dry weather pattern looks to persist through the remainder of
the forecast period, with temperatures initially near average
but warming back above average mid and late week.
Amplified mid-level short wave which transits the region
Saturday night into Sunday is progged to eventually close off to
the northeast of the Midwest by Tuesday. A series of smaller
amplitude short waves are expected to rotate southeastward
around the main circulation over the northern and
central/eastern Great Lakes through mid-week, while dry
northwest flow aloft continues across our area. At the surface,
high pressure drifts slowly east-southeast across the Corn Belt
and western Lakes through Wednesday. This looks to support
mainly sunny days and mostly clear nights, with daytime temps
slowly moderating from the upper 60s Monday to the low/mid 70s
by Wednesday afternoon. Nighttime temps in the low/mid 40s are
expected, though a few upper 30s are possible Sunday night in
our typical cool spots.
An upper level ridge is then forecast to build northeastward
across the Plains and into the upper Midwest Thursday into
Friday, nudging the northeastern NOAM upper trough off to the
east. This should maintain dry weather locally, and allow temps
to moderate back above average through the end of the week.
Friday looks to be the warmest day, as a low-amplitude short
wave progged to transit northern periphery of the upper ridge to
our north enhances warm advection on the west/northwest
periphery of the departing surface high. Current model guidance
supports daytime temps potentially reaching 80 degrees again by
Friday, nearly 15 degrees above average for this time of year.
Ratzer
&&
AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1237 PM CDT Sat Oct 5 2024
The main aviation weather concerns for the 18Z TAF period
include:
* Gusty winds through the period. SSE to southerly this
afternoon, veering to SSW this evening.
* LLWS this evening into tonight
Near southerly winds look to favor just east of south (160-170)
this afternoon, but we may very well find ourselves teetering
on either side of southerly at times into this evening. Winds
should solidify a SSW direction around mid-evening before
veering through the night to a NW direction by early Sunday. As
far as magnitude goes, we`ll find ourselves regularly gusting
to around 25 kt this afternoon but should occasionally tap 30
to near 35 kt, especially mid-late afternoon. Winds may subside
some for a brief, maybe 2-3 hour period early in the evening
before they are expected to pick back up as the low level jet
overhead ramps up closer to mid evening. It`s tough to say what
sort of winds we`ll be able to mix down to the sfc, and
therefore wind speeds mid evening into early overnight are
somewhat uncertain. It looks as though we should continue seeing
regular gusts into the 25 to 30 kt range, although gusts could
conceivably push the 40 kt mark from time to time. Additionally,
LLWS is included in the TAF for this period with upwards of 50
kt out of the SW expected at 2kft AGL.
Another few hour period of lesser winds is again possible very
late tonight into Sunday morning. 20 to 25 kt gusts will
return after mid morning and take us through the afternoon. VFR
can be expected throughout the period.
Doom
&&
LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 4 AM CDT Sunday for the IL
nearshore waters.
Small Craft Advisory from 7 PM this evening to 7 AM CDT Sunday
for the IN nearshore waters.
&&
$$
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