Buffalo Grove, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

322
FXUS63 KLOT 141709
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1109 AM CST Tue Jan 14 2025

.KEY MESSAGES...

- Travel will be slow and slippery due to falling snow this
  morning, including during the morning commute.

- Wind chills will drop below zero after daybreak with the
  coldest values of -10 to -15F near the Wisconsin State Line.
  Air temperatures will warm to the teens this afternoon.

- A brief period of snow is possible late Wednesday night into
  Thursday morning, which may result in slippery travel.

- A storm system may bring a mix of rain and snow to the
  general region in the late Friday through early Sunday
  timeframe.

- Another push of Arctic air will arrive by early next week.
  Temperatures early next week may be the coldest thus far of
  the winter season.

&&

.DISCUSSION...
Issued at 227 AM CST Tue Jan 14 2025

Through Wednesday:

Regional radar imagery depicts a band of snow knocking on the
doorstep of northwestern Illinois associated with a sharp upper-
level shortwave diving through the Lower Great Lakes. Curiously,
the observed path of the shortwave has been some 40 to 50 miles
further north than advertised in model guidance even just 12
hours ago, and some 100 miles further north than depicted in
guidance 36 hours ago. Given the system is now much further
removed from the impact of detrimental sinking air over central
Illinois (in the left entrance region of an upper-level jet
streak centered over Tennessee), forcing for ascent is much
stronger and more expansive than originally expected. So, we`re
experiencing the double whammy of both a shift in location and
an increase in snowfall amounts within the past 24 hours.

At this point, radar trends and the latest high resolution
model guidance favors the "core" of the snow moving right across
northern Illinois and northwestern Indiana this morning. Given
the compact nature to the wave, it will only snow for 3 to at
most 5 hours at any given location, favoring the I-39 corridor
between 2 and 6 AM, the Chicago metropolitan area between 4 and
8 AM, and northwestern Indiana between 5 and 9 AM. Needless to
say, the timing is about as bad as it can get from the
perspective of impacting the morning commute.

In terms of snowfall amounts, relatively strong forcing (-10 to
locally -15 ubar/sec) overlapping a relatively deep DGZ (5 to
10kft depth) point to efficient and fluffy snow ratios of 25:1
to 35:1, with snow rates peaking at 0.5 to 0.75"/hr. While the
limited duration should keep snowfall amounts in check (between
1 and 2 inches), relatively cold temperatures in the teens as
snow is falling may render traditional road treatments
ineffective. Indeed, webcams showing mostly snow-covered roads
across Iowa confirm the impending reality for our area. And, if
that is not enough, a cold front will sweep across the area from
north to south just as snow is tapering causing temperatures to
actually fall by several degrees before noon (which may make
snow removal efforts even more difficult). When paired with
breezy northwest winds behind the front (gusting 20 to 25 mph),
wind chills will bottom out between daybreak and noon from -5F
in central Illinois to -15F near the Wisconsin state line. So,
put altogether, the stage is set for an unpleasant morning with
slippery roads due to falling snow and very cold temperatures.

Given the overlap hazardous road conditions and cold
temperatures with the morning commute, we gave serious
consideration to issuing an impacts-based Winter Weather
Advisory for this morning. In all, we would like to see snow
amounts a hair higher (in the 2-3" range) to feel more confident
in true advisory- level impacts. So, we decided to go the route
of a strongly worded SPS for the entire area.

Tonight will be quiet as a surface high pressure system moves
overhead. Ideal radiational cooling conditions (snowpack, light
winds, and clear skies) point toward nosediving temperatures
with overnight lows falling toward 0F. Temperatures will
modestly rebound tomorrow as the backside of the cold airmass
finally shoves eastward, with highs expected to top off in the
upper teens to lower 20s (on Wednesday).

Borchardt


Wednesday Night through Monday:

Another potent upper-level shortwave trough is forecast to be
diving across the western Great Lakes region Wednesday night.
Given that forecast soundings show sufficient moisture in place
across northern IL and northwest IN, it seems likely that some
snow will be produced as the wave dives through the area.
However, the quick progression of the wave in combination with
quickly drying mid-levels does pose questions as to the snow
quality and whether or not the snow will transition over to a
brief period of freezing drizzle Thursday morning. That said,
have gone ahead and increased POPs to 20-30% Wednesday night
through Thursday morning across the eastern half of the area to
account for this potential but have kept the precipitation type
as just snow for now. With surface temperatures during this time
forecast to be in the low to mid-20s, snow should have no
issues accumulating especially on untreated surfaces and
resulting in slippery travel despite accums looking to be
generally under a half inch.

Aside from this brief hiccup, modest mid-level ridging is
expected to be building across the central CONUS on Thursday and
into the Great Lakes on Friday. As a result, strong warm
advection is expected to be in place which will allow
temperatures to warm above freezing for both Thursday and Friday
afternoons. In fact, Friday is on track to have the warmest
temperatures of 2025 thus far with highs forecast to be in the
upper 30s and lower 40s. Overnight lows during this period also
look to be on the seasonably mild side with readings in the mid
to upper 20s Thursday and Friday nights.

While our area enjoys a reprieve from the bitter cold, an upper
low is forecast to be moving onshore in southern California and
gradually broaden into a shortwave trough as it traverses
across the southwest CONUS on Friday. At the same time, a
broader trough associated with the Polar Jet is forecast to be
diving into the northern CONUS and eventually trying to phase
with the southern shortwave Friday night into Saturday. Guidance
(both ensemble and deterministic) seems to be coming into good
agreement that the two troughs should phase near the Lower
Mississippi Valley Friday night which should allow for the
development of a weak surface low and precipitation across the
Lower Mississippi and Ohio River Valleys heading into the
weekend. The question for our area, however, continues to be
whether or not the northern edge of the precipitation shield
will reach far enough to brush portions of northeast IL and
northwest IN.

At this point, guidance supports the idea that at least the
southern and southeast third of the area will have at least some
potential to see precipitation Friday night through Saturday,
but subtle shifts in the systems` track over the coming days
could change this thinking. If precipitation does occur, the
above freezing temperatures (both at the surface and the lowest
5000-7000ft) should start precipitation off in the form of rain.
As the system progresses east, much colder air is expected to
filter in which may shift precipitation over to either all snow
or a rain-snow mix Saturday morning. Though confidence on when
and how long this precipitation change will last before
precipitation ends remains uncertain. Furthermore, there is also
a growing signal in guidance for some lake effect snow to
develop along the southern and southeastern edge of Lake
Michigan late Saturday through Sunday. Obviously details in
duration, intensity, and location of any lake effect is low, but
have maintained a 15-20% chance in the forecast for northwest
IN and points east which seems reasonable.

Finally, the phasing of the two aforementioned features will
result in broad troughing establishing over essentially the
entire Continental United States from Sunday through at least
the end of next week. This troughing will also allow lobes of
Arctic air to dive into the region resulting in a return to more
below average temperatures and bitterly cold wind chills
heading into next week. In fact, there remains a strong signal
for highs to be in the teens to single digits while lows sit
near and below zero especially during this period. Additionally,
any shortwaves that dive through the pattern could bring the
chances for snow showers. While exact timing, location, and
intensity of any snow showers is hard to pinpoint at this range,
this is something we will have to monitor over the coming days.

Yack

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1109 AM CST Tue Jan 14 2025

No significant aviation concerns for the 18Z TAFs.

Snow has exited the region to the southeast as of late morning,
with VFR conditions expected to prevail through the forecast
period. Breezy northwest flow with winds gusting 20-25 kts will
diminish quickly after sunset this evening, and gradually back
to southwest at less than 10 kts (likely 5 kt or less later on)
overnight. Southwest winds will become a bit breezy again
Wednesday with gusts 15-20 kt developing by late morning, and
potentially some stronger gusts into the mid-20 kt range
toward/during Wednesday evening (just beyond the end of the
current ORD/MDW forecast). Otherwise, patchy VFR high clouds
will increase especially toward Wednesday evening.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 3 PM CST this afternoon for
     Winthrop Harbor IL to Gary IN.

     Small Craft Advisory until 9 PM CST this evening for Gary to
     Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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