Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/01/24
Area Forecast Discussion
National Weather Service Louisville KY
956 PM EST Sun Dec 31 2023
==============================================================
Key Messages:
- Cold front continues to move through the region and will bring
cooler temperatures tonight.
- Few flurries and sprinkles across southern Indiana into the
Bluegrass region tonight and New Year`s Day.
- Patchy slick spots on elevated surfaces possible tonight with
light precip and falling temperatures.
==============================================================
.Forecast Update...
Issued at 955 PM EST Sun Dec 31 2023
Widespread post-frontal stratus extends across the Ohio Valley as
the axis of the positively-tilted trough bisects the region. Even
though METAR and mPing reports have confirmed isolated -SN reports
across southern Indiana and northern Kentucky, most of the winter
precipitation activity is focusing closer to Lake Michigan via lake
effect snow. ACARS and cloud top temperatures show saturation barely
into the lowest portion of the DGZ, but given upstream radar
observations (leading nose of the lake effect moisture fetch) it is
anticipated an increase of the light snow/flurries coverage after
midnight. Given current above-freezing road temperatures,
accumulations will be light and restricted to elevated and grassy
surfaces. Nonetheless, persistent CAA tonight might promote pavement
temperatures at or below-freezing, especially on bridges and
overpasses, so isolated icy conditions cannot be ruled out. Last but
not least, some models are showing dry air scouring the DGZ around
sunrise that could influence a change from snow to drizzle.
&&
.Short Term...(Tonight through Monday evening)
Issued at 230 PM EST Sun Dec 31 2023
Currently... The cold front is currently along the Ohio River and
continue to track southeastward. As the front passes, winds shift
from SSW to WNW and low stratus clouds begin to fill in. With
temperatures in the upper 30s and low 40s in southern Indiana and
gusty winds around 15-20mph, wind chills are in the upper 20s and low
30s. These conditions will continue this afternoon and begin to
relax with sunset.
New Year`s Eve... The cold front will exit the region between by 1Z.
Since clouds will stick around through the night, cooler air will be
driven by CAA and bring low temperatures into the upper 20s and low
30s. Along the KY/TN border and in the Lake Cumberland region,
thinner cloud cover will allow temperatures to reach the mid 20s.
Behind the front, a few vorticity lobes will move through the region
and coupled with a 20-25kt LLJ, will provide enough lift for some
precipitation to form. Looking at forecast soundings, moisture will
be very limited and only up to about -11/-12C. This saturated layer
is large enough for some small flakes (or snow grains) to develop.
The thermodynamic profile remains at or below freezing at the
surface and aloft in the overnight hours. The 1000-850mb critical
thickness of 1300dm and the 850-700mb critical thickness of 1540dm
are oriented to suggest a rain to snow transition within the CAA
region. With this type of profile, freezing drizzle is possible,
however, have opted for snow in the grids due to the depth of the
saturated layer and the thickness orientation. Drizzle/snow grain
showers will be scattered, brief, and light. Greatest chance for
some festive flakes will be over the bluegrass, northern Kentucky,
and southern Indiana.
With some light precip possible and temperatures at or below
freezing, some patchy slick spots might develop on elevated
surfaces.
New Year`s Day... The positively tilted trough will slowly move off
to the northeast, which will keep the region with cooler
temperatures around the upper 30s and low 40s with overcast skies
for the first day of 2024. Through the day, a few vorticity lobes
will move through the region, similar to the overnight hours. Some
drizzle/snow grains may fall in the morning with scattered, brief
showers. These showers will transition to more rain dominant through
the day.
&&
.Long Term...(After midnight Monday night through Sunday)
Issued at 230 PM EST Sun Dec 31 2023
=============================================================
Key Messages:
* Brief/light precip event possible Wed Night.
* Stronger weather system to affect the region next weekend.
* Higher than normal forecast uncertainty.
=============================================================
Progressive split flow pattern will yield near-normal temperatures
and mostly dry weather through the upcoming week. Small chances for
precip on Wednesday night with a moisture-starved southern stream
system, but better chances on Saturday with a strong low pressure
system lifting across the Plains.
Monday night looks fairly chilly with clearing skies and elongated
sfc high pressure across the Ohio Valley. Tranquil weather continues
Tue into Wed under shortwave upper ridging, but the next southern
stream trof crosses the Deep South Wed night. A northern stream wave
will drop into the Great Lakes, but at this point it looks just a
bit too slow for the two streams to phase, leaving us with an
insufficient supply of moisture. This forecast will carry a 20%
chance east of Interstate 65, to account for the possibility of the
two systems phasing as the trof axes are overhead or just to our
east. However, do not expect any overlap between the moisture and
cold air required for accumulating snow, though we could see a few
flakes mix in, especially across the Bluegrass region.
Pattern amplifies later in the week as a wave kicks eastward from
the Four Corners and closes off over Texas. Deeper southerly flow
will set up a decent Gulf moisture tap, with widespread precip
likely at some point Saturday into Saturday night. At this time, we
can`t rule out a period of wintry mix at onset, and another as
precip shuts off. However most of the QPF will be accompanied by
temps just warm enough for all rain.
Confidence is limited in these split flow patterns, so this forecast
is subject to change. A southward shift in the storm track could
favor a more wintry solution for next weekend, so continue to
monitor the latest forecasts.
&&
.Aviation...(00Z TAF Issuance)
Issued at 540 PM EST Sun Dec 31 2023
SDF/LEX/HNB are all MVFR at the moment, and expect that could
persist at LEX for a few hours early this evening, before a brief
window of VFR for the first part of the overnight. Will start
SDF/HNB more optimistic on the VFR side of things, but do expect the
deterioration back to MVFR later tonight like LEX. This will occur
as a secondary wave of low level moisture and low MVFR ceilings is
expected from the pre-dawn hours through a good chunk of New Year`s
Day. There could also be some morning flurries or very light snow
showers at the northern TAF sites, and did mention with a VCSH given
low confidence. Outside of that look for steady W winds early in the
period, veering to a more NW component as a secondary cold front
passes. Some improvement in ceilings could occur late in the
forecast period, but not optimistic given the lingering nature of
low stratus.
BWG is currently VFR and should remain that way until around dawn on
New Year`s Day when another round of MVFR stratus builds in.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Update...ALL
Short Term...SRM
Long Term...RAS
Aviation...BJS
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
901 PM CST Sun Dec 31 2023
.UPDATE...
Issued at 901 PM CST Sun Dec 31 2023
Over the past hour or so the lake effect has become much less
organized and transitioned into broken dual bands, likely far
less impactful in its current state. RAP, HRRR, and NAM all
suggest convergence will strengthen some overnight, which could
allow for a reorganization of the band if that materializes.
However, ACARS soundings from ORD and MDW both show 2-3C of
warming in the low levels, centered around 875mb. The warming
noted in ACARS soundings is much more significant than the 0.5-1C
warming predicted by earlier model runs. The most recent HRRR did
initialize low level temps better and much more in line with ACARS
data, yet doesn`t show this warming extending east to over the
lake. Overall confidence is low, and given observational trends I
am growing increasingly skeptical regarding a meaningful re-ramp
up in LES intensity. The advisory is out and there is LES, so not
going to make any changes at this time, but if trends don`t
change, then oncoming midnight shift may be able to cancel the
winter wx advisory early.
Farther west across Illinois, flurries persist with regional
mosaic showing additional very light reflectivity (likely
flurries) upstream over southern Wisconsin. Have removed pops and
accumulations from Illinois and just maintained flurries
overnight. Can`t rule out a couple of lake effect snow showers
clipping the far southeast side of Chicago into Hegewisch and East
Side neighborhoods, but given the decreasing organization in the
LES, accumulations there seem pretty unlikely even if snow showers
do get that far west.
- Izzi
&&
.SHORT TERM...
Issued at 229 PM CST Sun Dec 31 2023
Through Monday night...
Key Messages:
* Lake effect snow showers develop tonight and persist through
Monday morning. Slushy accumulations away from the lakefront
with some patchy slick travel.
After a fairly prolonged period of drizzle and freezing drizzle
overnight and early this morning, cloud top temperatures have
continued to cool as saturated depths have risen steadily through
the day. Recent VAPOR AMDAR soundings show cloud top temperatures
are around -15C, which has been sufficient to inject condensation
nuclei into the cloud layer, leading to a changeover to all snow
across our area. We`re thinking that air temperatures held up just
enough last night to mitigate icing impacts. Had we been even a
degree or three colder, we likely would have seen much more
serious icing impacts in our region.
Through the rest of the afternoon, what you see is what you get.
Intermittent bursts of steadier snow will continue as several
sprockets of mid-level vorticity press overhead. Timing out one of
the last vort maxes (currently across central Wisconsin) suggests
we`ll eventually see snow coverage wind down through 6 to 9 PM
across most of the region. Can`t entirely rule out precip ending
as a little drizzle/freezing drizzle, but this should remain
pretty isolated and ephemeral. Not anticipating travel impacts
with road temperatures at/above freezing.
We`re starting to see the first signs of lake effect developing
off the Green Bay and Milwaukee radars, and this activity will
continue to expand southward through the evening and overnight.
Lake parameters aren`t particularly significant, with lake
surface-850 delta Ts around 12 C, and an incoming subsidence
inversion looks to hold equilibrium levels under about 6-7 kft.
Still, this will be sufficient to crank out some ephemeral heavier
convective elements tonight as convergence tightens up along the
lakeshore. Temperatures right at the lake will be influenced by
relatively mild (40+ F) lake air, but inland locales will likely
see temperatures hover in the 31-33 degree range tonight. This
will support some slushy snow accumulations away from the
immediate lakefront, perhaps locally up to 1-2 inches across
interior portions of Lake and Porter Counties in NW Indiana.
Cloud cover trends tonight and New Year`s Day are a bit unclear.
It`s possible we`ll see some holes develop in the cloud layer
overnight, but given how expansive the stratus deck is upstream
into Minnesota and western Ontario is, have greatly increased
cloud cover for tomorrow. With this in mind, also nudged low
temperatures up tonight and highs down tomorrow. Lake effect
precip will eventually diminish through midday Monday across
northwest Indiana.
Carlaw
&&
.LONG TERM...
Issued at 229 PM CST Sun Dec 31 2023
Tuesday through Sunday...
Key Messages:
* A brief breezy moderation in temps on Tuesday then more
seasonable thereafter, coldest on Thursday
* Chance (30-50%) of lake effect snow showers on Wednesday night
into early Thursday, primarily for northwest Indiana
* Low (~20% chance) of snow on Saturday
A fairly quiet shortened first work week of 2024 will give way to
a more active pattern next weekend and beyond. Expansive 1030 mb
high pressure will settle south Monday night as low pressure
tracks from Hudson Bay to northeastern Canada. A strengthening low
level jet in response to warm advection will result in increasing
west-southwest winds and slowly rising temps toward daybreak
following lows in the low-mid 20s outside of Chicago (upper 20s in
the city). Initial full sun on Tuesday will help mix into the base
of the departing low-level jet, yielding southwest gusts up to
25-30 mph through mid afternoon. Highs will reach the mid-upper
30s with upside potential to around 40F.
The cold front trailing from the aforementioned Canadian low
pressure system will move across the area Tuesday night with
little fanfare, other than shifting winds northwesterly on
Wednesday with fairly robust cold air advection in its wake,
resulting in highs in the lower 30s to perhaps mid 30s. While some
flurries getting wrung out of the closed cell strato-Cu deck
can`t be ruled out behind the cold front on Wednesday, most
guidance is too dry to support any explicit flurries mention.
Flow will turn north-northwesterly over Lake Michigan amidst
continued cold advection Wednesday night. GFS forecast soundings,
a decent proxy for the reasonably similar other guidance, indicate
respectable lake effect parameters with lake induced ELs peaking
at ~7,500-8,500 feet, lake surface to 850 mb delta Ts of 16-18 C,
and 250-350 J/kg of lake induced CAPE. Given a nearly full
northerly fetch, potential for lake enhanced low-level
convergence, and a mid-level trough axis providing synoptic lift,
the period will need to be watched for a period of potentially
robust lake effect snow showers. 330-350 deg synoptic flow
supports Porter and Lake Counties as the main threat zone with
PoPs peaking in the 40-50+% range. Steadily rising mid-level
heights on Thursday will quickly knock down inversion heights and
end any lingering snow showers Thursday morning.
Aside from the lake effect snow potential, the main story
Wednesday night into Thursday will be the chilly (by winter
2023-24 standards thus far) temperatures. Lows bottoming out in
the upper teens to lower 20s and steady northwest winds will
result in Thursday morning wind chills in the single digits to
lower teens. Afternoon highs will only recover to the upper 20s to
lower 30s, which may yield (remarkably) the first widespread sub-
freezing highs since late November. Following a chilly Thursday
evening, warm advection will ensue Thursday night into Friday,
bringing mid to locally upper 30s highs on Friday.
Our next chance for precipitation will arrive on Saturday as a
southern stream disturbance emerges from the Plains and tracks
east-northeast. While a distinct majority of super-ensemble
members keep the surface low pressure far enough south to likely
keep meaningful precip. south of our area, a few members are far
enough north to support slight chance (~20%) PoPs for snow.
Looking out beyond day 7, for multiple model cycles in a
row, the ensemble means have consistently depicted the ejection
of an anomalously deep western trough into the Midwest. The pieces
could thus come together to support a strong synoptic system
affecting the region (irrespective of precip. types) early in the
first full work week of January. Medium-long range ensemble
guidance also has been consistent in an active and colder pattern
continuing through mid January, so there may eventually be some
bonafide winter weather threats to track. Stay tuned.
Castro
&&
.AVIATION...
For the 00Z TAFs...
537 PM...Forecast concerns include...
Lake effect snow in Northwest Indiana.
Snow showers tapering to flurries this evening.
Gusty north/northwest winds this evening.
Mvfr cigs through Monday evening.
A band of lake effect snow will continue to affect northwest IN
this evening, and likely into the overnight hours. GYY will be on
the edge of the heavier snow, which may end up just east.
Elsewhere, current light snow/snow showers will taper off to
flurries this evening and the flurries will gradually end
overnight.
North/northwest winds may gust into the lower 20kt range this
evening and then gusts should diminish into the late evening and
overnight. Winds will turn northwest Monday morning, westerly
Monday afternoon and southwesterly Monday evening.
Mvfr cigs extend as far back as northwest MN and western IA and
this is little to support these mvfr cigs clearing before Monday
evening and mvfr cigs may persist longer than indicated. cms
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Winter Weather Advisory...INZ001-INZ002 until 9 AM Monday.
LM...Small Craft Advisory...IL and IN nearshore waters until 9 AM
Monday.
&&
$$
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