Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/08/23
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
850 PM CST Sat Jan 7 2023
.UPDATE...
Issued at 850 PM CST Sat Jan 7 2023
Regional satellite imagery depicts an area of stubborn low-level
stratus encompassing nearly all of northern Illinois and
northwestern Indiana beneath an impressive subsidence inversion
(low-level temperature rises by about 8C from 1500-2500 feet AGL
per 00Z DVN RAOB and recent AMDAR soundings). Meanwhile, a
sheared-out vort max continues to progress across central Missouri
and southern Illinois, with most radar returns apparently virga
thanks to a stout dry airmass atop the aforementioned inversion
and beneath decidedly upper-level convective forcing (e.g. steep
mid-level lapse rates and weak fgen). Interestingly, we`ve seen
evidence of gravity wave solitons atop the low-level stable layer
(instigated by the sheared-out system to our southwest?) leading
to a wavy "pond effect" to the stratus and even at times pockets
of clearing owing to deconstructive wave interference.
Going forward, the sheared-out vort max will continue to progress
eastward taking with it streaks of virga. A flurry or two cannot
be ruled overnight particularly south of a line from Pontiac to
Rensselaer though by and large most areas look to remain dry.
Toward daybreak, a surface pressure ridge is expected to stall
along the Mississippi River Valley leading to stagnating cloud-
bearing winds and lowering cloud bases. As a result, Sunday looks
to start out and perhaps remain gloomy especially in closer
proximity to the surface pressure ridge (e.g. west of I-39).
Observations of lowering cloud bases and visibility across
eastern Iowa leverage confidence in our forecast.
Updated products have been sent.
Borchardt
&&
.SHORT TERM...
Issued at 240 PM CST Sat Jan 7 2023
Through Sunday night...
The primary forecast challenges through the short term period
include:
* Cloud coverage trends tonight into Sunday.
* Threat for freezing fog tonight through Sunday morning,
particularly along and west of the I-39 corridor.
* Low threat of light snow late tonight into Sunday, primarily
south of U.S. 24.
Early afternoon GOES water vapor imagery depicts a spilt upper
level flow pattern across the central CONUS. Within this pattern,
a southern stream short wave impulse is currently shifting
eastward into the Lower Missouri Valley, while an upper level
shortwave ridge dominates across the Upper-Midwest. At the
surface, high pressure is centered across southern MN, with an
area of low pressure centered across western AR. These pressure
features are expected to shift eastward tonight and Sunday into
WI and TN, respectively.
Low clouds remain dominant east of the Upper Midwest ridge this
afternoon over the Great Lakes where a shallow moist layer
remains trapped beneath a subsidence inversion above 900 mb.
Temperatures under this deck of cloud cover in our area have
largely remained in the 20s to low 30s, and this will continue to
be case late this afternoon. While the low-level cloud cover has
remained persistent in most areas, recent satellite trends over
the past couple hours have shown a scattering trend across far
southern WI. A recent AMDAR sounding out of MKE suggests that the
subsidence inversion has become sufficiently low in this area to
allow the cloud deck to break up. While this scattering trend has
been gradually expanding southward into far northeastern IL across
some of the far northern Chicago suburbs, it appears the cloud
cover will persist across a vast majority of the area into tonight
as the cloud bearing layer flow around 950 mb gradually veers
easterly early this evening.
In addition to the cloud cover, there is also concern for the
development of freezing fog across western portions of the area
tonight. We should see another night a light to variable winds
across the area as the aforementioned surface high shifts into WI
tonight. The combination of this with continued ample near
surface moisture (current dewpoint depressions < 5 degrees) may
set the stage for ceilings to lower towards the surface through
the evening. The primary concern for fog tonight is for areas
generally along and west of the I-39 corridor, though some fog
could develop into parts of the Fox Valley as well tonight.
Temperatures in the in the lower 20s may result in the
development of slick surfaces tonight into Sunday morning,
especially in areas where the fog becomes dense. We will continue
to monitor trends tonight, but given the signal we have added a
mention for areas of freezing fog to the forecast tonight for
areas along and west of I-39.
Outside of the low clouds and fog threat tonight into Sunday
morning, we also continue to monitor the evolution of the impulse
tracking into the Lower Missouri Valley this afternoon. The
associated surface low is forecast to shift eastward into TN
tonight and Sunday. Overall, the track of this system continues to
favor the best moisture transport and main focus for precipitation
south of the area on Sunday. With that being said, we continue to
mention some low end chances for light snow and flurries across
our southern counties into central IL and IN, mainly south of U.S
24 late tonight into Sunday. Little to no accumulation is
anticipated, however.
KJB
&&
.LONG TERM...
Issued at 233 PM CST Sat Jan 7 2023
Monday through Saturday...
Following highs in the low and mid 30s this weekend, Monday will be
a tad bit warmer to kick off our next workweek. Mild southerly flow
diverging from a high to the south and modest ridging aloft will
allow much of the area to warm into the lower 40s while many will
top out in the upper 30s. Similar temperatures can be expected on
Tuesday as well. A system of low pressure is expected to move across
the area during the day on Tuesday. It seems with each passing day,
models have upped the intensity of this disturbance which was being
resolved as nothing more than a broad, dry surface trough a few days
ago. Despite this uptick, precipitation chances remain apparently
low, though they have improved some. Through this morning`s runs,
just about all model guidance remains dry on Tuesday. The idea is
that our saturated layer is too shallow and low level forcing is too
subtle to result in any measurable precip. The NAM strongly
disagrees and displays pockets of rain and snow through the better
part of Tuesday. This is likely due to the fact that the NAM is
resolving a deeper shortwave aloft with stronger flow resulting in
notably better low level forcing. Being such an outlier though, the
forecast remains dry for the time being. However, even with no
measurable precipitation likely, forcing looks sufficient enough to
pose a chance for some flurries or drizzle. In fact, there is
growing concern regarding a freezing drizzle potential with a
substantial warm nose expected to setup aloft. This is primarily a
concern for Tuesday evening considering the surface will be above
freezing during the day. Being such a subtle system that`s still
undergoing noteworthy changes with each model run, no mention has
been made in forecast but it`s certainly something to keep a close
eye on.
The other key feature in the long term is the robust storm system
slated to move across the Midwest Thursday into Friday. This storm
is expected to be abnormally warm for a mid-January Rocky Mountain
low. As it`s passing through the area, 850mb temps at the center of
the low will be pushing 7C. So, despite the low tracking southeast
of the CWA, as it stands, it appears that we will see majority
rainfall out of this system. In fact, the Euro is showing just about
all liquid precip through the duration of the event. This could
potentially prove troublesome as temperatures on the backside of the
storm are forecast to drop below freezing pretty readily which
provides a concern for freezing rain. The GFS on the other hand
tracks the storm a bit further south and keeps conditions slightly
cooler aloft resulting in a transition from rain Thursday to snow
Thursday night into Friday. The Canadian sits somewhere in between
the two suggesting a shorter duration of snow on the backside of the
storm, though its track lines up much better with that of the Euro.
Additionally, the GFS lags behind the Euro and Canadian by about 18
hours making it an outlier in that sense, including among GEFS
members. Even despite the mild low level air, it`s hard to believe
that we wouldn`t see at least some snow within the cold advection
behind the low. At the moment, the forecast shows a transition from
rain to snow occurring through the evening on Thursday. All mention
of freezing rain was omitted for now given the low confidence in
thermal profiles and P-type altogether. High pressure building in
from the northwest will pull temperatures back into the 30s area-
wide Friday and Saturday.
Doom
&&
.AVIATION...
For the 00Z TAFs...
Aviation weather concerns through Sunday evening consist of:
* BR and FZFG potential tonight. Worst conditions expected west
of the Chicago-area sites.
* Small threat for either flurries or FZDZ tonight into Sunday
morning. Chances too low for a formal mention at this time.
* Somewhat uncertain cig and vsby trends into Sunday afternoon and
evening.
MVFR cigs are forecast to prevail tonight, although can`t rule
out another brief period of scattering at RFD or even DPA.
Expecting that cigs will gradually build down through the night,
with IFR likely INVOF RFD and DPA, with a bit less certainty in
this farther east, including at ORD and MDW. Guidance continues to
suggest vsbys will deteriorate in the light wind regime, with a
threat for FZFG at RFD with no changes made to the inherited 1SM
and TEMPO 1/4 SM groups. Will need to monitor areas farther east,
but latest thinking is that any vsby reductions will be into the
MVFR range and somewhat more intermittent.
Also keeping an eye on a low threat for -SN or -FZDZ overnight and
into Sunday morning. At this time, it looks like the cloud deck
will be just a bit too thin to support precipitation, but will
continue to keep an eye on guidance trends tonight since, if
precip did develop, it`d likely be in the form of freezing drizzle
given cloud tops warmer than about -8 C.
Cigs should slowly rise through Sunday afternoon, but not by much.
While temporary improvements above 020 are plausible, opted to
continue prevailing low-MVFR through the rest of the TAF periods.
Steering flow will turn out of the west Sunday evening, indicating
that IFR cigs/vsbys may slosh across the Chicago-area sites Sunday
night. Surface winds will be light and variable through Sunday
morning, before trending westerly with time during the afternoon.
Carlaw
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
840 PM CST Sat Jan 7 2023
.UPDATE...
Issued at 836 PM CST Sat Jan 7 2023
Isentropic ascent to the north of a baroclinic zone across the
lower MS Valley and low level frontogenetic forcing is contributing
to banded as well as showery precipitation in a west-east corridor
of precipitation running along/parallel to I-70. The greatest
coverage of precipitation, which is snow with a number of mobile
east-northeast moving bands, is stretching from northern Boone
County through southern Pike County MO into central Macoupin County
where forcing is greatest and lapse rates are moderately steep.
South of I-70 the precipitation is light, scattered and showery and
has included rain and brief bursts of sleet. A number of ACARS
soundings from KSTL has been showing gradual erosion of the
elevated warm layer but still supporting mixed p-types.
The RAP has been resolving the forcing and favored location for
precipitation rather well since late afternoon. The expectation is
as the upper low currently in extreme SW IA slides east-southeast
tonight the low-mid level flow will veer to more westerly resulting
in weakening upglide and a northeastward shift of the main area of
banded precipitation. This should begin in earnest in the 03-06z
time frame and really accelerate overnight. A band of 1-2 inches
of snow and potential isolated amounts of 3 inches or so still
looks on target along an axis from northern Boone County into
northern Greene County. Impacts from the snow have been
locallized. Road conditions have been quite variable with some
slick and snow covered roads to just partially covered roads.
Even with the main forcing/bands shifting northeast the remainder
of this evening, weak forcing with the upper low will still bring
a chance of light snow/showers to portions of eastern MO and
western IL overnight into early Sunday morning.
Glass
&&
.SHORT TERM... (Through Late Tonight)
Issued at 226 PM CST Sat Jan 7 2023
Early this afternoon, water vapor imagery revealed an upper level
disturbance moving eastward across northern Missouri. This was
reflected at the surface by a low centered just south of Branson,
MO, with a warm front extending into the Ohio River Valley.
Frontogenetical forcing on the north side of the low, along with
falling heights aloft and modestly steep mid-level lapse rates,
resulted in a band of scattered rain/snow/sleet showers extending
from east-central KS to St. Louis, and an area of virga over
northern MO.
As the low drifts to the east this evening and overnight, the band
of frontogenesis/low level convergence will move further into the
Mid-Mississippi Valley. These features are expected to become
increasingly aligned with stronger mid/upper level support and
slightly steeper lapse rates, and will very likely result in a
band or a few bands of enhanced precipitation. High resolution
guidance continues to support this idea, with the vast majority of
models showing an axis of 0.15-0.25" of QPF somewhere in Missouri
to the east of Highway 63 and the north of Interstate 70.
Obviously band placement is once source of uncertainty with this
forecast. Another questionable aspect of this forecast is
precipitation type. Temperatures have risen to near or above
freezing for much of the areas this afternoon, but are largely
supporting sleet or snow as of this writing. Temperatures will
only fall farther this afternoon and evening, but somewhere across
our south, will likely be too warm to support any frozen
precipitation. It`s still uncertain where the rain/snow line will
set up, but for the time being, it looks like areas south of
I-70 will see mostly rain or rain and sleet, with areas further
north seeing mostly snow and sleet.
For areas that do see snow, snow-to-liquid ratios represent
another forecast challenge. Forecast soundings continue to show
limited moisture in the DGZ, and I`ve struggled to find a forecast
sounding with much lift in the DGZ. Moreover, relatively warm
ground temperatures will further limit accumulations. Given these
factors, I anticipate SLRs to generally remain well below
climatology (12:1). However, forecast guidance often struggles to
handle these mesoscale bands, and I wouldn`t be surprised to see
SLRs within the band briefly approach climatology, resulting in
snowfall amounts topping 2" in some areas. Precipitation will
begin to taper off by midnight as the surface low weakens and
frontogenetical forcing wanes.
BSH
.LONG TERM... (Sunday through Next Saturday)
Issued at 226 PM CST Sat Jan 7 2023
This evening`s system will move east of the area by tomorrow
morning, leaving rising heights and increasingly dry air in its
wake. Initially cool and cloudy conditions with NNW winds will give
way to clearing skies and more westerly winds, boosting temperatures
back toward just above normal. On Monday, a shortwave will move
into the Northern Plains and Upper Mississippi Valley. This will
spur weak surface troughing over the Plains, further backing low
level winds over our region and drawing in warmer air. Continued
WAA and limited moisture advection is expected to push temperatures
well above normal on Monday afternoon.
The above shortwave will continue to push southeastward on Tuesday,
dragging a weak cold front into the region. The majority of forecast
guidance shows only weak cold air advection behind the front on
Tuesday, with notably drier air pushing into the region. Mostly
clear skies will counter the weak CAA, and should keep afternoon
temperatures on Tuesday afternoon 10-15 degrees above normal. The
warmup will continue into Wednesday due to a combination of rising
heights aloft and increasingly southerly low level flow.
On Wednesday night and Thursday, forecast guidance is in strong
consensus depicting a closed low moving from the Four Corners region
into the Southern Plains. The associated surface low will hook from
the OK/TX panhandles into the Mid-Mississippi Valley on Thursday,
bringing widespread precipitation to the region. Unsurprisingly,
there are notable differences in the track and timing of the low,
which introduces considerable uncertainty to this portion of the
forecast. Anything from thunderstorms ahead of the low to snow on
the back side of the low is on the table, so this will be a system
to watch over the coming days.
Upper level ridging and dry northwest winds behind the mid-week
system should help dry things out beginning on Friday. The northwest
winds will also push temperatures back toward normal for the weekend.
BSH
&&
.AVIATION... (For the 00z TAFs through 00z Sunday Evening)
Issued at 543 PM CST Sat Jan 7 2023
A potpourri of precipitation is ongoing across the area as we
approach 00z. The greatest coverage of perception is generally
north of I-70 and south of KUIN, thus inbetween the terminals.
KCOU and KJEF will see bands of light wintry precipitation
(-RA/-SN/-IP) through 03z or so, occasionally bringing MVFR flight
conditions. The St. Louis metro terminals (KSTL/KSUS/KCPS) will
see more showery precipitation including rain showers, and at
times potentially short bursts of sleet. By 03z or so the majority
of the precipitation should be lifting northeastward and at that
time could impact KUIN, although the greatest coverage is expected
to remain south of them. From late evening through overnight and
into early Sunday morning flight conditions will deteriorate as
the result of lower ceilings with stratus. If we see any snow
after 06z, it generally should be light, not long- lived and non-
impactful. Improving flight conditions to VFR is expected on
Sunday afternoon as stratus slowly clears NW to SE.
Glass
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX