Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/13/21
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
926 PM CST Fri Feb 12 2021
924 PM CST
The main updates this evening were to attempt and refine PoP
trends and overall QPF/snow amounts tonight and into Saturday
00z RAOBs out of Davenport and Lincoln sampled quite a bit of
lingering dry air, with the near-surface dry layer initially noted
on the DVN sounding likely having saturated quite a bit since
then. Mid-level dry air was much more prevalent on the ILX
sounding, and with cloud bases still at or above 10,000 ft into
north-central Illinois, this is likely still the case. Given the
overall modest nature of ascent overspreading the area, have
trimmed PoPs quite a bit through tonight for areas south of a
roughly Pontiac to DeMotte line with it unlikely that light snow
will be able to chew through this dry layer. Have done the same
across far northern Illinois and to the state line for similar
reasons. In between these two areas, broad/disorganized f-gen will
continue to develop overnight as the exit region of an
anticyclonically-arcing jet streak pushes in overhead, and this
appears to be where the main focus will be for steady (mainly
light) snow overnight and into Saturday morning. Given the rather
lazy nature to the ascent, thinking that snow-to-liquid ratios
may end up a smidge lower than you`d otherwise expect given the
cold thermal profiles and deep dendritic growth zone...perhaps in
the 15-20:1 range.
The main axis of snowfall amounts in the 2-4" range has shifted a
bit north, focused more around the I-80/88 corridors with this
update, with amounts lowered to for our southernmost counties to
an inch or less. PoP trends for Saturday morning are a bit
unclear, as we`ll begin losing the better jet support, resulting
in an overall weakening to the already modest mid-level f-gen.
This may allow lingering light snow near/south of I-80 to
dwindle, before additional ascent from an incoming shortwave
pushes across our northwestern locales. Have trimmed PoPs south
and east of I-57 as a result, and left the categorical/definites
Lake effect is the next challenge. Near-surface convergence is
tightening up near the lake, with winds turning northwesterly at
the Crib, and veering more easterly across southwestern Michigan.
A single lake band is evident along the western Michigan
shoreline, and is starting to push west. Guidance like the 3-km
NAM and RGEM, which seemingly handled yesterday`s LES event fairly
well, continue to crank up quite a bit of QPF across far northern
Porter county, and have been joined by the Hires WRFs. Have
nudged snow amounts up in this localized area with some amounts
approaching 5-6" near the lake in the latest forecast. Not
entirely convinced of the double-digit output from some of the
guidance given the altogether marginal LES parameters, but we`ll
keep an eye on things. Either way, we`ll be continuing the Winter
Weather Advisory for Porter County, and could need to sneak it
into Lake County as trends become better established.
234 PM CST
Through Saturday night...
Currently, an elongated 130-150 kt jet streak extends from eastern
Minnesota to southern Ontario. In the right entrance region of the
jet streak is a similarly elongated zone of radar echoes stretching
from central Nebraska though northern Illinois. Recent AMDAR
soundings off aircraft departing Chicago terminals depict a short
but very dry layer centered at about 5000 feet, which is eating any
and all snowflakes on their trip to the ground. (So, most of those
aforementioned radar echoes are actually virga). The dry layer is
expected to remain in place through the remainder of the afternoon
and evening hours, acting to delay the onset of snow compared to
Using the RAP 850 mb relative humidity as a proxy to track the
elimination of the dry layer, it appears light snow should start
trickling down to the ground after dark and in the 9-11 pm window.
Thereafter, steady, light snow will continue through Saturday
morning. A deep snowflake growth layer of nearly 15,000 feet will
afford fluffy snow ratios of 20:1 to 25:1, with gradual lift
supporting a snow rate of 0.1 to 0.3"/hr. Upper-level lift will then
wane after daybreak Saturday as the jet streak scoots eastward,
though light snow showers will likely persist through much of
afternoon. Generally 1 to 3" of fluffy snow looks on track with the
highest amounts in the vicinity of I-80. Locally higher totals are
possible along the Lake Michigan shore of Porter county, Indiana
where an overnight land-breeze-forced lake effect snow band should
boost snow rates after midnight. The inherited Winter Weather
Advisory for Porter County thus remains appropriate. Regardless of
how much snow falls across the area tonight/Saturday, untreated
roadways may become slippery.
Snow will end quickly Saturday evening and clouds will attempt to
clear from west to east. With a fresh snowpack in place,
temperatures overnight into Sunday should drop below zero areawide.
Winds of 10 to 15 mph will make it feel more like 20 to 25 below
zero, especially west of I-39. Not much reprieve is expected Sunday
with highs in the single digits and wind chills of 5 to 15 below
zero. Such cold temperatures can lead to frostbite in as few as 20
minutes, so bundling up from head to toe in multiple layers is a
must if planning to head outdoors.
222 PM CST
Sunday through Friday...
Lake effect snow will likely continue Saturday night into early
Sunday across Porter and possibly Lake counties of IL as 925 mb flow
remains NE for a time on Sunday.
Sunday into early Tuesday... The anomalously lower heights in the
mid-levels with the aforementioned lobe of polar air, with 500 mb
values of 505 dm, will shift east/southeastward during Sunday into
Monday. This influence is more so Monday afternoon into Monday
night, with a more stout disturbance progged to eject northeastward
from Texas/southern Plains toward the Ohio Valley. But there are
still signs even late Sunday through early Monday the baroclinic
zone around 700 mb tightens over the southern CWA with some
saturation and possible light snow. There is some variance in
guidance on specifics as far as how far north the light snow
footprint may extend, still with our I-55 and southeastward corridor
While forecast adjustments from the blend were to still boost
PoPs along and south of I-80 for mainly Monday afternoon and
night, the signal for how widespread the influence of even this
stronger second system is not quite as robust. Cyclogenesis is
forecast over the southeastern U.S. tracking into the Appalachians
region and supports the best chances for some snow to inch
northward over our area. Again our highest chances remain along
and southeast of I-55, but even light snow will be fluffy and
could create impacts across the entire area. The potential is
there for a wind chill headline going through Sunday and into
Monday morning, but this may be confined to areas across north
central IL and west of Chicago. Still will be solidly below zero
and in some places well below to start the week on Monday morning.
Lake effect snow Monday into Tuesday...Lake effect snow during this
time may be ongoing through these several events, and there are
hints at the development of decent convergence zone/associated
surface low, in northwest Indiana Monday, and then shifting into
northeast IL later Monday and Monday night. There could be some
lingering snow/flurries Tuesday morning, but this period is of lower
confidence than Monday night.
Tuesday and beyond....
The strong arctic high will ever so slowly, but optimistically (for
those of you just looking for something to hang your hat on) lose
its grip on the region, and we will inch our high temperatures back
into the 20s mid week. Before we finally say good riddance to the
core of the arctic air, another system is currently advertised to
follow a similar Texas to Tennessee valley to the Appalachians
track late in the week. This could still graze our area with some
light snow before the weakening ridge axis finally makes its way
overhead toward week`s end and we shift the low level low back
around to the southwest for the first time in quite a while.
For the 00Z TAFs...
539 PM...Primary forecast concern is light snow developing this
evening and continuing through Saturday afternoon, along with
Light snow is expected to develop across the area by mid/late
this evening and continue through at least late Saturday morning
and possibly through mid afternoon. A narrow band of snow is
expected to develop and then expand in coverage and there remains
uncertainty regarding exactly where and when this will occur but
much of the latest guidance shows light snow developing along a
vys/lot/gyy line by mid evening and then expanding north through
early Saturday morning. Current forecast has this trend covered
well and made no significant changes. While prevailing 1-2sm vis
looks on track, through midday Saturday, there may be a corridor
of moderate snow that may reduce vis under 1sm but confidence for
location remains low and no mention of lower vis with this
forecast. Cigs are expected to lower into mvfr soon after snow
begins with several hours of low mvfr expected through early
Saturday afternoon. Ifr cigs will be possible if and where any
moderate snow develops. As the snow tapers off Saturday afternoon,
cigs will lift through mvfr with scattering/clearing expected
North/northwest winds around 10kt will continue through the period
with speeds increasing to 12-15kts Saturday afternoon along with
some gusts into the 15-20kt range possible Saturday evening. cms
IN...Winter Weather Advisory...INZ002 until 6 PM Saturday.
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Area Forecast Discussion
National Weather Service Lubbock TX
541 PM CST Fri Feb 12 2021
MVFR ceilings will continue at KLBB and KPVW this evening before
dipping back down into the IFR range late tonight. KCDS will
maintain VFR ceilings this evening but will also drop back down
into the MVFR range late tonight. With these low ceilings in place
aircraft icing on approach/departure will remain probable through
this TAF period at all terminals. There is the potential for
flurries or brief snow showers to occur once again late tonight
and early tomorrow morning however confidence in this activity is
too low to include at this time. /WCI
.PREV DISCUSSION... /issued 308 PM CST Fri Feb 12 2021/
Our weather will continue to feel like a Midwest winter with what
feels like never ending low cloud cover. Before the main winter
storm on Sunday, an initial short wave currently over the Great
Basin will dive fairly far to the south into northern Mexico. This
short wave will eventually emerge over south Texas having little
impact on the area locally. Generally, some occasional flurries can
still be expected for the rest of tonight and during the day on
Saturday. Closer to the South Plains, weak isentropic lift will
persist through Saturday morning providing the occasional flurry
chance. Temperatures at the surface and aloft are expected to be
cold enough for all snow instead of freezing drizzle. Min temps in
the fairly deep 3kft sub-freezing layer will be around -11 to -12C.
Subsidence will quickly move in during the day on Saturday as the
aforementioned short wave trough departs to the east and in advance
of the larger trough to the west.
The main two players in the upcoming winter event are a closed upper
low currently over the southwestern CONUS and a trough over the Gulf
of Alaska. The low over the SW CONUS will continue to dive to the
southeast towards Mexico and become an open trough. As this trough
moves to our southwest, it will help to induce southwesterly flow
aloft. These southwesterly winds will flow over the warm Baja
California Gulf, advecting some moisture to the northeast towards
the area. With the main vort max and surface boundary of the trough
moving well to our south, moisture advected into the system ahead of
the trough will be allowed to remain in place for the next system.
The trough currently over the Gulf of Alaska will enter the
northwestern CONUS early on Saturday and will begin its dive towards
the area. Late Saturday, the upper trough will approach the area,
bringing upper-level divergence to the area and our initial snow
chances. As the main wave approaches west Texas, lift will be
increased due to PVA associated with the mid-level trough and
frontogenetical forcing from the associated front. With temperatures
within the column being below freezing, this event will be all snow.
Progged soundings indicate that decent layers of the column are in
the sweet spot in regards to temperatures (DGZ) and saturation for
much of the day on Sunday. This will allow for significant snow
growth and periods of heavy snow. Unfortunately, with the
temperatures within the column being as cold as they are, the snow
will have limited liquid content. This is great if you want to have
several inches of snow but not so good if you want to make snowmen
or snowballs. Temperatures will continue to fall through the day on
Sunday, bringing sub-zero lows and wind chills -10 to
-25 F to the area for Monday morning especially from Lubbock
northward. As the system moves to the east, the snow will start to
taper off from west to east sometime Monday morning into early
afternoon. Because of the low liquid content of the snow and the
winds, blowing and drifting of snow will be a concern even after
the snow starts to diminish.
Temperatures will slowly creep back towards freezing by mid-week.
The next system is expected to affect the area late Tuesday into
Wednesday, bringing the next chance of snow to the area.
Temperatures will rise above freezing on Thursday, with highs this
weekend possibly reaching 50s and low 60s across the area.
Winter Storm Watch from late Saturday night through Monday
morning for TXZ021>044.
Area Forecast Discussion
National Weather Service Blacksburg VA
1035 PM EST Fri Feb 12 2021
An Arctic boundary will extend from the DelMarVa region west
into the Tennessee Valley and then southwest into deep South
Texas. This cold air will continue to filter southwest into the
Mid-Atlantic region from the northeastern U.S. Meanwhile, a
moist southwest flow aloft and a series of disturbances will
bring periods of precipitation across the region and into the
cold, below freezing air, mainly in the form of freezing rain
and sleet over the next few days. A significant winter storm in
the form of an ice storm is likely across the Virginia Piedmont
Saturday, with additional potential for winter storms well into
next week as cold, Arctic air remains firmly entrenched across
.NEAR TERM /THROUGH SATURDAY/...
As of 1030 PM EST Friday...
Have done some editing to better delineate locations where
freezing fog may be an issue, and have rolled this threat into
the existing Winter Weather Advisory. All else is on track with
no major changes needed at this time.
Significant Freezing Rain Event Expected Tonight and Saturday
Across the VA/NC Piedmont and Southside Areas.
The upper short wave that drove the sleet and freezing rain
last night and early this morning has moved to the southeast of
the area, where it will stall along the baroclinic zone/frontal
boundary. This afternoon, moisture overrunning the shallow wedge
of cold semi- Arctic air has kept low clouds, fog, and drizzle
in place. With temperatures remaining at or below freezing for
all except the far southwestern and southern fringes of the CWA,
freezing fog and freezing drizzle has continued across the
region and this will remain in place through the evening.
With regard to tonight, significant icing is expected as the
baroclinic zone lifts a bit northwest in response to upper
ridging off the southeast/Mid-Atlantic coast. A significant warm
nose aloft in the 3000-10000 ft. layer will result in
precipitation falling primarily as rain, thus freezing rain as
it falls into the cold boundary layer. The wedge is going
nowhere within at least the next 36 hours, perhaps even into
Sunday morning. Ice accumulations are expected to be some of the
most significant we have seen in a long time and in areas that
are less accustomed to winter weather, namely the Piedmont. Ice
accumulations of 1/4 to 1/2 inch appear likely from Reidsville
and Caswell northward toward Danville, South Boston, and
Lynchburg. Some sleet is possible further north, but primarily
this is a freezing rain event. Soundings do not support snow at
all at this point. A Winter Storm Warning has been issued for
areas along and east of the Blue Ridge with a Winter Weather
Advisory for areas further west, except the extreme western
fringe of the CWA which remains just outside of the wedge.
Significant and damaging accumulations of ice are expected in
the Winter Storm Warning area, with accumulations of ice
generally around 1/10 inch. Again, sleet and snow should be
limited with this event.
/Confidence Level in Forecast Parameters/
Temperatures - Moderate to High,
Precipitation Probabilities - High,
Winds - Moderate to High,
Winter Weather Threat - High east, Moderate west.
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 300 PM
Numerous Waves Of Wintry Precipitation Persist Into Tuesday
With Next High Impact System Expected Monday Night Into
The short term forecast starts with us wrapping up the freezing
rain/sleet system that first starts impacting the forecast area
Saturday. Sounding profiles continue to support freezing rain and
sleet through the morning, mainly for areas north of 460 and east of
220. Sleet amounts will be greater for areas in the west like WV,
over to the southern Shenadoah, while freezing rain will remain
favored down around southside, north to around Lynchburg.
Temperatures will gradually warm through Sunday, eventually bringing
most to a cold rain: however, moisture continues to linger into
Sunday night and early Monday AM at this point. This will lead to
some light icing opportunities Sunday night, as well as light sleet
As high pressure continues to strengthen out west, a deep trough
will remain dug out across the U.S., spanning overtop of the
region...this means more shortwaves and thus more low pressure
systems. Our next storm is set to arrive Monday into Monday night.
Once again, we are looking at a mostly freezing rain event, with
varying amounts between different versions of guidance. Overall, the
GFS and its ensembles members from the GEFS seem too fast and mostly
too warm with the beginning of work week systems. Instead, ECMWF and
its ensemble versions, as well as with plumes from the CMC seem to
have a better handle on the system. Overall, they are hinting at
another system that could bring some areas ~0.5" of ice.
As we head into Tuesday, high pressure will be moving westward,
reinforcing the cold air wedge and thus increasing our icing
potential through the day before moisture runs out and the front
When it came to building this part of the forecast, I went for the
cold side of guidance to try and help ensure a good reflection of
the wedge that will remain present throughout, but with varying
degrees. If you`re looking for warmer weather...this isn`t your
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 315 PM EST Tuesday...
Brief Break Expected Wednesday Before Another Impactful Weather
System Arrives Thursday Into Friday.
Guidance remains variable in exact timing and possible
amounts/precipitation types with a system that will arrive
Thursday into Friday. Prior to that storm, high pressure should
arrive to the region, allowing the opportunity to reinforce the
cold air wedge that will plague the forecast in earlier
periods. With this reinforcement, a larger spread in
precipitation types looks possible: it is still far too early
for specifics though as different guidance versions and even
runs are highly variable with the storm system`s track and
speed. It does look like a trend change is possible after this
last storm late in the week, but we will have to wait and see if
this remains true.
I continued to remain on the cold side of guidance with the
obvious wedge that will be holding our temperatures down. That
said, if the low`s track were to trend further west and north,
it could open us more into the warm sector of the system and
heat us up, but for now I`m not going for that.
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
As of 640 PM EST Friday...
LIFR ceilings and mainly LIFR/IFR visibilities were across the
region. Little change is expected in this scenario over the next
24 hours. Precipitation in the form of a sleet, freezing rain,
or freezing drizzle is expected overnight, with a trend to
freezing rain being the dominate weather feature by sunrise
Saturday. Areas of fog and freezing fog will also be across the
Much of the area will continue to see freezing rain or
freezing drizzle during the day Saturday. Southwestern and
southern sections are expected to see the temperature climb
slightly over the freezing mark by the afternoon to allow for
some plain cold rain or drizzle. Aircraft parked outdoors
overnight into Saturday will have some amount of icing on them,
as much as a 1/4 to 1/2 inch between the area of KLYH-KDAN.
Confidence in the above aviation scenario is high.
Extended Aviation Discussion...
Weather pattern is forecast to remain unsettled well into next
week with increasing threat for wintry precipitation as Arctic
air surges further southeast into the eastern United States.
Generally MVFR or worse conditions expected through the entire
The KFCX radar will be down through about Thursday, Feb 18th
for the replacement of a generator as well as other electrical
components powering the facility.
VA...Winter Weather Advisory until noon EST Sunday for VAZ010>016-
Winter Storm Warning until noon EST Sunday for VAZ017-032>035-
NC...Winter Weather Advisory until noon EST Sunday for NCZ001>004-
Winter Storm Warning until noon EST Sunday for NCZ005-006.
WV...Winter Weather Advisory until noon EST Sunday for WVZ042>044-