Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/18/22
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
519 PM CST Sat Dec 17 2022
...New AVIATION...
.SHORT TERM...
(Tonight through Sunday night)
Issued at 239 PM CST Sat Dec 17 2022
...Freeze Warning tonight for portions of the area. Arctic airmass
arrives Thur with the coldest temps of the season Fri AM...
The primary weather concern in the short term will be a potential
for the first freeze of the season for some areas. Surface high
pressure is currently centered near the Red River per RAP analysis
and is forecast to meander across northeastern TX and strengthen
tonight. Winds are likely to become light to calm over the northeast
quadrant of our area and with mostly clear skies expected across
these areas at least through 3am and likely through sunrise,
radiational cooling will be efficient. Model guidance often
underestimates the amount of cooling in these situations, so I`ve
lowered temperatures closer to MOS. The only limiting factor would
be if high clouds can move in more quickly than expected but even
then high cloud cover isn`t that efficient of an insulator. Thus,
while not a slam dunk, a couple hours of temperatures in the 30-32
degree range are likely over some areas that have not yet had their
first widespread killing freeze, so a Freeze Warning will be needed
for these counties: Hays, Caldwell, Bastrop, Lee, and Travis. Travis
County is being included despite a lower chance of a freeze within
the city limits and surrounding nearby suburbs. However areas on the
outskirts, especially east of I-35, should expect a freeze. Cover
any sensitive plants in these areas. The potential is there for a
need to expand this warning further south into mainly Comal and
Fayette Counties, although the city of New Braunfels is currently
forecast to see a low of 33.
During the day Sunday, mid and high level clouds will fill back in
and help keep temperatures from rising above the low to mid 50s. Low
level flow will turn slightly more to the SE/S just above the
surface and bring increased moisture to the region ahead of an
approaching shortwave that will reach TX Sunday night. This will
support strengthening of a coastal surface low at the end of the
short term period, with isolated to scattered showers and perhaps a
thunderstorm or two developing mainly after midnight. Sunday night
lows will be warmer, in the 40s.
&&
.LONG TERM...
(Monday through Saturday)
Issued at 239 PM CST Sat Dec 17 2022
The combination of a shortwave trough advancing across the South-
Central Plains and a developing surface low in the Gulf will result
in rain and elevated convection from Monday morning into Monday
afternoon across the eastern half of the CWA. Greatest focus likely
will concentrate along and east of I-35 where a region of locally
heavy rainfall will likely develop where rainfall amounts in excess
of 1 inch will be possible. Temperatures Monday trend coolest to the
east with the rain and cloud cover while the western areas are to
trend warmer into the 60s with sunshine.
Rainfall chances should come to an end into Monday evening over our
eastern zones as the Gulf low advances eastward along the northern
Gulf coast. Another upper level shortwave trough advancing from the
west into Central Texas also enters the picture from Monday night
into Tuesday. While this is not expected to result in additional
precipitation, it helps to advance a cold front (this will not be
the much anticipated arctic front later in the week) through the
region. Modest cold air advection with the northerly winds behind
the front should help to maintain below average temperatures. The
winds veer easterly then southerly into and through Wednesday night
ahead of the approaching arctic front.
The arctic front will arrive on Thursday but timing will be crucial
on how temperatures play out through the day. Latest deterministic
guidance from 12Z slowed the timing of the front to more around the
midday hour and allows with the southerly flow and daytime heating
ahead of the front to where temperatures could possibly warm beyond
60+ degrees across portions of the region. However, the ensemble
means from the 12Z guidance still indicates a faster solution where
temperatures warm little, if any, on Thursday prior to the front.
Trended a little warmer on the highs for the day but kept closer to
the ensemble means than the 12Z deterministic guidance with 40s in
the Hill Country and 50s south of I-35. However, these daytime high
temperatures will quickly become a distant memory, as temperatures
will immediately plummet with the passage of the arctic front and
then continue to fall into the night with strong cold air advection
from the brisk northerly winds from strong surface high pressure
building south.
The coldest air and a hard freeze will occur into Friday morning
where temperatures are expected to start off in the teens and low to
mid 20s. Additionally, wind chills will range from below 0 degrees
across portions of the Hill Country into the teens elsewhere across
the region. Wind Chill Advisories and Warnings will likely be needed
to be issued. Additionally, a Freeze Warning will also be likely for
locations that have yet to sustain a freeze this season. The very
cold air will persist during the daytime Friday as well with highs
only topping in the 30s and Wind Chills in or below the 20s. Some
locations in the Hill Country may remain below freezing through
Friday and not recover to above freezing until Saturday. The cold
air remains entrenched during the rest of the period with additional
area wide freezes Friday and Saturday nights. Saturday will have
enough daytime heating to allow for locations to climb back above
freezing area wide. This is time to prepare for this hazardous cold
weather. Remember the 4 P`s of Cold Weather: People, Pets, Plants
and Pipes.
Regarding any thoughts on precipitation chances for this very cold
period, the deterministic and ensembles collectively overwhelmingly
remain dry over the past several runs.
&&
.AVIATION...
(00Z TAFS)
Issued at 449 PM CST Sat Dec 17 2022
Highs clouds are forecast to push across South-Central Texas tonight
into Sunday. Otherwise, VFR conditions are expected for area
terminals through the forecast period. Light and variable winds are
forecast to dominate the local area tonight into Sunday morning. A
southeast flow is forecast for the I-35 sites on Sunday afternoon
into the evening with speeds around 5 to 10 knots. A stronger
southeast flow is expected for KDRT on Sunday afternoon as pressure
gradient increases due to a developing surface low across
southeastern Colorado with speeds around 10 to 14 knots with gusts up
to 25 knots.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 34 55 44 52 / 0 0 50 80
Austin Bergstrom Intl Airport 29 55 44 51 / 0 0 50 80
New Braunfels Muni Airport 33 56 45 53 / 0 0 50 80
Burnet Muni Airport 32 55 43 51 / 0 0 30 50
Del Rio Intl Airport 38 54 44 66 / 0 0 10 0
Georgetown Muni Airport 28 55 43 50 / 0 0 40 70
Hondo Muni Airport 34 55 45 62 / 0 0 40 50
San Marcos Muni Airport 31 56 44 52 / 0 0 50 80
La Grange - Fayette Regional 32 55 46 52 / 0 0 50 90
San Antonio Intl Airport 35 53 45 56 / 0 0 60 70
Stinson Muni Airport 37 55 47 57 / 0 0 60 70
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
Freeze Warning from midnight tonight to 9 AM CST Sunday for Bastrop-
Caldwell-Hays-Lee-Travis.
&&
$$
Short-Term...17
Long-Term...Platt
Aviation...17
Area Forecast Discussion
National Weather Service Wichita KS
542 PM CST Sat Dec 17 2022
.SHORT TERM...(This evening through Tuesday night)
Issued at 308 PM CST Sat Dec 17 2022
Near normal highs are expected Sunday out ahead of a shortwave
trough that will eject into Kansas late Sunday night or early
Monday morning. Models have trended a little more amplified with
this trough along with better moisture to work with. The question
is how cold does it get and if we transition to all snow. The GFS,
Canadian, and HRW FV3 all hint at us wet bulbing down to at or
below freezing, which would favor all snow and potentially
accumulating snow. However, the ECMWF, RAP, and HRRR are all
warmer and would support only a mix. For now will keep portions of
south central and southeast Kansas with mostly mixed rain and
snow with very light accumulations possible. For portions of east-
central Kansas where confidence is higher for cooler temps, a
transition to all snow appears more likely. This area could see 1
to 3 inches of snow. One positive for this system is that it will
be hitting late at night and early in the morning where the
diurnal cycle is more favorable for accumulating snow. If
temperatures cool even a couple of degrees below the current
forecast, then a more significant winter event will be possible. A
cold front will move through behind the system and we should see
highs below freezing for most of the area except for southeast
Kansas.
.LONG TERM...(Wednesday through Saturday)
Issued at 308 PM CST Sat Dec 17 2022
Guidance continues to be chaotic for the Wednesday and Thursday time
frame and the evolution of the potent trough. What we do know is
that Arctic air is coming and will likely bring strong winds with
it. Confidence is high that many will see wind chills between -10
and -30. The cold air alone will cause significant impacts. Anyone
caught outside as the front moves through will be at risk of frost
bite and hypothermia if not dressed appropriately. The temperatures
will drop fast behind the front with some areas potentially going
from the 20s to below 0 in a couple of hours. There is still some
uncertainty in just how cold the airmass will be but life
threatening cold does look to be likely.
The 12z model suite has continued the trend towards a deeper trough
digging to our west and southwest. Chances are increasing for a
significant winter storm, but being 5 days out there are still a ton
of wrinkles to iron out. For one, models are likely still under doing
the push of the cold air down the western High Plains based on a
potentially record breaking surface high over Montana. This would
shift the storm track further southwest and could increase the
threat of a winter storm or potentially suppress all the moisture
south of us. There are also some subtle shortwaves that could impact
the track of the storm. We will continue to monitor these trends
over the coming days.
Williams
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 536 PM CST Sat Dec 17 2022
Minimal aviation concerns over the next 24 hours. VFR conditions
expected with light variable winds overnight, transitioning to
southerly by tomorrow morning. Expect winds speeds to increase
during the afternoon hours tomorrow.
&&
.PRELIMINARY POINT TEMPS/POPS...
Wichita-KICT 20 45 32 44 / 0 0 60 40
Hutchinson 18 44 30 42 / 0 0 50 30
Newton 19 44 31 42 / 0 0 60 50
ElDorado 21 44 31 41 / 0 0 60 50
Winfield-KWLD 22 47 33 45 / 0 0 60 30
Russell 13 46 25 39 / 0 0 20 20
Great Bend 15 45 27 41 / 0 0 20 10
Salina 16 45 29 41 / 0 0 40 40
McPherson 16 44 29 42 / 0 0 50 40
Coffeyville 22 47 32 43 / 0 0 50 60
Chanute 20 45 31 42 / 0 0 50 60
Iola 19 43 30 40 / 0 0 50 70
Parsons-KPPF 21 45 32 42 / 0 0 50 60
&&
.ICT WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...CRW
LONG TERM...CRW
AVIATION...KMB
Area Forecast Discussion
National Weather Service Indianapolis IN
1005 PM EST Sat Dec 17 2022
.Forecast Update...
Issued at 1005 PM EST Sat Dec 17 2022
...SLICK SPOTS POSSIBLE TONIGHT ESPECIALLY NORTH OF I-70 AND EAST
OF I-69...
Web cams were showing a dusting of snow at Anderson, Muncie and New
Castle and ILN also passed along some issues over their counties
north of I-70. After inter-office coordination, decided to ramp up,
the Special Weather Statement wording for those areas. Kept chance
PoPs in overnight supported by radar mosaic showing upstream snow
showers over north central Illinois, associated with an upper wave
rounding the base of the Great Lakes upper low. This feature will
move across north central Indiana overnight. A dusting appears
more and more likely north of I-70. However, thin saturated layer 2-
5K feet per BUFKIT and ACARS soundings and lack of strong lift
precludes anything more.
&&
.Short Term...(This evening through Sunday)
Issued at 211 PM EST Sat Dec 17 2022
- Overcast tonight with Scattered Flurries
Surface analysis early this afternoon shows deep low pressure in
place across eastern Lake Superior. The deep low was providing broad
cyclonic flow across Indiana and the Ohio Valley. GOES16 shows
abundant cloud cover across the area with any breaks across the area
filling in quickly due to daytime heating. Radar shows some flurries
across southern parts of Central Indiana and another area of
flurries was found over Central and northern IL. Aloft a weak short
wave was found entering Indiana, pushing east, and poised to pivot
around the low and across Central Indiana. Temps were in the upper
20s to lower 30s.
Tonight...
Models tonight suggest the short wave to the west will push across
Central Indiana, as the deep low to the north pushes east across the
Great Lakes effectively keeping broad cyclonic flow in place across
Central Indiana. Forecast soundings show ample saturation within the
lower and middle levels overnight as this wave passes with pwats
only around 0.25in. Models do suggest saturation in the dendritic
growth zone overnight. With some lift as the short wave passes,
chances for snow showers will be needed. Best moisture still looks
to remain across the northern parts of the forecast area. However
the HRRR suggests more of a uniform coverage of precipitation. Given
this, will trend toward low chance pops tonight with little to
minimal accumulations. With clouds but not much temperature
advection expected, will trend overnight lows toward the lower 20s.
Sunday...
Models suggest the large low pressure system to the north will
finally begin to drift east exiting the area. Within the upper flow,
weak ridging is noted across the plains as the low departs by midday
Sunday. This results in northwest flow aloft across Indiana and
subsidence on the lee side of the approaching ridge. Within the
lower levels a large area of cold high pressure is suggested to
stretch from the northern plains to the Tennessee Valley. Forecast
soundings and time heights trend toward a dry column amid the
subsidence. Thus we will expect a decreasing cloudiness type of day
with some sunshine expected by afternoon. The cold air that we have
recently experienced will be exiting east on Sunday, allowing some
warm air advection from the northwest. Thus this along with some
sunshine should allow highs to push into the lower 30s.
&&
.Long Term...(Sunday night through Saturday)
Issued at 211 PM EST Sat Dec 17 2022
* Continued cold with an Arctic blast arriving late in the period
* Mostly dry through early next week
* Potential for an impactful winter system late next week
Monday through Wednesday...
The beginning of the long term features a quasi-zonal pattern in the
wake the deep low departing to the northeast. Strong 1030mb surface
high pressure builds over the region Monday, then becomes centered
over the Northeast by midweek maintaining influence over the region
and keeping conditions mainly dry.
With high pressure directly overhead Monday, expect a larger diurnal
range in temperatures as optimal conditions set up for radiational
cooling Monday morning. Thin, high clouds stream in by Monday
afternoon ahead of a weak system developing in the Plains; however
enough solar heating should take place to allow the surface to
"warm" afternoon temperatures into the low to mid 30s.
Quiet yet cold conditions persist Tuesday as a weak system passes
just north of Indiana. Weak low pressure in the Plains weakens and
falls apart considerably as it ejects northeast through the Midwest
into an area dominated by high pressure. Main energy with this
system moves off into Central Ontario while the upper trough passes
by to the north. With such a disorganized system and such strong
surface high pressure maintaining influence near the surface, do not
expect impacts other than increased cloud cover.
Uncertainty begins to increase Tuesday night as longer range
ensemble and deterministic guidance disagree on the timing of the
arrival of a colder airmass to the north. Cross sectional analysis
reveals upper moisture and high clouds beginning to stream in from
the west Tuesday night and lowering into Wednesday. While conditions
for radiational cooling are not optimal, light northerly winds
overnight from the incoming arctic high should result in
temperatures dropping considerably overnight despite cloud cover.
Keeping lows Tuesday night in the upper teens across the north to
lower 20s in Southern Indiana.
Uncertainty continues to build into mid next week as guidance
struggles with the evolution of the major pattern change expected to
take place. While confidence is high in a much colder pattern
developing, the details regarding the transition period and
associated winter storm are lower. High pressure maintains influence
at the surface on Wednesday; however moisture streaming in aloft as
troughing begins to dig out west should result in persistent mid to
high clouds. Southerly return flow ahead of the developing system
likely will not reach the Ohio Valley by Wednesday as high pressure
to the north works to suppress everything southward, keeping a colder
airmass locked in place at the surface and highs generally in the
30s across the state.
*********************************************************************
Thursday through Saturday(Potential Winter System)...
Latest guidance continues to signal towards the potential for an
impactful low pressure system to pass through the Ohio Valley
sometime between Thursday morning and Friday. With that said, there
is still significant variability amongst both ensemble members and
various deterministic runs.
******************************************
Differences in Deterministic Solutions: *
******************************************
First, lets discuss the deterministic runs. The GFS has continued to
be an outlier, mainly due to the position of the ridge axis over the
Western CONUS. The American model has had the ridge axis over the
intermountain west, leading to a shorter wavelength and therefore a
neutrally tilted amplified trough over the Midwest.This solution
would result in more impacts over the eastern US versus the Midwest.
Of note is a slightly weaker thickness gradient prior to
cyclogenesis. With the high likelihood of a rather anomalous cold
sector within this system this leads to the belief that this
solution may be misleading. Another note to point out, deterministic
GFS solutions have not been consistent with the track of the system
over the past few days, waffling significantly from run to run...
leading to lower confidence in solutions. However, latest 12z run
today has trended in the direction of the ECMWF and other models
tracking the low through the Ohio Valley.
On the other hand is the remainder of the deterministic suite
(Canadian, ECMWF, UKMET). These three are much more aligned on the
ridge axis placement further west over the Pacific Coast. In return,
the wave length is larger, allowing for a more negatively tilted
upper trough and less subtropical jet influence. The polar jet in
this instance in piece-wise with a strong jet streak upstream of the
trough and a supergeostrophic jet streak near the ridge over the
Northeast. A coupled jet streak provides an efficient environment
for surface cyclogenesis, as seen near the surface of these various
solutions. All three of these solutions also seem to better
represent the anomalous Arctic air expected in the cold sector,
increasing baroclinicity and the rate of surface pressure depletion.
This is not to say that these solutions will end up being the result
next week, but the meteorological interactions over the 150 hours of
output do have plausible explanations.
Another note for the ECMWF solutions, while there has been some
waffling (which is expected) regarding timing and track of the
system. There has been significantly more consistency in the ECMWF
track and timing compared to the GFS... resulting in increasing
confidence in an ECMWF based solution with a powerful low pressure
system deepening and tracking through the Ohio Valley.
**********************************
Ensemble and Probabilistic Output: *
**********************************
These deterministic solutions can help dissect the probabilistic output
given through various ensemble members of each parent model. With
the conceptual model chosen (longer wave length, positively tiled
trough, coupled polar jet), we can narrow the expected solutions to
those that align. There is still a wide range of solutions even
through this process, but this does show a trend of some sort of
deep surface cyclone over the Midwest, Ohio Valley, or Tennessee
Valley Thursday into Friday. This leads to a greater likelihood of
an impactful winter storm within the vicinity of central Indiana.
The track of the surface low will still have a significant influence
on the severity and type of impact central Indiana will witness. Any
track south of central Indiana will lead to a greater chance of
significant snow fall, whereas north or through central Indiana will
limit snow, but increase rain and even thunderstorm chances.
This process also shows a wide array of temperature outcomes for
late next week, ranging from low 50s in the warm sector, to mid 20s
in the cold sector. For now, temperature forecasts are more aligned
with the ensemble mean, but the result with much more likely be on
the lower or higher extremes (10th or 90th percentile).
****************************************************
Winter Storm and Arctic Outbreak Brief Conclusion:
****************************************************
Through a diagnostic synoptic process, discussed above, trends are
leaning towards an impactful low pressure system with a low track
ranging from Chicago to Nashville. Many potential solutions and
outcomes remain in play including the potential for significant
snowfall sometime between Thursday morning and Friday. There are
still many factors that will influence the forecast in the coming
days ans this system will continued to be monitored very closely.
Despite uncertainties regarding the potential winter storm Thursday
into Friday, there are a few areas where forecast confidence is very
high. No matter the track of the upcoming storm system, confidence
remains very high that some of the coldest air of the year will
arrive by the holiday weekend with temperatures potentially falling
below zero! Any snowpack will further allow temperatures to plummet
into the negatives and possibly into record territory. Signals for
an arctic outbreak are strong, so while there may be uncertainties,
one thing that is certain is the extremely cold air coming down from
the arctic. Along with the cold air will likely be dangerously cold
wind chill with values possibly below -20F. Take precautions now to
prepare for the upcoming brutally cold weather this holiday
weekend.
********************************
Long Term Forecast Updates
********************************
Increased winds and gusts Thursday through Saturday morning toward
NBM 90th percentile to account for significantly strengthening storm
system in the region and to match with neighboring offices. Lowered
temperatures towards NBM 25th percentile Friday into the weekend to
account for NBM likely not catching the full extend of the cold air
coming that time frame. Kept PoPs as is for now as there is still
too much discrepancy within deterministic guidance to deviate from
NBM on timing of precipitation.
&&
.Aviation...(00Z TAF Issuance)
Issued at 614 PM EST Sat Dec 17 2022
Impacts:
- MVFR/VFR ceilings improving to VFR after 11z-15z Sunday
- Light snow showers and flurries ending after 04z-06z
- Winds 260-280 degrees near 10 knots
Discussion:
Impulse around the base of a Great Lakes upper low will
result in MVFR/VFR stratus and light snow showers and flurries
tonight. Flying conditions will improve to all VFR toward midday
Sunday as the low moves to the east and high pressure builds in in
its wake.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Update...MK
Short Term...Puma
Long Term...CM
Aviation...MK
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
720 PM CST Sat Dec 17 2022
.UPDATE...
Issued at 721 PM CST Sat Dec 17 2022
Have made some minor adjustments to snow shower/flurry forecast
for tonight. Over the past couple hours, have seen an area of
light snow blossoming over western WI, with this activity heading
toward northern IL. Couldn`t find any model guidance with a handle
on this activity and hard to key in on any identifiable shortwave
in water vapor imagery responsible for this recent enhancement of
light snow. However, this light snow is blossoming within an arc
of higher moisture/implied ascent on low level water vapor
channel. Have also seen an uptick in very light echos (likely
flurries) across southern WI and northern IL. Have beefed up pops
somewhat and hit the flurry chances harder in the grids and
forecast tonight. If the activity over western WI holds together,
will need another update to beef up snow chances after midnight as
well, especially northern CWA. Not expecting snow to amount to
much, but an slight coating is possible with any heavier snow
burst, which given temps could lead to some patchy slick spots.
Updated grids and text products have been sent.
- Izzi
&&
.SHORT TERM...
Issued at 143 PM CST Sat Dec 17 2022
Through Sunday night...
The forecast messages for the rest of this weekend are:
* Spotty snow showers this evening but not at the intensity of
snow showers seen yesterday / last night.
* Clouds being stubborn to depart throughout Sunday, especially
the Chicago metro into northwest Indiana
Deep cyclonic flow continues across the entire Great Lakes and
Corn Belt regions from a closed low across central Ontario. The
depth of the saturated layer has diminished some today, per
satellite and aircraft soundings, as well as just visually seeing
some hints of brightness (or less opaqueness) outside. For much of
the day, the forecast area has been under a corridor of negative
vorticity advection (NVA) resulting in much less snow shower and
flurry coverage. There are two last upstream sheared waves, which
as of 130 PM are just southwest of the Quad Cities and in
southwest Minnesota. These will rotate within the cyclonic flow
near/just south of I-80 area late in the afternoon through the
evening. Each of these will re-enhance the lift and saturated
depth slightly, as well as cool the cloud layer a smidge bringing
it back into the dendritic growth zone (DGZ), resulting in an
uptick in flurries and spotty to scattered snow showers. With
these vorticity maxima being more sheared and the moisture depth
having diminished, the snow shower intensity is unlikely to be
what it was at times the last 48 hours. Still, with it being after
dark, spotty dustings may occur, and to a lesser degree than the
last couple nights, spotty black ice may return.
Temperatures have gone nowhere today with the clouds and westerly
winds gusting to 25 to 30 mph. These should continue a steady
trend this evening before a slow fall overnight. The rate of drop
will only be slight given the expectations for clouds to remain.
Forecast soundings show the saturation becoming thin by Sunday
morning, however with the subsidence inversion strengthening in
tandem with height rises, what is left of the clouds may very
well get caught underneath this inversion. Feel that this will be
the case given the guidance trend and how the RAP and HRRR have
consistently been showing clouds sluggish to depart. Confidence
is low in just how long the clouds persist though. By late
morning, much of the western and southern halves of the forecast
area could be clear, and then by early afternoon the sun may break
out over Chicago. But have trended later with the departure with
eastward extent in our forecast area given how guidance as a whole
tends to be too quick with departure in these setups. If clearing
has occurred by evening, with ridging passing over the area,
temperatures that will have only peaked in the mid 20s could drop
sharply. Some single digit lows may unfold for outlying areas.
MTF
&&
.LONG TERM...
Issued at 300 PM CST Sat Dec 17 2022
Monday through Saturday...
Key Messages:
* Brief chance for snow (possibly ending with freezing drizzle?)
Monday PM into Tuesday AM with no more than a dusting expected
* Strong winds, some snow, and bitter cold arriving late week
resulting in travel impacts heading into the holiday weekend.
* Confidence is increasing in an impactful winter system,
potentially significant, somewhere in the region. Still too soon
to discuss details!
* Now is the time to complete your winter prep for your home and
car if you haven`t already!
At the start of the extended period, Monday will start off chilly
with early morning low temperatures potentially in the teens and
near the single digits in outside of the Chicago metro. A weak
disturbance will begin lifting toward the area during the day
which could bring the potential for a quick hit of snow late
Monday into Tuesday morning. At this time it does not look overly
impactful, with perhaps a dusting of snow possible mainly
northwest of a LaSalle to Chicago line. There are hints that we
could briefly transition over to light freezing drizzle or
"snizzle" on the back edge of the system early Tuesday with the
loss of cloud ice as mid-level moisture exits a bit quicker than
in the low levels. Always want to watch out for those "event
before the event" scenarios that can always sneak up on us but for
now impacts with this system appear low.
It is also worth acknowledging the elephant in the room, which is
that there are model solutions suggesting a potentially higher
impact winter weather scenario may unfold somewhere in the region
during the Thursday-Friday timeframe, a peak travel period heading
into the upcoming holiday weekend. We are monitoring this very
closely, though we want to add that there remains a lot of
uncertainty in how things will ultimately unfold given it is still
several days away and urge caution to not lock onto specific
operational model runs as there remains a lot of spread among the
various ensembles. We encourage everyone to stay up to date with
the latest forecasts over the coming days as we get closer and
confidence in how this event will ultimately play out increases.
Where confidence is higher, however, is in the potential for at
least some accumulating snow falling across the area during the
Wednesday night-Friday timeframe, which combined with gusty winds
would result in some travel impacts and bitter cold wind chills
below zero heading into the holiday weekend -- regardless of how
much snow ends up falling and how high the winds end up getting.
If you haven`t already, winter prep for your home and vehicles
should be done early in the week!
The last thing to add is that due to the long stretch of below
freezing temperatures anticipated and resultant higher river
levels from this past week`s rainfall, there will be an increased
risk for ice jams along area rivers.
Petr
&&
.AVIATION...
For the 00Z TAFs...
Aviation weather concerns for the 00Z TAFs:
* Continued widespread MVFR ceilings overnight, then gradually
becoming VFR by late morning and scattering in the evening.
* Light off and on snow flurries until around midnight tonight.
* Snow showers likely this evening, with occasional IFR
visibilities possible but very little if any accumulation.
* Westerly winds with gusts of 20 to 25 kt.
Upstream observations are showing MVFR vsbys with a few areas of
IFR in the steadier snow bands, but most locations are seeing just
flurries with minimal reductions. Confidence is not high on the
vsby trends locally this evening, but the duration of any heavier
bands should be fairly brief. Confidence also is not high on the
end time of the flurries, as these have a tendency to linger in a
cold and moist airmass.
Lenning
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...nearshore waters until 9 AM Sunday.
&&
$$
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Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
610 PM CST Sat Dec 17 2022
.SHORT TERM...(This evening through Sunday night)
Issued at 317 PM CST Sat Dec 17 2022
KEY MESSAGES:
- Light snow will continue through early this evening, with little
to no additional accumulation.
Low pressure continues to propagate eastward as cold air builds in
with the high pressure from Canada. Lingering light snow should come
to an end from west to east early this evening. Nothing more than a
dusting is anticipated from the snow at this point. Winds remain
relatively breezy west of I-35, gusting up to 30mph. With fresh
snowpack, blowing snow remains a concern out west. Winds are
forecast to gradually lighten this evening in addition to a break in
the clouds. With an Arctic high pressure on its way and the clearing
skies, temperatures will get chilly tonight. Single digits across
the board, with a few sub-zero single digits out in western
Minnesota.
On Sunday, we will see the sun for the first time in a while, but
this doesn`t mean much for temperatures. Highs tomorrow in the low
teens to single digits are expected as the upper level jet roars
overhead with northwesterly winds. However, we will see a break in
the precipitation on Sunday before several chances for it return
early to mid-week.
.LONG TERM...(Monday through Saturday)
Issued at 317 PM CST Sat Dec 17 2022
KEY MESSAGES:
- The active pattern continues with a round of snow Monday and a
highly impactful storm possible mid to late week.
- Dangerously cold air will arrive mid to late week with wind chills
colder than 40 below zero possible.
On Monday, a progressive shortwave trough over the northern Rockies
late Sunday night will rotate eastward to the Upper Midwest Monday
evening. Increasing isentropic lift and a deep, moist DGZ should get
a large area of light snow to develop in the WAA regime. QPF looks
light, but there is a potential for high snow ratios so even 0.05-0.1
inches could equate to an inch or two of snow. Snow will break out
over MN Monday afternoon, then expand eastward into WI. The best
accumulations will occur across the east where snow should persist
the longest.
The early week system will exit to the east quickly and the first
surge of arctic air will move in behind it. Advisory-level wind
chills of 25 below to 30 below seem probable Tuesday morning across
western MN. Lighter winds but even colder air temperatures Tuesday
night will keep the hazardous wind chills in place across MN,
especially the west.
How the early week trough eventually lifts out of southeastern
Canada will determine how a large storm system will evolve and track
mid to late week. A very deep trough will dig down the Plains with
cyclogenesis occurring over the southern Plains Wednesday night. The
southwest flow aloft may bring a band of light snow to the Upper
Midwest well in advance of the main part of the system as early as
Tuesday night. QPF during this period would be light and with very
cold air already in place, the whole column may be colder than the
DGZ, but it will be close. The difference could mean low ratios and
needle flakes or very high ratios and dendrites. Winds at the surface
will be light, further favoring very high ratios if the column ends
up just warm enough.
The big question mark comes with where the surface low will
eventually track. There appear to be 2 main solutions in ensemble
guidance. One, the trough remains in place over eastern Canada,
resulting in a less amplified ridge over the eastern U.S., more zonal
flow, and a track farther south along the Ohio River (similar to the
12Z GFS). The other, similar to the 12Z ECMWF, lifts the trough out
of eastern Canada with southwest flow across the central U.S. As the
wave rounds the base of the trough, the system takes on a very
negative tilt with a considerable deformation band in the northwest
quadrant. Impressive snow accumulations would be likely. In addition,
as the system deepens, the pressure gradient would increase winds
substantially...resulting in blowing snow, possible blizzard
conditions, and dangerously cold wind chills. This system has the
potential to bring major impacts to a large chunk of the Great Lakes
and Upper Midwest and will need to be watched. At this time, either
scenario is equally likely, but it should be noted the GFS has been
trending closer to the ECMWF in recent runs.
Arctic air will remain in place through the rest of the period. Gusty
winds behind the departing system will keep dangerous wind chills
going with readings possibly colder than 40 below across western MN.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 539 PM CST Sat Dec 17 2022
We promise, operation snow globe is winding down! We still have a
couple of more hours of snow possible at MSP, with snow possibly
lingering as late as 6z out at EAU. After that, it`s a low confidence
night for cig heights. With drier air trying to push into the back
side of the system over the Great Lakes, we`re seeing highly variable
cig heights and that will continue to be the case until these low
clouds move out, which may actually never completely happen before
the next snow arrives on Monday. Still, with a surface ridge axis
finally moving in Sunday afternoon, we should see some sizable
breaks in the clouds Sunday afternoon.
KMSP...We do end the snow at 2z, though RAP soundings show the moist
layer below 5k feet residing within the dendritic snow growth zone,
so to be honest, as long as there are clouds, there will be a
continued chance for seeing flurries/light snow into Sunday, though
anything like we`re seeing now should be done this evening.
/OUTLOOK FOR KMSP/
Mon...VFR. MVFR/IFR/-SN likely in evening. Wind E 5-10 kts bcmg NW.
Tue...VFR. Wind NW 10 kts.
Wed...VFR. Chance MVFR/IFR/-SN . Wind N 5-10 kts becoming NE.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&
$$
SHORT TERM...PEM
LONG TERM...Borghoff
AVIATION...MPG