Jan 24-26th Potential Something Part 2

[mimillman]

Man Iowa. What a winter there

[Chicago Storm]

Yea I guess the question is, do you believe that solution. I know the NAM is not alone 

It’s definitely a believable scenario.

However, I would be cautioned regarding it until the 0z runs tonight. Currently the wave that leads to the increased confluence is well north in Canada, across the Northwest Territories and Nunavut. There is some sampling that occurs up there, but it’s sparse. For the 0z runs tonight the wave will have pushed south into Saskatchewan and Manitoba, which has a bit more RAOB coverage.


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[Chicago Storm]

No matter the solution, hopefully ORD has corrected their recent track record of 2-inches-lower-than-measured-a-block-away snowfall measurement issues.

Measuring will be in good hands for this event.


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[mimillman]

Wild to me that Chicago’s last 6”+ snowstorm was November 2018, and that at ORD. For the Loop, last 6” storm I can remember was Feb 2018. Has been a horrendous stretch and it is finally coming to an end.

[SchaumburgStormer]

9 minutes ago, michsnowfreak said:

Event after event, whether it's small or large, it just boggles my mind how often we weenies look at storms that show up on the long range models and even when a threat is legit, until zero hour there are ridiculous swings. Look at that intense snow squall in Chicago the other night, a few days prior to that you thought maybe they would pick up a snow shower at best. Look at our East Side 3 to 4" snowfall on christmas. The news was literally telling people Christmas Eve morning we might see a few flurries but nothing to whiten the ground. 

Or the surprise downstate IL event where 1-2 was predicted and areas got smoked with 10”

[purduewx80]

What's also interesting about the synoptic light snows into Tuesday, is that we have steady cold air advection in the lowest 3KM or so with a lengthening fetch over the Lake. This 12Z RGEM sounding for Tuesday afternoon would result in a much deeper DGZ, high-ratio snow and the potential for significant additional accumulations. Most other guidance isn't quite as cold though. 

[ILSNOW]

Even the ICON is coming on board

[purduewx80]

2 hours ago, TheRegionRat said:

Where is the energy for the storm, and has it been sampled? The LOT AFD says it's coming ashore this morning.  Fully sampled for the 12Zmodel suite?  

The overnight AFD didn't say that. It's definitely still offshore. The system tomorrow is already well inland now.

AFD for reference, it's a doozy:

Quote

Sunday night through Friday...

We continue to focus in on the Sunday night-Tuesday morning
timeframe (and moreso specifically Monday afternoon/night therein)
for the potential for an impactful winter storm across a large
swath of the forecast area. We`ll continue to note that while
deterministic and ensemble guidance alike continues to trend
towards a general similar solution, the parent wave packet is
still just now dropping southward off the central California coast
and has some 2,000 miles to traverse before reaching our longitude
later Monday afternoon and evening. Thus, while the ensemble
envelopes are gradually narrowing, we`d be remiss if we didn`t
address the lingering large degree of uncertainty, especially
considering somewhat marginal thermal profiles with a likely
degree of mixing taking place somewhere in the CWA (near and south
of I-80). In addition, we at least have to entertain the idea of
dry slot issues impacting parts of the area given the latest 700
mb low track across central/north-central Illinois.

Before we get to the "main event," do want to quickly address a
low (yet nonzero) potential for freezing drizzle Sunday
evening/overnight within the forecast area. Global guidance has
held onto a pretty steady signature during this period, squeezing
out some very light precipitation amounts (<0.02") in a corridor
that`s waffled between I-88 and I-80 and just south. This seems to
be in response to a combination of increasing upper jet
divergence, and incoming sheared lead shortwave out of the
Rockies, and an attendant tightening of the low-level baroclinic
zone. Our first wave (addressed in the short term discussion) will
have likely scoured out a good deal of our mid and upper-level
moisture, leaving behind profiles that are just marginally-
supportive of ice nucleation. Depending on the depth of the mid-
level dry air, could be a bit of a seeder-feeder type mechanism to
drive more in the way of light snow, but the latest look of
forecast soundings is one more of drizzle at this time. As a
result, we`ve added in some slight chance wording for freezing
drizzle, mixed perhaps with a little light snow. This is still
somewhat of a conditional threat, but subtle/modest isentropic
upglide is noted within a fully-saturated 10,000 foot lower
tropospheric column that will likely be below freezing.

Evening model guidance continues to slightly delay the onset of
stronger forcing for ascent associated with the main vort max,
with the main region of warm-advection/DCVA looking to spread into
the region as early as late Monday morning, but more likely now
more fully into Monday afternoon and evening. Deterministic GFS
has trended notably farther northwest, and seems to now, along
with its ensemble counterpart, be on the northwestern periphery
of the guidance suite. ECMWF and EPS, while also trending perhaps
a smidge northwest, has maintained a remarkable degree of run-to-
run consistency, with the rest of the global suite seemingly
aligning towards it with time. Categorical PoPs are warranted at
this time, and have also smeared PoP chances well into Tuesday as
deformation area precipitation now looks to hold on through the
day.

With the slightly farther northwest movement, mixing with freezing
rain and possibly some sleet is becoming a bit more likely as far
north as the I-80 corridor Monday afternoon and evening before the
thermal profiles cool with the passage of the low to our south.
Bourgouin based layer energy grids don`t seem to support an overly
high potential for sleet given a lack of deeper near-surface cold
air for refreezing, with mainly a snow/freezing rain ptype
forecast although could certainly see some sleet working its way
into the picture. With the close approach of the 700 mb low, there
is some concern that the system`s dryslot may start to come into
play, especially south of I-80 Monday afternoon and evening, which
would start to toss more drizzle/rain into the equation as well.
For now, given the uncertainties here, we won`t be slicing the
onion that thin at this point, but something to be aware of. We
are showing some ice accumulations nudging up towards 0.10"--
locally a bit higher--but the assumption is that the dearth of
more persistent CAA and colder surface temperatures will help
temper icing impacts south of I-80.

As the system passes to our south and east through Monday evening
and overnight, winds will turn more northerly and the column
should cool sufficiently to turn most--if not all--of our area
over to snow within the deformation axis. This would likely be the
period of highest impacts given the potential for fairly high
snowfall rates under the core of the 500 mb upper low. Light snow
looks to continue through Tuesday morning and may now extend
through the afternoon hours, with a transition to some marginal
lake effect as precipitation comes to an end.

Regarding potential snow-to-liquid ratios: storm track
climatology (Southern Plains/Panhandle low) and lack of a colder
antecedent airmass (warmed up by preceding disturbances) likely
spell an overall lower-than-normal (wetter/heavier) snow when the
event is taken as a whole. A somewhat mismatched ascent profile,
maximized just above the dendritic growth zone, combined with a
fairly deep layer in the 0 to -5 C range atop surface temperatures
only around 30 portend sub 10:1 ratios to start Monday afternoon,
dryslot issues notwithstanding. Through Monday evening/overnight,
guidance suggests we should start to volley sufficient ascent
through the DGZ to nudge ratios upwards within the deformation
zone. Eyeballing a rough 8-11:1 type ratio with our first stab at
amounts here, which overall aligns well with SPC SREF max
saturated temperature and Cobb ratio output.

We`ve noted tonight that the deterministic ECMWF and GFS are right
towards the top end of their corresponding ensemble counterparts
regarding QPF amounts. For the first pass at amounts, in
coordination with surrounding offices and WPC, elected to maintain
more of an ensemble-based flavor to things, which results in a
swath of amounts near 5-6" through the heart of our CWA. These
amounts will more than likely undergo some re-working with
subsequent forecast updates, however, as confidence in storm
evolution grows. Do think there is a decent potential for some 8"
amounts somewhere in the CWA with this system, with some potential
for lake enhancement (although marginal) as well, but it`s still
too soon to bite off on totals this high.

Finally, strong and gusty northeasterly winds, gusting at times
towards 30 to perhaps 40 mph, will likely build wave action into
the northeast Illinois and possibly northwest Indiana shore. While
lake levels have diminished from last year, still-elevated levels,
combined with wave heights building towards 10 ft suggest a decent
threat for at least minor lakeshore flooding Monday night into
Tuesday.

We`ll get into a brief reprieve Tuesday night into Wednesday
morning as ephemeral shortwave ridging builds in overhead.
Another rather potent, fast-moving disturbance continues to be
well-advertised in the extended guidance. Very cold temperatures
aloft and steep lapse rates support some threat for some bursts of
heavier snowfall with this system, although what appears to be
a short residence time and moisture-starved nature should help
hold additional snow totals down. Guidance additionally remains
split on this feature`s track, so broad-brushed chance PoPs
continue to be the way to go at this juncture.

Carlaw

 

[Sciascia]

Low looks a few hairs NW on 12z GFS compared to 6z

[Winter Man]

21 minutes ago, mimillman said:

Wild to me that Chicago’s last 6”+ snowstorm was November 2018, and that at ORD. For the Loop, last 6” storm I can remember was Feb 2018. Has been a horrendous stretch and it is finally coming to an end.

It's been longer than that for me personally because of college. 

https://www.weather.gov/lot/21Nov2015snowfall

[Chicago Storm]

12z GFS a bit south.

[mimillman]

1 minute ago, Chicago Storm said:

12z GFS a bit south, but just about noise level.


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It’s beautiful. Any further north than 6z was getting cringeworthy for the metro 

[mimillman]

Lake showers still going in NE Illinois

[Sciascia]

Snow numbers around Chicago & lakeside just keep slowing ticking upward as the run goes on

[hawkeye_wx]

GFSv16

[ChiTownSnow]

9 minutes ago, hawkeye_wx said:

GFSv16

Rockford would cash in again on that run

When would we expected watches to go up?

 

 

[mimillman]

GEFS similar trend, slightly further south and weaker.

[Chicago Storm]

12z GEM bumped north, to the current consensus.

 

 

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[Chicago Storm]

GEM has 30” in parts of IA.


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[Cary67]

11 minutes ago, ChiTownSnow said:

Rockford would cash in again on that run

When would we expected watches to go up?

 

 

Rfd doing well this year with respect to being a bit further east. Most years the Lake influence pushes ORD past RFD later in the winter for season totals

[Chicago Storm]

12z GEM

[ChiTownSnow]

All models seem to be In relative agreement now?

With track at least?

[mimillman]

Should start seeing the watches hoisted with evening AFDs. Going to need blizzard warnings in Iowa

[Cary67]

7 minutes ago, mimillman said:

Should start seeing the watches hoisted with evening AFDs. Going to need blizzard warnings in Iowa

Would LOT need to issue watches before tomorrow evening? Another 24hrs to see if short range models agree?

[Sciascia]

I start work in 10 minutes. Not sure when I’ll be able to check in again, but please don’t get to a part 3 without me. 

[RogueWaves]

2 hours ago, dmc76 said:

3-6” for SEMI. 

Traditional 5-9 incher incoming.

[RCNYILWX]

Would LOT need to issue watches before tomorrow evening? Another 24hrs to see if short range models agree?

I could see waiting until tomorrow morning for the watch.

Sent from my SM-G965U using Tapatalk

[hawkeye_wx]

UK is a bit south and more progressive.

[mimillman]

4 minutes ago, RCNYILWX said:

I could see waiting until tomorrow morning for the watch.

Sent from my SM-G965U using Tapatalk
 

Interesting. I’d have thought there’s enough consensus now you can be reasonably confident issuing a watch.

[RCNYILWX]

Interesting. I’d have thought there’s enough consensus now you can be reasonably confident issuing a watch.

I could go either way, there's enough supporting evidence to issue today but sometimes it's not the worst to wait. My guess is DVN issues today. So it would be up to our forecasters whether to hoist a watch too because MKX would have too much uncertainty.