Beware the Ides of March (and into the 16th)

[OrdIowPitMsp]

2-3” in the forecast for mby. With the snow falling during the day I have a hard time believing rates will be strong enough to efficiently accumulate. 

[Hoosier]

I'll go 1-2" of snow/sleet here.

The wave swinging in Monday night looks a little too warm locally and is not factoring into my call.

[CheeselandSkies]

Wow, MKX actually went with a WWA for Dane.

[Natester]

12k NAM caved to the HRRR when it comes to extent of snow in Iowa.  NAM3k similarly although it shows a couple hours of sleet in east central Iowa.  Also of note that both of the NAMS really diminish the freezing rain threat in Iowa to almost zero.  Not so in Illinois and Indiana.

[hlcater]

There's this super subtle detail on the HRRR that I think is likely responsible for the heavier snow further south. 

On the 18z run, there's a patch of really quite dry surface dewpoints in the mid to upper teens that gets advected in later tonight. As this area of lower dews gets moistened, it increases the effects of evap cooling and leads to an overall cooler column than other models at the same time ---> heavier snow further south.

It's more evident on skew Ts but I cant gif those

[Hoosier]

LOT had a rather lengthy discussion for this.  Here's part of it.  I think there is some upside to these forecast snow amounts and would not be surprised to see a band of 3-5" somewhere in the northern tier or two of counties.

 

The precipitation type forecast remains challenging and convoluted
even as we are within 24 hours of the event now, and our forecast
grids reflect that as they seem to resemble a child`s finger
painting with all of the various colors representing different
precipitation types and mixes splattered across the area. This is
primarily due to the combination of the presence of a 850-700 mb
warm (above freezing) nose, which will melt some amount of snow
aloft; sub-700 mb temperature profiles generally hugging the
freezing line, meaning that even a 1-2F degree difference
somewhere in the temperature profile could swing precipitation
type from one mode to another; and the continuing feed of dry air
that will keep wet-bulb temperature profiles mainly below freezing
in the lower levels, allowing for evaporative cooling to offset
much of the ongoing low-level warm air advection.

That being said, based on our current forecast, the general
precipitation type evolution looks to feature a wintry mix including
sleet and possibly freezing rain across the southern two-thirds
of the forecast area during the morning and early afternoon with
the main bout of precipitation likely ending as rain or a
rain/snow mix by late afternoon. Across our northern counties, we
look to have a more homogeneous precip type forecast of mainly
snow during the morning and early afternoon. Although, it is
likely that some other precip types will at least briefly mix in
somewhere here before most of the precipitation ends (a rain/snow
mix seems to be the favored solution, but a mix including sleet is
not entirely out of the question either).

Moderate to briefly heavy precipitation rates would be favored to
occur shortly after precipitation onset and will generally diminish
as the precip shield marches northeastward with time as the upper
low starts shearing out more and the associated sources of lift
weaken. The majority of any precipitation looks to end by the early
evening as a mid-level dry slot slides through the area, but some
patches of drizzle and/or snizzle could hang around into the
overnight hours. Additionally, as the occluded surface low tracks
across central Illinois, a wave tracking overhead should induce a
more concentrated area of rain showers across mainly the southern
half of the forecast area Monday night, although some of this
activity will likely sneak into the Chicago metro. Some of these
showers would be convectively-driven, and it`s not entirely out of
the realm of possibility that we get an isolated lightning strike
or two somewhere in the forecast area. All precipitation should
be out of the area by daybreak Tuesday.

The going precipitation accumulation forecasts of up to 0.5" of
sleet, up to 0.1" of ice accumulation generally south of I-80, and 1-
3" of very wet 5:1 to 8:1 SLR snow generally north of I-80 (highest
accumulations towards the Rockford metro and northwest Illinois
where better forcing with the right entrance region of an easterly
upper jet streak will be present) with 1" or less generally south
of I-80 seem adequate. However, with surface temperatures expected
to mainly be at or above freezing by the afternoon, any ice
accumulations from freezing rain would likely not last long, and
the wet snow may have difficulty accumulating on relatively warm
roadways, which should limit the overall impacts that we see with
this system. We opted to not issue any Winter Weather Advisories
for both this reason and because of the persisting uncertainty
with exact precipitation types and rates. Nevertheless, the potential
for slushy snow accumulations on colder roadways and the brief
potential for freezing rain to impact travel will be messaged via
SPSs and graphics.

[Chicago Storm]

LOT had a rather lengthy discussion for this.  Here's part of it.  I think there is some upside to these forecast snow amounts and would not be surprised to see a band of 3-5" somewhere in the northern tier or two of counties.
 

The precipitation type forecast remains challenging and convolutedeven as we are within 24 hours of the event now, and our forecastgrids reflect that as they seem to resemble a child`s fingerpainting with all of the various colors representing differentprecipitation types and mixes splattered across the area. This isprimarily due to the combination of the presence of a 850-700 mbwarm (above freezing) nose, which will melt some amount of snowaloft; sub-700 mb temperature profiles generally hugging thefreezing line, meaning that even a 1-2F degree differencesomewhere in the temperature profile could swing precipitationtype from one mode to another; and the continuing feed of dry airthat will keep wet-bulb temperature profiles mainly below freezingin the lower levels, allowing for evaporative cooling to offsetmuch of the ongoing low-level warm air advection.That being said, based on our current forecast, the generalprecipitation type evolution looks to feature a wintry mix includingsleet and possibly freezing rain across the southern two-thirdsof the forecast area during the morning and early afternoon withthe main bout of precipitation likely ending as rain or arain/snow mix by late afternoon. Across our northern counties, welook to have a more homogeneous precip type forecast of mainlysnow during the morning and early afternoon. Although, it islikely that some other precip types will at least briefly mix insomewhere here before most of the precipitation ends (a rain/snowmix seems to be the favored solution, but a mix including sleet isnot entirely out of the question either).Moderate to briefly heavy precipitation rates would be favored tooccur shortly after precipitation onset and will generally diminishas the precip shield marches northeastward with time as the upperlow starts shearing out more and the associated sources of liftweaken. The majority of any precipitation looks to end by the earlyevening as a mid-level dry slot slides through the area, but somepatches of drizzle and/or snizzle could hang around into theovernight hours. Additionally, as the occluded surface low tracksacross central Illinois, a wave tracking overhead should induce amore concentrated area of rain showers across mainly the southernhalf of the forecast area Monday night, although some of thisactivity will likely sneak into the Chicago metro. Some of theseshowers would be convectively-driven, and it`s not entirely out ofthe realm of possibility that we get an isolated lightning strikeor two somewhere in the forecast area. All precipitation shouldbe out of the area by daybreak Tuesday.The going precipitation accumulation forecasts of up to 0.5" ofsleet, up to 0.1" of ice accumulation generally south of I-80, and 1-3" of very wet 5:1 to 8:1 SLR snow generally north of I-80 (highestaccumulations towards the Rockford metro and northwest Illinoiswhere better forcing with the right entrance region of an easterlyupper jet streak will be present) with 1" or less generally southof I-80 seem adequate. However, with surface temperatures expectedto mainly be at or above freezing by the afternoon, any iceaccumulations from freezing rain would likely not last long, andthe wet snow may have difficulty accumulating on relatively warmroadways, which should limit the overall impacts that we see withthis system. We opted to not issue any Winter Weather Advisoriesfor both this reason and because of the persisting uncertaintywith exact precipitation types and rates. Nevertheless, the potentialfor slushy snow accumulations on colder roadways and the briefpotential for freezing rain to impact travel will be messaged viaSPSs and graphics.

I’ve been pretty much think 1-3” for the CWA along and north of I-80. However, I fully agree that there is much more upside potential. If thermals work out as the GFS/RAP and others show, definitely could see an axis of 3-6”+ into the CWA.


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[Hoosier]

Alek is like 4 days late with a call.

The people want to know.

[Frog Town]

The Thursday system has so much potential with the position of the high in Canada and the track of the low.  I'm curious why there isn't more wintery precip on the northern edge with that?? one.  

[Chicago Storm]

Alek is like 4 days late with a call.
The people want to know.

he’s still digging out from february.


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[Hoosier]

Not 100% convinced but if it can stay predominantly sleet for long enough, then I think somebody south of I-80 in the LOT cwa could end up with a good inch of sleet, particularly on colder surfaces.

[Natester]

First one to call in predicted total.  Going to go with 5 inches here although there's a chance it'll bust low based on the HRRR runs but 5 inches total is realistic here.

[Hoosier]

Poor Kankakee 

[Natester]

Huge jump in accumulated snow totals via 10:1 ratio for here on the 0z HRRR.  0z HRRR says we get a foot but that is very unlikely.

[madwx]

HRRR which had been on the low end of totals jumped up to 5" here.  Paved surfaces won't accumulate as much but models are honing in on the high end advisory scenario here.

[madwx]

also with all the talk of warm air and surfaces before the storm, we're going to be below freezing for a solid 12 hours before the snow starts falling

[hawkeye_wx]

I think 3-4" is much more likely than the 8+ the latest HRRR is predicting.

[hawkeye_wx]

The change to snow over here this morning is not going well.  It was supposed to be all snow by now, but it's still just rain and sleet.  I have not seen a flake.  3" is probably the best we could do now.

[Malacka11]

TWC got me goofed up with that 5-8" forecast. This is a very funny storm 

 

[Cary67]

Going with 2" call

[cyclone77]

Rain mixed with sleet and a few rogue flakes.  0.16" rain so far.  Using ILX radar since DVN has been unplugged.  

[Chicago WX]

Sleet. 32˚/17˚ at my house. East winds have gusted as high as 43 mph this morning. Just a nasty nasty day.  

[cyclone77]

Mostly snow now here

[Chicago Storm]

Mostly snow now here

Can see CC quickly crashing east on KLOT and SE a bit on ILX. Probably all snow to near I-39 now, north of I-80.


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[cyclone77]

11 minutes ago, Chicago Storm said:

Can see CC quickly crashing east on KLOT and SE a bit on ILX. Probably all snow to near I-39 now, north of I-80.


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The transition here was sort of bizarre.  Dry (normal) flakes started mixing in with the rain/sleet.  Usually you get the white rain/partially or mostly melted flakes pouring down first.  Dry flakes just started fluttering down in the midst of the rain and sleet.  Don't think I've ever seen that before.

Snow is getting pretty close to heavy with the ground quickly whitening.

EDIT 9:32- Heavy sleet has mixed back in and knocked the snow intensity back quite a bit.

[SchaumburgStormer]

10 minutes ago, Chicago Storm said:

Can see CC quickly crashing east on KLOT and SE a bit on ILX. Probably all snow to near I-39 now, north of I-80.


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Looking like most of NW LOT will have a very short mix prior to being all snow. Should rip for a while later this morning. 

[Sciascia]

I’m currently at home in Poplar Grove, a little less than 10 miles east of I-39. If/when it starts ripping later, I’ll see what kind of pics I can grab.

[A-L-E-K]

been so busy i haven't really been paying attention, some snow will be a nice distraction later

2 or so sounds right 

[cyclone77]

Pounding sleet.  Snow completely ceased.  Close to an inch of snow/sleet so far.

[A-L-E-K]

wind is absolutely biting, feels terrible after our recent warmth

should be a plaster job tho