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AppsRunner

Winter Storm - February 11-13, 2019

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I think it’s intriguing to say the least in why GRR issued a warning for 4-7” of snow for their northern zones tonight but issued an advisory for 6-10” for their southern zones two weeks ago... There is some favoritism in the CWA. It’s alright, give us to IWX or LOT. I wouldn’t complain haha.

 

Looks like things will get d ICE y around here tonight. Strong WAA should dump a quick 2-4” followed by an extended period of ice (.10-.30”) as the warm nose pokes into the area followed by a brief shot of rain as the the low travels overhead, but some guidance keeps it cold enough for a mix I-69 points west. Then we should get into the trowel feature with some lake enhanced snow to drop another 2-4” as temps plummet and winds ramp up. Looks rather nasty around here for tonight/tomorrow with 25-35mph wind.. Hoping the RAP and NAM are being a little too agreesive with the ZR but with a large warm nose (48° at 925mb) and sleet looking minimal at best with lack of refreeze before precip makes the surface - this kinda screams freezing rain. We shall see. 

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14 minutes ago, hlcater said:

Snow is ahead of schedule out here in Iowa. Already past US34 and almost to I80. Still dry in IC.

Yeah she's moving in pretty fast.  Wasn't expecting any precip here until at least 4, and it's already knocking on the back door.

 

38 minutes ago, Chicago Storm said:

Can't wait to see negative nancy Cyclone roll in with another 6"+ event when it ends. :guitar:

I've been called worse! ;)

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36 minutes ago, RCNYILWX said:

This is a very tough ptype forecast, especially between the I-80 and I-88 corridors and about 10-15 miles either side. Despite what I posted earlier, having looked more at the soundings, I'm not buying sleet being much of an issue other than mixing in at times.

 

It should be primarily either snow or freezing rain. The big question is the northern extent of the warm nose and if it's enough to get full melting or do heavier rates keep it more as snow. The NAM and RGEM are by far more aggressive with the magnitude and northern extent of the warm nose around 850 mb, with the other guidance much more muted and farther south.

 

Given lack of stout low level cold wedge around 925 mb, it doesn't appear there will be enough refreezing energy for widespread full freezing of melted hydrometeors into sleet, except maybe far north for a time if warm nose does get that far north.

 

The pivotal weather soundings show this better with the temperature and wet bulb profile positive and negative energies. A modified version of the wet bulb is what we're using for ptype derivation in our grids, rule of thumb is negative energy of 100 j/kg or more gives 100% sleet probability and less than 50 gives 0% sleet, while for positive energy, I believe 20 j/kg gives full melting. So the big thing to watch on mesoanalysis this evening is the 850 mb zero line. Within the vicinity of that will be transition zone likely driven by rates to go over to all snow and far enough south will be solidly freezing rain.

 

 

 

 

There are no absolutes, but normally I'd be very nervous completely discounting models that have the warm nose aloft farther north.  So probably not a bad idea to weight that in but to what extent is the big question.

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A look at current obs.  Note that much of the anticipated icing area is not really starting out with excessively low dewpoints, although dews are running lower in Michigan and the northern row of Indiana.  That air will be advecting in on strengthening E/ENE winds and trying to combat the increasing waa.

 il_sfc.gif.665fa350e12b267d820991b045ba1cc4.gif

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There are no absolutes, but normally I'd be very nervous completely discounting models that have the warm nose aloft farther north.  So probably not a bad idea to weight that in but to what extent is the big question.
Yup, what makes this such a tough call. 18z NAM didn't back down and has a big ice storm for much of the CWA. Comparing initialization and 21z to most recent mesoanalysis depiction of 850 0 line, it appears it'll be a bit farther north, though that doesn't mean it'll be wrong this evening. With earlier precip onset, we should at least start as snow.

Certainly have seen NAM be right on the warm nose before, though often in those cases it has support of RAP/HRRR, which instead this time have been generally ticking colder aloft. Maybe a blend is ultimately the way to go. Such a tough forecast and gonna come down to real time/nowcast.

Sent from my SM-G965U using Tapatalk

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17 minutes ago, Hoosier said:

A look at current obs.  Note that much of the anticipated icing area is not really starting out with excessively low dewpoints, although dews are running lower in Michigan and the northern row of Indiana.  That air will be advecting in on strengthening E/ENE winds and trying to combat the increasing waa.

That's one big positive from the last ice event...

With that event we had temps of mid to upper 30's being advected in from MI/IN, but this go around we have temps in the mid 20's to low 30's being advected in.

Additionally, we are going into this event colder days prior, unlike last time where there was that brief mild period prior.

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Interesting battle between NAMs and HRRR/RAP.  NAMs have bumped back north a bit with the 18z, and bring mostly sleet and eventually even rain into the QC.  HRRR and RAP continue to show mostly snow with a few brief periods of sleet.  It's always tough to bet against an aggressive layer of warm air aloft in a situation like this.  

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19z RAP gets the icing concerns fairly far south, and it looks like it's doing ok with the current placement of the 32F isotherm.  

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Few weak LE bands pushing inland across NE. IL currently.

It's actually snowing here now because of them.

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1 hour ago, Harry Perry said:

I think it’s intriguing to say the least in why GRR issued a warning for 4-7” of snow for their northern zones tonight but issued an advisory for 6-10” for their southern zones two weeks ago... There is some favoritism in the CWA. It’s alright, give us to IWX or LOT. I wouldn’t complain haha.

 

Looks like things will get d ICE y around here tonight. Strong WAA should dump a quick 2-4” followed by an extended period of ice (.10-.30”) as the warm nose pokes into the area followed by a brief shot of rain as the the low travels overhead, but some guidance keeps it cold enough for a mix I-69 points west. Then we should get into some wrap-around lake enhanced deformation snow to drop another 2-4” as temps plummet and winds ramp up. Looks rather nasty around here for tonight/tomorrow with 25-35mph wind.. Hoping the RAP and NAM are being a little too agreesive with the ZR but with a large warm nose (48° at 925mb) and sleet looking minimal at best with lack of refreeze before precip makes the surface - this kinda screams freezing rain. We shall see. 

I was reading this feeling immense appreciation for LOT. They improve  every single year and they keep us appraised of all forecast changes and thought processes. 

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18 minutes ago, Maneee said:

I was reading this feeling immense appreciation for LOT. They improve  every single year and they keep us appraised of all forecast changes and thought processes. 

Agree 100% - one of the best offices around IMO. 

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5 minutes ago, ILSNOW said:

Good LOT update 3-6 from I-88 north with additional 1-2 tomorrow from wrap around snows.

to me, if the weather discussed in the AFD comes to fruition we'll have an upgrade to a warning in these parts by the late evening update if trends play out. Of course, advisory vs. warning is all just wording to me. Though I suppose the designation is important in communicating to the general public. Just read the updated forecast for Dupage (which is mostly north of I-88)and it differs somewhat from the AFD: 1-3" with .10 of ice. No anticipated trowal accumulations tomorrow despite the AFD stating concens for a couple of additional inches.  Little bit of disconnect between the actual zone forecast and the AFD...but I'm sure it's hectic.

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-SN started about 30 minutes ago, we're probably down to moderate SN with about a 1/2 to 3/4 SM visibility. Really good dendrites to start the event off. 

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2 minutes ago, hawkeye_wx said:

Large flakes ripping in Iowa City.  Radar shows pretty heavy snow over the area.

I’d upload the 2 pics I took but amwx is like nah. So theyll have to wait until later. 

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4 hours ago, snowcaine said:

I'd be shocked if we got less than 6". I'd go more for 7-11" come Wednesday morning

It'll be impressive enough, given our crappy snow climo, to get two 10" storms within 2 weeks of one another.  To think both could be from storms that cut to our NW is really mind boggling.

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