01/02/2006 - WINTER STORM / ICE STORM: MIDWEST

[Robert Dewey]

With this next system coming through, someone in the Midwest and / or Great Lakes will see a large helping of ice and / or snowfall. Latest 00Z NAM continues with the southward trend that it has been showing for the past several runs; digging the system further south and increasing moisture.

Model QPF's along the baroclinic zone are in the range of 1.00 to 1.50 inches depending on how close you zoom in... There is quite a decent convective potential as well with TT's getting up there and good conditional instability.

As of now, NAM has a strong baroclinic zone at 850MB stretching from northern IL across lower MI where 850MB T's climb upwards of 5-8C... At the same time down at the SFC, a strong northeasterly fetch exists with a strong high centered near Hudsons Bay. This keeps SFC temps at or below freezing for some areas, creating a significant ice potential. The SFC features are all indicitave of a classic ice storm for northern IL / southern WI eastwards towards lower MI.

It will be interesting to see if the convective potential plays out... I always like a nice light show with heavy freezing rain

Also, too early to tell... But we could be looking at a mixed precipitation event if the NAM pans out... More in the way of sleet / snow / freezing rain versus pure freezing rain, due to dynamic cooling...

 

[Robert Dewey]

Opps... Had to change the date. At least it falls on a somewhat infamous day :lol:

 

[Scott Olson]

Quite an impressive display from the NAM tonight, a trend I hope continues.
My bet is currently on MN, High QPF output which needs no NE fetch to bring on ZR as many other areas may start as rain. Good upper support should make for .20-.30 of ZR and probably a couple inches of snow a bit farther north. I've seen trees and powerlines snap with just .10" so it should be an interesting event.

-Scott.

 

[Robert Dewey]

Things are usually a bit different around these parts... We NEED a NE flow to get ZR, or else the strong WAA would pump in above freezing temps. This event looks just like every other ZR event as far as MI goes... It's not the beginning of the events that are usually our problem, it's how it wraps up - usually ZR first, rain towards the end as WAA overtakes the NE flow.

GFS also trending towards the NAM, but I will likely side with the NAM since it handles low level thermal profiles rather well...

I just went over some NAM forecast soundings for the event (PTK), and it has a nice subfreezing SFC temp with a very warm wedge aloft. A couple things concern me though as far as precipitation type. Just prior to the onset of precipitation, Td's are around -5C through the column, with wet bulb temps 0C all the way up. I guess the strong WAA would certainly overcome the evaporational and dynamic cooling process, but one never knows. I just hope we don't end up sleet. I want either SN or ZR! :lol:

This event certainly has the potential to produce widespread and significant icing... In fact, the icing may be a bigger hazard than the associated severe weather threat.

 

[Scott Olson]

Things are usually a bit different around these parts... We NEED a NE flow to get ZR, or else the strong WAA would pump in above freezing temps.

Absolutely, I was just talking about here where we got our freezing temps and cP not that a CAA regime isn't necessary for sustaining tempatures supportive of ZR/SN/ETC. Just that the airmass was already in place as in a lot of situations for us we also start off above freezing and then have the backside cold air intrusion, thus the reference to NW flow.

Im sure you remember a couple weeks ago we had that warm wedge from 850 coming into SD while temps dropped below freezing and the ensuing ice storm pratically shut down half the state. So despite the SREF/HPC indications that ZR will be the primary mode for MN it looks like you will have a better shot and MN will probably start off as ZR and switch to snow quite quickly.

 

[Robert Dewey]

I remember that event - I completely missed the ice potential

I was just reading through some discussions and NCEP basically says to ignore the 00Z NAM... But with the other models trending further south, I wouldn't completely discount it.

If the older NAM / GFS solutions verify, I'd likely be looking at rain with the best ZR axis to the north. If the southward trend continues, I could very well envision a significant overrunning snow threat as the 0C 850MB isotherm drops southward...

Only time will tell... If the 12Z models come in and are similar to the 00Z runs, or continue the southward trend - I will be alot more convinced that something big will happen in my area. At this point it's not a question of whether it will happen, it's a question of where...

Alot of "ifs"...

 

[Joel Wright]

There doesn't seem to be enough cold air at the surface for an ice storm. It looks like mainly a plain ol' rain even for the south half of lower MI to me. There may be a thin ribbon of ice, near the rain/snow line up in northern lower MI back into central WI.

This is just my opinion, but that's the way it looks to me. It does look like a decent amount of rain will fall though from southern WI into lower MI. Kind of seems like kind of a waste of QPF this time of year if you're like me and like winter weather this time of year...

 

[Robert Dewey]

Well, the 12Z NAM is back with a further northward track and a slightly weaker system (and thus slightly warmer). The 12Z GEM has actually trended further south with this 12Z run compared to the 00Z run. The 06Z GFS was actually colder than the 00Z GFS, but not neccesarily deeper...

It's really going to depend on just how strong the high to the north is, and where it sets up... But the current models don't look good. Instead, I'll probably be sitting through a cloudy day with nothing but scattered showers as the dry slot slams overhead - while all the action is to the south and north...

If something like the 00Z NAM would have panned out, we would have had ALOT of ice here in southern lower MI / southern WI! Soundings had a sub freezing layer through the entire event (points north of Detroit to around Milwaukee)... Too bad that didn't remain the case (well, hey... There's still 48 hours left until the precipitation actually starts)...

EDIT: Well, the 09Z SREF came in and it shows quite a bit of uncertainty out at the 48-60 hour period. At 500MB, there is a pretty good height spread - approximately 40-50 meters. 850MB temps also show a 2.5 to 3.0C spread over my region (the mean temp is 4C)... While at the SFC we are at roughly 3C with a 2-5C spread. Lots can happen with spreads like that...

Latest 12Z GFS is yet again colder than both the 00Z and 06Z runs, but it's also weaker - up to 60 meters weaker at 500MB...

 

[Robert Dewey]

18Z models continue to show a slightly weaker / colder solution (well, at least the NAM)...

In fact, latest soundings show all snow for central lower MI northward (more like MBS northward) ... With storm total QPF of 1.14 inches. The strength of the WAA and isentropic upglide is beyond impressive to say the least, and is most likely the cause of the high QPF (which looks reasonable)... We are looking at 12 to nearly 18 hours of this setup. In addition, there is very good conditional instability along and just north of the baroclinic zone... I could envision some pretty significant snowfall accumulations along and to the north of that boundary with a high potential for thundersnow - wherever things decide to setup. Strong dynamic cooling should keep things from going above 0C in that area, so it seems as though it would remain primarily snow...

Further south, from DTX / GRR northward... Things are a bit trickier. The WAA brings in warm temperatures aloft (though quite a bit colder than what was shown several runs ago)... SFC temps are the big question. Obviously if they are AOB 32F, we will see ZR... Otherwise it's just plain rain. Given that the models have been cooling down with each run (well, sliding the baroclinic zone further south)... I would give a 55/45 chance of happening / not happening - i.e. pretty close.

There are also a couple things I don't like about this system... Each run shows the system being a bit weaker (though in strong baroclinic cases, you can still have a significant overrunning potential). The other thing that I don't like is is the very strong dry punch from the south that could cut everything off (regardless of what the models say)...

 

[Joel Wright]

Models all still point to an unusual storm for this time of year. Almost entirely all rain, except in northern lower MI back into central WI where there will be a thin band of snow/sleet. Maybe a very thin line of ZR just south of that, but probably pretty spotty.

Rdewey it looks like you'll be right on the border between the heaviest rain amounts, and much lesser amounts where the dry slot wedges in. It looks like you'll largely stay in the steadier rains though.

Kind of weird that in early January, with a 995mb low having all this rain on the "cold" side of the storm.. :?

 

[Robert Dewey]

Models all still point to an unusual storm for this time of year. Almost entirely all rain, except in northern lower MI back into central WI where there will be a thin band of snow/sleet. Maybe a very thin line of ZR just south of that, but probably pretty spotty.

Rdewey it looks like you'll be right on the border between the heaviest rain amounts, and much lesser amounts where the dry slot wedges in. It looks like you'll largely stay in the steadier rains though.

Kind of weird that in early January, with a 995mb low having all this rain on the "cold" side of the storm.. :?

It depends on what maps you're lookin at... If you are using the 850MB chart to determine precipitation potential, alot of areas appear as rain... There are more complicated processes involved as well, like dynamic and evaporational cooling that will play a LARGE role in this event. I have a few case studies where an event that was forecast to be primarily rain (with a +5C 850MB temp) quickly turned to heavy snow / convective snows dropping over 2 feet over a narrow band...

If you look at soundings for central and northern lower MI, they are roughly at 0C the entire column, and heavy precipication rates (in the form of snow initially) would keep it snow... The overall trend is for less of a warm up via WAA - which would support a more frozen / freezing precipitation type. Further south, soundings indicate a 1C-3C wedge of warm air, with 0C temps only found at the SFC. I would like to see a slightly deeper 0C layer before jumping on the ZR band wagon though...

One thing that has and continues to concern me is the Tw and Td temps. Right up until the precipitation starts, Td's are well below 0C - with Tw hovering around -1C. Evaporational cooling down to the Tw temp would leave us at 0C the entire way up - and cold air is rather hard to displace. Think of all the times you wait for that warm front to blast north, but it doesn't... The models are poor at handling this stuff, so I don't trust them 100%.

The 00Z stuff should be rolling in in the next hour and a half, my bet is that the 00Z NAM is even colder with this run...

 

[Robert Dewey]

Well, trends are toward a stronger system - again LOL...

The 12Z NAM has a very similar profile to the 18Z run, while the 00Z GFS is yet again colder. Areas north of DTX have a skinny warm layer on the sounding, nearly isothermal at 1C (yeah, that got me into trouble with the last event!). The warmest the profile gets is 2C, but that's after moisture strips away and precipitation stops (perhaps the GFS is picking up on some dynamic cooling?).

Not much else to say that hasn't already been said. I did notice that the Canadian GEM outputs nearly 55MM of QPF in 24 hours (roughly 2 inches) - not sure if that model has any bias, but it does run at a pretty high resolution. I just can't get over the amount of instability around the baroclinic zone where freezing precipitation may be falling. There is even some CAPE present in areas that are forecasted to be primarily < 0C.

All of this typing, and I still don't know who is gonna get what and how much...

 

[Tim Gonyo]

Here's my forecast for Saukville, WI:

Sunday Night: Occasional rain. Low around 35. East wind between 10 and 20 mph. Chance of precipitation is 80%.

Monday: Occasional rain possibly mixed with snow and sleet, becoming all rain after noon. High around 37. Northeast wind between 15 and 20 mph. Chance of precipitation is 80%

I'm wondering if they will bomb this forecast and we will get ZR or PL. Notice how my surface winds go East, then Northeast... Usually this time of year if I get Northeast winds I'm frozen... if I get Southeast, then yes, WAA all the way to the surface and I get rain.

I kind of hope the forecast is rain... for the sake of the general public... if we get a surprise ZR, no one will know about it until they are out and about and its too late.

 

[Robert Dewey]

Notice how my surface winds go East, then Northeast... Usually this time of year if I get Northeast winds I'm frozen... if I get Southeast, then yes, WAA all the way to the surface and I get rain.

That's what I'm saying... Our typical ice storm here in MI is usually underforecast until 12HRS before the event (typically a ZR Advisory goes into effect, followed by an update to an Ice Storm warning). In the 20 years that I have been here, that's how it always goes down. If there is a strong high to the north with a ENE wind (and model progs SFC temps of 35F or less (they do horrible around the lakes)), then it's usually ice.

Then again, the latest GFS and now 06Z NAM shows us within 2C of the freezing line all the way up on the sounding. If that very strong forcing and CSI is realized, we could actually be looking at a surprise snowstorm... This is what I thought was going to happen with the Christmas Day rainstorm, but heavy precipitation rates never materialized (light rain / drizzle all day).

Very interesting and complex to say the least.

EDIT... Okay, just rechecked the latest NAM... It actually has us SUBFREEZING the entire layer now. Most likely a result of dynamic cooling. We shall see...

 

[Tim Gonyo]

What are your thoughts today rdewey?