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

[Joel Wright]

I still only foresee rain except the very northern edge of the precip. For lower MI there may be a brief mix at first before it becomes all rain, and stays that way. Maybe portions of northern lower MI may see snow, but no way in southern MI. Way too much warm air wrapping up in this storm.

 

[Robert Dewey]

I still only foresee rain except the very northern edge of the precip. For lower MI there may be a brief mix at first before it becomes all rain, and stays that way. Maybe portions of northern lower MI may see snow, but no way in southern MI. Way too much warm air wrapping up in this storm.

I generally agree that it will be rain, but you just can't deny that if precipitation rates become heavy, the rapid melting of heavy snowfall (aloft) might cool the layer to isothermal 0C. We aren't too far off from 0C anyway (-3C), but the layer is rather thick... I thought this would happen last event too, but it didn't (precipitation was mostly light). FWIW... The latest NCEP WRF suggests precipitation rates of up to 0.75 to 1.00 per three hours for two timesteps (mostly elevated convective precipitation). That's alot more QPF than the other models were indicating, but I believe it is trying to depict convection.

I have been reviewing a few case studies where such events have occured. Look here, particularly at page 8: http://www.spc.noaa.gov/publications/goss/kaingoss.pdf

It's a very slim chance and I certainly wouldn't be forecasting snow, but I won't completely rule it out.

Anyway, for other areas... I pulled up some soundings for Central and Eastern WI (ISW, GRB)... They are primarily AOB 0C all the way up. Looks like a SN/IP sounding to me versus ice, but then again QPF isn't really all that great up there. MKE has some good QPF amounts on the NAM, and it's profile is similar to areas east of there (GRR, DTX) with that pesky 2C-3C warm layer just above 850MB... SFC temps are a tough call, but it will be daytime and the sun would have an adverse affect on ice accumulations.

The 12Z run of the NAM is actually slightly warmer than it's 06Z run in the low levels. Interestingly, the 12Z NAM has slightly lowered QPF amounts, which may have a relationship to the temperature profile (even if it didn't drop the profile to 0C, it would still have SOME affect). I'm not sure if models can or even try to resolve dynamic cooling...

 

[Jayson Prentice]

Looks like the northern plains has the winter weather advisory and then a freezing rain advisory for northern Iowa. It isn't looking to great if we get the two tenths of an inch of ice. That along would be bad enough, but we already have ice on the trees and power lines from the last system.

At least it looks like the ice is going to hold off until after midnight which should limit the amount of traffic on the roads. If it starts off earlier then traveling will be huge issue with a lot people coming back from more get to gethers this afternoon.

 

[Robert Dewey]

Well... The 18Z NAM just came in, and....

QPF has been significantly reduced due to convection south of the Great Lakes. That greately reduces the chances of any dynamic cooling, even though the soundings are slightly cooler. At this point, it's looking like light rain, or possibly just drizzle with an isolated rumble of thunder or two...

Too bad the 06Z NAM didn't hang on... It was an AOB 0C sounding, which would have likely been snow... :cry:

This is getting pathetic, I'm sick of nasty rainy days... I need snow. :lol:

EDIT: Just some information I received from Dr. Greg Mann...

Dynamic cooling is a result of adiabatic expansion of the parcel set that is experiencing the strong ascent rates. So, if the model is resolving the ascent appropriately, then the cooling effect should be accounted for directly in the thermodynamic equation calculation (the adiabatic term). The catch is whether the model is adequately resolving the region of ascent.

Cooling due to melting is typically handled by sophisticated microphysics schemes…but I am not sure if the Ferrier scheme used by the Eta or the WRF-NMM threats runs account for this source of negative heat. The impacts are important when the precipitation rates are high enough to offset warm advective processes and saturated condition aloft. The influence of cooling due to melting is maximized in an unsaturated environment – typically sub-cloud base where greater precip rates will keep precip snow by locally cooling the column below freezing through melting and evaporation. The change of phase from solid to liquid does not require as much heat as the change from solid to vapor; therefore, when evaporation can occur it is more efficient at removing heat from the surrounding air parcels.

Greg

 

[Robert Dewey]

Pretty interesting... SFC temps have tanked about 8F in the past 4 hours on an ESE wind. We were sitting at 41.5F at 1PM, now down to 34.5F as of 5PM. My thermometer is pretty accurate, within a tenth of a degree... It will be interesting to see how much further it drops, as it will be pretty hard to recover tomorrow morning with the precipitation, clouds, and strong NE flow from southern Canada.

 

[Joel Wright]

Pretty interesting... SFC temps have tanked about 8F in the past 4 hours on an ESE wind. We were sitting at 41.5F at 1PM, now down to 34.5F as of 5PM. My thermometer is pretty accurate, within a tenth of a degree... It will be interesting to see how much further it drops, as it will be pretty hard to recover tomorrow morning with the precipitation, clouds, and strong NE flow from southern Canada.

That may be just enough cold air, combined with the dry air to allow a brief mix before it liquifies totally.

This may be one of those situations when you get sleet and big wet/fat flakes for the first few minutes, just enough to grab your attention before the rain takes over.

After how the winter was a few weeks ago, who'd ever thought that a storm system like this would have almost entirely all rain on it's cold side!?

 

[Robert Dewey]

After how the winter was a few weeks ago, who'd ever thought that a storm system like this would have almost entirely all rain on it's cold side!?

Definitely not me... I can't really complain TOO much though, December was above average snowfall for us. I just wish we could have a monster snow storm - the kind that breaks records.

Anyway, we're now down another degree to 33.5F... Latest RUC shows SFC temps holding steady through about 09Z. It's interesting though, when we saturate the column, a good portion of the column is 0C or less... But as soon as things let up/VV's drop off, we warm right up to >0C.

As a matter of fact, the RUC has us at 39-40F by 03Z... Not sure that will verify too well given the current temperatures / SFC flow. The 18Z GFS actually verifies SFC temps quite well at 33.5F, but then raises them to 35-36F by 06Z. I'll probably still be awake at that time, so I can verify that as well.

 

[Robert Dewey]

Well, the RUC didn't quite verify with that warm of temps... About an hour or two after the rain started, a few METAR stations reported snow... That may have been the tail end of evaporative cooling and some dynamic cooling. That's where I get confused, I'm just not sure how high precipitation rates have to be to dynamically cool the profile and/or overcome WAA. The whole dynamic cooling thing is new to me (only been researching it the past couple of weeks)...

Hopefully we can get some thunderstorms up here... But we're currently sitting at 38F :shock:

 

[Dan Cook]

All we're getting is rain. Oh rdewey why has your snow skills failed me? :cry:

 

[Robert Dewey]

All we're getting is rain. Oh rdewey why has your snow skills failed me? :cry:

Haha... It's my new techniques that are failing... :lol:

It used to be low level dry air wedges that always caught me (when I first started trying to forecast snow, and didn't have cross sections). The dynamic cooling is brand new to me... From now on, if there is a >500m thick layer with T's AOA 2C, then I'll call it rain (or sleet, depending on where at in the sounding) regardless of suggested precipitation rates. Live and learn is how I do it :lol:

 

[nickgrillo]

All we're getting is rain. Oh rdewey why has your snow skills failed me? :cry:

Haha... It's my new techniques that are failing... :lol:

It used to be low level dry air wedges that always caught me (when I first started trying to forecast snow, and didn't have cross sections). The dynamic cooling is brand new to me... From now on, if there is a >500m thick layer with T's AOA 2C, then I'll call it rain (or sleet, depending on where at in the sounding) regardless of suggested precipitation rates. Live and learn is how I do it :lol:

Nope, it's just global warming... It has come to take away all winter weather from the people of MI

 

[Robert Dewey]

All we're getting is rain. Oh rdewey why has your snow skills failed me? :cry:

Haha... It's my new techniques that are failing... :lol:

It used to be low level dry air wedges that always caught me (when I first started trying to forecast snow, and didn't have cross sections). The dynamic cooling is brand new to me... From now on, if there is a >500m thick layer with T's AOA 2C, then I'll call it rain (or sleet, depending on where at in the sounding) regardless of suggested precipitation rates. Live and learn is how I do it :lol:

Nope, it's just global warming... It has come to take away all winter weather from the people of MI

LOL!

It's days like this that piss me off... Too warm for any significant winter stuff, but too cold for any strong thunderstorm action. I absolutely _HATE_ days that are "in between" (cloudy, drizzle, cold, etc.).