12/08/2009-12/09/2009 Winter Storm

[Jeremy Den Hartog]

The NWS just issued a winter storm watch for parts of Minnesota and Wisconsin and a blizzard watch for far southern Minnesota and northern Iowa...here we go

 

[Mike Hollingshead]

DVN mentioned everything but the 1000 years of peace after the storm.

What impresses me about this system today is the snow forecast maps between the NAM and GFS.

http://wxcaster4.com/nam/CONUS1_ETA212_SFC_ACCUMSNOWFALL-KUCHERA_84HR.gif

http://204.2.104.196/gfs/CONUS_GFS0P5_SFC_ACCUM-SNOW_84HR.gif

That is some scary agreement for them this far out yet. I mean track, but even amounts. Usually one or the other is more nuts. 12 inch line is pretty much Sioux City to St. Joe on them both. That doesn't happen every day/system.

http://www.wxcaster2.com/CENTRAL_MESO-ETA_SFC_SLPTMPDPTWINDSBLI_84HR.gif

Wonderful, -5F Wednesday midnight. Too bad the system is moving so fast and seems so "east sided" with winds. Might go deep deep but seems all that wind ends up on the east side off the ground.

 

[Chris Heater]

Wow...everyone else is going to get nailed. I've seen this happen before though. All models will be in agreement then just before the storm it will shift the storm south or something. Happened to us several times last year...so I still have hope! Doesn't look too good for me though still.

I did notice the 18Z NAM shifted the low pressure slightly south. A trend?

 

[Michael O'Keeffe]

Yes it all depends on this arctic airmass that is moving south right now through Nebraska and Kansas. If the temperatures are colder than forecast which appears possible than the low will likely be pushed a bit further south which would shift the heaviest snow further south obviously.

http://www.hpc.ncep.noaa.gov/lowtracks/lowtrack_ensembles.gif
The HPC agrees with this and if this verifies than areas closer to I70 will receive the brunt of the heavy snow.

As of right now I am not sure what to think but based on the RUC the front is moving through quicker than expected so we may see this south trend continue.

 

[Adam Lucio]

Wow I suck, I cant believe I didn't notice this discussion till now. Ive been watching this system like a hawk for days.

This mornings 6Z NAM and GFS were nearly identical with a 988 low just about overhead here in Chicago.

http://www.twisterdata.com/index.ph...nglemap&sounding=n&output=image&archive=false

http://www.twisterdata.com/index.ph...nglemap&sounding=n&output=image&archive=false

I don't think Ive ever seen such agreement this far out between those two. Impressive.

If the system deepens that fast there is going to be some serious WAA and that would likely toss in a rainy mix to the bunch so the track is more than critical. 18Z runs show a similar track as well and it looks like the NAM wants to bring more of that WAA into this area.

LOT hasn't bitten the bullet yet with a WSW as a result it looks like. Still though, this looks like its going to be a very windy, powerful system. Why couldn't we get one of these in May.

EDIT: just checked LOT again...WSW up for areas west of the city...still betting on the rain/snow mix here greatly reducing totals.

 

[Chris Heater]

Yes it all depends on this arctic airmass that is moving south right now through Nebraska and Kansas. If the temperatures are colder than forecast which appears possible than the low will likely be pushed a bit further south which would shift the heaviest snow further south obviously.

http://www.hpc.ncep.noaa.gov/lowtracks/lowtrack_ensembles.gif
The HPC agrees with this and if this verifies than areas closer to I70 will receive the brunt of the heavy snow.

As of right now I am not sure what to think but based on the RUC the front is moving through quicker than expected so we may see this south trend continue.

I-70? That doesn't seem so right. Maybe closer to I-74. You also have to worry about all the warm air getting pushed into the storm. I'm still hoping for a southern track. Give us some snowdays! I won't be convinced on a certain track till Monday afternoon

 

[Robert Dewey]

Too bad the system is moving so fast and seems so "east sided" with winds. Might go deep deep but seems all that wind ends up on the east side off the ground.

I noticed this too. Winds within the mixing layer (at least over lower MI) are within the 40-50knt range. That's really not that impressive for this deep of a system; I've definitely seen stronger (upwards of 70-80knts in the mixing layer near APX) back during one of those "Witch of November" storms a few years back (leading to 60-70mph gusts). This far out, the models could be under-forecasting things a tad, as I fully expect some places will experience 60-65mph gusts.

In regards to the track, I'm not really seeing the southward trend. If anything, models seem to keep increasing strength and wanting to shoot it further NW (18z GFS + 12z GEM support this, NAM doesn't seem consistent with it's weaker / stronger / weaker solutions).

As Chris Heater mentions, I have also seen models make very drastic changes to output within the last 30hrs preceding an expected event, so it wouldn't surprise me to see a track error of 100 miles N/S, particularly at >60hr.

 

[Joel Wright]

In regards to the track, I'm not really seeing the southward trend. If anything, models seem to keep increasing strength and wanting to shoot it further NW (18z GFS + 12z GEM support this, NAM doesn't seem consistent with it's weaker / stronger / weaker solutions).

As Chris Heater mentions, I have also seen models make very drastic changes to output within the last 30hrs preceding an expected event, so it wouldn't surprise me to see a track error of 100 miles N/S, particularly at >60hr.

The 12z Euro shifted south 50-100 miles. Last night it had the surface low southwest of Chicago early Wednesday. The 12z had it further south near Danville IL. Not a big change though. The GEM was about the same as last night and so was the GFS.

Northeast KS/southeast NE/northwest MO/southwest IA to about Madison WI, into northwest lower MI look like they could get the most snow. Areas to the south and east will have to deal with mixing issues. Northwest of that band there should be a rather large area of respectable snow accumulations aided by high ratios. Even as far north as the Twin Cities they could get a good dumping.

Places like Chicago and Detroit have an interesting challenge since it will be a race between the best precip and the WAA out ahead of the storm. For Chicago it looks like snow will begin in the afternoon Tuesday. Then accumulate a few inches before mixing with gobs of sleet and possibly plain rain in the evening. If the WAA can hold off long enough decent snow amounts could be seen, but my gut feeling is the warm air will rush in pretty quickly. The far north and west side will probably having mixing issues too, but to a lesser extent. Throw in the relatively warm waters of Lake Michigan and it really makes for a challenging forecast for the city.

 

[Chris Carter]

Has anyone noticed that today's snow bands have set up further south than what the GFS/GEM have been pointing at the past few days, only the most recent 18Z run did the GFS change the heaviest snows over where it developed? Not jumping to conclusions on this next storm, but couldn't the recent snow cover over southeast NE northeast KS, push those snowfall totals a little more south?

http://wxcaster4.com/nam/CONUS1_ETA2...CHERA_84HR.gif

http://204.2.104.196/gfs/CONUS_GFS0P...-SNOW_84HR.gif

 

[Chris Heater]

When does the storm come ashore on the west coast? Sometimes the models change drastically when they sample the storm when it comes ashore...i've seen it happen before.

As Joel was saying...there is a south trend. I just hope it continues to shift southward to get me out of the freaking rainy mess.

Chris Carter raises a good point...what does everyone think about that?

EDIT: I noticed the 12Z GFS pushes the low to my southeast, putting me closer to getting all snow. Just a little further south and I'll be good to go

 

[Chris Carter]

When does the storm come ashore on the west coast?

It should already be taking shape in Northern California right now.

 

[Chris Heater]

It should already be taking shape in Northern California right now.

Cool. I'm interested to see how it changes the models, if at all. I noticed the 12Z GFS pushed the low to my southeast a bit putting me much closer to the freezing line. Just a little further south and i'll be in for all snow

 

[Chris Carter]

Wow. I have never seen a storm have a 20 : 1 ratio for snow. Just so i am understanding that right. Its 20" of snow to 1" of liquid, right? Seems like in the early stages of the storm, snow rates over much of NE and KS will be 10 : 1 or 15 : 1, but as the atmosphere cools and allows the storm to deepen, snow rates will drop to as low as 20 : 1. So i guess the big question for the plains is how long will the snow period last?

 

[Chris Heater]

Wow. I have never seen a storm have a 20 : 1 ratio for snow. Just so i am understanding that right. Its 20" of snow to 1" of liquid, right? Seems like in the early stages of the storm, snow rates over much of NE and KS will be 10 : 1 or 15 : 1, but as the atmosphere cools and allows the storm to deepen, snow rates will drop to as low as 20 : 1. So i guess the big question for the plains is how long will the snow period last?

Yeah...thats correct. The drier the snow the higher the ratios. 20:1 is pretty high though! You don't want the atmosphere too dry though otherwise you run into "virga" aka "evaporation". Radar will show snow on you, but your seeing nothing on the ground. That really sucks when that happens/ When do the next batch of models come out? 18Z ones? What time is that in PM?

 

[Chris Carter]

18Z GFS is already out.