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Feb 3rd - 5th Potential strong stm threat


Brian D
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This system is a far cry from what was modeled a few days ago and still may try to bomb out Thursday night. Gone are the 40-50-degree snow-eating dew points. 

The complication with this one is due to the number of shortwaves that make up the trough, and of course all of the blocking. Models are now cutting off the southern wave shown on WV below and are showing increasing separation between it and the trough that affects us. That energy off the coast of Alaska is what ends up triggering cyclogenesis that passes through the area Thursday. The 18Z Euro and EPS made baby steps towards a more southerly solution. With screaming southerly flow ahead of the long wave trough, warm air will at least sneak in for a bit, perhaps after most of the WAA precip has shut off for many areas. Note that guidance is also trending wetter with the WAA and possible comma head precip associated with the new low. Snow can definitely occur closer to the low track than usual due to the amount of lift and dynamic cooling that occur. LOT's concern for a flash freeze Thursday night is legit should all of this pan out.

1313842349_ScreenShot2021-02-01at10_05_36PM.png.49247748e96147c3ac1c020e376e0589.png

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This is more for W IL and IA, but one thing to keep in mind with this system are the pristine conditions that will exist for blowing and drifting snow associated with the passage of the arctic front and departing low. GFSs gust 45-50mph, NAM/Euro 40-45. Additionally, rain showers and melting in the warm sector will ensure that the existing snowpack will have a layer of ice on top of it, exacerbating any blowing that does occur. 

sfcgust_mph.us_mw.png

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For those up tracking, we will be ramping up our winter weather messaging for Thursday in collab with WPC. Still concerned for freezing rain within the CWA earlier and now with trends of a lot of the guidance and strong ensemble support with a decided shift southward we're liking idea of accumulating snow, strong winds and blowing snow across northern IL Thursday night. Flash freeze scenario still in play as well since it does look like all areas should briefly rise above freezing.

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2 minutes ago, hawkeye_wx said:

12z NAM has jumped nw big time.  Models will need more time to figure this out.

I'm not a great model output guy. But I'm not seeing that. In fact, snowshield  here minus the actual low pressure seems to have improved versus 00Z, Again, surging arctic fronts with a a wave riding along it can over perform nicely beyond model output....sometimes. This looks like it has this make up from a weenies blind eye. 3K even better. Not sure it matters at this long distance.

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4 minutes ago, hawkeye_wx said:

12z NAM has jumped nw big time.  Models will need more time to figure this out.

It is totally different with the upper energy on every run. Most of the short waves involved still aren’t in its domain so it will probably jump around for at least another 24 hours. 
trend-nam-2021020212-f054.500hv.conus.gif.8f7d49fdfec7696ca514b916dd3384fa.gif

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4 minutes ago, Baum said:

I'm not a great model output guy. But I'm not seeing that. In fact, snowshield  here minus the actual low pressure seems to have improved versus 00Z, Again, surging arctic fronts with a a wave riding along it can over perform nicely beyond model output....sometimes. This looks like it has this make up from a weenies blind eye. 3K even better. Not sure it matters at this long distance.

Agree there are now 2 precip maxes 1 which did jump nw and 1 over chicago metro which the 6z had .2 the 12z now has .5 to .7 (i am not sure that all of the 12z precip would be snow)

qpf_acc.us_mw.png

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3 minutes ago, Baum said:

I'm not a great model output guy. But I'm not seeing that. In fact, snowshield  here minus the actual low pressure seems to have improved versus 00Z, Again, surging arctic fronts with a a wave riding along it can over perform nicely beyond model output....sometimes. This looks like it has this make up from a weenies blind eye. 3K even better. Not sure it matters at this long distance.

It's NW some, definitely not "big time." And yes, temps are cooler and shows much more snow across the area than 0z. Though the 3K totals around hour 60 make more sense than the 12k imo. 

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1 minute ago, McHenrySnow said:

Might the NW burbs win this round? @Cary67 and I would appreciate it.

Early on you are correct, but any time after 84 hours or so any place down wind of the Great Lakes will wind up being the winner.  Looks like the lakes will finally produce snow in many of the normal LES regions.

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