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February 8th-11th Overrunning Event


Snowstorms

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3 minutes ago, StormChaser4Life said:

Anyone noticing some thermal profile issues on nam and hrrr? They both are showing rain/mixed precip developing south of the snow band tmrw morning. Not sure if I buy that unless models are under estimating surface temps but with some snow pack I think it should stay under 32

Can't rule out some mix, but I think the higher probability scenario is a transition toward a wetter snow on the southern edge tomorrow.

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1 hour ago, snowstormcanuck said:

Last few frames of the HRRR are showing the LES potential. Maybe our saving grace as it's becoming patently clear the best synoptic snow for wave one will be well south of us.

I'm not overly optimistic about wave one on Friday. It's waves 2 and 3 (Saturday and especially Sunday) that I'm hoping will deliver.

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1 hour ago, Snowstorms said:

The secondary and third wave punch the Nam, CMC and EURO advertise is key. Good moisture and baroclinic energy to work with to allow for some deformation bands to form and for the storm to strengthen as it moves north. I'd watch it closely, it might hopefully deliver. 

 

As I said to canuck, this is what I'm hoping for too. Regardless, looks to be an interesting weekend weatherwise!

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Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
813 PM CST Thu Feb 8 2018

.UPDATE...
813 PM CST

No big changes planned to the overall forecast for the storm,
however, will likely move up the end time of the warning Friday as
the brunt of the snow will likely have fallen by mid-late morning
Friday in the warning.

Regional radar composite shows a long band of mostly light to
moderate snow extending from northern IL WNW into SD. A short wave
trough over the Dakotas early this evening shows up fairly well
on GOES-16 differential water vapor RGB. This shortwave is
forecast to shear quickly into the western Great Lakes Friday
morning, shearing out/weakening as it translates eastward.

Primarily light-moderate snow will continue this evening as
thermally direct circulation in the right entrance region of
120kt+ 250mb jet supports continued low-mid level frontogenesis
over about the northern 2/3rds of the CWA. As the Dakota`s
shortwave translates eastward, guidance suggests a strengthening
of the lower level f-gen and a resultant uptick in the UVVs over
northern IL.

Forecast vertical cross sections through the frontal band are a
bit worrisome for our double digit snowfall forecast amounts. The
last several runs of the RAP and 18z run of the NAM show virtually
no negative saturated EPV, which indicates that the atmosphere is
progged to be relatively stable and not primed for narrow intense
banded snow. In addition, guidance suggests that areas of stronger
f-gen will be somewhat transient in nature. While these factors
are concerning, short range high-res guidance continues to
advertise very beefy QPF values overnight into at least the first
part of Friday morning, so not planning any changes to our
forecast snowfall totals at this point.

There has been a pretty consistent signal across the spectrum of
model guidance suggesting that the meaningful snowfall will shift
mainly south of the winter storm warning area between 12-18z
Friday as shearing out shortwave passes east and associated height
falls nudge the upper jet and associated entrance region a bit
farther south. Given the expectation that snowfall across much of
the warning area will waning prior to 18z, think that for
messaging purposes an earlier end time to the warning is
justifiable. Latest guidance suggests that additional snowfall
accumulations beyond late morning would be somewhat trivial where
the warning is in effect.

Working on some fine tuning to grids and will have an updated WSW
and grids/derived products out shortly.

- Izzi
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1 minute ago, beavis1729 said:

I actually think it is surprising. There were several models showing at least 0.8” liquid, which means 12” at 15:1 ratios. 

I'm not seeing a reason for panic yet. Maybe the amounts over a foot are a little optimistic for tonight/tomorrow, but I think the double digit totals are still plausible.

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1 minute ago, Hoosier said:

I'm not seeing a reason for panic yet. Maybe the amounts over a foot are a little optimistic for tonight/tomorrow, but I think the double digit totals are still plausible.

On a different note, I am 100% expecting double digit totals in north Linn county, hwy-20 under the fgen band. 35 dbz, likely big flakes and thus high ratios. Interested to see what totals we can pull out of Waterloo, independence and coggon.

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9 minutes ago, Hoosier said:

Nice (narrow) band headed toward Tim in Kankakee.

It’s actually snowed pretty decently here tonight. Considering no guidance had this, I’ll take it as a gift, haha. Over soon though. And the 0z NAM’s take all of Saturday’s action to the north of here too, so this is probably it for me, lol. Good luck the rest of the way man. Hope it overachieves. :D

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8 minutes ago, mimillman said:

It’s not surprising. It’s a different meteorologist, different views, different biases. I think Izzi is right to lower totals personally.

Particularly with that met. Shaved timing of warning expiration from 9pm Friday until Noon. So in less than 5 hrs time that decision is made at the onset of an event? Just odd.

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I tried getting the HRRR up, but cannot understand how it really works.  There were like 9 pictures, which is the ensemble maybe?  Like I said, have no clue.  And trying to tell a disabked vet that were  gonna get 2-4 or 7-8 is funny because he knows I love weather, but he thinks I should KNOW how to read the maps.  This winter every single time they said and inch or two we ended up with 6-8, so he thinks it will be like that.  Just at a loss.

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2 minutes ago, Chicago WX said:

It’s actually snowed pretty decently here tonight. Considering no guidance had this, I’ll take it as a gift, haha. Over soon though. And the 0z NAM’s take all of Saturday’s action to the north of here too, so this is probably it for me, lol. Good luck the rest of the way man. Hope it overachieves. :D

Somebody should've told the NAM about your precip.

namconus_apcpn_ncus_3.thumb.png.7f2188dd65de811274d136f880433e9d.png

 

namconus_apcpn_ncus_1.thumb.png.1ff029a9982d14428262d0d9e9fdd246.png

 

May be a long haul but I think even you could grind out several inches by the time this is all over

 

 

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The H5 differences past 54 hrs between the 0z and 18z Nam is just terrible. Upper air instability would be favorable for partial phasing and good development on the north side of the system which I think will be more properly handled through tomorrow's runs. The spinning energy across Hudson Bay, which is actually a part of the PV, plays a key role in the development of the secondary wave. I could be wrong but let's see! 

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Ok, I need to clarify. I am talking about double digit totals for both waves for Chicago metro, not just wave 1.

Agree that double digits with just wave 1 is not likely in all areas. 

However, if anyone in the 6-county metro area ends up with under 10” by the end of the weekend, it will be a disappointment. 

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1 minute ago, Snowstorms said:

The H5 differences past 54 hrs between the 0z and 18z Nam is just terrible. Upper air instability would be favorable for partial phasing and good development on the north side of the system which I think will be more properly handled through tomorrow's runs. The spinning energy across Hudson Bay, which is actually a part of the PV, plays a key role in the development of the secondary wave. I could be wrong but let's see! 

Agree, the energy moving in from the west is slower stronger and less flat this run.

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