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January 6-8 Snow/Ice/Rain


Hoosier

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1 minute ago, Baum said:

Checking in on the 00Z NAM......oh for the good ole days.....

Actually looks pretty icy toward the Ohio Valley.  But it might be too early to trust its thermal profiles.  Overall synoptic setup is what it has been... I think the lack of a surface high to the north and southerly low level flow should keep ice amounts in check (generally less than 1/4"). That being said, if there's any southerly flow setup that could pull off more significant icing, it would be this one given the antecedent cold and fairly weak surface low, which keeps the low level wind speeds in check even though they are southerly.

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7 hours ago, RCNYILWX said:

Hopefully the GEM is onto something this far north but not holding my breath lol. One thing to hang onto for still getting a minor (moderate by 2017-18 standards) event up here is that the models have been terrible even at this range all winter. With that being said, there's good validity to the points made about why this could get squashed south. I'll give it through tomorrow night's 00z runs to show hints of a recovery.

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The 00z GEM actually looks better than the 12z run for Chicago.  Haha

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I'm trying to come up with something to post on our EMA Facebook page concerning Sunday night/Monday, but after perusing the models, I'm at a loss. Latest NAM soundings show surface layer barely reaching freezing.  All snow (2-3") or a snow zr mix? I guess it's too early to tell for this area. At least it's not going to be anything major other than the roads will be trashed.

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The GEM continues to be hellbent on producing snow across northern IL into Indiana on Sunday. The 12z NAM also stepped toward more precipitation farther north Sunday evening and night after some initial light WAA snow earlier Sunday, though thermal profiles are a bit messier. Not gonna be a big event but a few inches of snow would qualify as decent up here lol.

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7 minutes ago, RCNYILWX said:

The GEM continues to be hellbent on producing snow across northern IL into Indiana on Sunday. The 12z NAM also stepped toward more precipitation farther north Sunday evening and night after some initial light WAA snow earlier Sunday, though thermal profiles are a bit messier. Not gonna be a big event but a few inches of snow would qualify as decent up here lol.

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It feels like a losing battle anyway considering the pattern shift lurking out in the extended.  :lol:

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From IWX earlier today...

Split stream wave complex starts the period on Sun with inverted 
trough pushing through the cwa Sun night. Guidance similar to prior 
days guidance with good 12Z consensus seen especially with initial 
yet subdued warm nose. Brief mix of rain probable with precip onset 
Sun evening but overwhelmed by diabatic offsets and mainly a snow 
event still expected and several inches likely. Sfc temp profile 
tricky however cold ground and nighttime timing likely to induce 
an icing problem esp with sewd extent where warm nose persists 
longest. Too early just yet for headlines. 

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Looking a little better for tomorrow's event as we transition to a new pattern. Still going to ride my 1-2 ending as frizzle. Probably closer to an inch, but I don't need a blizzard to be happy all the time in the winter weather department. RC with another tremendous write up in today's LOT AFD. Maybe models will continue trending wetter today.

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21 minutes ago, michsnowfreak said:

Now it is looking good to add a few inches to the snowpack here. GEM remained firm and other models catching on. Heavier amountrs to my south perhaps. Luckily no icing here, it could be a mess where ice sets up.

The good ol' warministas of GRR are still honing in on freezing drizzle, despite models showing us getting several inches of snow here. (Looks like some lake enhancement?) I sure wish the northern and southern waves could phase together. Well, even if we do get some freezing rain, it could be a positive in preserving the snowpack more during the late week thaw.

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2 hours ago, StormChaser4Life said:

12z nam. Both the 3km and 12km are looking a little alarming for more significant icing

Here's the ice maps from the NAMs and GEM.  The GFS has very little icing. Various offices seem to be skeptical of the magnitude of the NAM warmth aloft. Though there could be freezing drizzle potential even in some areas where the entire column is below freezing if enough moisture gets stripped aloft.

 

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Looks like the new Euro, and the rest of the 12Z data is keying in on around a slushy 1" or so from the wintry mix around the Quad Cities on Sunday. Most data now brings the precip up to at least the I-80 corridor, with of course the NAM and RGEM being the wetter solutions. Either way, should be a nice, novel event for us. 

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It's been a little while since I can remember that models have been in this kind of disagreement with a matter of hours until the event kicks off. 

Maybe an inch of snow north of I-80, though it looks like the Canadian & NAM want to lay down a bit of freezing rain too...

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This continues to be a tricky forecast, and worrisome because we (my office and surrounding) are basically discounting the NAM solution farther north, which would be much worse from an impacts perspective. I believe we're doing so for sound meteorological reasoning, but ultimately observational data tonight and tomorrow will tell the story if the NAM doesn't back off.

 

Coming out of the entrenched Arctic air, the air mass tomorrow, while warming and moistening, should still be rather dry up where the warm nose is, centered roughly around 850 mb. The magnitude of warning aloft on the NAM has also been much more aggressive than other models, including other meso models, the RGEM and 2.5 km HRDPS nest. Our assessment has been that the magnitude of warming aloft is likely somewhat overdone on NAMs.

 

Also, with the antecedent dry air mass (12z PWAT 0.06 and 0.07 at ILX and DVN respectively) and lack of a strong synoptic low, the thinking is that the moisture return will also be lacking at the level of the warm nose. Evaporational cooling is favored to quickly cool the warm nose, to the extent it exists with northward extent, to a snow supportive profile, with sleet possible as wetbulbing occurs. I just find it unlikely that the warm layer will simultaneously saturate above freezing like the NAM is showing. Nonetheless, if observational data tonight and tomorrow supports it, then hats off for scoring the coup and ring up the WWA lol.

 

 

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17 minutes ago, RCNYILWX said:

This continues to be a tricky forecast, and worrisome because we (my office and surrounding) are basically discounting the NAM solution farther north, which would be much worse from an impacts perspective. I believe we're doing so for sound meteorological reasoning, but ultimately observational data tonight and tomorrow will tell the story if the NAM doesn't back off.

Coming out of the entrenched Arctic air, the air mass tomorrow, while warming and moistening, should still be rather dry up where the warm nose is, centered roughly around 850 mb. The magnitude of warning aloft on the NAM has also been much more aggressive than other models, including other meso models, the RGEM and 2.5 km HRDPS nest. Our assessment has been that the magnitude of warming aloft is likely somewhat overdone on NAMs.

Also, with the antecedent dry air mass (12z PWAT 0.06 and 0.07 at ILX and DVN respectively) and lack of a strong synoptic low, the thinking is that the moisture return will also be lacking at the level of the warm nose. Evaporational cooling is favored to quickly cool the warm nose, to the extent it exists with northward extent, to a snow supportive profile. I just find it unlikely that the warm layer will simultaneosly saturate above freezing like the NAM is showing. Nonetheless, if observational data tonight and tomorrow supports it, then hats off for scoring the coup and ring up the WWA lol.

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Excellent point. I wasn't thinking of evaporative cooling. That would def favor more snow/sleet vs frzn rain. The 850 winds are crossing the isotherms nearly orthogonal in sw MO where 850 temps are above freezing so we will get maximum transportation of that aloft. The million dollar question is how far north it gets and how deep it is. A lot of nowcasting will be happening 

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