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January 2-3 Winter Storm Potential


Ralph Wiggum

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6z gfs bounced back from 00z dip. Supports 3-5 in area with good ratios. More to the N+E of Trenton.

Nice changes but still nowhere near the nam. Hopefully by 12z we can get a compromise with the models in between the 3.-5 gfs and 10+ nam.

I would guess that there is a good chance that the nam backs off. It went crazy, but with ratios it might be on to something.

A general 3-5 seems to be supported, possibly 4-8 with ratios. The 4-6 forecast from yesterday is looking more like a winning medium range forecast.

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Current Wxsim with latest 6z run has what appears to be a healthy snow event for NW Chesco (potentially our largest since October 2011). Water equivalent is up to 0.55" here is the breakdown.
A mix of precip during the PM transitioning to heavy snow during the evening a tapering off during toward dawn on Friday. Total snow accumulation between 5" to 7"

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Since ratios will play a factor in this upcoming storm, perhaps someone could explain something to me:

Cold air is generally drier air, right? So, at what point does the colder air become too dry, and limit the amount of moisture in the atmosphere? Or is this just simply a case where there is ample moisture to override the dry air?

Is there a scenario in this current set up where the air will be too dry, thus limiting snowfall amounts?

Thanks, just trying to understand things that are probably over my hear! lol

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Easton, crystal growth can be complicating at times...since different layers of the atmosphere factor in.   Just because the surface is very cold, doesn't take into effect what's going on above 5,000 feet.     (which could vary wildly from storm to storm)

 

A Met here could probably elaborate more.

Can be *very* complicating at times, but if you're someone who just wants to go off of the pre-canned 'snow-maps' then rather than add to the totals, I'd consider actually taking them closer to verbatim for 10:1 if you're in a fringe area.

 

Most everyone has concluded it won't be 10:1 ratios, but take into account that the 'lighter' snowfall while it will accumulate slightly, is easily absorbed and almost counts for nothing.

 

That being said, I'm buying into the NAM @ H5 - I'd just be very cautious of the fringe areas in SC-PA and Maryland. Large bust potential one way or the other, and a bulk of the precip is 'lighter' and may/may not exist.

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Easton, crystal growth can be complicating at times...since different layers of the atmosphere factor in.   Just because the surface is very cold, doesn't take into effect what's going on above 5,000 feet.     (which could vary wildly from storm to storm)

 

A Met here could probably elaborate more.

Thanks, yea the whole upper level physics thing is really tough for me the grasp. 

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Since ratios will play a factor in this upcoming storm, perhaps someone could explain something to me:

Cold air is generally drier air, right? So, at what point does the colder air become too dry, and limit the amount of moisture in the atmosphere? Or is this just simply a case where there is ample moisture to override the dry air?

Is there a scenario in this current set up where the air will be too dry, thus limiting snowfall amounts?

Thanks, just trying to understand things that are probably over my hear! lol

 

Just wanted to add that if the NAM were to play out verbatim from the 'top down' so-to-speak, I wouldn't expect there to be too many issues getting the atmosphere wet enough for snow. You may need a quick burst of heavier precip to turn the faucet on, but I'm not overly concerned about it. Again, save for the lighter precip that may/may not actually exist - IE .05 one hour, .05 the next and someone saying: 

 

"That makes .1, which at 15:1 ratios is 1.5" extra!" -- I'd be cautious about that.

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Ratios are extremely complex.  Areas that get good lift in the snow growth zone (-12 to -18C) can see 20:1 ratios, assuming there isn't a warmer layer (-2 to -5C) below that where the snowflakes will rime (which reduces ratios).  Even if its cold, if you have wind (which reduces ratios by breaking up the flakes) and poor lift in the snow growth zone, you can still get lame ratios.

 

For example, under the core of the CCB during Boxing Day, ratios were 16:1 or more.  But, northwest of there, ratios dropped off precipitously, due to much poorer lift and wind breaking up the flakes.

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Just wanted to add that if the NAM were to play out verbatim from the 'top down' so-to-speak, I wouldn't expect there to be too many issues getting the atmosphere wet enough for snow. You may need a quick burst of heavier precip to turn the faucet on, but I'm not overly concerned about it. Again, save for the lighter precip that may/may not actually exist - IE .05 one hour, .05 the next and someone saying: 

 

"That makes .1, which at 15:1 ratios is 1.5" extra!" -- I'd be cautious about that.

 

 

Ratios are extremely complex.  Areas that get good lift in the snow growth zone (-12 to -18C) can see 20:1 ratios, assuming there isn't a warmer layer (-2 to -5C) below that where the snowflakes will rime (which reduces ratios).  Even if its cold, if you have wind (which reduces ratios by breaking up the flakes) and poor lift in the snow growth zone, you can still get lame ratios.

 

For example, under the core of the CCB during Boxing Day, ratios were 16:1 or more.  But, northwest of there, ratios dropped off precipitously, due to much poorer lift and wind breaking up the flakes.

Thanks guys. Wow, very complex indeed. Another facet of forecasting that has many components that are not easy to predict!

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Ratios are extremely complex.  Areas that get good lift in the snow growth zone (-12 to -18C) can see 20:1 ratios, assuming there isn't a warmer layer (-2 to -5C) below that where the snowflakes will rime (which reduces ratios).  Even if its cold, if you have wind (which reduces ratios by breaking up the flakes) and poor lift in the snow growth zone, you can still get lame ratios.

 

For example, under the core of the CCB during Boxing Day, ratios were 16:1 or more.  But, northwest of there, ratios dropped off precipitously, due to much poorer lift and wind breaking up the flakes.

Ray, if all else was equal (including qpf rates and temperatures), except for the wind, and with say 20-30 mph winds reducing the ratio vs. light winds, would visibility be affected or would it be the same? (Not talking about snow blowing across the ground). Thanks!

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My first call was 4"-8" here, but might bump to 6"-8" after this suite.

 

12z NAM showed around 10" here.

 

I don't think I'd disagree, particularly if the upper levels translate like they should. I think the thing that's going to throw most people attempting to map this (as if there is only one thing to throw you) is that this is not an 'east to west' snow gradient, nor is it a true 'north/south' - after the 12z kickers, I'd start comparing progged reflection to reality and looking at the shorter range models for localized verification to compare to the NAM.

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I don't think I'd disagree, particularly if the upper levels translate like they should. I think the thing that's going to throw most people attempting to map this (as if there is only one thing to throw you) is that this is not an 'east to west' snow gradient, nor is it a true 'north/south' - after the 12z kickers, I'd start comparing progged reflection to reality and looking at the shorter range models for localized verification to compare to the NAM.

I personally thought it was going to show a SECS by hour 18 at H5. It looked even better then 6z. Might be true, but also might be feedback.

 

H7 was nearly perfect with the GOM connection with more energy at H5. I personally would not use the EURO/GFS after 12z, and would rather use the SR and NAM/RGEM models. Interesting storm for sure. Thought all along, it would have surprises.

 

Thoughts on ratios? 12:1 or 15:1?

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Ray, if all else was equal (including qpf rates and temperatures), except for the wind, and with say 20-30 mph winds reducing the ratio vs. light winds, would visibility be affected or would it be the same? (Not talking about snow blowing across the ground). Thanks!

 

I think the greater wind would result in lower visibility overall.  You would have the same *amount* of matter in the air, but distributed in finer bits. 

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