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March 5th Snow Threat


WxUSAF

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My guess is that this ends up as a 6-10 inch solid snowfall. I think the upside is beginning to diminsh a bit because the trajectory of the precip is less southwest to northeast and more west to east, which is limiting gulf moisture. Just my thoughts.

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    There are no different versions of the NAM.    There are different ways that a user can convert QPF to inches of snow, and that's what you're seeing.   In an event with multiple ptypes and close calls on warm layers aloft,  I'm not stunned to see varying answers.

Isn't there the regular Nam which is 12k and a higher resolution one which is 4K?.

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   I assumed that the poster knew the difference between the NAM and NAM nest, but that was probably a bad assumption on my part. 

Figured he was trying to figure out why different "accumulation" maps from the parent NAM looked so different.

 

Isn't there the regular Nam which is 12k and a higher resolution one which is 4K?.

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I take it this is the downsloping?

I see that quite frequently on the high res models.  It normally doesn't verify..I think it's a mix of downsloping and a fake rain shadow.  I normally don't see less snow than LKU in these situations...

 

For example- have you ever seen a situation where Madison county gets 2" and EZF gets 8" like that GFS shows?

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I see that quite frequently on the high res models.  It normally doesn't verify..I think it's a mix of downsloping and a fake rain shadow.  I normally don't see less snow than LKU in these situations...

 

For example- have you ever seen a situation where Madison county gets 2" and EZF gets 8" like that GFS shows?

 

and you def don't get half the snow that EZF does in a situation like this as you'll both start cooler and cool faster.  the hi res often shows and never/extremely rarely verifies it.

 

eta: you ninja'd me w/ your edit/add-on comment.

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Ok, so what about the GGEM, the RGEM, the NavGEM, the Ukie?

 

I don't feel comfortable with yesterdays 18z NAM still on the table.

 

Or with the smoldering hot ground that this will encounter.

 

I think the models that show a later flip should be considered, which at this point would lead me to not be so gung-ho about a flip for DC until around 12z, which would cause me not to forecast the snow totals that the GFS is showing.  Right now I'd stick with 2-5/3-6 for DC metro and maybe if guidance trends towards the GFS tonight bump that to 4-8.

 

ETA: flip to snow, not flip to frozen

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Ok, so what about the GGEM, the RGEM, the NavGEM, the Ukie?

I don't feel comfortable with yesterdays 18z NAM still on the table.

Or with the smoldering hot ground that this will encounter.

Yesterdays 18z Nam is last night is look long off the table, and there is no such thing warm ground in nonvolcanic areas. Warm air, ****ty rates and ****ty sun angle account for every white rain instance.

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Right or wrong, gfs has been steadfast with the earliest flip. Seeing it bump even earlier today is interesting but also in the face of other guidance (for now). This is a good test for the model to see what kind of bias it may have in a particular setup.

I personally think the new gfs is a good bit better than the old one inside of 3-4 days but like others have said, the early flip is suspect.

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