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Saint Patrick's Day Snow Event


stormtracker

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it's usually pretty smart to take an ensemble range of start/stop time -- find a 15 hour duration then divide the mean qpf by 15 hours because you know it's probably going to have a linear precip rate over those 15 hours 

 

:lmao:   Now that's pretty funny...

 

So...rough math suggests DCA gets 0.5" snow an hour for 15 hours per SREF.  So what accumulates will be the hours

without March high sun angle.

 

I do believe chris87 was being a bit sarcastic, not serious, with the "linear precip rate" comment!  Well, I think so anyhow! ^_^

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The NAM did nudge the .25 and .50 contours a little farther north compared to the 06Z, with the .01 just south of the Mason/Dixon line. 

 

However, I wouldn't look at the 4km high-res NAM (Conest).  As one would expect, an even tighter gradient on the northern fringe, as in 0.0 for northern Mo. County.  I will say it again, outside of the .30 to .40" of QPF that was wasted away to rain/sleet, and the fact that the event will be more of a late evening/overnight/early AM one instead of pre-dawn to early afternoon one, the concerns here are remarkably similar to that of 03/03..

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The NAM did nudge the .25 and .50 contours a little farther north compared to the 06Z, with the .01 just south of the Mason/Dixon line. 

 

However, I wouldn't look at the 4km high-res NAM (Conest).  As one would expect, an even tighter gradient on the northern fringe, as in 0.0 for northern Mo. County.  I will say it again, outside of the .30 to .40" of QPF that was wasted away to rain/sleet, and the fact that the event will be more of a late evening/overnight/early AM one instead of pre-dawn to early afternoon one, the concerns here are remarkably similar to that of 03/03..

 

Pretty much.  Who would have thought that in March, we'd be nervous about too much of a cold air push suppressing precip too far south!  For two events, no less.

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:lmao:   Now that's pretty funny...

 

 

I do believe chris87 was being a bit sarcastic, not serious, with the "linear precip rate" comment!  Well, I think so anyhow! ^_^

Yeah, i see that but the precip rate will probably be fairly linear, the important point being that accumulation

may be very limited during daylight hours due to light intensity.

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Just for reference, didn't we all complain about the NAM on the 3/3 storm... then cheer when the 0z run that night finally get a clue?  I know NAM was off a bit on snow accums, but NAM did come north at the last min on  that storm... just the dry cold air ate alot of our snow

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this airmass is definitely less impressive if still impressive. the NAM does a good job modeling the sharpness of an edge which is perhaps legit but location is another story.

 

It just seems too tight. You go from .50 to nothing in 30 miles. High res has a gradient so tight that you go from 1" to zero in 60 miles. I would expect the lighter amounts away from where the jackpot is to be spread further north with broader contours. I may not know what the heck I'm talking about but it doesn't seem probable with this setup. 

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The SREF and 12z NAM support each other although the NAM shows the south trend and therefore the SREF is overdoing north of DCA.

Tell me how I busted Tuesday. 

 

so your forecast is 0.5 qpf at DCA with no accumulation -- i can't speak for everyone, but i'll give you that and hold you to it!  :lmao:

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It just seems too tight. You go from .50 to nothing in 30 miles. High res has a gradient so tight that you go from 1" to zero in 60 miles. I would expect the lighter amounts away from where the jackpot is to be spread further north with broader contours. I may not know what the heck I'm talking about but it doesn't seem probable with this setup. 

Bob, the system last week that hit NC was super juicy at the NC/VA line, but it did not make it very far north at all.. it hit a dry HP that just killed northward movement and ate any precip headed this way. I think we have the same scenario. on 3/3 the HP was pressing as the precip arrived.. maybe I am wrong, but I think the HP is outpacing the moisture this time and thus we are missing whatever bit we got last time... If I lived in SC I would watch out (LOL) - just thinking of how far south that system went from NY to below us last time!

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Bob, the system last week that hit NC was super juicy at the NC/VA line, but it did not make it very far north at all.. it hit a dry HP that just killed northward movement and ate any precip headed this way. I think we have the same scenario. on 3/3 the HP was pressing as the precip arrived.. maybe I am wrong, but I think the HP is outpacing the moisture this time and thus we are missing whatever bit we got last time... If I lived in SC I would watch out (LOL) - just thinking of how far south that system went from NY to below us last time!

 

 

That's a bad comparison. Last week was a cutoff. If you weren't near the ull then you got nothing (as expected). This system is completely different with a plume of waa far out in front of the slp/850 low. 

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GFS very consistent QPF-wise, at least through 18Z Monday. 06Z run was a tad under .75" for DCA through 18Z Mon, the 12Z GFS is a tad higher, closer to 0.80".  The bulk of which is through 12Z.  GFS is very similar with the amounts around the M-D line.  

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so your forecast is 0.5 qpf at DCA with no accumulation -- i can't speak for everyone, but i'll give you that and hold you to it!  :lmao:

My impression is for accumulation around DCA but not after about 9 am or 10 am unless the rates are

moderate.  Light daytime snow isn't going to accumulate around DCA in mid-March on south-facing sidewalks and on most street surfaces; grass and shady areas, maybe so.  Late night, no problem.

 

Anyhow, the 12Z NAM gives me 3" to 5" in N MD with 8:1 ratios.

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NAM 0" here and GFS 5-7". 36hrs out. Good old models. 

 

sure for your discrete point -- what do you expect out of models? this is an extremely tight gradient -- i'm sorry you're on the edge of it -- the current 12z guidance that has come out are all in an expected range of uncertainty for the current lead time

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sure for your discrete point -- what do you expect out of models? this is an extremely tight gradient -- i'm sorry you're on the edge of it -- the current 12z guidance that has come out are all in an expected range of uncertainty for the current lead time

 

What do I expect? I expect some consistency. Model went from being near NY with snow to now barely scrapping PA in like 24hrs. Also 36hrs away from an event would think maybe we have a clue what might happen. 

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