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February 16th-17th Obs & Nowcasting


nj2va

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I'm not sure why people are so reluctant to go with 20:1 ratios or even higher. I think this easily ends up in the 6-10 inch range. .4 or .5 qpf with those kinds of ratios, perhaps even higher. Didn't we have a storm last year with 30:1 ratios? We could even have higher ratios than 20:1. This isn't the wettest storm, but it's not like you are talking about a couple of tenths of precip. We could be around a half inch of liquid, give or take.

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I honestly believe 15:1 is a reasonable # ratio wise. I'm not as verses as many in this department but the basic things in place for high ratio snowfall are there. It's not going to be windy either so the bigger dendrites won't get beat up on the way down. Fluff factor should be high with this one. 

 

just looking through the model soundings and such (you can argue, justly [at least IAD and BWI -- DCA was stupid wrong], about the ratios measured on 1/30/10 but at least from a sounding aspect, that day is a good analog for tonight when you plot up each days temp/rh profiles -- was too lazy to go find RUC or other model output from that day to look at omega structure on 1/30/10) -- 15:1 is very reasonable -- wouldn't be surprised to see a bit higher for the N. MD folks -- nobody should be down on this, even if you only see 0.25 liquid it will be one of the most efficient quarter inches we can see around these parts.

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https://www.facebook.com/HeadfulOfSnow?ref=aymt_homepage_panel

 

Final call for DC proper: 5-8"

Start time: Around 5pm

End time: Around 6am

Heaviest: Between 10pm and 4am

Temperature: Mid to Upper Teens

 

I would say 6 to up to 10, I am not sold that we are limited to 0.5 and the 20-1 ratios that I discussed yesterday are still most definitely on the table.

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just looking through the model soundings and such (you can argue, justly [at least IAD and BWI -- DCA was stupid wrong], about the ratios measured on 1/30/10 but at least from a sounding aspect, that day is a good analog for tonight when you plot up each days temp/rh profiles -- was too lazy to go find RUC or other model output from that day to look at omega structure on 1/30/10) -- 15:1 is very reasonable -- wouldn't be surprised to see a bit higher for the N. MD folks -- nobody should be down on this, even if you only see 0.25 liquid it will be one of the most efficient quarter inches we can see around these parts.

Both the NAM and GFS have a "warm layer" of about -5 or -7C from 800-700mb around 6z when we should be getting our best rates.  That's making me a bit cautious on going 15:1.  Not sure where the best omega is falling.  If it's a little higher, that would be good.  The profiles around 0z tonight look ideal for dendrite growth, so we should maximize that lighter precip this evening. 

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just looking through the model soundings and such (you can argue, justly [at least IAD and BWI -- DCA was stupid wrong], about the ratios measured on 1/30/10 but at least from a sounding aspect, that day is a good analog for tonight when you plot up each days temp/rh profiles -- was too lazy to go find RUC or other model output from that day to look at omega structure on 1/30/10) -- 15:1 is very reasonable -- wouldn't be surprised to see a bit higher for the N. MD folks -- nobody should be down on this, even if you only see 0.25 liquid it will be one of the most efficient quarter inches we can see around these parts.

 

Thanks Chris. I use simpleton analysis and it's usually pretty close. Once I see the column, 700mb rh vv panels, and the type of storm it's kind of easy to "get a feel" for it. We have good temps in the dgz, fairly moisture laden system, deep arctic airmass, and decent lift/fg forcing in the area. It's a really good setup for efficient snowfall. Definitely reminds me of 1/30/10 and st paddy's last year. 

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Both the NAM and GFS have a "warm layer" of about -5 or -7C from 800-700mb around 6z when we should be getting our best rates.  That's making me a bit cautious on going 15:1.  Not sure where the best omega is falling.  If it's a little higher, that would be good.  The profiles around 0z tonight look ideal for dendrite growth, so we should maximize that lighter precip this evening. 

 

Overall 15-1 is a fair guess on my part without getting into the #'s too much. I expect higher ratios for some of early and possibly tail end stuff. In the middle could easily be 10-12:1. I highly doubt any period will feature less than 10:1 around here. 

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