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2/19-20 Winter Storm Observations

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Just now, yoda said:

If we can keep the heavy rates, I think we can hold off the flip until 18z

I think that's a tall order.  That WAA push at 700 will be strong...I'd be happy if we can hold the snow until 11a.

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Down in Seaford DE doing my emergency medicine thing till 2400 hrs then drive back home to Hockessin, DE. Paying attention to the PBP in the Mid Atlantic forum on AmerWx. 

 

In the 19707 ... 30F. 47% RH. Winds Calm 

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3 minutes ago, WxMan1 said:

Yes, but not very good dendrites before the flip to sleet according to the Ferrier or rime corrected SLR per the NAM3. I'm hoping we're closer to the 2-3" bar I've set for our BY, which is on the 10-1 NAM3 map, vs. the 1-ish inch per the NAM3 Ferrier.  The Ferrier has consistently been 1 maybe 2 inches for the I-95 corridor. Now it's barely 1" (2nd and 3rd from the bottom blue colors). Hoping it's more of a QPF issue, but as you said, with 0.27" by 15Z, that tells me we've got a) riming problems (less than a 10-1 ratio) and/or b) a quicker transition to a snow-sleet mix (way less than 10-1).

nam3km_asnow_ferrier_neus_18.png

nam3km_asnow_neus_18b.png

Yeah, by 15Z, DCA is at -1C at 700, which is less than ideal for snow. Should want something around -2/-3C or we're already mixing.

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2 minutes ago, WxMan1 said:

Yes, but not very good dendrites before the flip to sleet according to the Ferrier or rime corrected SLR per the NAM3. I'm hoping we're closer to the 2-3" bar I've set for our BY, which is on the 10-1 NAM3 map, vs. the 1-ish inch per the NAM3 Ferrier.  The Ferrier has consistently been 1 maybe 2 inches for the I-95 corridor. Now it's barely 1" (2nd and 3rd from the bottom blue colors). Hoping it's more of a QPF issue, but as you said, with 0.27" by 15Z, that tells me we've got a) riming problems (less than a 10-1 ratio) and/or b) a quicker transition to a snow-sleet mix (way less than 10-1).

nam3km_asnow_ferrier_neus_18.png

nam3km_asnow_neus_18b.png

I’d have to think that there is something amiss with the Ferrier scheme in this scenario.  That is implying a sub 5:1 ratio which is really hard to come by.

That said, if you thought the 00z HRRR was bad, 01z upped the bar there.

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9 minutes ago, WVclimo said:

29/9 with high clouds covering the full moon.  LWX mentioning 2" per hour rates here tomorrow morning.  :o

i’m so psyched!  :guitar::bike:

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1 minute ago, jewell2188 said:

Right on que, CWG lowers amounts again....dry air will delay the onset apparently.

They went from 3-7” to 3-6” for NW of 95.  From 2-5” to 2-4” for 95.  Seems reasonable given where we’ve been the last 48 hours.  

And knowing the CWG, they’ll keep updating their map until the storm is over to make sure they can give themselves an A for their forecast.

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Just now, PhineasC said:

Do they still use their boom and bust scenarios that allow them to cover every outcome and never bust?

Yeah, it’s a pretty brutal way to go about it.  They should really just make a forecast. 

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In my experience here in the Shenandoah Valley, the HRRR does poorly until the moisture has cleared the Alleghenies.  It's almost as if it can't decide how much will make it over, but since it runs every hour it starts to show better results once it samples how much precip actually did make it over. *

*Official Weenie Handbook Rule #3241

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Just now, PhineasC said:

Do they still use their boom and bust scenarios that allow them to cover every outcome and never bust?

Yep, they give me a 50% chance of 2-4”, 25% chance of less than 2”, and 25% chance of up to 7”.  Way to go out on a limb and actually make a forecast.  

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Just now, DCTeacherman said:

Yeah, it’s a pretty brutal way to go about it.  They should really just make a forecast. 

It is the new wave in forecasting. There is a (insert %) this will happen. I actually like it, statistics.

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5 minutes ago, DCTeacherman said:

Yeah, it’s a pretty brutal way to go about it.  They should really just make a forecast. 

It just gives them the ability to never be “wrong”

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4 minutes ago, DCTeacherman said:

Yeah, it’s a pretty brutal way to go about it.  They should really just make a forecast. 

They do. It's called probabilistic forecasting. And if they fall outside their core ranges, they'll grade themselves lower.

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Just now, Interstate said:

29/12

I'm thinking 2-5" with some ZR for you and my old stomping grounds. Going to look pretty nasty around the area. Can only imagine Harford Rd Jarretsville Pike will be a complete mess

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