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February 19-20th Threat - STORM MODE


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3 minutes ago, mappy said:

^^ talking about Richmond.

Folks, if you are going to be doing model play by play, please please please be specific on what area you are talking about when you do so.

 

Just now, Eskimo Joe said:

This.  Especially if you're on mobile, it's hard to understand where a poster is talking about.

Apologies.

 

3 minutes ago, BristowWx said:

in RIC?  so you are frozen until that point?  interesting I wouldn't have thought that.  location dependent there too for sure. 

This was per the 12zNAM, subject to change.

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1 minute ago, jaydreb said:

Close call for OPM.  2-4” is usually not shutdown worthy but the timing is dicey.  

it's not close at all

Snow starts before dawn

the storm lasts all day

LWX has ridiculous snow numbers

they're going to close unless the storm changes completely according to guidance today

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the key is how long we can hold off on the sleet.  given the less than ideal setup, i agree with others that are thinking 1-2/2-4 for dc and tbh i wouldn't be suprised if we ping for a few hours after if the cad is strong enough.  the 540 line is all the way up into canada before the precip even gets here.  i know that's not the end all, but i don't recall any setups where that's a good thing.

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12Z NAM3 continues to be underwhelming with the QPF prior to the changeover (~17Z). Generally .15-.20" liquid equivalent. I trust these Ferrier-based SLRs implicitly when riming snow and eventual ptype issues arise, but I still think the continued 1-2" general area-wide average for the cities and I95 corridor through 17Z is lacking with the QPF.  I hope so, anyway. 

nam3km_asnow_ferrier_neus_30.png

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1 minute ago, osfan24 said:

It has lower totals than almost every other model, which is odd for the NAM, but given the CAD setup, it's hard not to lean on it. And if it can't be used for this type of storm, what can it be used for?

A euro/3k NAM blend is usually a good forecast in a CAD situation like this. That’s where I’d lean.

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22 minutes ago, WxUSAF said:

Outside of yesterday’s 12z run, the 3k NAM has been pretty consistent with the front end snow. 2-4”/3-5” depending on latitude and elevation. 

Where’s your bar set on this one? I’m sure the inquiring minds of the Columbia / Elkridge snow geek crew would appreciate your thoughts. :)

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I know it isn't worth using as a forecasting tool, but as an example of how we at the DC latitude could potentially maximize this storm is the 12z extended HRRR.  The sleet line approaches at 15z after 2-3" like the NAM, but then the precipitation ramps up in intensity and effectively "beats back" the mix line so that we end up with 6-7" by 19z.

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13 minutes ago, Ji said:

whats frustrating is the 850s are good through 2pm. Is there any chance of a slight error at 700mb? Is that what the canadien high res is seeing?

 

nam3km_T850_neus_32.png

The issue with the NAM's are where they set up the best banding.  They push the best fronto banding north of our area.  Even north of my area.  After an initial short thump around 7am it focuses the best banding up in PA.  You can see the cooling from the heavy band in the morning at 700 mp and then once that lifts north with only lighter rates the WAA takes over and without heavy rates to mix the column we torch at the mid levels.  That is how this works.  If we stay under heavy banding like the GFS/FV3/GEM/RGEM/HRDRPS/ICON suggest the flip will be delayed a couple hours plus combined with more qpf and we get those 4-8" numbers NWS is pimping.  But if the NAM's are right that the best lift and banding ends up to our north in PA, this will be very disappointing to most in here IMO.  I am NOT saying I think the NAM is right here...but the NAM progression of this would be a quick 1-3" followed by ice across most of our area.  That would probably be considered a fail by most in here considering what the official NWS forecast is right now!

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8 minutes ago, WxMan1 said:

It still very much feels like a 2-4" thump for most before a layer of sleet and a coating of ice for us along the urban corridor. Hoping for closer to 4" with the snow IMBY, but I have a feeling it'll be closer to 2-3" before the flip. 

You literally took the words right out of my mouth. I'd say in Baltimore it snows approximately from 7 AM- 12 PM. That's 5 hours. I'm not buying the NWS 4-6 inches. That would mean averaging inch per hour rates and during the day I just don't see that happening. I think 2-3 inches is a much safer call and if I'm being honest, I could even see areas near the cities busting low on that, NAM supports that. Typical colder areas could get in the 4-6 inch zone. I expect the sleet to last from 12 PM until about 2 PM at the latest, then freezing rain/rain rest of the day. Honestly when all is done, I think it's going to look a lot like the outcome of last week's storm. 

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