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February 7th Storm Threat Discussion/Obs


mappy
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1 minute ago, LeesburgWx said:

Based on this thread, We are 18 hours out and still do not if it is going to snow. God help us

It’s going to snow. The problem is how much. And that’s tricky because of very marginal temps. If this was cold smoke a general 4-8” with local 10” call would be pretty safe. But the problem here is with very borderline barely cold enough to accumulate temps rates are important.  Normally the difference between getting .4 qpf and .7 would be 4” or 7” which would both ball in a 4-8” range. But there is a huge difference here where .7 over 6 hours could be a 6” thump that overcomes temps while .4 over that same 6 hours doesn’t cool the boundary layer as much so it’s 34 instead of 33 and with lighter rates it’s 1-2” of slush on non paved surfaces!  Now the forecast busted. 

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Seems like everything is still on the table at this point. I would take Millville's 4-7 with spots up to 9 and run with it right now given some of the trends. Agree with PSU that, with marginal temps, we looked great with 1-2+ inch per hour rates, but now that the models are lightening up on qpf, it's easy to go from 4-8 to almost nothing due to rates not allowing the snow to accumulate.

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The NAMs sometimes set the narrative too much since they come out first. But the fact is 18z yesterday was the high water mark wry amplitude across guidance. Since then taken in totality there has been a trend weaker with the system. The NAMs are the only guidance I’ve seen 12z yet that bucked that trend. Everything I just said is simply observation of guidance. No prediction. I’ve expected a continued trend towards a more amplified system but the truth is that halted 18z and since gone the wrong way. 

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So we're riding the NAM and Euro it seems. And the HRDPS I suppose. Really need the euro at 12z to hold firm with its call; more ticks lower on QPF would have us knocking on slush territory. I forget who said it, but one of the mets mentioned the 12k NAM and 3k NAM difference a day or so ago was worth paying attention to, as the 12k was much less amped and could signify something to watch since the 3k likes to overamp. Looking like a great call.

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5 minutes ago, 87storms said:

gfs looks like mostly a hold from 6z.  maybe even a slightly better qpf output for dc/bmore.  at this point, probably just need to hand things off to the next euro run/nam and whatever happens, happens.

You and I shouldnt sweat too much. Whatever happens *should* treat moco fairly well in comparison region wide. I never had big hopes for totals. Standard 2-4/3-6 thoughts have been stuck in my head all week. I'm in it for the scene more than ground truth. Snow on superbowl sunday is special. 2015 superbowl sunday is the polar opposite if anyone want to think it cant get worse

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Guys remember, I haven't looked at EVERYTHING and this was an on the fly forecast with a perusing through a few things. I may adjust numbers for a final call. For now, the thermal profile north and west of the fall line are pretty climo oriented, so just a matter of precip in liquid equivalent and potential banding during the best mid-level frontogen. 

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10 minutes ago, Bob Chill said:

You and I shouldnt sweat too much. Whatever happens *should* treat moco fairly well in comparison region wide. I never had big hopes for totals. Standard 2-4/3-6 thoughts have been stuck in my head all week. I'm in it for the scene more than ground truth. Snow on superbowl sunday is special. 2015 superbowl sunday is the polar opposite if anyone want to think it cant get worse

agreed, and just posted something similar in banter lol.  i'm good with it just snowing and, of course, there's always the possible nw shift closer to gametime.

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8 minutes ago, losetoa6 said:

I was referring to the 9z Srefs ARWs that come out at 8-830am. They trended wetter from 3z

I’m not predicting. I said I expected this to continue to amp up. But fact is on most guidance it’s going the wrong way right now. I did see the SREF run and that followed by the NAM was a good start to 12z. Since then it’s been a huge letdown. Everything else has gone the wrong way.  We joke about hug the model with the most snow but how often does that work?  It’s usually preponderance of evidence that wins. Maybe this is the time the snowy one wins. It happens. I have expected to see a continued amp trend and am kind of shocked this reversed course. Maybe it juices up at 18z or 0z. That’s very possible. I’m simply making observations and there are more not good ones then I like to see right now.  Let me finish by saying we’re probably still safe for some snow but I’m worried the :o solutions yesterday we were giddy over with talk of crazy fgen and 2”hr rates and someone getting 10” is slipping away and that’s what I’m in this for. I don’t really invest in 1-3” events. 

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12 minutes ago, MillvilleWx said:

Guys remember, I haven't looked at EVERYTHING and this was an on the fly forecast with a perusing through a few things. I may adjust numbers for a final call. For now, the thermal profile north and west of the fall line are pretty climo oriented, so just a matter of precip in liquid equivalent and potential banding during the best mid-level frontogen. 

Which could mean just west of the fall line like let’s say 18.7 miles jackpots even with less precip...going with that for now

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My write up on my weather page...you can pull the QPF images for yourselves lol. 
 

Ok let’s look at a couple things folks. As you recall, I’ve been saying this storm tomorrow will be all about the rates and heavy precipitation. The amount of precipitation we call it in the weather world QPF (quantitative precipitation forecast). In my opinion at least .5 of precipitation is the magic number here. If we get .5 precipitation (which is the blue shaded color in these maps) then I think we have a good shot at picking up a quick 3-4-5” of snow Sunday morning. The NAM model is showing this for most of the region as you can see in the 2nd image. On the other hand the Canadian (pictured first) and the GFS models have the .5 line over onto the eastern shore. So if those models are right the Baltimore area would only get about .3 of precipitation. In my opinion that WONT work for significant snow accumulations with marginal temps as the precipitation will be only light to moderate and any snowfall rates won’t be able to overcome the warmer ground so we would mainly just see a little slush and that’s it. We NEED the models with the .5 and above QPF to verify so that we get moderate to heavy snow and the rates overcome the warm ground. Unfortunately we just don’t have the best data agreement right now, so we’ll have to see how this plays out thru the day and into the morning.

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