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January Storm Term Threat Discussions (Day 3 - Day 7)


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24 minutes ago, psuhoffman said:

Notice...the GEFS have not shifted that NE wall to the precip running through central NJ at all the last few runs...but are tightening up the precip south of that line.  That is about what I expect in the end.  Somewhere between Philly and NYC is going to be a very very sharp cutoff and south of that gets a good snow and north is smokin cirrus 

So could you explain again your confidence that the cutoff sets up there and why it's less risk that it sets up south of us?

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38 minutes ago, Maestrobjwa said:

So could you explain again your confidence that the cutoff sets up there and why it's less risk that it sets up south of us?

The latitude the wave is coming across, the amount of ridging, where the confluence is, and history of these setups. That doesn’t mean it cannot happen. There was a storm in 1980 in a somewhat similar look that fringed us. But that’s pretty rare. The gfs jumps the upper low southeast to phase with the coastal. That part looks overdone.  If the wave is amplifying my guess is that process happens without as much of a sink south among the coast and that tucks the low in a little further north. The threat of it going south is a weaker wave that’s de amplifying and in that case given the flow it’s likely to get crushed way south.  I think the in between option is less likely. 

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Some of the guidance has suggested the potential for a moderate to significant snowfall (4" or more snow) in and around Richmond next week. An AO-/PNA- pattern is a favorable pattern for snow events in Richmond.

Since 1950, there have been 24 days on which 2" or more snow fell during the January 20-February 10, 1950-2020 period in Richmond. Based on the AO/PNA states, the breakdown was as follows:

AO-/PNA-: 25%
AO-/PNA+: 46%
AO+/PNA-: 4%
AO+/PNA+: 17%

AO-: 71%
AO+: 29%

PNA-: 29%
PNA+: 71%

Below is a bubble chart showing the distribution of such days, with bubble size based on the amount of snowfall.

RIC01222021.jpg

The AO and PNA are forecast to be negative through the remainder of January. Richmond's largest snowstorms during the above January 20-February 10, 1950-2020 timeframe were:

6.4", February 7, 1979 (AO: -1.696; PNA: -1.080)
5.6", January 22-23, 1954 (AO: -0.082; PNA: -0.747)
5.3", February 2, 1972 (AO: -1.896; PNA: -1.097)

In addition, a storm brought 3.0" on January 20, 2000 during an AO-/PNA- state. A much larger snowstorm occurred shortly thereafter.

The three largest AO-/PNA- storms also brought accumulating snowfall to to Washington, DC:

January 22-23, 1954: 6.4"
February 2, 1972: 3.4"
February 7, 1979: 5.6"

Only one of those storms brought more than 1.0" snow as far north as New York City: the February 7, 1979 storm, which brought 5.0" to Central Park.

 

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4 minutes ago, Wentzadelphia said:

I cant see the euro being like the gfs or cmc from what im seeing so far through 117, it sped up the wave idk if itll have any room 

No it’s not gonna do it. Wave is weaker. And faster which is no good because it’s coming across before ridging can really get going behind the Tuesday wave. That’s the biggest difference the last 2 euro runs v the one that had a good outcome yesterday 12z. Weaker wave and faster so less ridging in between it and the departing wave. 

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7 minutes ago, Wentzadelphia said:

I cant see the euro being like the gfs or cmc from what im seeing so far through 117, it sped up the wave idk if itll have any room 

I think with the euro upgrades in an effort to rid the Southwest bias of holding back shortwaves and energy it is notably overcompensating in the MR/LR  these days and has been too fast at times with the stj coming out of the Southwest. Likely one of the many reasons the model isn't quite as reliable as it once was.

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1 minute ago, psuhoffman said:

No it’s not gonna do it. Wave is weaker. And faster which is no good because it’s coming across before ridging can really get going behind the Tuesday wave. That’s the biggest difference the last 2 euro runs v the one that had a good outcome yesterday 12z. Weaker wave and faster so less ridging in between it and the departing wave. 

this is incredibly frustrating. ALl the good that happened at 12z is now vanished

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