February 7th Storm Threat Discussion/Obs

[jaydreb]

1 minute ago, BTRWx's Thanks Giving said:

What about total between the two?

It’s about .45” qpf in DC.  More SE, less NW.  

[BTRWx's Thanks Giving]

The origin of the low gives hope that the storm could really blossom.

[WinterWxLuvr]

6 minutes ago, NorthArlington101 said:

Love seeing a fair number of jackpots to the SE. Anything that gives us some wiggle room has got to be good.

I’m gonna go with number 9 as the most likely scenario 

[jayyy]

6 minutes ago, NorthArlington101 said:

Love seeing a fair number of jackpots to the SE. Anything that gives us some wiggle room has got to be good.

P09 please! 

[MillvilleWx]

Well well well, looks like we have ourselves a nice little event on the horizon. As we've seen the model corrections back to the NW have been due to backing from the extreme cold scenarios that place the baroclinic zone further to the south, as well as the amplification of the southern wave that descends from the Rockies down into the south-central plains to the Tennessee Valley. A couple of things to point out so far with current model progs. 

The first thing I wanted to touch on is how the trough behavior has been important in getting the precip field further to the NW and why there is still a bit more room for further westward expansion. Below is a gif of the 5H vort panels off the 18z GFS which now has the precip field well to the NW of where we were this time yesterday.

Notice the vort as it swings east of the Mississippi begins to take on a more neutral position with a slight negative tilt by the end of the gif as it enters VA. This is important as this places the best diffluent signature further to the north and east ahead of the amplifying wave. In turn, this promotes better mid-level lifting mechanisms to come further NW as the trough pivots east of a longitude of Nashville/Indianapolis. 

 

Here's a look at the GFS 700mb frontogenic forcing for Sat night into Sunday morning. Notice the expansion of the lift further NW with SE to NW progression of the mid-level frontogen placement. This will allow for an expansion of the precip field, imo, to be a bit more pronounced to the NW, and maintains a strong lifting signature for Central MD over to the western portion of the eastern shore. This is why the GFS now has the max precip field bisecting the I-95 corridor to about 50 miles on either side. It will be important to maintain the current wave amplification in order to capitalize not just the precip field expansion, but promotion of the best forcing to the NW.

The NAM is fairly aggressive with the 7H frontogen as well. In fact, it's incredibly robust and should favor a period of 1-2"/hr rates within the northern periphery of the frontogen placement. Again, this is due to the negatively tilted trough axis as it pivots to the east. Check it out below:

Here's the trough axis during the prime time period of the incoming precip field....

The area in the box ahead is a strong diffluent signature that provide the sufficient lift ahead of the pivoting trough, leading to not only precip expansion, but also better lift to generate mesoscale banding structures with persistence as they trek to the north and northeast. One thing I haven't shown is a strengthening 25H jet signature to the northeast that amplifies and places the region right within the right entrance region of the jet. This is why the precip blossoms so quickly on the QPF side of guidance.

As long as we continue to keep the current 5H presentation, I think the stars will align for a progressive event, but will have thumping potential given the current lift progged. Lowest boundary layer is the primary concern at the moment, but a marginal setup overnight can absolutely score. I think a general 3-6" with max of 10" somewhere is well within reason considering the trends. A slight tick colder and we'd really be in business. 

[MillvilleWx]

1 minute ago, losetoa6 said:

The French model gives our vort steroids 

 

Have you ever just wanted to eat a baguette in driving snow?  

[osfan24]

24 minutes ago, NorthArlington101 said:

Love seeing a fair number of jackpots to the SE. Anything that gives us some wiggle room has got to be good.

There are some big hitters in there. Must snow like crazy for an 8-10 hour storm.

[Scarlet Pimpernel]

14 minutes ago, MillvilleWx said:

Have you ever just wanted to eat a baguette in driving snow?  

Pardon me, have you any Grey Poupon??

[The Ole Bucket]

Panel 1 there would let everybody get in on the action..

[Heisy]

36 minutes ago, MillvilleWx said:

Well well well, looks like we have ourselves a nice little event on the horizon. As we've seen the model corrections back to the NW have been due to backing from the extreme cold scenarios that place the baroclinic zone further to the south, as well as the amplification of the southern wave that descends from the Rockies down into the south-central plains to the Tennessee Valley. A couple of things to point out so far with current model progs. 

The first thing I wanted to touch on is how the trough behavior has been important in getting the precip field further to the NW and why there is still a bit more room for further westward expansion. Below is a gif of the 5H vort panels off the 18z GFS which now has the precip field well to the NW of where we were this time yesterday.

Notice the vort as it swings east of the Mississippi begins to take on a more neutral position with a slight negative tilt by the end of the gif as it enters VA. This is important as this places the best diffluent signature further to the north and east ahead of the amplifying wave. In turn, this promotes better mid-level lifting mechanisms to come further NW as the trough pivots east of a longitude of Nashville/Indianapolis. 

 

Here's a look at the GFS 700mb frontogenic forcing for Sat night into Sunday morning. Notice the expansion of the lift further NW with SE to NW progression of the mid-level frontogen placement. This will allow for an expansion of the precip field, imo, to be a bit more pronounced to the NW, and maintains a strong lifting signature for Central MD over to the western portion of the eastern shore. This is why the GFS now has the max precip field bisecting the I-95 corridor to about 50 miles on either side. It will be important to maintain the current wave amplification in order to capitalize not just the precip field expansion, but promotion of the best forcing to the NW.

The NAM is fairly aggressive with the 7H frontogen as well. In fact, it's incredibly robust and should favor a period of 1-2"/hr rates within the northern periphery of the frontogen placement. Again, this is due to the negatively tilted trough axis as it pivots to the east. Check it out below:

Here's the trough axis during the prime time period of the incoming precip field....

The area in the box ahead is a strong diffluent signature that provide the sufficient lift ahead of the pivoting trough, leading to not only precip expansion, but also better lift to generate mesoscale banding structures with persistence as they trek to the north and northeast. One thing I haven't shown is a strengthening 25H jet signature to the northeast that amplifies and places the region right within the right entrance region of the jet. This is why the precip blossoms so quickly on the QPF side of guidance.

As long as we continue to keep the current 5H presentation, I think the stars will align for a progressive event, but will have thumping potential given the current lift progged. Lowest boundary layer is the primary concern at the moment, but a marginal setup overnight can absolutely score. I think a general 3-6" with max of 10" somewhere is well within reason considering the trends. A slight tick colder and we'd really be in business. 

Amazing post! I’ve been looking at the fronto on the mesos. While out of range it highlights the potential. If this shortwave can neg tilt and the trough axis aligns perfectly this will be a classic heavy wet snow event for someone. Could be a lot of 30-35dbz type in the radar inside the max axis of the precip. Hope the trends continue because I love fat white out flakes  regardless of how quick it moves

[EastCoast NPZ]

23 minutes ago, MillvilleWx said:

Well well well, looks like we have ourselves a nice little event on the horizon. As we've seen the model corrections back to the NW have been due to backing from the extreme cold scenarios that place the baroclinic zone further to the south, as well as the amplification of the southern wave that descends from the Rockies down into the south-central plains to the Tennessee Valley. A couple of things to point out so far with current model progs. 

The first thing I wanted to touch on is how the trough behavior has been important in getting the precip field further to the NW and why there is still a bit more room for further westward expansion. Below is a gif of the 5H vort panels off the 18z GFS which now has the precip field well to the NW of where we were this time yesterday.

Notice the vort as it swings east of the Mississippi begins to take on a more neutral position with a slight negative tilt by the end of the gif as it enters VA. This is important as this places the best diffluent signature further to the north and east ahead of the amplifying wave. In turn, this promotes better mid-level lifting mechanisms to come further NW as the trough pivots east of a longitude of Nashville/Indianapolis. 

 

Here's a look at the GFS 700mb frontogenic forcing for Sat night into Sunday morning. Notice the expansion of the lift further NW with SE to NW progression of the mid-level frontogen placement. This will allow for an expansion of the precip field, imo, to be a bit more pronounced to the NW, and maintains a strong lifting signature for Central MD over to the western portion of the eastern shore. This is why the GFS now has the max precip field bisecting the I-95 corridor to about 50 miles on either side. It will be important to maintain the current wave amplification in order to capitalize not just the precip field expansion, but promotion of the best forcing to the NW.

The NAM is fairly aggressive with the 7H frontogen as well. In fact, it's incredibly robust and should favor a period of 1-2"/hr rates within the northern periphery of the frontogen placement. Again, this is due to the negatively tilted trough axis as it pivots to the east. Check it out below:

Here's the trough axis during the prime time period of the incoming precip field....

The area in the box ahead is a strong diffluent signature that provide the sufficient lift ahead of the pivoting trough, leading to not only precip expansion, but also better lift to generate mesoscale banding structures with persistence as they trek to the north and northeast. One thing I haven't shown is a strengthening 25H jet signature to the northeast that amplifies and places the region right within the right entrance region of the jet. This is why the precip blossoms so quickly on the QPF side of guidance.

As long as we continue to keep the current 5H presentation, I think the stars will align for a progressive event, but will have thumping potential given the current lift progged. Lowest boundary layer is the primary concern at the moment, but a marginal setup overnight can absolutely score. I think a general 3-6" with max of 10" somewhere is well within reason considering the trends. A slight tick colder and we'd really be in business. 

Looking at the 500 chart, what feature illustrates the diffluent signature?  I dont really see the height lines diverging.

[psuhoffman]

2 hours ago, Cobalt said:

 

PSU mentioned this in the 3-7 day chat but this feels similar to Feb 17 2018..

Also reminds me of boundary waves in April 2018, Feb 2017 and early Feb 2014.  They all trended north the final 48-72 hours. There are examples of ones that didn’t but unfortunately when they don’t it’s usually because the wave got squashed somehow and we don’t remember those. We got some of these waves to work in 2014 and 2015 but if I recall the move north didn’t start until 48 hours. I remember from 72 they all looked south. It’s not 100%. Sometimes something happens the guidance didn’t see to suppress but the trend historically with these kinds of boundary waves is north the last 72 hours.  Even up here often it goes from south of me to north of me the final 72 hours.  One red flag is that the temps aren’t really that cold. The flow isn’t suppressive either. If this continues to amp there isn’t much to prevent further north adjustment. Even up here I might be more worried about north then south.  Before people jump it’s not set. I’m mostly going off historical model bias but it’s like 80% not 100%. If it does go north at least I REALLY like the look next week for the whole area. It’s a look we usually score in. 

[SnowenOutThere]

If this event does end up giving us 5-10 inches of snow I would be very concerned. I love snow I want this to happen but there is a good risk of area wide power outages because the snowfall rates will be super high and the snow super wet and thus heavy. This would lead to heavy wet snow falling heavily overnight onto trees that have just recovered from the snow earlier in the week. So if we connect the dots this would mean wide scale power outages which is concerning and something I have not seen discussed. That said I want a foot plus overnight with super heavy rates and big flakes. 

[bsperlin]

East Coast NPZ said: " Looking at the 500 chart, what feature illustrates the diffluent signature?  I dont really see the height lines diverging. "

That was my question, too. However, I can see that the boxed area has an increase of wind speed over the upstream flows, so that would tend to pull in air from below to replace it, but I'd like to hear someone discuss those dynamics further.

[WxUSAF]

 

[MillvilleWx]

14 minutes ago, EastCoast NPZ said:

Looking at the 500 chart, what feature illustrates the diffluent signature?  I dont really see the height lines diverging.

It's pretty subtle on the 5H plot, but you can see it a little better on the 2PVU panels where there is a bit of a "fanning" signature on the lead side of the shortwave trough as it pivots through the Tennessee valley. The amplifying 250mb trough with jet core strengthening to the north is also a classic sign of diffluence developing under the right entrance region of the jet. Hope this helps!

[MillvilleWx]

Just now, WxUSAF said:

 

I just peeked over my shoulder to see if John is watching me or something. Eerie timing man on this post right before what I just posted 

[SomeguyfromTakomaPark]

4 minutes ago, SnowenOutThere said:

If this event does end up giving us 5-10 inches of snow I would be very concerned. I love snow I want this to happen but there is a good risk of area wide power outages because the snowfall rates will be super high and the snow super wet and thus heavy. This would lead to heavy wet snow falling heavily overnight onto trees that have just recovered from the snow earlier in the week. So if we connect the dots this would mean wide scale power outages which is concerning and something I have not seen discussed. That said I want a foot plus overnight with super heavy rates and big flakes. 

This does not look like enough snow to cause major power outages.  If we were talking widespread 8-12+ of heavy wet snow it might. 

[SnowCane]

4 minutes ago, SnowenOutThere said:

If this event does end up giving us 5-10 inches of snow I would be very concerned. I love snow I want this to happen but there is a good risk of area wide power outages because the snowfall rates will be super high and the snow super wet and thus heavy. This would lead to heavy wet snow falling heavily overnight onto trees that have just recovered from the snow earlier in the week. So if we connect the dots this would mean wide scale power outages which is concerning and something I have not seen discussed. That said I want a foot plus overnight with super heavy rates and big flakes. 

Eh, I don’t see that happening. Maybe an isolated outage but it’d take a bigger storm to cause any widespread issues. 

[EastCoast NPZ]

3 minutes ago, MillvilleWx said:

It's pretty subtle on the 5H plot, but you can see it a little better on the 2PVU panels where there is a bit of a "fanning" signature on the lead side of the shortwave trough as it pivots through the Tennessee valley. The amplifying 250mb trough with jet core strengthening to the north is also a classic sign of diffluence developing under the right entrance region of the jet. Hope this helps!

It does!  Interesting stuff!

[Chris78]

@MillvilleWx

Great write up. You have a great way of explaining things.

Appreciate it!

[CAPE]

1 minute ago, EastCoast NPZ said:

It does!  Interesting stuff!

 Air flow converges into the base of a trough, then diverges, or accelerates out of it (just east of the vorticity max at h5) and you can also see this by looking aloft at the jet streak.

[CAPE]

20 minutes ago, MillvilleWx said:

It's pretty subtle on the 5H plot, but you can see it a little better on the 2PVU panels where there is a bit of a "fanning" signature on the lead side of the shortwave trough as it pivots through the Tennessee valley. The amplifying 250mb trough with jet core strengthening to the north is also a classic sign of diffluence developing under the right entrance region of the jet. Hope this helps!

Left rear quad looks favorably placed. Hope this pretty much holds as is.

[MillvilleWx]

1 minute ago, CAPE said:

Left rear quad looks pretty favorably placed. Hope this pretty much holds as is.

These are some of my favorite types of events when they materialize. They are quick hitting, but they come in like a banshee and can just dump for 6-10 hrs and scoot on out. I was looking at PWAT Anomalies for the time frame and they jump to 140-180%, or ~1 StDev above normal for the entire area. Classic for a solid high level advisory to WSW type event. Nothing over the top, but above the premise for a lower end event. Keep the 5H progression tilting negative and it'll be a very white Sunday for everyone. 

[CAPE]

Just now, MillvilleWx said:

These are some of my favorite types of events when they materialize. They are quick hitting, but they come in like a banshee and can just dump for 6-10 hrs and scoot on out. I was looking at PWAT Anomalies for the time frame and they jump to 140-180%, or ~1 StDev above normal for the entire area. Classic for a solid high level advisory to WSW type event. Nothing over the top, but above the premise for a lower end event. Keep the 5H progression tilting negative and it'll be a very white Sunday for everyone. 

Just juicing up a bit pretty much gets the whole region into the good precip shield. Maybe just wishful thinking, but I cant see this amplifying too much more given the flow and the configuration at h5. Maybe a slight tick NW, which is about all I can afford here lol.

[psuhoffman]

2 hours ago, WxUSAF said:

RGEM actually does get snow into the metro area and MD. 

Not sure we want more of a jump in one run this early...

1 hour ago, clskinsfan said:

Damn Mappy you should not have deleted that post. The trolling that I had lined up for it was legendary.

She did him a favor actually. 

[CAPE]

18z Euro looking maybe a tad more suppressed than 12z.

[CAPE]

Shortwave is not as sharp and dampens as it comes east. Weak pos this run.

[aldie 22]

5 minutes ago, CAPE said:

Shortwave is not as sharp and dampens as it comes east. Weak pos this run.

it's over if the shortwave dampens like that not going to make anyone happy

[CAPE]

Just now, leesburg 04 said:

it's over

Banter.