Jan 6/7 "Event" and obs

[TowsonWeather]

1 hour ago, NorthArlington101 said:

We #abscond.

[DCAlexandria]

Boooo no 4”+ Lolis near dc. Toss it


.

[jaydreb]

[MillvilleWx]

excellent as always.  BTW it would be awesome if you are ever free to pop into one of our zoom chats.  I'm sure everyone would love to hear your analysis.  I set them so that anyone can take over and share their screen.  

Thanks! I was actually at work when I typed that one up, so I couldn’t do the Zoom call this go around either. Last one I was driving 85 mph coming home from Taos, NM lol

I am on work in the evenings next 3 nights too, but I promise when there is a chance, I will be there!!

Edit: Just a heads up, we legit had no weather going on in my CWA. My TAFs were set, the Upper Air flight was done and I was waiting for long range guidance to come out. I promise I was still working!! Multi-tasking is something I’ve gotten really good at last 6 years haha

[Ji]

I think ultimately the consensus forecast will be 3-6" in the usual favored spots and over the delmarva, and 2-4" in immediate DC metro.

The euro drying up is the most predictable thing since the wizards losing

[ErinInTheSky]

I’m gonna get more snow in this one than the last one lol.

In other news schools are never gonna reopen haha.

[Jebman]

4 hours ago, MillvilleWx said:

Well, with finally some time tonight, thought I'd throw out some thoughts on the setup for Thursday Night into Friday AM for a nice little snowfall entering the area. There's another pretty decent signal for a marginal to moderate event areawide given all the different features at play. So first off, our culprit is currently peddling out over ID/WY border with sites on the central plains by morning indicative of very progressive flow within the northern region of the jet. This system will be quick mover, but there's some definitive details that make this a chance to a more prolific storm than many of our rapid movers in the past. 

First off, the thermal environment is pretty ripe with the 95 corridor only going a bit above freezing for tomorrow PM before slowly taking a dive after peak diurnal max. West of the fall line should stay near to below freezing, which bodes well for the "stickage" factor. Every single flake outside the beltways of the big cities should stick pretty quickly at the first snowfall. So, one of the factors we have going in the positive is one we often fight in these parts. That should not be a problem this go around!

Now lets take a look at the meat and potatoes of the event with the mid and upper levels that will make this event.

First image below is the 00z NAM Nest from this evening at 500mb

There is a prolific 500mb jet max that will be rounding the base of the trough with the left exit region placed over our area (Inside the box). The divergent depiction out ahead of the main trough axis is a classic for developing qpf fields downstream of the mean trough axis. Also notice the tilt of said 500mb axis going negative as it progresses through the OH Valley. This is also a positive indication for the area as historically, we tend to see a robust response east of the BR with ascent maximized along the Alleghany front out into the Piedmont area. This is no different, and the signals below 500mb are certainly there.

Below is a gif of the same 00z NAM Nest run of the 700mb  horizontal temp advection and frontogenic forcing. 

Something important to note here is the robust warm horz. temp advection signal developing over SoVA, moving NE into the sub-forum. This is also a classic indication of a good moisture signal for the area when it comes to these events. If you take a look at the concurrent 700mb temperatures within that area of + horizontal temp advection, you can see these are very cold temps aloft within the mid-levels, which is very important for snow growth and attendant ratios that could occur where there is precip. -11 to -17C is the sweet spot for the DGZ (Dendritic Growth Zone) as this is where ice crystallization has the best environment for developing its core structure and maintaining a defined appearance upon its descent. But, temps are not the only thing of note here when it comes to the best snowflake formation....lift is also necessary. This is where that + horizontal temp advection comes into play. This provides a great deal of ascent within the 700mb layer, which is important for crystallization and snow structure. It is apparent that there is a 6 hr window where this is a huge positive for much of the area from SW VA up into portions of Southern PA (Mainly up into I-81 corridor near Chambersburg) then east into much of NoVA/Central MD/Northern half of the Eastern Shore. This is where banding is most likely to occur and there WILL be maxima and minima that occur due to the prominent banding features likely within this setup. Someone will get crushed and someone settling outside a band can get squeezed here, so despite being a solid areawide snow potential (forecast later) there will be big winners and losers. 

So, how good is the profile we are talking about for this system? Let's take a look at a few examples of areas that get hit pretty solidly during the event.

Here is an example from JYO that shows a robust area of ascent within that layer b/w 850-600mb, which are the most important layers for snow growth and expected ratios from a storm. This snapshot was taken at the peak of the mid-level ascent caused by the frontogenic forcing at 850-700mb when the jet streak pinpoints the area within the left exit region of the core jet max. With a sounding like this, 12-15:1 are not just a possibility, they are a given. 

Here's an image an hour later downstream near BWI

This is an even more robust signature of mid-level ascent within the DGZ, indicative of a potential for pretty sizeable flakes within a significant band presence. This is what we want to see in a setup like this where the pattern is progressive, but the upper levels are favorable. As long as we can right the path here with the current outlook, this will be a nice storm for a majority of the sub-forum.

So, how much snow we talking? Well, let's take a look at a few things. For me, precip panels will tell a lot of the story because ratios for the storm will be congruent with the banding and overall precip totals throughout the event. Here's a 3hr precip gif for the area leading in till 12z Fri AM

Notice there is a primetime period likely just before midnight until about 5am Friday AM. This is when most of the snowfall will occur, so any totals we have will be in a relatively short period of time. However, considering the banding potential and primed thermal environment, an advisory snowfall for pretty much everyone is well within reason. Someone will likely get the benefit of the deformation band that develops on the western flank of the developing SLP off the Atlantic coast, and that's where the WSW criteria snowfall will have the best chance. Here's a snapshot of the total precip for the event.

The maxima on the eastern shore is a product of the deformation axis being pegged in that location via the NAM Nest, but of course that is not set in stone and will not likely be solved until late tomorrow when the ingredients all come together. 

Here's my current thinking in terms of snowfall for the storm

This a general 2-6" event for most, but the upslope areas out west are an area I have higher confidence in the biggest totals of the event. Secondary maxima near the Catoctin front and on the Eastern Shore where I believe the deformation axis provides a big punch. The caveat is if the low gets cranking earlier, that could be on the other side of the bay, so keep an eye out for those next 12-18 hrs of model runs to see if any trends are picked up. That's all for now y'all  

Edit: Bit of a crude transition across St. Mary's county. Apologies for that look! 

 

Thanks, MillvilleWx! I really look forward to your writeups on upcoming winter storms!

[Weather Will]

WB 6z 3K NAM.  Widespread 1-3 expectations you won’t be disappointed.  If you get 4 or 5 you are lucky.

[yoda]

Morning AFD from LWX... they thought of upgrading to warnings around DC metro 

This system will continue to carve out an upper-level trough
upstream today, and that jetmax and the upper-level trough axis
will pass through the region tonight. This will cause surface low
pressure to strengthen on the boundary to our south. The jetmax
will track far enough to the south to put is in a favorable
region of upper-level divergence, and the upper-level trough
axis will actually turn toward a negative tilt as it passes
through our area. This will case the coastal low to strengthen.
While this system will not phase until it is well to our
northeast, it does appear that the negative tilt will have
enough of a reflection in the lower levels and at the surface to
produce an area of low-level frontogenetical forcing.
Temperatures will remain plenty cold enough due to the high
settling overhead today. Therefore, a band of moderate to
perhaps even heavy snow is expected tonight. The one thing
preventing higher snowfall amounts will be that this is fast
moving.

Snow is expected to overspread the Allegheny and Potomac
Highlands later this afternoon, and then across the rest of the
area from southwest to northeast this evening. This system will
quickly move off to the east late tonight with snow dissipating
from west to east. A Winter Storm Warning is in effect for the
Blue Ridge Mountains, and portions of the Potomac Highlands and
a Winter Weather Advisory is in effect for all other locations.

The band of snow combined with higher SLR`s is why the warning
was issued for those areas. Snowfall totals around 4 to 8
inches are most likely. Across the rest of the area, snowfall
totals around 2 to 4 inches are most likely. However, there are
signs that a localized band of heavier snow is possible. There
is still some uncertainty as to exactly where this will setup
and exactly how strong it will be. The more negative tilt to the
trough, the stronger the low-level frontogenetical forcing will
be. The 00z GFS is most bullish with this. As of now, the most
likely area for it to setup would be somewhere near central
Maryland (southern suburbs of Baltimore) to around Washington DC
and the nearby suburbs. Confidence was not high enough to
upgrade to a warning due to the uncertainty previously
mentioned, but localized amounts around 5 to 6 inches are
possible.

Either way, with cold temperatures in place and accumulating
snow, conditions will deteriorate once precipitation begins.
Even though it is a short duration event, snowfall rates around
1 inch per hour (due to the banding snow) are likely, and this
will cause snow covered and slippery roads to develop quickly
for most areas. Snow may mix with a little sleet/rain at the
beginning across our extreme southern zones in central VA and
southern MD, but if there is a mix it will change to snow.

 

[yoda]

06z GFS says it's not backing down and goes all in again

[NorthArlington101]

06z GFS says it's not backing down and goes all in again

Love it. While it’s late and I feel less bad about map spam, WPC is all in in its own way. I’ve always liked their maps for expectation setting. Note these aren’t necessarily 10:1.

[NorthArlington101]

06z GFS

[LeesburgWx]

Wow, GFS 

If the GFS was right, when is the last time our region had back to back WSW events in the same week?

[Jebman]

2 minutes ago, LeesburgWx said:

Wow, GFS 

If the GFS was right, when is the last time our region had back to back WSW events in the same week?

Jan 1987

[yoda]

The model jousting always makes think of this when we come down to the final hours before the storm

 

[NorthArlington101]

Wow, GFS 
If the GFS was right, when is the last time our region had back to back WSW events in the same week?

Charlotteville had 4 WSW in about a four week period last year — it’s not too rare. As I think Bob Chill mentioned, when we get hot, we get hot.

Feb 2010 is definitely on the list. Feel like there must be something else recent.

[WxMan1]

2 minutes ago, Jebman said:

Jan 1987

What a glorious 4-5 day period that was. 

In West Springfield I had 11.5" on Thursday 1/22/87, then another 11" the day and night of Super Bowl Sunday, 1/25 into the early morning hours of 1/26. Fond memories. 

[MJO812]

12 minutes ago, LeesburgWx said:

Wow, GFS 

If the GFS was right, when is the last time our region had back to back WSW events in the same week?

Enjoy

Nothing like snow on top of snow to preserve the snowpack.

[Solo2]

18 minutes ago, LeesburgWx said:

Wow, GFS 

If the GFS was right, when is the last time our region had back to back WSW events in the same week?

Better question might be when was the last time DCA had back to back snow storms with higher accumulation than northern burbs in a week...

[Interstate]

2 hours ago, Weather Will said:

WB 6z 3K NAM.  Widespread 1-3 expectations you won’t be disappointed.  If you get 4 or 5 you are lucky.

That hole has been floating on or by me too much. I am expecting an inch or less. 

[BlizzardNole]

28 minutes ago, Solo2 said:

Better question might be when was the last time DCA had back to back snow storms with higher accumulation than northern burbs in a week...

Right?  Total snowfall to date for DC south and east compared to say northern Frederick County will look crazy 

[yoda]

hmmm

[WinterWxLuvr]

18 minutes ago, yoda said:

hmmm

Same as it was right?

[yoda]

1 minute ago, WinterWxLuvr said:

Same as it was right?

Slowly increasing

[toolsheds]

4 hours ago, Ji said:

5 hours ago, Deck Pic said:

I think ultimately the consensus forecast will be 3-6" in the usual favored spots and over the delmarva, and 2-4" in immediate DC metro.

The euro drying up is the most predictable thing since the wizards losing

that last foul on Beal was marginal at best. 

[nj2va]

LWX expanded the WSW to Garrett County (which makes sense based on guidance).  

URGENT - WINTER WEATHER MESSAGE
National Weather Service Baltimore MD/Washington DC
334 AM EST Thu Jan 6 2022

MDZ001-061645-
/O.UPG.KLWX.WW.Y.0003.220106T2000Z-220107T1500Z/
/O.EXA.KLWX.WS.W.0002.220106T2000Z-220107T1500Z/
Garrett-
334 AM EST Thu Jan 6 2022

...WINTER STORM WARNING IN EFFECT FROM 3 PM THIS AFTERNOON TO
10 AM EST FRIDAY...

* WHAT...Heavy snow. Additional snow accumulations of 4 to 8
  inches. Northwest winds will increase and gust around 30 to 35
  mph Friday morning. Wind chills around zero to -10 degrees are
  possible along the ridge tops Friday morning.

* WHERE...Garrett County.

* WHEN...From 3 PM this afternoon to 10 AM EST Friday.

* IMPACTS...Travel could be very difficult. The hazardous
  conditions could impact the Thursday evening commute and the
  Friday morning commute.

* ADDITIONAL DETAILS...The heaviest snow is expected this evening
  with snowfall rates around 1 inch per hour possible. Visibility
  will be reduced to below one half mile at times in snow and
  blowing snow.

[SnowenOutThere]

2 hours ago, NorthArlington101 said:

06z GFS

gives as much snow as the last event, lock it IN!

[T. August]

1 hour ago, Interstate said:

That hole has been floating on or by me too much. I am expecting an inch or less. 

The euro kind of had that too. I am concerned as well.

[mappy]

red sky at morning, sailors take warning. Its gonna snow yall. 

[nj2va]

6z Euro 2-4” for the area, except far eastern and western areas.