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January 29-30th Rain/Flurries coastal and IVT

WxUSAF

By WxUSAF,
in Mid Atlantic

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Bob Chill

Bob Chill

Posted
Posted
Just now, psuhoffman said:

I think a 1-3" in general is likely and some lucky isolated 4" totals are possible with this. 

Agree. The one good thing going for it will be rates. Unlike lame drawn out light events this one will be a quick hitter with good rates so snow shouldn't melt as fast as it hits the ground. I'm setting my bar at 1" while hoping for some lucky banding in real time hitting my yard. 

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Bob Chill

Bob Chill

Posted
Posted
12 minutes ago, clskinsfan said:

When Dr. No says no we should all be concerned.

I was a little surprised. Everything else shifted south with best dynamics and the euro made more than a little move to the north. These events are tricky though. We'll prob keep seeing shifts in all directions until game time. Hopefully by 12z tomorrow there is consenus....that includes all of us...

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usedtobe

usedtobe

Posted
Posted
5 minutes ago, Bob Chill said:

I was a little surprised. Everything else shifted south with best dynamics and the euro made more than a little move to the north. These events are tricky though. We'll prob keep seeing shifts in all directions until game time. Hopefully by 12z tomorrow there is consenus....that includes all of us...

Jason and I wrote this article for CWG. I kind of think the Euro precip may be too light but that's a guess. 

https://www.washingtonpost.com/news/capital-weather-gang/wp/2018/01/28/snow-could-sweep-through-during-rush-hour-tuesday-with-minor-accumulations/?utm_term=.6f8ce997bf6e

For those who don't get the post,  below is the rough draft that I sent Jason. 

Snow is becoming increasingly likely Monday night into Tuesday.  The culprit producing the snow is another one of those clipper type upper level disturbances that will be crossing the region. The questions that remain about the system is whether the event will be a mostly cosmetic dusting of snow that leaves roads, driveways, and walkways wet rather than slick, or whether temperatures will fall quickly enough to allow a dusting to an inch or two to accumulate. This might cause untreated surfaces to become slush covered as temperatures fall below freezing.  The models offer either possibility depending on which one you choose to believe.  There are a couple of factors arguing against this being a significant snow event.  1). A low is forecast to develop well east of the coast and the north to northwest winds west of it will prohibit Atlantic moisture from being tapped so it will only be working with residual moisture.  2). The ground temperatures initially will be above freezing due to the warm temperatures of the last couple of days. That's a departure from the frozen ground temperatures during the last couple of light snow events so it might take awhile for the snow to stick.  The one favorable aspect of the system is the track and strength of the upper level system which is favorable for producing snow. 

Timing:  The snow is expected to start between midnight and 4 AM  Tuesday over the far western suburbs.The snow  will work its way eastward to the city by around 7 AM and the entire region shortly thereafter.  Temperatures over the far western and northern suburbs may fall quickly below freezing as the snow commences.  However, elsewhere temperatures will generally run in the mid 30s as the snow starts;  in the city it may not fall below freezing until after the sun rises.  How quickly the temperature falls may depend on the intensity of the snowfall. Temperatures may have a hard time falling below freezing if the snow remains very light.  If the snow falls a little heavier than expected within a banded feature, temperatures could fall below freezing even in the city by the latter half of the morning rush.  Marginal temperatures at onset are always a forecast bugaboo.

The latest NAM would support a dusting to an inch or two with the heaviest accumulations falling north of the city where untreated surfaces might become slick.   By contrast,  last night's European would argue for only a dusting with little or no accumulation on the roads.   

Right now we see two possible scenarios.

1).  A band of moderate  snow develops in response to the the strong upper system.  As the snow commences, temperatures rapidly fall towards freezing and most of the area sees a dusting to 2 inches with untreated roads possibly becoming slick especially in the colder locations north of the city. In this scenario, a heavy, quick moving snow band could hit the city right at the peak of rush hour.  Because of the falling temperatures,  commuters would need to pay close attention to the temperature and to road conditions.  Both the 12- and 3-km NAM models support such a scenario.

2).  In the second scenario, the lack of moisture keeps the precipitation light enough that only a dusting to 0.50 accumulates on leaves, mulch and grassy surfaces.  The light precipitation and warm initial road temperatures keep the roads wet rather than slushy. The snow is more cosmetic than a commuting problem.

Hopefully we'll have a better feel for which scenario will play out tomorrow.

Snow lovers can take heart.  There is another snow threat on the horizon for Friday.  It's way too early to discuss the possibility in any detail.  We'll be watching it and will post an article on it if the models hold onto the possibility. 

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WEATHER53

WEATHER53

Posted
Posted
4 hours ago, MillvilleWx said:

 


Still looks solid for MoCo Bob. Decent band rolls through overnight from west and increased upper forcing over the area enhances a secondary swath before shutting off once we get into NVA. 1-2” across the county with areas like Damascus to Mt Airy a bit more. These setups can offer some decent banding structures. We know where the main band will setup, but a few other nice ones will be at play. Sparky better sharpen up his broom at this rate.


.

 

What upper air in situation graphic or visual device would best display the occurring path of the Vort  when it is passing us?

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CAPE

CAPE

Posted
Posted
27 minutes ago, MD Snow said:

The 18z nam just randomely Nam’ed the eastern shore with the coastal...came out of no where. No accumulation but to go from nothing to a band of snow is crazy...

Mount Holly mentioned this possibility in their AFD this morning- a little stronger coastal/heavier precip and dynamical cooling on the backside could produce a period of wet snow tomorrow evening- so this might not just be the NAM being the NAM lol.

Doubt it amounts to much if it does occur.

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psuhoffman

psuhoffman

Posted
Posted
6 minutes ago, Bob Chill said:

18z rgem pushes the back side of the coastal precip all the way to Winchester with a rain snow mix out there. All 18z runs are showing something similar with a more expansive precip shield. I'll laugh if that happens as we quibble over 120 hour ops in the LR thread. 

Yea but as I just said the introduction of a stronger coastal threatens our nice little snow setup. If the coastal intensifies but too late for us all it will do is enhance subsidence and a dry NW flow behind it and mute our chances for good banding with the upper low and associated  Vort.  It's introducing another wild card to what was becoming a straight forward setup. And while there are some paths to victory with that setup let's be honest this year tricky complicated has been a disaster for us. We seem to find the worst case scenario each time lately. So I'm not throwing in any towel.  Have to see how things settle this evening with all the guidance. But I'm not thrilled at the introduction of a new variable at the last minute. 

ETA: and it makes sense to me because I saw mdsnows comment about the nam hitting the shore with the coasral before looking at the run and my immediate reaction was "that's not gonna be good for our vort pass snow" 

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psuhoffman

psuhoffman

Posted
Posted
11 minutes ago, Ji said:

Gfs shows more coastal too

Sent from my SM-G930V using Tapatalk
 

Wonder if we're gonna end up rooting for the coastal by tomorrow morning. It's now only a slight intensity nudge from getting good qpf into our area. Of course we have temp issues though. Shame the upper low and coastal wave aren't in sync. Time those two up and we would have a nice snow. This is still a fluid situation and at 24-48 hours.  Should be a lesson, as bob said, to those getting worked up about day 5 trends. 

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MD Snow

MD Snow

Posted
Posted
21 minutes ago, psuhoffman said:

Wonder if we're gonna end up rooting for the coastal by tomorrow morning. It's now only a slight intensity nudge from getting good qpf into our area. Of course we have temp issues though. Shame the upper low and coastal wave aren't in sync. Time those two up and we would have a nice snow. This is still a fluid situation and at 24-48 hours.  Should be a lesson, as bob said, to those getting worked up about day 5 trends. 

If we end up rooting for the coastal then we’re going to want to root for good rates. That’s the only way we get temps to drop. If not it’ll most likely be rain for the cities with a rain snow mix for anybody with any elevation at best. 

 

On a a side note, I keep telling myself that any snow we get this week is a bonus. It helps my attitude and helps me not get down from run to run. 

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Bob Chill

Bob Chill

Posted
Posted
15 minutes ago, psuhoffman said:

Wonder if we're gonna end up rooting for the coastal by tomorrow morning. It's now only a slight intensity nudge from getting good qpf into our area. Of course we have temp issues though. Shame the upper low and coastal wave aren't in sync. Time those two up and we would have a nice snow. This is still a fluid situation and at 24-48 hours.  Should be a lesson, as bob said, to those getting worked up about day 5 trends. 

We all play this game differently. I never get mad or upset when something disappears d3-4 and beyond. When a long range threat materializes, I just pass time and not get married to any one solution. Hoping for the best and expecting the worst basically. Back in 2006-2011 I would get invested in long range stuff to the point where it would be emotional. I'm long past that now because what happens in real time vs what the long range guidance shows is almost always different. Not always significantly different but op runs will tear at you if you let them. I don't. Inside of 3 days I definitely get invested when there is consensus but always wary of things coming apart at the seams. 

I'd say half of our events don't really take shape until d5. Not saying it materializes out of thin air just that long range will consistently show something near by but not effecting us. Then when things come into clearer focus it can morph into an event. Usually at the expense of someone else but it happens to all of our regions at long leads. 

I will say that ensembles have not been doing well this year. We've seen multiple occasions where the EPS or GEFS will mostly agree with an op at 5-7 day leads but then change all at the same time. For the worse so far this year but there's probably going to be an event in Feb that happens the other way around. Especially if it stays active. 

 

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Cobalt

Cobalt

Posted
Posted
1 minute ago, MD Snow said:

If we end up rooting for the coastal then we’re going to want to root for good rates. That’s the only way we get temps to drop. If not it’ll most likely be rain for the cities with a rain snow mix for anybody with any elevation at best. 

Seems like it would be that way. On the GFS during the precip, 850s say snow, temps at the ground are upper 30s/low 40s. 

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