January 29-30th Rain/Flurries coastal and IVT

[Bob Chill]

9 minutes ago, psuhoffman said:

 I'm happy that most guidance is converging on the right track.

I'm pretty surprised. When we first started seeing it show up I was like "these things can work but they never hit us. Always NJ or SNE". But it's looking like a direct MA hit. Bizarro world and stuff 

[psuhoffman]

4 minutes ago, Bob Chill said:

I'm pretty surprised. When we first started seeing it show up I was like "these things can work but they never hit us. Always NJ or SNE". But it's looking like a direct MA hit. Bizarro world and stuff 

We had some legit decent setups and everything went wrong. Perhaps we score on an incredibly flawed one. 

[Ji]

We had some legit decent setups and everything went wrong. Perhaps we score on an incredibly flawed one. 

2 snow events in the worst pattern of the season lol....

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[yoda]

Decent IVT at hr 60 on 00z GGEM... I  think, right?

[psuhoffman]

Umm whats the Cmc smoking and more importantly why didn't it share???

Oddly I've wondered looking at the setup that it wouldn't take much to get enough interaction between the coastal and the approaching trough and h5 energy to create more lift and precip. The coastal itself is a lost cause but sometimes those sneaky jet enhanced bands that setup between an offshore system and an approaching h5 low can pop up late. But it's been abandoned by pretty much all guidance except the Cmc. Would be an epic win if it happened but I wouldn't hold my breath. 

[psuhoffman]

3 minutes ago, Ji said:

2 snow events in the worst pattern of the season lol....

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I was never sold it was going to be that bad or for that long but so many people were having a pity party I just gave up and took a break. 

[psuhoffman]

5 minutes ago, yoda said:

Decent IVT at hr 60 on 00z GGEM... I  think, right?

Ggem is more amped with the coastal and creates enough moisture transport to get an area of precip going under the pva as the h5 trough approaches.  Seen that before and they can be nice little surprises but I'm skeptical given it's the ggem all alone. If the U.K. or euro comes in that way then maybe. 

[Interstate]

5 minutes ago, psuhoffman said:

Umm whats the Cmc smoking and more importantly why didn't it share???

Oddly I've wondered looking at the setup that it wouldn't take much to get enough interaction between the coastal and the approaching trough and h5 energy to create more lift and precip. The coastal itself is a lost cause but sometimes those sneaky jet enhanced bands that setup between an offshore system and an approaching h5 low can pop up late. But it's been abandoned by pretty much all guidance except the Cmc. Would be an epic win if it happened but I wouldn't hold my breath. 

Even with the interaction with the coastal... The CMC gives us the lightest snowfall

[Ji]

I was never sold it was going to be that bad or for that long but so many people were having a pity party I just gave up and took a break. 

Mitchnick apparently quit the hobby. The bad pattern did have 2 Windows. Jan 25 and Jan 30

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[CAPE]

17 minutes ago, Bob Chill said:

I'm pretty surprised. When we first started seeing it show up I was like "these things can work but they never hit us. Always NJ or SNE". But it's looking like a direct MA hit. Bizarro world and stuff 

Yup I said the same thing multiple times over the last couple days. Thus my skepticism. But this is looking less and less like a norlun deal on most guidance, other than maybe the NAM.

[clskinsfan]

10 minutes ago, C.A.P.E. said:

Yup I said the same thing multiple times over the last couple days. Thus my skepticism. But this is looking less and less like a norlun deal on most guidance, other than maybe the NAM.

Yep. The GFS has had it as a vort pass for days. If it ends up verifying then the GFS pulled a massive one this time.

[SnowGoose69]

UKMET = congrats DT 

[psuhoffman]

[cae]

00z RGEM ensemble mean.

[MillvilleWx]

All modeled snow totals aside. If the 3km vort pass is this nice Monday night into Tuesday, there will be some nice surprises abound. Pretty nice area of diffluence over the entire Western side of the Bay. Lots of upside in the typical areas and 1-2” in the cities.




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[arlwx]

The latest from LWX:

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/...
The rain will continue to gradually taper off from northwest to
southeast, however progress will slow considerably as cold front
stalls near the Outer Banks and wave low moves along it. The
southeastern coastal low will also be moving northeastward and
will be near the North Carolina coastline by Monday morning.
These features will keep rain chances elevated along the I-95
corridor into this evening and southeast of I-95 well into the
night, possibly even into Monday morning across southeast
Maryland. Cold air will be gradually filtering into the region,
so a few snowflakes are possible across the higher terrain
before ending, but no impact expected. Lows by Monday morning
will range from the 30s to near 40F.

Coastal low will track from near Cape Hatteras Monday morning
northeastward well offshore by the evening. An upper level trough
carving through the Midwest and Ohio Valley will then move into
the region by Monday afternoon, with a strong low level cold
front setting up to the west Monday evening. Therefore, Monday
should be considerably drier than today, although some showers
remain possible, especially across southeast Maryland. Highs
generally in the mid/upper 40s.

The upper trough will move overhead Monday night into Tuesday
morning with the strong low level front crossing the area from
06z to 15z west to east. This will likely bring a period of
snow showers to the area, with the potential for some
accumulation. Will currently show a coating to up to one inch
for much of the area, with 1-2" across some of the higher
terrain and for the far northern/western suburbs of
Washington/Baltimore into central/northern Maryland. Along and
west of the Allegheny Front could see some higher amounts in the
westerly upslope flow as well. Temperatures should fall into the
20s to low 30s by morning.

Colder and blustery conditions are expected for Tuesday with
highs only reaching the 30s. High pressure will build in Tuesday
night with clearing skies and lows in the teens to around 20F.
 

[CAPE]

Latest from Mount Holly's morning AFD. Interestingly, they think there is still a chance for some snow on the backside of the departing coastal low tomorrow evening before the upper level energy swings through on Tuesday...

Monday and Tuesday... Despite models coming into better agreement regarding the general northeastward movement of a coastal low along a stationary front (from near the NC coast early Monday to around 300 miles east of the NJ coast sometime late Monday-early Tuesday), there continues to be considerable differences among the guidance regarding the timing (speed) of the low, the rate of deepening and even if there will be two separate low centers or just one. Until the above issues can be resolved by NWP or eventually nowcasting techniques, it will be difficult to determine how quickly the transition from rain to snow occurs. A slower/stronger coastal low would not only enhance precip on the backside of the low (likely S/E of I-95) Monday afternoon and evening, but it would also imply a quicker/earlier changeover to snow in the coastal plain owing to stronger CAA (from northerly winds on the backside of the low) and dynamical cooling in the column. Accordingly, plausible scenarios for the Monday evening commute (particularly S/E of I-95...where precip will likely be confined to) include (1) dry, (2) continued light rain, (3) rain mixing in with snow but no snow accumulation or (4) rain quickly changing to wet snow and becoming heavy enough for slushy accumulations (<1") mainly on grassy surfaces.

There will likely be a lull in the precip overnight Monday as the forecast area becomes situated in between the downstream departing low off the coast and an upstream shortwave trough approaching from the Ohio Valley. DPVA ahead of this shortwave trough will provide lift for a period of snow across a portion of the CWA on Tuesday. While the snow looks to be mainly light, the one wild card that could be responsible for a heavier burst of snow for a brief (2-4 hour window) is mesoscale banding. Model diagnostics from the 00Z NAM, GFS and ECMWF show a decent signal for mesoscale banding (850- 700 mb layer Fn vector convergence and weak moist symmetric stability present in a moistening column) passing over southeastern PA, southern NJ and Delmarva on Tuesday. The highest snowfall amounts in our latest snowfall graphic have shifted south but were capped at 1-2" since snow may struggle to accumulate initially due to a warm surface. However, snowfall accumulations will more than likely change with future forecasts given how low the skill is wrt/ predicting the location of mesoscale banding this far out.

[psuhoffman]

4 hours ago, MillvilleWx said:

All modeled snow totals aside. If the 3km vort pass is this nice Monday night into Tuesday, there will be some nice surprises abound. Pretty nice area of diffluence over the entire Western side of the Bay. Lots of upside in the typical areas and 1-2” in the cities.




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Yea the models will struggle with these things but they tend to squeeze whatever they can out of the atmosphere. Get a perfect vort pass like that and things could be fun. 

[nw baltimore wx]

The 6z gfs shows a pretty quick inch at bwi from 4-7AM. Surface looks marginal at onset but falling temps could make for and an ugly commute. Upper levels look good.

[showmethesnow]

6 minutes ago, psuhoffman said:

Yea the models will struggle with these things but they tend to squeeze whatever they can out of the atmosphere. Get a perfect vort pass like that and things could be fun. 

I like our chances better with depending on the upper level energy swinging through to give us our snow as opposed to depending on a fickle Norlun setting up.

[Bob Chill]

NAM shifted best lift south. Now it basically passes right over Psu's house instead of PA. Couple more ticks and the fabled rockville/Columbia deathband will be in play. 

[MillvilleWx]

NAM shifted best lift south. Now it basically passes right over Psu's house instead of PA. Couple more ticks and the fabled rockville/Columbia deathband will be in play. 

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.


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[Bob Chill]

2 minutes 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.


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3k read your post and obliged 

[ThePhotoGuy]

1 hour ago, nw baltimore wx said:

The 6z gfs shows a pretty quick inch at bwi from 4-7AM. Surface looks marginal at onset but falling temps could make for and an ugly commute. Upper levels look good.

Do you have a link to that site? I used to have it but lost it a while ago. 

[cae]

5 hours ago, MillvilleWx said:

All modeled snow totals aside. If the 3km vort pass is this nice Monday night into Tuesday, there will be some nice surprises abound. Pretty nice area of diffluence over the entire Western side of the Bay. Lots of upside in the typical areas and 1-2” in the cities.

Thanks.  Novice question:  I've noticed that the precip appears to occur under an area of 700 mb diffluence.  Does this drive the lift that leads to the precip? 

[87storms]

3k sim radar implies a pre-dawn start time ending around noon.  not sure how accurate that is, tho.  shave off for virga and looks like a few hour period of snow for the morning commute.

[clskinsfan]

Surface temps on the 3K are a bit warm out here while the snow is coming down. They do cool off for you guys to the east. I will be happy with an inch at this point.

[MillvilleWx]

Thanks.  Novice question:  I've noticed that the precip appears to occur under an area of 700 mb diffluence.  Does this drive the lift that leads to the precip? 

Yes. There’s a pretty good area of mid and upper forcing with the shortwave trough axis swinging through. That’s what generates the expanding precip field overhead, as well as providing an opportunity for mesoscale banding structures within the generated QPF shield. Add in the typical orographic effects over areas like the Catoctins and Parrs Ridge and that’s why these setups can be sneaky good to our northern tier with mini enhancements and better banding up that way. Wouldn’t be shocked at all at 2-4” across Northern Frederick/Carroll/Baltimore with the kind of vort pass the NAM’s are implying, but I’d stick with 1-3” for now due to ground temps at the start. Main road stickage should be fine, but untreated sidewalks and side roads could be a little slick for the morning commute. Hopefully there can be some other nice bands that initiate away from the northern tier so we can see areas south of I-70 cash in well. Certainly has the feel of a surprise.


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[Bob Chill]

@MillvilleWx

Totally agree that start temps will fight impact. The only wildcard would be 1"/hr+ rates. If that happens then road stickage is no problem even with temps above freezing. A well timed heavy band can do some damage with 35 degree temps

@87storms

Shouldn't be much virga as there really isn't much if any dry air to overcome. The cold/dry stuff is back behind the shortwave. This event will likely be one where it's snowing shortly after radar light up overhead. It's pretty dynamic even if compact. Could go from flakes to mod snow in 15 minutes for those that get under the good stuff. 

[MillvilleWx]

[mention=9895]MillvilleWx[/mention]
Totally agree that start temps will fight impact. The only wildcard would be 1"/hr+ rates. If that happens then road stickage is no problem even with temps above freezing. A well timed heavy band can do some damage with 35 degree temps

Oh no doubt. Seen it happen lots of times. I think those types of bands are possible, but not probable everywhere. I think the main thoroughfares like 270, 70, 32 and what not will be fine because they’ll likely put something down to protect them. Other roads could be in for some impact though with any good rates. Snow starting before sunrise too. It’ll come in like a banshee, so little wasted as you stated. I like those types of setups. Just get right to the good stuff.


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