Jan 16/17 Event Obs/Disc

[mappy]

With 12z models to start soon, a new thread sounds good. Please keep banter in the banter thread. Posts will be hidden as needed. 

be sure to blame Bob if his 1-3" call fails   

[Kmlwx]

Pretty sure at this point we are in chips fall mode as Bob Chill would say. I'll hope for an inch IMBY - and hopefully the timing is enough to get a delayed opening for the office  

They have of course already pre-treated the roads into oblivion around here. 

[RevWarReenactor]

Woke up with a slightly surprising cartopper.

 

I am going with a T- to an inch for I-95, we are in the no man's land between the two precip blobs. Most models have been advertising this.

 

But I guess its good that there is a delay with whatever little precip we might get. If it hit mid day today, we'd be looking at a few rain showers.

[psuhoffman]

Navgem looks good but unfortunately probably because it's not good enough to pick up on the subtle interplay between the arctic front and the coastal wave that is screwing us over potentially. 

 

[Eskimo Joe]

Woke up to a T in Reisterstown. Roads aren't brined here in Baltimore or Montgomery so I'm happy with that.  Silly to so that with less than 6" snow forecast.

[mappy]

1 minute ago, Eskimo Joe said:

Woke up to a T in Reisterstown. Roads aren't brined here in Baltimore or Montgomery so I'm happy with that.  Silly to so that with less than 6" snow forecast.

Drive north, friend. 83 and all local roads in my area are brined

[osfan24]

95 just south of the city was brined yesterday.

[mappy]

HRDERPS is not kind to most

[LP08]

12Z nam will make no friends

[osfan24]

Wow, nice storm just north of NYC and northeast into NE. Double digits up there for sure.

[CAPE]

12z 12km NAM is pretty meh for most of the region. Sight improvement here though over 6z, which was a complete shutout.

[mappy]

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

12z 12km NAM is pretty meh for most of the region. Sight improvement here though over 6z, which was a complete shutout.

about the same IMBY, which still isn't all that great lol

[MDstorm]

8 minutes ago, osfan24 said:

Wow, nice storm just north of NYC and northeast into NE. Double digits up there for sure.

It's been leaning that way for a while now.  No stopping it now.  Likely just some scraps in this forum.

 

MDstorm

[WxUSAF]

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

12z 12km NAM is pretty meh for most of the region. Sight improvement here though over 6z, which was a complete shutout.

3k is drier also. Ugh. Outside of December 9,  every event has trended drier at the end for the metro corridor. Nina always wins I guess.  Coastal is clearly robbing our moisture and giving it to the poconos and Catskills.

[clueless]

Weatherbug says less than an inch MBY.  And most maps have me in a snow hole. My revised forecast is lucky I see flakes.  

[CAPE]

Just now, WxUSAF said:

3k is drier also. Ugh. Outside of December 9,  every event has trended drier at the end for the metro corridor. Nina always wins I guess.  Coastal is clearly robbing our moisture and giving it to the poconos and Catskills.

Sure looks like it. I will give kudos to the Mount Holly mets, who days ago when we were getting some good looking runs for our region, were convinced this was going to be an event for the northern part of their FA with the late developing coastal.

[RevWarReenactor]

The end of the HRRR shows precip being enhanced once it gets into the Poconos, eastern PA.

 

Just too little, too late for the Mid Atlantic. Talk about kicking you while you are down. Man.

 

 

[psuhoffman]

Thought I would illustrate for those that want to better understand why we're potentially stuck in a dead zone between two better areas of snow this week.  I know this isn't anything many don't already know but some of the new members might want to learn.  

First we have what's going on right now and causing the band of snow to our west/northwest.  The convergence along the front between the westernly cold flow behind the front and the backing SW flow ahead of it causes lift along the boundary and the snow that is to our west.  Problem is that boundary is slowing/backing, which is good in that it causes increased cross boundary flow and more lift, but if the boundary never actually gets to us that does us no good. 

Later today a coastal wave starts to develop off to our southeast.  The flow around this wave is going to inhance the lift along the arctic boundary.  Unfortunately that boundary is off to our northwest at this time so that does us no good. 

Finally, by the time the frontal boundary pushes east enough that we WOULD have been under the better lift the coastal wave has developed enough circulation to disrupt the convergence.  The wave is off to our northeast by that time so we don't ever really benefit from the easterly moisture feed from the wave, but the wave circulation cuts off the southwest flow along the front and thus kills the frontal band as it would have been over us.  To make matters even worse the closed circulation associated with the upper low swinging by to our further disrupts any weak moisture convergence we might have had along the front.  

There were so many ways this could have worked out better.  Had there been no wave at all, eventually the frontal boundary would have slowly pushed east and we would have had a decent 2-3" snow from that IMO.  

Had the coastal wave formed further south OR had the frontal boundary been situated over us as it developed (like that one good 0z GFS run 2 nights ago) we would have done very well.

Had there been no coastal wave with the front running weak piece of energy then perhaps the trailing vort (which is the better one honestly) would have developed like those euro runs a few days ago and we would have had the big coastal outcome like those couple of JMA/GGEM/Euro runs that teased us.  

But there was one scenario that sucked for us, get stuck between multiple waves, and that is exactly what "SEEMS" to be happening.  

Keep in mind I wrote this before any 12z data comes out and the one hope is that because this is a messier more complicated setup then a simple SW flow frontal passage perhaps the guidance is screwing it up enough that some of the better banding makes it across the area.  My heart says hold out hope, but everything the last 24 hours has been slowly bleeding towards my worse case scenario I threw out there a couple days ago so my brain says don't hold your breath.  Hopefully the guidance "sucks" one more time but in our favor.  They did totally miss the band that went just to the north last night and gave my area a coating, and they missed it by a LOT, if they are equally off by 40 miles or so with the next wave perhaps we get a surprise.  

[cae]

Looks like the RGEM made a good call on the overnight snow in northern MD.  The high-res RGEM missed it again.  That's two light events in the last 24 hours that the RGEM saw and the high-res missed.  The high-res RGEM seems to do well when the RGEM is too wet, but it misses some of these light events that the RGEM does well on.

[RevWarReenactor]

5 minutes ago, psuhoffman said:

Thought I would illustrate for those that want to better understand why we're potentially stuck in a dead zone between two better areas of snow this week.  I know this isn't anything many don't already know but some of the new members might want to learn.  

First we have what's going on right now and causing the band of snow to our west/northwest.  The convergence along the front between the westernly cold flow behind the front and the backing SW flow ahead of it causes lift along the boundary and the snow that is to our west.  Problem is that boundary is slowing/backing, which is good in that it causes increased cross boundary flow and more lift, but if the boundary never actually gets to us that does us no good. 

Later today a coastal wave starts to develop off to our southeast.  The flow around this wave is going to inhance the lift along the arctic boundary.  Unfortunately that boundary is off to our northwest at this time so that does us no good. 

Finally, by the time the frontal boundary pushes east enough that we WOULD have been under the better lift the coastal wave has developed enough circulation to disrupt the convergence.  The wave is off to our northeast by that time so we don't ever really benefit from the easterly moisture feed from the wave, but the wave circulation cuts off the southwest flow along the front and thus kills the frontal band as it would have been over us.  To make matters even worse the closed circulation associated with the upper low swinging by to our further disrupts any weak moisture convergence we might have had along the front.  

There were so many ways this could have worked out better.  Had there been no wave at all, eventually the frontal boundary would have slowly pushed east and we would have had a decent 2-3" snow from that IMO.  

Had the coastal wave formed further south OR had the frontal boundary been situated over us as it developed (like that one good 0z GFS run 2 nights ago) we would have done very well.

Had there been no coastal wave with the front running weak piece of energy then perhaps the trailing vort (which is the better one honestly) would have developed like those euro runs a few days ago and we would have had the big coastal outcome like those couple of JMA/GGEM/Euro runs that teased us.  

But there was one scenario that sucked for us, get stuck between multiple waves, and that is exactly what "SEEMS" to be happening.  

Keep in mind I wrote this before any 12z data comes out and the one hope is that because this is a messier more complicated setup then a simple SW flow frontal passage perhaps the guidance is screwing it up enough that some of the better banding makes it across the area.  My heart says hold out hope, but everything the last 24 hours has been slowly bleeding towards my worse case scenario I threw out there a couple days ago so my brain says don't hold your breath.  Hopefully the guidance "sucks" one more time but in our favor.  They did totally miss the band that went just to the north last night and gave my area a coating, and they missed it by a LOT, if they are equally off by 40 miles or so with the next wave perhaps we get a surprise.  

Thanks for the detailed explanation.

 

This is a brutal one given all that has transpired so far this year.

[Interstate]

As the front slows... The QPF will be robbed from our area.

[vastateofmind]

10 minutes ago, psuhoffman said:

Thought I would illustrate for those that want to better understand why we're potentially stuck in a dead zone between two better areas of snow this week.  I know this isn't anything many don't already know but some of the new members might want to learn.....

Thanks VERY much for this kind of explanation WITH visuals, psuH...helps long-time lurkers/learners like myself. Quick follow-on question -- how does all of this relate, if at all, to the IVT that was around yesterday, giving some of us pixie dust flurries just after the noon hour?

[Bob Chill]

Just now, vastateofmind said:

Thanks VERY much for this kind of explanation WITH visuals, psuH...helps long-time lurkers/learners like myself. Quick follow-on question -- how does all of this relate to the IVT that was around yesterday, giving some of us pixie dust flurries just after the noon hour?

That feature is completely separate from today. There was a slp spinning off the coast yesterday. The IVT was just a byproduct of proximity and is unrelated to was it coming through later. 

[mappy]

Great post, PSU 

[yoda]

Was this posted in the locked thread?  Sorry if it was, but interesting read -- morning AFD from LWX:

.NEAR TERM /THROUGH WEDNESDAY/...Cdfnt will cross the
Appalachians later today and slowly progress ewd reaching the
I-81 corridor by 00Z Wed. Snow today will fall mainly over the
upslope areas of the Appalachians behind the front/wind shift.
Some snow could also affect nrn MD counties along the Mason-
Dixon line but this is not a done deal as some models and
ensemble keep this area dry through much of the day.

Tonight and the first half of Wed is when the majority of
precip will fall as heights fall in response to approaching
upper level trof and forcing for upward vertical motion
increases. Deterministic models and their respective ensembles
depict precip breaking up as it crosses the mtns with a
secondary area of snow over the VA piedmont late tonight into
Wed. Ensemble QPF is generally 0.1 to 0.2 inches along and south
of the I-64 and west of the I-81 corridors. A big minima or hole
in the precip is shown over nrn VA and central MD. Even with
these small amounts of QPF, the very cold temperatures will
result in SLRs in the order of 15 to 1 and even a little bit of snow
potentially causing moderate impacts given sfc temps expected in
the mid 20s. It is possible that additional advisories may be
needed for the Charlottesville and Fredericksburg areas, but
since precip is not expected to begin until late second period
or perhaps closer to 12Z Wed decided to hold off on any
advisories. Also, our snow probs indicate only a 50% prob of
snow exceeding 2 inches and 80% confidence is needed. For the
metro areas, the prob of exceeding one inch is about 50-60%
which would require an advzy given snow is expected to impact
the Wed morning commute, but this is again late second or even
third period event.

[psuhoffman]

6 minutes ago, vastateofmind said:

Thanks VERY much for this kind of explanation WITH visuals, psuH...helps long-time lurkers/learners like myself. Quick follow-on question -- how does all of this relate to the IVT that was around yesterday, giving some of us pixie dust flurries just after the noon hour?

You're welcome.  The IVT was a neat little feature yesterday but it really had little to do with what is going on now.  Just was enough of a trough with a southeast flow along it to create some convergence/lift as it banked up against the cold air to get some light snow to some.  Those can be fun, and sometimes if there is enough moisture and a strong enough convergence zone along the boundary to create convection you can see some crazy results.  They tend to really be potent in the spring for that reason.  There was one in the 1940s on March 30th I think that gave Baltimore 20" and some places just NW of the city 30".  I had 3" in late March last year from one up here.  They are rare, very hard to predict accurately because of their meso scale features kind of like lines of thunderstorms, but they can be fun.  But that feature had no real effect on whats going on after.  

[ldub23]

23 minutes ago, Mdecoy said:

The end of the HRRR shows precip being enhanced once it gets into the Poconos, eastern PA.

 

Just too little, too late for the Mid Atlantic. Talk about kicking you while you are down. Man.

 

 

What  hour  is that?

 

[RevWarReenactor]

2 minutes ago, ldub23 said:

What  hour  is that?

 

Gonna be honest, I don't know how to determine times on the HRRR.

It says valid 6:30UTC, do I subtract 6 hours from that like the models?

[KingJWx]

1 minute ago, Mdecoy said:

Gonna be honest, I don't know how to determine times on the HRRR.

It says valid 6:30UTC, do I subtract 6 hours from that like the models?

6:30 UTC would be 1:30am

[eurojosh]

1 minute ago, Mdecoy said:

Gonna be honest, I don't know how to determine times on the HRRR.

It says valid 6:30UTC, do I subtract 6 hours from that like the models?

Minus 5 hours now we are in Standard Time.