March 13/14th PSU Storm

[Maestrobjwa]

Just now, NorthArlington101 said:

Yep. And you can tell that map is valid because of the D.C. snowhole as well. 

That ain't even right, lol How does that even happen? (and it's the only spot in the region!)

[Bob Chill]

2 minutes ago, Maestrobjwa said:

That ain't even right, lol How does that even happen? (and it's the only spot in the region!)

For reasons only the dead know, it happens more often than you think. 

[nj2va]

Snowfall contest:

 

[das]

1 hour ago, leesburg 04 said:

DTs says GFS has been terribly inconsistent 

This just does not jive with reality.  The GFS has been a rock for 3 days now.  It'll either score the coup.  Or not.

[Thanatos_I_Am]

Haven't seen anyone comment on SREFs lol. Are they in range yet?

[Cobalt]

Just now, Thanatos_I_Am said:

Haven't seen anyone comment on SREFs lol. Are they in range yet?

Not sure about that either. Anyone got a picture of the SERF plume?

[DanTheMan]

[dallen7908]

Was comparing the 18Z GFS and 12Z Euro for DCA

Both show an 8 PM start and ~0.1, 0.15, and 0.2" of QPF between 8-11 PM , 11 PM to 2 AM, and 2-5 AM; GFS 850 hPa temperatures decrease from -2 to -4 during that period while EURO 850 hPa temperatures increase from -3 to 1. GFS surface temperatures fall from 33 to 30 while Euro surface temperatures hover around 34/35. 

From 5 AM to 11 AM the GFS continues to show moderate snow with QPF values of 0.2 and 0.2 (~ 1 1/2 inches of snow per hour if we go with an 8 to 1 ratio); Surface temperatures rise slowly from 30 to 32. 

From 5 AM to 11 AM the Euro shows heavy precipitation with QPF values of 0.36 and 0.27. 850 temperatures plunge during this period of heavy precipitation and are -4.5 by 11 AM; surface temperatures decrease slightly from 34/35 to 33/34. 

Both models show intermittent light snow /flurries through the afternoon into the late evening with post-11 AM accumulations of ~1". 

 

[Cobalt]

7 minutes ago, DanTheMan said:

That's really good. 1"-1.25" of QPF, all snow or near im assuming?

[high risk]

      With the GFS being, for the most part, the coldest and snowiest model for DC Metro, it's worth pointing out that the GFS often underdoes those "sneaky warm layers."   In the January 7-8 storm, our friends in the Raleigh-Durham area though they were headed towards an awesome snow total, and they ended up with a big 'ole sleet fest.   The GFS led the way in the cold, snowy camp.    Overall, the hi-res guidance did better than the lower-res with figuring out the snow/non-snow line, and we looked at the performance of most of the NCEP production suite on the thermal profiles in central NC, and the new 3 km NAM nest led the way.      We've found that the GFS ends up too far southeast with the position of the snow/mix line in a lot of big eastern systems.

        I'll readily admit that it's possible that the GFS has the best handle on the synoptics, and that's what is driving its snowier solution.   And my example is a single case.   But as we get closer to game time, it becomes less wise to ignore the thermal profiles of the regional/hi-res models.

      

[Cobalt]

1 minute ago, high risk said:

      With the GFS being, for the most part, the coldest and snowiest model for DC Metro, it's worth pointing out that the GFS often underdoes those "sneaky warm layers."   In the January 7-8 storm, our friends in the Raleigh-Durham area though they were headed towards an awesome snow total, and they ended up with a big 'ole sleet fest.   The GFS led the way in the cold, snowy camp.    Overall, the hi-res guidance did better than the lower-res with figuring out the snow/non-snow line, and we looked at the performance of most of the NCEP production suite on the thermal profiles in central NC, and the new 3 km NAM nest led the way.      We've found that the GFS ends up too far southeast with the position of the snow/mix line in a lot of big eastern systems.

        I'll readily admit that it's possible that the GFS has the best handle on the synoptics, and that's what is driving its snowier solution.   And my example is a single case.   But as we get closer to game time, it becomes less wise to ignore the thermal profiles of the regional/hi-res models.

      

Euro was very South in last year's blizzard, just to name it as well

[eurojosh]

Just now, high risk said:

      With the GFS being, for the most part, the coldest and snowiest model for DC Metro, it's worth pointing out that the GFS often underdoes those "sneaky warm layers."   In the January 7-8 storm, our friends in the Raleigh-Durham area though they were headed towards an awesome snow total, and they ended up with a big 'ole sleet fest.   The GFS led the way in the cold, snowy camp.    Overall, the hi-res guidance did better than the lower-res with figuring out the snow/non-snow line, and we looked at the performance of most of the NCEP production suite on the thermal profiles in central NC, and the new 3 km NAM nest led the way.      We've found that the GFS ends up too far southeast with the position of the snow/mix line in a lot of big eastern systems.

        I'll readily admit that it's possible that the GFS has the best handle on the synoptics, and that's what is driving its snowier solution.   And my example is a single case.   But as we get closer to game time, it becomes less wise to ignore the thermal profiles of the regional/hi-res models.

      

Buzzkill.

 

Just kidding - thanks, this is really great insight.  But would you prefer GFS over regional/hi-res models for track?

[Yeoman]

Radar sim from latest WRF run..

[nj2va]

2 minutes ago, Cobalt said:

That's really good. 1"-1.25" of QPF, all snow or near im assuming?

The SREFs are mostly useless, especially in events like this.  Better to go with a blend of global/hi res for now but defer to hi res beginning tomorrow to pick up on Synoptics, deform band, dry slot, thermals, etc.

[Eskimo Joe]

Man that WRF run is something nice...has a decent comma head too.  Would be money for everyone.

[snjókoma]

Here's a nice site to watch the NAMs roll in with precip contours every .1 inch.

http://www.atmos.albany.edu/student/tburg/analysis/loop.php?model=nam3

[yoda]

Updated AFD from LWX as of 9:30 PM

.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
Winter storm warnings out for the most confident where majority
of zones will meet warning criteria of 5" in 12 hours and 7" in
24 hours; roughly west of I-95 including DC and Arlington/
Alexandria. Confidence fairly strong on track from NC capes
northeast along, just off the Delmarva Monday night through
Tuesday morning. SEly low level flow on the north side of the
low center will send a warm nose into the CWA and produce rain
and sleet. This nose will likely be stopped by strong dynamic
cooling in the deformation zone of the warm conveyor wrapping
and lifting around the low. The snow/wintry mix line looks to
reach inland as far as I-95 per the GFS and a little farther
west in the NAM/ECMWF.

Sweet spot still in the deformation zone band where max lift is
in the dendritic growth zone. This looks to set up west of mix
line to the Shenandoah Valley where a foot or more is possible.
The addition of elevation to places like the Blue Ridge and
Parr`s ridge in northern MD will maximize snow in that area.
Should the peak band be over areas with higher elevation, 18"+
are possible as indicated on our max snow graphics at
weather.gov/lwx/winter/.

This will be a heavy/wet snow, sub 10:1 snow to liquid ratios
while the low is south/east of the area. Wrap around snow after
the low passes will occur for a few hours over the area. Lower
temperatures at this time will allow ratios above 10:1. This
wrap around band looks to cross the Balt-Wash metro area during
the Tuesday AM commute, roughly 6am to 10am. This could be the
heaviest snow of the event for areas along/east of I-95.

The low is expected to track northeast off the New Jersey shore
Tuesday afternoon with the heavy band shifting northeast of
Harford county by noon or so. However, as the surface low moves
out, the upper level closed low approaches from the northwest.
PVA ahead of this low will result in intermittent snow Tuesday
afternoon and evening. Max temps Tuesday low to mid 30s. Perhaps
some peaks of sun between showers Tuesday afternoon.

The actual upper low crosses the area Wednesday morning with
persistent flurries/light snow showers and more robust upslope
snow west of the Allegheny Front.

[winterymix]

For the Winchester peeps, here is the sref plumage fwiw.

 

 

[Warm Nose]

2 minutes ago, yoda said:

Updated AFD from LWX as of 9:30 PM

 

 

North and West of 95 - all snow.

East and south of 95 - mixing.

Pretty safe bet around here.

[dallen7908]

6 minutes ago, snjókoma said:

Here's a nice site to watch the NAMs roll in with precip contours every .1 inch.

http://www.atmos.albany.edu/student/tburg/analysis/loop.php?model=nam3

Thanks for the site ... and it automatically links to the "best" NAM, i.e, the 3-km one off of the parallel 12, although I see that is the 18 UT run. 

[Eskimo Joe]

Sterling's evening AFD did a great job of laying out all the pieces.  I think Das mentioned it a page back, but it would be interesting to see if LWX entertains the idea of splitting AA & PG counties along US 50 next winter.  This certainly is a scenario where that county split would help.

[WinterWxLuvr]

2 minutes ago, winterymix said:

For the Winchester peeps, here is the sref plumage fwiw.

 

 

Thanks for posting

[BTRWx]

2 minutes ago, Warm Nose said:

North and West of 95 - all snow.

East and south of 95 - mixing.

Pretty safe bet around here.

Not to banter, but is this really out of here before the Tuesday A.M. rush or did they mean Wednesday? lol

[high risk]

6 minutes ago, eurojosh said:

Buzzkill.

 

Just kidding - thanks, this is really great insight.  But would you prefer GFS over regional/hi-res models for track?

 

        Yes.    But my point is that as we get close to gametime, the GFS and the regional and hi-res models *should* start to agree on the overall synoptics, including track.     Right now, the GFS and the regional models disagree on the thermals, but that could be because the GFS is handling the synoptic pattern better.    Once they agree on the synoptics, I would tend to give less weight to the GFS thermals.

        Of course, with this storm, we may not reach synoptic accord until halfway through the damn event.....

 

[winterymix]

4 minutes ago, WinterWxLuvr said:

Thanks for posting

The mean is 12", I hope you have that by sunrise.

[high risk]

12 minutes ago, Yeoman said:

Radar sim from latest WRF run..

  

         It looks beautiful, but can you please be more specific about where this run comes from?    Calling it WRF tells us nothing.     The NAM is a version of the WRF.  The Hi-Res Windows are a version of the WRF.    The RAP and HRRR are versions of the WRF.     Many universities and WFOs run their own version of the WRF.

 

[Yeoman]

3 minutes ago, high risk said:

  

         It looks beautiful, but can you please be more specific about where this run comes from?    Calling it WRF tells us nothing.     The NAM is a version of the WRF.  The Hi-Res Windows are a version of the WRF.    The RAP and HRRR are versions of the WRF.     Many universities and WFOs run their own version of the WRF.

 

Sorry - GFS-WRF out of Stony Brook

[Bob Chill]

11 minutes ago, high risk said:

 

        Yes.    But my point is that as we get close to gametime, the GFS and the regional and hi-res models *should* start to agree on the overall synoptics, including track.     Right now, the GFS and the regional models disagree on the thermals, but that could be because the GFS is handling the synoptic pattern better.    Once they agree on the synoptics, I would tend to give less weight to the GFS thermals.

        Of course, with this storm, we may not reach synoptic accord until halfway through the damn event.....

 

Really appreciate the insight and pointing out performance with the NC storm earlier this year. Honestly, I'm surprised the GFS pretty much makes it an all snow storm for the majority of our region. I've been looking at it like having wiggle room because I fully expect to mix at some point. Places further east are a near certainty. I'm just hoping to minimize the loss of precip to something other than snow. I made a post earlier today saying that regardless of what models are spitting out, past history tells us that the likelyhood of mixing in the typical areas is very high with this type of storm. There's going to be strong atlantic fetch at the surface and midlevels for a time while the pivot happens. 

My guess is the WAA part with southerly flow will be all snow for most everyone. Midlevels are really good leading in an it's really cold right now leading in. Once radar takes on that strong east-west component I'm sure the CC panels on radar are going to show the classic sleet line bearing down on us. How far east it gets before the pivot is anyones guess. My guess is it makes it to my house. Hopefully it's short lived before high ratio CCB/deform kicks in. 

[Buddy1987]

Watch the NAM again. 500 is digging again on the 0z and the southern energy is significantly more west than the 18z position at hr 12 0z

[eurojosh]

6 minutes ago, high risk said:

 

        Yes.    But my point is that as we get close to gametime, the GFS and the regional and hi-res models *should* start to agree on the overall synoptics, including track.     Right now, the GFS and the regional models disagree on the thermals, but that could be because the GFS is handling the synoptic pattern better.    Once they agree on the synoptics, I would tend to give less weight to the GFS thermals.

        Of course, with this storm, we may not reach synoptic accord until halfway through the damn event.....

 

Thanks, I'm learning a lot from this.

So what do you do when the tracks are different for the global vs regional models?

For example, if we compare the 18z GFS and NAM at 36 hrs, the NAM has the LP further offshore, but despite this, has warmer 850s approaching DC.  So, if we take the GFS track, but the NAM thermals, we get even warmer temps near DC.  OTOH, if the NAM's thermals depend on its track, why would we use it at all when the track is different?

 

Images for reference: