Weekend Snowfest/Rainfest/Mixed Mess?

[psuhoffman]

Just throwing out some similar setups... the h5 definitely supports the threat here but we have had mixed results in similar situations.  

This is the current and its similar across guidance right now.  EPO and AO ridge pressing the cold into the CONUS...lower heights centered to our NW but with a transient 50/50 feature to hold the cold in as the wave approaches...timing will be everything.  Need enough separation to allow the front to clear to our south, but not enough to let the return flow push it back to our north.  We have won with this look before but its a timing thing and not something that is high probability...we need to get lucky.  

This is a somewhat similar setup from March 2015.  No two are exactly alike but its close enough to notice.  This was a win.  One difference was the front was pressing as the second wave came across.  Much less separation.  Actually the cold almost didn't make it in and we lost some good qpf to snow but the second wave was slow enough that we still did good.  These things are tricky...not enough separation or too much and its rain.  Its a thread the needle for sure.

This is the wave the day after the Super Bowl in 2014.  This teased the area but then ended up trending north the last 24 hours and was a fail.  The setup is also similar but just ended up 50 miles north of where we want...thats just bad luck.  Parts of extreme northern MD and southern PA had 6-10" from this.  There was less of a 50/50 feature with this wave so perhaps that was the death blow for our area. 

 

[usedtobe]

12 minutes ago, high risk said:

      That's certainly possible.   I suspect that sleet explains much of the difference between the NAM snow accum and positive snow depth;  I'm just too lazy to track it down...

The sounding for DCA at 84 hrs has the deep isothermal layer with the temp and dewpoint right at 0.2 C.  That could be heavily rimed snow or sleet.  My guess if the sounding were perfect that would get you heavily rimed snow.

[Maestrobjwa]

4 minutes ago, psuhoffman said:

Just throwing out some similar setups... the h5 definitely supports the threat here but we have had mixed results in similar situations.  

This is the current and its similar across guidance right now.  EPO and AO ridge pressing the cold into the CONUS...lower heights centered to our NW but with a transient 50/50 feature to hold the cold in as the wave approaches...timing will be everything.  Need enough separation to allow the front to clear to our south, but not enough to let the return flow push it back to our north.  We have won with this look before but its a timing thing and not something that is high probability...we need to get lucky.  

This is a somewhat similar setup from March 2015.  No two are exactly alike but its close enough to notice.  This was a win.  One difference was the front was pressing as the second wave came across.  Much less separation.  Actually the cold almost didn't make it in and we lost some good qpf to snow but the second wave was slow enough that we still did good.  These things are tricky...not enough separation or too much and its rain.  Its a thread the needle for sure.

This is the wave the day after the Super Bowl in 2014.  This teased the area but then ended up trending north the last 24 hours and was a fail.  The setup is also similar but just ended up 50 miles north of where we want...thats just bad luck.  Parts of extreme northern MD and southern PA had 6-10" from this.  There was less of a 50/50 feature with this wave so perhaps that was the death blow for our area. 

 

So do we have more of a 50/50 feature with this one than the one from 2014?

[showmethesnow]

44 minutes ago, BristowWx said:

Agree I suppose.  Still lean on GFS.  Either way you won’t care about anything once the fever takes hold and you get a bonus except where is the waitress with your drink.  NAVGEM gives pause.  NAM does too.  Not sold on anything yet

Not a knock on you whatsoever but of all the models I could care least about, the Navgem and the NAM at range are probably at the top the list (guess you could throw in the RAP, HRRR, etc... as well). But as far as the GFS, yeah its weaker more progressive solution could very well be the correct one. For the southern section of our region that is probably a winning solution though the upside would be limited. But the one problem with the GFS is that it can flip from one extreme to another from one run to the next. 12z could very well come out with an over amped low running through our region and I would not be surprised. So at this range I still put more weight on the GEFS. Euro on the other hand is less prone to extreme flips and normally slowly moves to a final solution so it is much easier to gauge what that final solution is. Of course I still depend on the EPS a good deal too at this range (probably 50/50 between the op and ensembles).

Of course I just looked at the NAM and like what I see so maybe it isn't as bad as I think. 

[psuhoffman]

2 minutes ago, Maestrobjwa said:

So do we have more of a 50/50 feature with this one than the one from 2014?

Yes, but we also don't have quite as much EPO and AO ridging...so it might be a wash.  Every setup is slightly different and with so many variables that play off each other its hard to use an h5 analog to pin the rain snow line within a few miles like that.  Missing a wave by 30-50 miles like that is more bad luck then the upper level pattern not supporting it.  Small variances that would be hard to pinpoint can lead to that.  I was just pointing out how we have both won and lost with this kind of setup so its not out of the question that we walk away with our biggest snowfall of the season (not saying much) but its also possible this fails...(if it does my bet is it trends north as I've said).  

For every one of those H5 analogs I posted for an HECS I can find a similar one that failed and the storm didn't come together at the surface.  Even in a perfect setup we need some luck.  Its just a matter of how much luck we need.  Less for a better setup obviously.  This isnt an awful one, its a typical way we can win in a progressive pattern with a southeast ridge...but we can also lose too.  Lets just roll the dice and see what happens.  

[yoda]

From this morning's LWX AFD

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Main focus of the long term is Saturday and Saturday night. The
latest guidance has trended towards better odds of wintry
weather.

Guidance is in good agreement regarding a dry start to Saturday,
with high pressure centered to our north allowing chilly
Canadian air to dominate. A wave of low pressure will be
developing along the front which moves through Friday in the
southern Plains, however, and it will rapidly spread clouds and
precipitation east-northeast. The GFS, GGEM and ECMWF all
overspread the region with precipitation during the afternoon
Saturday, with precip ending from west to east as the low heads
out to sea Saturday night. There remains some uncertainty about
low and mid level temperatures, with potential for a mid-level
warm layer resulting in some sleet and freezing rain, as well as
potential for warm surface temps to limit accumulations or even
cause snow and ice to mix with rain. Greatest potential for this
is naturally across southern portions of the CWA, from
Charlottesville eastward towards Patuxent River, but mixing
could easily occur further north. In addition, not all models
show a significant snowfall just yet, with potential for the
wave to take a course a bit further north or south than the
current consensus. That all having been said, potential is
definitely there for a significant snow storm. This potential
will be closely monitored over coming days.

[BTRWx's Thanks Giving]

The high moves off the coast too fast for enough frozen precip on the gfs.

[yoda]

2 minutes ago, BTRWx's Thanks Giving said:

The high moves off the coast too fast for enough frozen precip on the gfs.

Its a decent snowstorm for those in N MD and N and W of I-95

[yoda]

Piecing together the jumpy 12z GGEM hours via 2mT looks like snow for us... hr 90 2mT is 31 at DCA

[Maestrobjwa]

Hm...Is this GFS run a touch colder than the 06z? (a touch less amped?)

[BristowWx]

This is deadly range for GFS.  This season at least it is.  Doubt it at your own peril.    

[yoda]

5 minutes ago, yoda said:

Piecing together the jumpy 12z GGEM hours via 2mT looks like snow for us... hr 90 2mT is 31 at DCA

Hr 84 is 32 degrees at DCA... so perhaps a nice wet snowstorm...

850s good to go... nice precip slug comes through.. should be decent QPF total

[BristowWx]

1 minute ago, yoda said:

Hr 84 is 32 degrees at DCA... so perhaps a nice wet snowstorm...

On the GGEM or GFS?

[yoda]

Just now, BristowWx said:

On the GGEM or GFS?

12z GGEM

[BristowWx]

Just now, yoda said:

12z GGEM

Thanks.  12z GFS looks like rain...all rain south of roughly N. MD based on 850s...and each run since 0z has increased 850 temps and 2m.  Do you agree?

[yoda]

QPF is ~1.25" at DCA through 102... subtract 0.3 as rain before the weekend system... and you get .9 QPF as snow on 12z GGEM

[yoda]

4 minutes ago, BristowWx said:

Thanks.  12z GFS looks like rain...all rain south of roughly N. MD based on 850s...and each run since 0z has increased 850 temps and 2m.  Do you agree?

no... its snowing at IAD hrs 84 and 90

[Bob Chill]

Going with climo (and stating obvious things), far northern areas have the highest chance at all snow...duh. This is an insitu cad situation. That can work for ALL of us IF precip comes in hot an heavy as quick as possible. If the column is all snow at onset it will take some work to break the midlevels. Probably happen slower than what the globals show. There are plenty of cases in the past when snow hangs on longer during a thump. 

If precip lags and comes in tepid...then the column has an easier time turning on you. My guess is my yard almost surely mixes but if the front side thump is real I'll already have a decent accum on the ground before mixing. Just a guess. 

[BristowWx]

3 minutes ago, yoda said:

no... its snowing at IAD hrs 84 and 90

Ok.  Sounds good.  Didn’t look like snow to me at 84 but you are a Jedi...no position to argue.  

[Bob Chill]

Even though TT shows mix, this is an all snow sounding. Mix is based on surface temps only and we're only talking 34 degrees. No warm nose here. It's all snow. 

[MN Transplant]

This is the warmest sounding at DCA, where we lose the 850s barely.  After this, the 850s cool and the 900-950 layer warms so the whole thing just rides the 0C line.

 

[CAPE]

Per WB CMC looks like a 3-5" storm for much of the region. The 5 is in PSU's yard.

[Interstate]

10 minutes ago, yoda said:

QPF is ~1.25" at DCA through 102... subtract 0.3 as rain before the weekend system... and you get .9 QPF as snow on 12z GGEM

That would be some heavy wet snow

[Bob Chill]

Midlevel winds start off SE @ hr 84 and then switch to W-NW by hr90

 

Verbatim for DC it would start as snow...then mix for a bit...then end as snow. If the GFS is just 1 degree too warm in the mids then it's all snow. 

[Eskimo Joe]

Looks like DP is in the low 20s upper teens before precip starts Saturday.  As Bob said, if precip comes in hot and heavy folks could wet bulb down quick and get a decent pasty surprise.

[Bob Chill]

1 minute ago, Eskimo Joe said:

Looks like DP is in the low 20s upper teens before precip starts Saturday.  As Bob said, if precip comes in hot and heavy folks could wet bulb down quick and get a decent pasty surprise.

Yea, this is when knowing your yard > models. We've all had borderline events break good and bad. The good ones are usually the ones that start off right and not the ones where you wait for the flip. This one is starting off right. That's a big deal for areas walking the line. I'm good with rime, sleet, rain, or whatever as long as I start and finish with snow and measure a couple inches. That seems like exactly what "should" happen in my yard. Upper moco will be a sweet spot as will be parrs and the northern tier. This looks like a standard climo borderline storm that starts off on the right foot. I like it. 

[psuhoffman]

8 minutes ago, Bob Chill said:

Going with climo (and stating obvious things), far northern areas have the highest chance at all snow...duh. This is an insitu cad situation. That can work for ALL of us IF precip comes in hot an heavy as quick as possible. If the column is all snow at onset it will take some work to break the midlevels. Probably happen slower than what the globals show. There are plenty of cases in the past when snow hangs on longer during a thump. 

If precip lags and comes in tepid...then the column has an easier time turning on you. My guess is my yard almost surely mixes but if the front side thump is real I'll already have a decent accum on the ground before mixing. Just a guess. 

Feb 25 2007 was a nice surprise where marginal temps held on with insitu cad because precip came in as a thump and dynamic cooling was able to hold off WAA until it was basically over.  

[Eskimo Joe]

1 minute ago, Bob Chill said:

Yea, this is when knowing your yard > models. We've all had borderline events break good and bad. The good ones are usually the ones that start off right and not the ones where you wait for the flip. This one is starting off right. That's a big deal for areas walking the line. I'm good with rime, sleet, rain, or whatever as long as I start and finish with snow and measure a couple inches. That seems like exactly what "should" happen in my yard. Upper moco will be a sweet spot as will be parrs and the northern tier. This looks like a standard climo borderline storm that starts off on the right foot. I like it. 

Maybe we'll get lucky and everyone jackpots with a 8" - 10" paste bomb.

[MN Transplant]

5 minutes ago, Bob Chill said:

Midlevel winds start off SE @ hr 84 and then switch to W-NW by hr90

 

 

Verbatim for DC it would start as snow...then mix for a bit...then end as snow. If the GFS is just 1 degree too warm in the mids then it's all snow. 

Conversely, a degree the other way and this is white rain for DC.  Much better to be N&W for this one.

[Bob Chill]

1 minute ago, psuhoffman said:

Feb 25 2007 was a nice surprise where marginal temps held on with insitu cad because precip came in as a thump and dynamic cooling was able to hold off WAA until it was basically over.  

I remember that one. Potatoes and pretty. lol

As long as the track holds (seems like it is right now) then I know what to expect. An acceptable storm but unlikely to hit warning criteria in my yard. GFS/CMC/ICON all have near identical tracks. And they all work for most everyone until you get pretty far SE. Pretty good look so far @ 12z.