high risk

Most of the 12Z mesoscale guidance today showed that the organized snow would have a really tough time making it into the DC Metro area, and that seems to be playing out.

10 minutes ago, WxUSAF said:

Think we can get the snow band to hang on over the mountains with it? Euro and NAM have hinted at it…

     Maybe?    I haven't looked at the mechanics of why this band is way out ahead of the actual arctic boundary.    Another possibility is a few scattered bursts of snow right on the late night front....

Looks like roughly 3AM(west)-5AM(east) timing for the passage of the arctic front.      

32 minutes ago, ThePhotoGuy said:

Single digits forecast but so far haven't hit it yet this year. Will this break the streak? Probably not. 

     I understand the skepticism, but those forecasts were relying on intense radiational cooling late at night, and clouds/wind seemed to wreck those opportunities.   This will be pure advection of an intensely cold air mass, and it's legit arctic air.   I think this has a much better chance (and I'd say it's very likely) of single digits.

46 minutes ago, MN Transplant said:

We are going to ruin a top-tier cold day on Saturday with a midnight high.  

   Indeed.    Looks like mid 20s at midnight.   In fact, it stays in the mid 20s through around 4am, and we then drop at least 20 degrees in the 4-5 hours following.

33 minutes ago, North Balti Zen said:

Ucinelli - I'd rather be in Bismarck...

      I gave 1/2 of a laughing emoji for the concept of this comment and 1/2 for the utter butchery of Louis' name

4 minutes ago, MillvilleWx said:

HRRR is best when it's inside 8 hrs, but can more useful up to 12 hrs if it is assimilating the data correctly. It has its struggles with certain setups and is best within convective environments or well-established thermal environments. Winter is not its strong suit, but can be useful at times. Right now, regional CAMs are better at handling this type of setup. Best ascent has been modeled south through the day, but some very light precip is still plausible north of I-66,  but not looking likely at this point. 

       VERY well stated.   The HRRR is generally pretty good with warm season convection (minus some flaws and the inherent challenges with modeling weakly-forced storms) but has never proven itself as a winter weather model.

Saturday looks brutal, with temps in the mid to upper teens and sustained winds in the 20-30mph with higher gusts.

2 minutes ago, Maestrobjwa said:

Just enough to make the commute messy? Haha

          With how cold surfaces have been, even a half inch of snow at night would likely cause problems on some of the roads, with the ungodly amount of leftover salt possibly saving us from a complete mess.    School systems will have a complicated decision.

16 minutes ago, bncho said:

AI-GFS south again,

 

     Was not a total miss.   It had a very modest amount of snow about 24 hours earlier than the map you showed, with some sort of lead wave.

15 minutes ago, T. August said:

It precipitates for like 48 hours with no panel getting over .1” lol. Yeah technically it is indeed half an inch of liquid.

       AI models don't do particularly well with QPF.    They get a general shape of the field but struggle to resolve amounts and detail.    I'd focus far more on 500 heights and SLP.

3 minutes ago, SomeguyfromTakomaPark said:

Is it just me or is this product virtually useless?  Every time it gets posted in here it's like a crucial step behind the good models.

             The mean has very limited value at this range, because a few snowy ensemble members can skew it.    The probabilistic output is far more useful, but I'm not sure how easy it is to find that on the web.

I'm looking forward to those 4 hours above freezing on Tuesday!    

13 minutes ago, Amped said:

Hugging the nbm 

 

          This is exhibit A for the problem with using mean values from a large ensemble.    There are a handful of GEFS and ECMWFE members with huge snowfall totals, so the mean value ends up as a couple of inches.   But the 50th percentile map shows 0 for our area, and the chance of 1" of snow at KDCA is under 30%.

7 minutes ago, MN Transplant said:

Sunday is going to be nasty with temps in the teens for much of the day and wind gusts at least into the 30s.

      Absolutely.   With that low pretty much guaranteed to bomb somewhere east of us, there is solid model agreement in a strong wind field over the Mid-Atlantic.   

49 minutes ago, Chris78 said:

I thought @high risk stated a few days ago that it's heavily weighted with ensembles leaning more on the EPS family  if I understood him correctly. 

    Ok, 3 things going on here:

  1)   The winter suite in the NBM is only updated at 01, 07, 13, and 19Z.    So, if you're showing an 18Z cycle for this medium range case, it's as "stale" as you can have it.

  2)  In the medium range, the only inputs are the 50 ECMWF ensemble members, the 30 GEFS members, and the GFS.   It doesn't even include the deterministic ECMWF run (don't ask).    Some of the CMC members are now included in the parallel.   Here is what you're going to hate:   the NBM does not yet receive the 06/18Z ECWMF data.   And at 19Z, the ECMWF ensemble has not yet arrived.    So, the 18z cycle in question is still using the very snowy 00Z ECMWF ensemble.   That's what's driving the big numbers.    

  3)  One additional factor:  bias correction is performed for QPF for the global model inputs, and the bias-corrected QPF is used by the NBM winter suite.   The bias correction, based on the based 90 days of forecasted and observed QPF in this case is bumping up the QPF for the event, as it believes that the ECMWF ensemble has been running dry.    So, you have some inputs with high raw precip values that are being further adjusted up.    

            That's why the 18Z NBM looks so snowy.   The 01Z cycle coming out soon will use the 12Z ECMWF ensemble and the 18Z GEFS;  based on what I see in the QPF of those systems, my guess is the NBM snowfall will be a fair amount lower, although the bias correction might boost it a bit more than I expect.

27 minutes ago, Weather Will said:

WB 18Z NBM

 

          Always like seeing NBM images here, but    1) this cycle reflects the 00Z Euro ensembles and not the less snowy 12Z        2) The NBM mean, like any ensemble mean, can be skewed by a handful of very snowy members.   FWIW, the latest NBM cycle still keeps the probability of an inch or greater of snow this weekend at under 50%.

8 minutes ago, yoda said:

Hmmmm... 13z NBM

     The NBM at this range gives heavy weight to the 00Z EPS, so this is exactly what I'd expect to see.

1 hour ago, WxUSAF said:

@high risk your 13-14z call for the mix time was spot on.  Was about 1330z for MBY.  But this mix of sleet and needles is interesting.  Visibility is way lower than normal for a predominant sleet precipitation event.  I'm curious how this will accumulate.  I think @csnavywx and @Terpeastwere suggesting we're getting snow to crystallize below the inversion to mix with the sleet that's coming from higher up?

               I'd like to take credit for a call, but I rode the NAM Nest.    If I had a dollar for every "LOL NAM" and "the NAM sux" posts in the past 3 days, I could have retired early.   I completely understand the skepticism back on Thursday and Friday, but once we got inside of 36 hours and it didn't budge, I thought it had a high likelihood of verifying with p-type, even if it did a poor job with QPF prior to the flip.

1 hour ago, bncho said:

Will this greatly improve the verification scores of the American models? Will the GFS be an actual model to consider once this new core is implemented?

         I'm not a huge fan of FV3, so I would hope so.   One big thing is that a fully-coupled GFS will be implemented later this year, which should be very helpful.   That means a lot of things, but it means that the atmosphere, water, land-surface, and sea ice will all "talk" to each other.

1 minute ago, WxUSAF said:

Definitely not dismissing it for us. I’m mentally assuming a changeover somewhere between the times the NAM and euro suggest. Maybe 15-16z for us?

      I would love if it takes that long, but I'm mentally prepared for 13-14z.  

7 minutes ago, MN Transplant said:

 

I have just enough knowledge of this to be dangerous, but high risk can correct me.  Models have a dynamical core and various physics packages.  About a decade ago NOAA/NWS decided to try to align all of the operational models with a single dynamical core.  The FV3 was chosen but there have been some problems with it when it is run at finer convection-allowing resolution.  So, the alternative was MPAS (model for prediction across scales) from NCAR.  I know that NSSL has been testing out MPAS a lot and that one may end up being the dynamical core.  One of the problems with MPAS, though, is that it is computing-hungry compared to FV3.  So, NOAA is weighing pros and cons.

              You are spot on.   MPAS is going to replace FV3 in RRFS Version 2, and it will probably be used across the board eventually in the NWS models.

Just now, DDweatherman said:

I thought the fv3 was the next gen gfs? And I had heard here it wasn’t going to make it to the big game for a while still if it did

        The GFS does use the FV3 core now.     That has been the case since 2019.

4 minutes ago, DDweatherman said:

that actually made me laugh out loud. Serious question for a sec, why did the FV3 GFS replacement never game big time? 
 

on this storm, it has been consistently colder and snowier for most than the other suites, but not all that different than the OP GFS. Does it have a published cold bias that just can’t be corrected? 

     With apologies, what do you mean by the "FV3 GFS replacement"?   

6 minutes ago, stormtracker said:

maybe @high risk can explain.  Maybe lends to NAM being too dry.   Weenie hope

        It's pretty clear that the NAM is slow with the leading edge of the precip.    It definitely has a bias of being too slow to advance precipitation into very dry air.     The 18Z cycle doesn't bring snow into DC until 6Z, and I doubt it will take that long.   It's probably good reason to ignore its QPF for the front end thump and go with wetter models.    That said, none of that means that it must be off with the timing of the transition to sleet.    It might very well be too fast with that, but I wouldn't base that off of not getting snow to the ground quickly enough at the leading edge.