high risk

13 minutes ago, TSSN+ said:

How anyone can even talk about the Nam seriously is hilarious. Just in comparison here’s the last 3 runs of Rgem and Nam for current 6hrs Rgem pretty steady, nam not so much 

 

        There are plenty of valid arguments against the NAM, but making that point by showing changes across cycles of an forecast of what the lowest level radar reflectivity will look like at one particular moment, and then comparing that to a 6h-averaged precip rate from a different model doesn't make your case.

5 minutes ago, Eskimo Joe said:

IMO, it's rimmed snow, but that's snow.

                  God, I really hope you meant "rimed". 

24 minutes ago, Weather Will said:

WB 12Z NBM para

  Love that you showed the para!   Friendly reminder that the NBM winter fields update at 01, 07, 13, and 19Z, so instead of showing the 12Z, it's best to wait one hour and use a version that incorporates more recent guidance.

2 minutes ago, TSSN+ said:

Where is the cold air btw? Temps are running +5 to +10 over modeled currently around our region.

   The arctic front doesn't come through until Friday evening, but when it does, the freeze is on.    Multiple models show upper 30s at 4pm falling to low teens by 1am.

2 minutes ago, wxmeddler said:

I was aware that the FV3 based RRFS got absolutely shellacked in testing with offices and centers. It originally also supposed to go to 72hrs only and there was outcry of loosing the extra 12 hrs the NAM provided. They *points vaguely* folded on both thankfully 

        Yes, but we're still going to get 2 years of the FV3-based RRFS in operations.

2 minutes ago, wxdude64 said:

Temps at a first glance, but I have a hard time thinking it would be off that much ?

    Big warm layers can easily reside in between those two levels.   Some of the forecast soundings I have seen for this event show that exact scenario.    The NAM precip type code is rock solid, based on the forecasted temperature profile.

Just now, wxdude64 said:

Somehow the column between ground/850/700 is -2 to -8 and it is showing sleet?? Right. 

    Are you looking at the actual sounding, or just the temperatures at those levels??

17 minutes ago, Terpeast said:

Thanks for pointing that out. The 12k and 3k might as well be two different models. May sound like a weenie, but I’d lean more on the 3k within 48 hours of onset. 

        They differ in more than just resolution, so they effectively are two different models (even though they have obvious commonalities).    As you said, though, the 3 km is a far superior model, except for when it deepens hurricanes down to 850 mb.

3 minutes ago, wasnow215 said:

Sorry off the topic here High Risk but since you're a met maybe you can help.

Why do you think Wakefield is using such strong verbiage about concern with an ice storm for Richmond then?

Are they basing it solely on the Euro?

In this area many businesses and obviously hospitals etc. etc. are making some difficult decisions, grocery stores have been ransacked with everything bought off the shelves in cases, because we keep being told that we are going to have a massive ice storm, and that it's not possible but actually probable most of the area loses power.

Because let's face a few inches of snow here and then sleet that is not a big deal at all.

       The Euro and its ensemble contribute heavily to the NBM, which is the starting point for these forecasts.   And I disagree with you:  several inches of snow followed by a ton of sleet would be a very big deal at these temperatures.

2 minutes ago, Ralph Wiggum said:

Exactly. @high risk already mentioned this would be ran on Saturday 1/24

   No, no, sorry.   I clearly wasn't nearly as clever as I thought with that post.   I am expecting that the happy hour NAM Nest cycle right before the storm will go bonkers.   

5 minutes ago, bncho said:

To straighten things up.
There are only two versions of the NAM Nest. The regular 'ol 12k NAM and the hi-res 3k NAM. There is no such thing as a 1.33k NAM (that I know of).

The 3k NAM should start to get into range for this storm by 0z tomorrow night, where it starts to enter its useful range.

Hoped that helped.

        Apologies for bursting your bubble, but @wxmeddler is correct.    There is a 1.33 km relocatable NAM Nest used for fire weather purposes that can be used for other types of events during non-fire-weather season.    There used to be graphics online, but I don't think that there are anymore.    And I think they've stopped running it for events like these. 

6 minutes ago, T. August said:

Not only that, but the individual panels are eerily uniform. Almost no variation in track or strength. I wonder how useful they truly are for precipitation.

   The AI ensembles tend to me under dispersive even in the medium range, so it's really no surprise that you're seeing very little spread as we enter the short range.

I'm sure that this has been hashed out, but I want to emphasize that we're in that time range at which the differences in NAM precip type could simply be driven by synoptic errors, common for a regional model at this range, but they can't be discounted completely due to the NAM being the absolute best at precip types *once it has nailed down the synoptics*.      I also would never fully trust the GFS precip type maps *even when it has nailed down the synoptic*.   It often underplays the coverage of IP/ZR.

Oh, and a friendly reminder that the model cycles all start at the same time every day, and they don't ever "stop".   (They can crash once or twice per year, but it's so rare.)   There can easily be dissemination issues, usually driven by way too many hits to a server during exciting events, which delay the arrival of everyone's favorite online maps.

Curious 18z GFS evolution for the Thursday wave

46 minutes ago, Jersey_Snowhole said:

Anyone know what the accuracy skill is of the NBM?

I could tell you what its Critical Success Index value for 24h snowfall at Day 3 is, but what would you do with that number?         For the most part, it’s as good as the inputs it uses, but the operational version right now is running high, because it’s bias correcting QPF upward based on a very limited sample of recent significant QPF events in the very dry Mid-Atlantic.  

37 minutes ago, anotherman said:

It's just a blend of ALL the models.  Not sure how accurate it is, but I do know it includes some of the models we always make fun of.

So, you don’t actually know that.    The winter part of the NBM at this range only includes the NAM, GFS and its ensembles, and the Euro and its ensembles.   The para includes some of the Canadian system as well. 

5 minutes ago, stormtracker said:

      Just some speculation that this cycle will NAM the crap out of us.

If you liked that GFS run, you're going to LOVE the 18Z NAM Nest on Saturday.    

1 minute ago, midatlanticweather said:

Does it have a score for accuracy? 

    Stats are generated, but the comparisons are to the WFO forecast grids, since the NBM is the starting point.   It generally scores well if the input models are doing well;  it performs bias correction, but that has limitations.    

Just now, nj2va said:

It seemed way more reasonable than the ‘regular’ NBM.  Are they retiring the ‘regular’ in favor of the parallel?

        It's not really a retirement.   It's an upgrade, just like is done routinely with models.    Goal is to live in April.

1 minute ago, nw baltimore wx said:

That’s got to be kuchera, right?

      The NBM does not use Kuchera.   It uses a mix of different SLR techniques.

1 minute ago, nj2va said:

Actually that was the NBM Parallel, so many models geez.  Here’s the ‘regular’ NBM…never knew there were multiple NBMs.

             I recommend using the parallel for the winter stuff - it's much improved for those products

2 minutes ago, baltosquid said:

Lol I mentioned how rough it was earlier. Idk I have a suspicion this thing ain't ready for prime time but I guess I have to look closer at <48 hrs to see how it really fares. Or maybe we will get skunked.

            The issue is that any regional model is likely to struggle beyond Day 2 due to the influences of the boundaries.    People love to punch the NAM, but a lot of good mets realize that the NAM Nest can do some great things inside of Day 2.    I suspect we're going to find out the same for RRFS......

4 minutes ago, psuhoffman said:

HRRR at range is pretty useless 

        The bigger issue is that the critical wave is near the western boundary of the HRRR.

quick NBM comment:  thrilled to see lots of NBM images, but it should be noted that the parallel NBM is about 3-5" lower with snow totals in the local area.   The issue is that the QPF feeding into the winter suite is bias-corrected based on the forecasts and observations over the past 3 months, and it has been very dry here.   As a result of the training sample having few high QPF events, the bias correction breaks down a bit, and for this case, it is boosting the already high QPF amounts even higher.   The parallel has some changes to prevent seeing this as an extreme event, and it is not adjusting the QPF upwards like the ops.   To be clear, the para still has a major event for us, as it should;  it's just not in the HECS category.