Christmas Blizzard 12/20 - 12/28

[Tom]

8 hours ago, gabel23 said:

Looks like the current gfs and today’s euro. 

My gut the other day was right and I firmly believe your in the game!  I had a thought the other day that this storm had some '09 flavor and wouldn't ya know...now a lot of our NE members could see the flakes flying on Christmas night!  What a delight that will be!

[Black Hole]

I picked up 0.43" at my place from the rain last night. That puts me at 0.99" on the month. 

 

The next leg of the storm ought to be wetter. Models disagree on totals as convection looks to be active, but 1-2" seems like a reasonable bet with some locally higher spots southeast of here. So this ought to bring us up to about normal for the month. I don't see any other big systems through the end of the year down here. 

[Tom]

6 hours ago, gabel23 said:

Looks like euro is holding true. I’m loving the trends tonight… The only problem is what happens to the area of low pressure? Looks like trends are slowing down and the euro has occlusion occurring over Iowa; that would bode well for heavy snow to the northwest. Gfs, cmc, and nam are also starting to show that as of tonight…

I would love to see this storm create that tight spin on radar and satellite which can produce an "Eye" like in a Hurricane.  Based on what I'm seeing, this system can certainly produce such an event.  There is no doubt in my mind that this system will be dynamic.  The valley out here is expecting to see training thunderstorms as the powerful ULL tracks into the area.

Speaking of rain, a wall of rain just started to come down out here....let it rain!

 

[Madtown]

anyone got the Euro 6z snow through the 27th?

[Clinton]

Using the LRC and thinking about where the precip has fallen and where it hasn't since October, I really lean more toward the Euro with the majority of the snow falling from northern Nebraska into SC Minn.

 

[bud2380]

1 hour ago, Madtown said:

anyone got the Euro 6z snow through the 27th?

6z Euro only goes out to 90 hours, which is 6pm on Christmas Day.  But here it is.  

 

 

[bud2380]

12z NAM, not terribly far off from the Euro.  Further SE with the SLP, but both throw snow back into Nebraska. 

 

[hawkstwelve]

A nice improvement in snow totals on the latest NBM this morning.

I've been hesitant to share this model because NWS FSD has mentioned a couple times in recent AFDs that they believe it's bias-correcting temperatures are overdoing it. They have said that it doesn't always perform the best during a pattern change because it bias-corrects based on recent observations, which in this case it has been warmer than modeled for so long that it wants to automatically correct in that direction. They expect it to lower temperatures in upcoming runs, which this could be a sign of it starting to do.

[bud2380]

The NBM is just the NWS Blend of Models, so it's taking all the models input and "blending" them together to put out essentially an average forecast between the models.  In a sense it's an ensemble forecast.  Without knowing or understanding the inputs it's hard to make a lot of conclusions, but in my experience looking at it, it usually is slow to update to new trends. I'm guessing because it probably includes older model runs in it, so until those filter out it still influences it's final forecast.  I could be off base, but that is how I have understood it over the years.

[Black Hole]

The further north track on the low makes sense to me that we are seeing this morning. It keeps the snow out of here too but I never really expected it either. 

[hawkstwelve]

7 minutes ago, bud2380 said:

The NBM is just the NWS Blend of Models, so it's taking all the models input and "blending" them together to put out essentially an average forecast between the models.  In a sense it's an ensemble forecast.  Without knowing or understanding the inputs it's hard to make a lot of conclusions, but in my experience looking at it, it usually is slow to update to new trends. I'm guessing because it probably includes older model runs in it, so until those filter out it still influences it's final forecast.  I could be off base, but that is how I have understood it over the years.

Here's a snippet from yesterday morning's FSD AFD that explains a little better what I ineloquently discussed above. You're correct in that it blends models together to give a single output but it also has bias-correcting features baked in that cause it to struggle a little more when experiencing a pattern change.

Adding to this challenge
is NBM probabilities for rain remain higher than the freezing/frozen
precip types at times, even while the NBM mean surface temperature
falls below freezing. This may be due, in part, to NBM temperatures
incorporating some level of bias-corrected members (correction to a
model forecast based on previous verification errors), and this bias
correction tends to be overdone during pattern significant pattern
changes such as we are seeing with this system, coming out of a
prolonged dry stretch in which diurnal ranges were maximized. At the
same time, precipitation probabilities do not take these temperature
corrections into account, which would seem to imply that the raw
membership of the NBM is favoring a warmer scenario despite what the
mean temperatures may indicate.

[hawkstwelve]

12z vs 06z ICON. Most of this falls between 9PM Christmas and 6AM Wednesday.

[Grizzcoat]

12Z RDPS- still snowing. Would be doozie for many 

[hawkstwelve]

12z GFS already with much more snow than the 06z run showed for Nebraska through 3PM Christmas.

[Hawkeye]

There is a terrible model trend for eastern Iowa.  For days, models showed the north-south band of rain training up through the area.  However, the upper low is now being shifted west, which leads to the training rain shifting west and dry air being pulled into eastern Iowa from the east.  Also, the surface low now stalls farther west and north, so we now get dry-slotted with no wrap-around precip.  At this point I think 2" of rain is gone and we have to hope we can get 1".  

Look at this ridiculous change on the GFS in only 24 hours. 

[hawkstwelve]

12z GFS is much further to the northwest with the low than previous runs. Comparing this to the 06z GEFS member low locations map from earlier, it's on the extreme NW side of possibilities so take that for what it's worth.

 

[hawkstwelve]

Meanwhile, the 12z CMC is way heavier on the backside of the initial band on Christmas Eve. Some spots wake up Christmas morning with 2-6 inches on the ground. This is before the second low really gets its act together over Iowa.

 

Which leads to this by the time we get to midnight on Wednesday (and it's still snowing by this point). Wow. I guess you could say the CMC has come around big time to the GFS/Euro solutions.

[CentralNebWeather]

5 minutes ago, hawkstwelve said:

12z GFS is much further to the northwest with the low than previous runs. Comparing this to the 06z GEFS member low locations map from earlier, it's on the extreme NW side of possibilities so take that for what it's worth.

 

That wraps way back over me. 

[CentralNebWeather]

12z GFS 

[MIKEKC]

What the heck is going on here, weird path to the storm and it snows in KC for 24 hours...and many other places too.

[CentralNebWeather]

We will have to see what the 12z Euro does. It’s 06 run that ends at 90 hours, looked similar to the 12z GFS. 

[hawkstwelve]

Here's a comparison of the 12z GFS and CMC side-by-side by the time the snow has ended. Add in recent Euro runs and I'd say it's starting to become a better bet that some places are going to get slammed, barring a last minute collapse in the models.

What a nice trend we are experiencing down the home stretch...

[gabel23]

No thank you on the 12z gfs. That retrograde west shuts off precip and snow. I continue to like the look of the early stages of the nam. Come on and hold serve euro.

[bud2380]

Models always seem to struggle with these types of systems.  This one seems no different with wild swings from run to run and widely varying solutions.  The general idea is there, so that's the good news.  But where this thing ultimately ends up and how much is anyone's guess right now.  Gonna be fun to watch it unfold, even though I'm clearly on the warm side of this storm through it's duration.  Just hoping to get some heavy rain out of it. 

[Black Hole]

The CMC is the last model showing any snow here in Christmas. It doesn't look realistic either so I am just banking on enjoying the heavy rains the day before at this point. 

[Grizzcoat]

 12zUkmet about 2-3 counties E compared 00z.

[Tom]

I’m sitting here reading all your posts and watching the models and thinking I’m right with y’all tracking a potential Christmas festive miracle!  It’s exciting to see this storms evolution in the data that’s coming in.  @Grizzcoat, I pray that the snow Gods deliver for your area so that the NWS Mets eat crow!  They should know better.

[hawkstwelve]

12z vs 00z CMC ensembles. Big jump in the mean for many spots...

Also, some probability maps for 1+ and 3+ inches...

[Clinton]

1 hour ago, MIKEKC said:

What the heck is going on here, weird path to the storm and it snows in KC for 24 hours...and many other places too.

One can dream that the Canadian pulls it off lol.  But I like it!

[bud2380]

Everyone in here waiting for the Euro to run.

[bud2380]

Euro with a shift NW. 

[bud2380]

The Euro just hammers parts of SD and NE.

 

 

[gabel23]

Gfs and euro almost exact same spot. CMC on its own now…wouldn’t surprise me if this is what will happen. I’m cursed!

[james1976]

TC went from looking pretty good back to zilch 

[CentralNebWeather]

At one point, maps had heavy snow in KC. Now Nebraska and South Dakota. Who knows, might be in North Dakota in later runs if this continues. 

[CentralNebWeather]

9 minutes ago, gabel23 said:

Gfs and euro almost exact same spot. CMC on its own now…wouldn’t surprise me if this is what will happen. I’m cursed!

You and I would be about the same on this Euro run. 

[bud2380]

Rain totals dropping on the Euro, but still good.  

 

[CentralNebWeather]

Western Nebraska, Eastern Colorado and Wyoming were supposed to get hammered. They will seemingly be left with little or nothing if trends continue. 

[hawkstwelve]

12z vs 00z EPS...

[bud2380]

Placement is very similar there.  Just got a lot stronger.  A bit of a NW shift, but well within expected shifts at this range.