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Wintry Jan 27-28 Snow Potential Official Thread

I'm still amazed at how this has trended. I haven't seen any trends this wild since I've been following models
 
I can't stress this enough: the window for accumulating snow is about 4 hours, maybe 5 (for the Triad). That's not much time for accumulations, but then again the lift is super impressive.
 
This stuff will clump to any and everything. Should make for some pretty sights Thursday, assuming we get that 3 to 6 hour paste bomb. Stretch the branches out for the big one Sunday lol.
 
The ETA Model in 2000 is The Nam today. Has trouble with these storms deepening off the coast. Good read on model error back then , that took everyone by suprise.
Model Error


In general, forecast models preformed very poorly during this event. An example of this is shown in the image below which compares the 48 hour, observed liquid equivalent precipitation with the Eta model 48 hour forecast valid at the same time (click on the image to enlarge, image provided by Michael Brennan, NC State University). The model failed to capture the significant precipitation over the Carolinas and Virginia; in fact the Eta forecast had no precipitation over Raleigh and Richmond where over an inch of liquid equivalent was observed.

Eta model precipitation error

As forecasters scrambled to adjust forecasts to reflect the unfolding snowstorm, there was little time to analyze the full reason why the forecast had gone bad. In the wake of the storm, many were left wondering how nearly two feet of snow could have fallen in less than 24 hours with very little warning. Was there something that could have been analyzed ahead of time that would have lead to questioning of model precipitation forecasts? Or was there a physical mechanism that was misunderstood, or missed by the models? Below is a brief summary of some of the forecast errors and research topics that arose from this case.


Incipient Precipitation and Latent Heat

An area of precipitation developed along a frontal system over southern Alabama and southern Mississippi at around 06Z on January 24, 2000. The area of precipitation expanded and intensified as it moved into the cold airmass north of the front in Georgia by 12Z on January 24. Analysis of surface observations and radar imagery show that this area of precipitation was poorly forecast by the Eta model. Research into this storm indicates that this under forecasted area of precipitation that fell into a cold and somewhat dry airmass across the Deep South had a significant impact in how the models handled the developing storm system.

Based on quasi-geostrophic (QG) theory, height rises (falls) occur above (below) a mid-level latent heating maximum, due to changes in the density of the air above and below. This response also creates a low-level maximum in cyclonic potential vorticity (PV), as low-level static stability is increased. The effects of the induced cyclonic PV max are manifest in wave amplification and enhanced rotation around the PV center. The precipitation across the Deep South induced a PV anomaly that enhanced the easterly flow downstream, creating stronger westward moisture advection over the Carolinas from off the Atlantic (Brennan and Lackmann 2005), thereby extending the heavy snowfall further inland. The inability of the models to accurately predict the precipitation across the Deep South was a major reason that the model forecasts of this storm were so inaccurate.

The combination of increased moisture advection, enhanced dynamics, and a deep subfreezing column of air (see GSO soundings below), created an environment that was primed for intense winter weather
 
Great trends all day. Wonder what the NAM will show, but all the globals and the other short range models continue to look better.
 
ryan1234 said:
Yup. But why is that surprising? I don't think I could ever have zero respect for anyone in the scientific community. But JB takes the cake. I can't stand that man. Anyhow, let's focus on this next week. Hoping for the best, for all of us!
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I have nothing against Bastardi other than if weather isn't affecting the NE, it's not happening lol. Good luck to you snowbirds to the north of me, I hope you guys cash in!
 
The one thing that's sort of irked me about this setup is the track of the 850 mb low directly through NC. We ideally would have that track further south, so as to avoid any warm nose woes. This problem has been largely offset by the strong confluence from a 50/50 low, giving a decent cold air source and the system a NW --> SE dive. Even as our wave has trended slower and more amped, the slowdown has allowed the second piece of cold air push (the upper level low over Canada) to pull a bit further ahead of the wave, reinforcing (improving even!) our cold air source.

But the 18z --> 00z HRRR trend is the first I've seen to buck that, with a slightly stronger, worse-oriented 850 low and warmer temps as a result. The sensible effects are minor in part because QPF was better this run, but changeover in Wake County was delayed by a few hours this time around. That changeover always seems to be done too fast, for that matter- don't need to go back more than a few weeks to find an example of that. If there's one thing I'm watching over the next day it's this- the only potential wrench I see for the time being.
hrrr_850_caution.gif
I'm actually hopeful for the time being that this 18z/00z change was more random noise/a blip, because it doesn't really fit the rest of the steady trends we've seen today. It's just a subtle thing I wanted to point out to keep an eye on. It's also something that I'd guess would be a problem for Raleigh and points SE. Those further north seem to be, as expected, timing things better with the cold air.
 
Broken024 said:
I don't doubt the nam. I've had gfs and ensembles show 8 inches while nam show all rain and goose egg. Good luck sir
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After today I bow down to the NAM. It is my savior . Whenever I go to pray to it on tropical tidbits I make sure to bow down, and not make eye contact unless told to. NAM is life .

Anyways the trends on the HRRR and NAM would give places like Greenville and Raleigh a tad to worry about . We shall see what they say tomorrow .
 
Lickwx said:
After today I bow down to the NAM. It is my savior . Whenever I go to pray to it on tropical tidbits I make sure to bow down, and not make eye contact unless told to. NAM is life .

Anyways the trends on the HRRR and NAM would give places like Greenville and Raleigh a tad to worry about . We shall see what they say tomorrow .
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Yep it may show some crazy snow totals but if it showing dogshit I'd be concerned.
 
We haven't had any problem getting precip all month. Really going back to all of last year. I just don't buy the NAM over all the other models that have continued to increase or hold steady with the precip and snow amounts. I really wonder when they tried to fix the NAM's bias of overdoing precip if they made it just as bad in undergoing precip.
 
I'm booked for Gatlinburg. Leaving 3 am in the morning.
 
Broken024 said:
I don't doubt the nam. I've had gfs and ensembles show 8 inches while nam show all rain and goose egg. Good luck sir
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It's not just the GFS. It has support from other global and short range models.
 
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