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Wintry Feb. 19-20

word to the wise if the gulf convection sets up like that then this is one of those rare times it needs to be watched for moisture transport issues (gulf stealing our moisture, in the parlance)
Yes and both the HRRR and 3k NAM have been consistent on showing that since last night
 
Seems like gulf coast convection is gonna play a big part in how much qpf there is to go around and who gets what. Idealy we get almost no gulf convection and everybody gets better qpf.

Worst case we get a horizontal line of convetion racing out over the gulf and hardly anyone gets qpf except Far NE NC, and they can actually get even more in this scenario b/c it seems to initiate a transfer to the coastal quicker.

Models are all over the place with how the convection works out. The RAP is the best case scenario, imo. It basically has no convection in the gulf.
 
Below is the early Jan event and the GFS/3km 24 hr out...different event and all but the 3km was too aggressive with the warm nose...GFS was more right at 24 hours out. The RGEM was clearly too cold though.


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Rap: Best case with gulf coast convection
Hrrr: Worst case with gulf coast convection

View attachment 170370View attachment 170371
Now, the question is ... how can you possibly know which one is going to pan out? Also, what minor tweaks need to happen upstream to prevent the transport issue from occurring? At what point do these two models diverge?
 
My takes.

1-3" seems like a safe bet for CLT, though the WRF-NSSL provides an example of what the boom potential could be with this storm. My caveats on both sides is one, a potent band could set up giving a few localized areas more snow and two, mixing is becoming a worry for me.

Even with the worst possible convection, I feel like there would be more expansive(note: I said expansive, not heavy) precip than a lot of the models are showing given the jet streak, RH, and the frontogenesis. The past two storms had dry air be an issue, dry air isn't an issue this time. Precip might be light, but I won't be surprised if by early afternoon tomorrow light precip goes up to the foothills.

That post-storm feature could easily beef up final totals for the western half of NC if everything goes right.
 
Now, the question is ... how can you possibly know which one is going to pan out? Also, what minor tweaks need to happen upstream to prevent the transport issue from occurring? At what point do these two models diverge?
To directly answer your question, just a matter of luck. Same way you don’t know if the summer thunderstorm is going to soak Raleigh or Zebulon.

Since the RAP is a coarser resolution, I also don’t think it’s the best comparison.

Honestly I wouldn’t *stress* about this feature, if gulf storms are the do-or-die thing that kills your chances of snow, well, you were on a fine line anyway lol
 
from a degreed climate scientist I know...he blew the last one, didn't think we'd get much, but is usually good on these hard to predict
systems(he's mainly talking far north Ala/south Tenn.
Somebody in our area is gonna get a good snow out of this. One thing intrigues me about some of the latest simulated soundings. Models are now indicating a mostly isothermal layer from surface to near 700 mb, which is absolutely classic for heavy snow aggregate formation. Noticed NAM has increased our totals again, although it has been back and forth. Low track/frontogenesis location looks good to me. Most of the data show us being immediately downstream of where 300/200 mb height contours transition from cyclonic to anticyclonic which is awesome too. Also get the feeling that we may not be getting the whole story yet from the model output snow amounts. Those simulated profiles are looking better and better. Wouldn't be surprised if someone nearby gets 4 to 6" out of this. Could be wrong.
 
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Seems like gulf coast convection is gonna play a big part in how much qpf there is to go around and who gets what. Idealy we get almost no gulf convection and everybody gets better qpf.

Worst case we get a horizontal line of convetion racing out over the gulf and hardly anyone gets qpf except Far NE NC, and they can actually get even more in this scenario b/c it seems to initiate a transfer to the coastal quicker.

Models are all over the place with how the convection works out. The RAP is the best case scenario, imo. It basically has no convection in the gulf.

Haven’t models recently overdone Gulf Coast convection? Or am I hallucinating lol


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12z Trends on the ICON/Rgem/GFS were wonderful for the upstate. They're all bringing a band over heavier qpf right over i85 tomorrow morning. That's what it will take to get any accumulations here.

06z runs had this band too far south on all those models.
 
I'd shove the southern edge of the big snow gradient a bit north of the GFS and drop it right over central Wake County instead of central Johnston-Harnett.
Any thoughts on western regions? Triad, CLT, etc... Looks like there might be a sliver of precip max in the I-85 corridor.
 
I'd shove the southern edge of the big snow gradient a bit north of the GFS and drop it right over central Wake County instead of central Johnston-Harnett.
I agree with you Webb, but other than the NAM it looks as if other models are trending to having the boundary layer and sleet skewed further east. Probably won’t know until game time, however.
 
Flow starting to look solid along the NC/TN border. These things tend to overperform. FV3 starting to pick up on it. 12+ Newfound gap?IMG_1645.jpeg
 
I agree with you Webb, but other than the NAM it looks as if other models are trending to having the boundary layer and sleet skewed further east. Probably won’t know until game time, however.

Most models (esp globals) just don't have sufficient vertical resolution to fully resolve the warm nose aloft, or even spatially to see the kind of horizontal snow gradients we're likely gonna have near the US 64 corridor.
 
The kind of snow gradient we might see in/around Wake County here could definitely rival storms like Dec 2018 & Feb 2015.

There will probably be a massive sensible difference between places like Wake Forest vs say Garner & Fuquay-Varina.
Its ok we're used to it in Garner. Happy to get anything based on how the last few years have gone!
 
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