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Wintry Dec 8-10th Winter Storm

Bsud said:
Myself I think the cutoff for wintry weather will be the I85 corridor. If you are North of there in upstate or NC then I think you are ok. Everyone else its gonna take a bit more luck to get anything frozen.

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I hope your right I’m just north of 85
 
NAM has the energy digging into Baja but it digs it a bit further north with a 1039 high at the end of the run.
 
The NAM will bring in the goods in a couple days and re amp everyone including myself, always does haha
 
Once were close to this event, I'm talking <18 hours, remember that the hrrr typically shows it way to warm for cad areas, very notorious for that until it is 4 hours out then it changes it back to a colder solution, just like those 2 November events for the mtn/foothills, just had to put this out there even tho were still days out
 
The s/w entering California by 48 hours is noticeably less consolidated & more diffuse on the 0z NAM than it is on the 18z GFS. We still have a few days to sort this out & either one of these solutions could be correct, but small details like this grow upscale non-linearly into large ones and are important to monitor for those of us downstream
nam_z500_vort_namer_17.png
gfs_z500_vort_namer_10.png
 
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Myfrotho704_ said:
Once were close to this event, I'm talking <18 hours, remember that the hrrr typically shows it way to warm for cad areas, very notorious for that until it is 4 hours out then it changes it back to a colder solution, just like those 2 November events for the mtn/foothills, just had to put this out there even tho were still days out
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The HRRR has a pretty horrendous BL mixing bias that causes it to scour out CAD too quickly, if we end up w/ a CAD event, I would definitely caution those on this forum from using it except when its within several hours or so of verification.
 
BirdManDoomW said:
Nothing “brutal” or “dramatic” has occurred today. Governmental agencies (like the WPC) have a good hand on things with current probabilities. They do not swing with op runs or wish cast. There is a clear signal for our first snowy winter storm for many people on this board. The sleet lines and etc. that skew totals will always be unclear..sometimes they can be revealed early but we are nowhere near that stage yet.
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This is a really good post. There has not been any dramatic shifting. But there has been some shifting. And it just illustrates how precarious this situation is. Small shifts in feature position or interaction can quite substantially change the outcome for many. There will be a lot more shifting.

My guess is what I said earlier: I think the SW will come ashore stronger than modeled. I think the CAD will be slower to erode than modeled. I do not see enough blocking to press everything far enough south for a southern sliding Miller A that wallops the entire SE. It will end up being Miller B-ish with marginal cold. CAD regions end up with a good winter storm. That’s what seems most likely to me, especially given the fact that models seem to always overestimate the cold press at 5-10 day leads.
 
Robert West said:
I don’t think anyone is giving up, I think being a little realistic and realizing, with the information we have, we aren’t heading in the right direction. I don’t see why taking notice to that is giving up.
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At this range it’s more about confidence not direction for anyone in this line of work. No one wants to be buried on a model solution on a Monday when the snow is several days away. There is no need to be overly realistic or concerned about specifics when we know that we don’t have all the data that we need to make a legitimate forecast.
 
Sandstorm94 said:
I live in Orangeburg, how do you think I feel?
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Well, you got hit last year. I heard Orangeburg county did pretty well depending on what part of the county you were in. So technically, it's been longer for us in Columbia. But as a whole, yes. Yall see it a lot less than us.
 
Webberweather53 said:
The HRRR has a pretty horrendous BL mixing bias that causes it to scour out CAD too quickly, if we end up w/ a CAD event, I would definitely caution those on this forum from using it except when its within several hours or so of verification.
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is there a study on this you can link?
 
*If* the CAD areas do score there is a growing chance of damaging floods by the end of the week. More heavy rain on top of muddy or leftover wintry mess would not be good. Could be the bigger story for some, two major precip events in early December on top of a wet Fall.
 
The icon established the cold temp but they quickly receded I can’t figure out why.
 
If 850s are below freezing on the icon for charlotte north, second half of the storm would support wet snow since temp hovers at 37 then drops
 
EastAtlwx said:
is there a study on this you can link?
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I've seen the model do this over & over again and this recent study justifies my presumptions and experience in using the HRRR for CAD. Other convective modeling and observational studies have pointed to a mixing bias, this one in particular noted weaknesses in the HRRR especially when mixed precipitation types are involved which only become exacerbated during cold air damming. The model represents the thermal profile reasonably well except the near-surface cold layer is either much weaker than observations or completely absent in the cases this study analyzed. It's a good paper worth reading over, I have denoted some of the highlights so others can get the gist of the paper's findings in a condensed manner.


"However, the surface temperature bias was ~4°C in weather systems involving cold-air damming in the eastern United States, resulting in an incorrect surface precipitation phase or the duration (areal coverage) of freezing rain being much shorter (smaller) than the observation"

"the model (HRRR) is generally less skillful in the mixed-phase precipitation areas than the rain and snow areas"

"The 24 January 2015 case (event F) also involved a pool of cold air (;08C), in a confined area in western Virginia to the east of the Appalachian Mountains after a passage of the rain–snow transition boundary. However, because of a warm bias the forecast did not represent the cold-air damming well. This is reflected in the disagreement in the lower-altitude profile structure between the model and the Roanoke, Virginia (RNK), skew-T sounding (Fig. 5f). The surface inversion is much weaker and the upper layer above the inversion layer is colder in the model than in the observations, implying very different microphysical processes."

"The surface temperatures from the HRRR model forecasts were too warm yielding precipitation phase errors in the examined cases with thin cold-air layers related to cold-air damming, which produced longlasting and widespread freezing rain in the eastern United States. For a few of the examined cases, the predicted precipitation phase maps showed a region of mixed-phase precipitation associated with the cold-air damming and observed mixed-phase region; however, the spatial extent was smaller and the temporal duration was shorter than the observations."

"The warm bias in surface temperature was as large as 4C and was much larger than the ‘‘close call’’ cases mentioned above. This is perhaps partly related to the HRRR model not having enough evaporative cooling from precipitation (in terms of strength and duration) based on the time history comparison of the observed and predicted precipitation rates among other possible reasons that were not fully investigated in this study."

https://journals.ametsoc.org/doi/pdf/10.1175/WAF-D-16-0171.1
 
Webberweather53 said:
I've seen the model do this over & over again and this recent study justifies my presumptions and experience in using the HRRR for CAD. Other convective modeling and observational studies have pointed to a mixing bias, this one in particular noted weaknesses in the HRRR especially when mixed precipitation types are involved which only become exacerbated during cold air damming. The model represents the thermal profile reasonably well except the near-surface cold layer is either much weaker than observations or completely absent in the cases this study analyzed. It's a good paper worth reading over, I have denoted some of the highlights so others can get the gist of the paper's findings in a condensed manner.


"However, the surface temperature bias was ~4°C in weather systems involving cold-air damming in the eastern United States, resulting in an incorrect surface precipitation phase or the duration (areal coverage) of freezing rain being much shorter (smaller) than the observation"

"the model (HRRR) is generally less skillful in the mixed-phase precipitation areas than the rain and snow areas"

"The 24 January 2015 case (event F) also involved a pool of cold air (;08C), in a confined area in western Virginia to the east of the Appalachian Mountains after a passage of the rain–snow transition boundary. However, because of a warm bias the forecast did not represent the cold-air damming well. This is reflected in the disagreement in the lower-altitude profile structure between the model and the Roanoke, Virginia (RNK), skew-T sounding (Fig. 5f). The surface inversion is much weaker and the upper layer above the inversion layer is colder in the model than in the observations, implying very different microphysical processes."

"The surface temperatures from the HRRR model forecasts were too warm yielding precipitation phase errors in the examined cases with thin cold-air layers related to cold-air damming, which produced longlasting and widespread freezing rain in the eastern United States. For a few of the examined cases, the predicted precipitation phase maps showed a region of mixed-phase precipitation associated with the cold-air damming and observed mixed-phase region; however, the spatial extent was smaller and the temporal duration was shorter than the observations."

"The warm bias in surface temperature was as large as 4C and was much larger than the ‘‘close call’’ cases mentioned above. This is perhaps partly related to the HRRR model not having enough evaporative cooling from precipitation (in terms of strength and duration) based on the time history comparison of the observed and predicted precipitation rates among other possible reasons that were not fully investigated in this study."

https://journals.ametsoc.org/doi/pdf/10.1175/WAF-D-16-0171.1
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awesome. i will read before bed. currently being tortured with finals.
 
Southern s/w looks weaker thru hr 48.
gfdLQly.gif
 
ICON looks down right chilly compared to seasonal norms for days leading up to the storm. This is an alarming signal to me for better confidence of wintry pecip. There IS going to be dry cold air that gets locked in esp mountains/foothills. Most winter storms (when they do occur) tend to find the tail end of cold air that is hard to dislodge. It’s likely going to end up colder and colder. Watch out and pay attention to what is occurring leading up to the storm in these micro areas..possibly Piedmont included.
 
Man some of y'all got to learn to look at the big picture and not just whether or not a model is showing blue or pink over your house. The end of the NAM and that ICON run should give you hope, that was a huge improvement on the very warm biased ICON imho
 
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