• Hello, please take a minute to check out our awesome content, contributed by the wonderful members of our community. We hope you'll add your own thoughts and opinions by making a free account!

Wintry Dec 8-10th Winter Storm

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?
Click to expand...

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
Click to expand...
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
 
You must log in or register to reply here.
Back
Top