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Wintry February 19-21, 2020 Winter Storm

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Other than the change in blocking sig, not totally sure why we see the big change in temperatures. Maybe Webb or somebody will know but this is the big kicker of this run.

In terms of the setup in general, I have no doubt that most of our areas will get the precip. The question is temperatures.
 
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Meanwhile Canadian is slightly colder with good moisture


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There's a healthy amount of precip on the UKMET that is south of I-20 at the end of the run (when you do 24 hour QPF).

Surface temps are blazing though and the 850s look meh.

Edit: And based off the GEFS that I just glanced at, we better start praying that the Euro reverses the concern of cold air more than precip honestly.
 
Euro spins in some refreshingly low DP’s after we all get whiffed. So that’s a pretty cool consolation I think62D57233-48CA-48A3-8E92-7D14A61586AA.jpeg
 
Looking at the surface it’s actually not that bad of a trend here...euro looked completely different yesterday, now it’s moving away from forming an ULL at all. Maybe we can actually hit the lottery and trend stronger with the northern stream and trend back toward the snowy solution. Here’s hoping
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Along with low-mid level warm advection & isentropic upglide, another important source for lift in an overrunning setup like this is frontogenesis, especially in the mid-levels of the troposphere (often ~700mb) where snow growth is occurring in clouds.

In addition to stereotypical NWP biases w/ warm advection, I also have a real hard time believing the GFS precipitation distribution being entirely south of I-20 given how strong the frontogenetical forcing is in the dendritic growth zone (DGZ) over northern AL & GA, upstate SC, and southern NC in the model (purple contours). Strong frontogenesis like you're seeing on the GFS, is often (but not always) a harbinger of intense, banded precipitation, especially for locations just on the warm side of where the frontogenesis is occurring. In this case that would be just to the south of where the most intense frontogenesis is occurring over far northern SC, southern NC, northern GA & AL. Basically, the I-20 corridor from Atlanta to Columbia to roughly Wilmington NC would be most favored for intense banded precip attributable to frontogenesis.


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To offset imbalances imparted by increasing frontogenesis, a thermally direct secondary circulation is created, wherein those just to the warm side of the most intense frontogenesis also correspond to strongly forced ascent and vis versa on the cool side. I suspect here that if the frontogenesis is actually as strong as advertised in a global model like the GFS, that a significant fraction of the total frontogenesis & forced ascent is possibly being smoothed out (& hence being removed) due to the coarse spatiotemporal resolution of the model. Thus, its precipitation & corresponding temperature output may also be erroneous.



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Webberweather53 said:
Along with low-mid level warm advection & isentropic upglide, another important source for lift in an overrunning setup like this is frontogenesis, especially in the mid-levels of the troposphere (often ~700mb) where snow growth is occurring in clouds.

In addition to stereotypical NWP biases w/ warm advection, I also have a real hard time believing the GFS precipitation distribution being entirely south of I-20 given how strong the frontogenetical forcing is in the dendritic growth zone (DGZ) over northern AL & GA, upstate SC, and southern NC in the model (purple contours). Strong frontogenesis like you're seeing on the GFS, is often (but not always) a harbinger of intense, banded precipitation, especially for locations just on the warm side of where the frontogenesis is occurring. In this case that would be just to the south of where the most intense frontogenesis is occurring over far northern SC, southern NC, northern GA & AL. Basically, the I-20 corridor from Atlanta to Columbia to roughly Wilmington NC would be most favored for intense banded precip attributable to frontogenesis.


View attachment 34425





To offset imbalances imparted by increasing frontogenesis, a thermally direct secondary circulation is created, wherein those just to the warm side of the most intense frontogenesis also correspond to strongly forced ascent and vis versa on the cool side. I suspect here that if the frontogenesis is actually as strong as advertised in a global model like the GFS, that a significant fraction of the total frontogenesis & forced ascent is possibly being smoothed out (& hence being removed) due to the coarse spatiotemporal resolution of the model. Thus, its precipitation & corresponding temperature output may also be erroneous.



View attachment 34426
Click to expand...

Elongated, quasi-stationary, frontogenetically forced bands of precipitation that tend to characterize overrunning events are often a reason why they can be so awesome for snow lovers in the SE US.
 
National Weather Service Greenville-Spartanburg SC
345 AM EST Sat Feb 15 2020

In terms of the potential for moisture return over the post frontal
air mass later in the new week, while the Canadian GEM still offers
some potential for wintry weather on Thursday, the 00Z ECMWF
continued its "clean" fropa and cold/dry trend of the past couple of
model runs, while the GFS is showing signs of coming around to an
ECMWF-like solution. We have therefore begun trending toward a drier
forecast Wed through early Thu, but will still retain small pops
(generally 20-30%)...with snow mtns and rain elsewhere...until
run-to-run consistency has been established in both major global
models. After beginning the period above normal, temps will fall to
below-normal levels by the end of the period, and actually a solid
10 degrees below normal for next Thu night/Friday.
Click to expand...
 
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