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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.


gfs_temp_adv_fgen_700_seus_23.png





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.



gfs_mslp_pcpn_frzn_seus_22.png
 
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...
 
Even w/ all of the aforementioned information, we still definitely need the synoptic pattern to trend in our favor and create the type of pattern that can trend the way we want it to, and it's definitely not going that way on the GFS.

Remember yesterday how I mentioned the northern stream is also very key in this setup and that we really need that northern stream wave to slow down & dig further W? it's doing exactly the opposite on the last 3 GFS runs, which is why we've seen an increasingly suppressed look

gfs_z500_vort_us_fh132_trend (1).gif
 
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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...

These NWP biases are only applicable if the pattern actually supports overrunning in the first place and it's pretty obvious that we've been going away from that on the GFS.

gfs_temp_adv_fgen_700_seus_fh126_trend.gif
 
GaWx said:
I didn't experience it, but I sure followed it! There was a 1007 mb GOM low, phase 7 MJO, strong +PNA, -EPO, -NAO, and neutral AO. At KATL, 4.6" of 10:1 ratio. SN from Montgomery to NC.

Yes, the setup looks to me like it could produce a long duration SN of 12+ hours.
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Thanks for the great info!! Your btr than NWS database I’m sure! I was thinking same thing, it’s obv different Synoptics but I love it when something rare is able to occur. IIm also stuck in full selfish weenie mode since I missed accumulations last weekend by less than 5 miles......
 
I havent written it off yet but these trends are disheartening to say the least. We've never achieved any model agreement for more than just a couple of runs. I'll watch it through the weekend but my hopes are significantly diminished.
 
We need models to trend colder... fast. Look at progged 2m temps. 40s to 50s aren't gonna cut it for a snow event.
 
bouncycorn said:
We need models to trend colder... fast. Look at progged 2m temps. 40s to 50s aren't gonna cut it for a snow event.
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It's not all about temps. We need the moisture and it'll drop the temps as the air is really dry at the time the event should be happening. Temps if wetbulbed did go up partially because there's no moisture or cloud cover to lock in the cooler temps. Ne need to lose this suppressed look or else it's gone.
 
FWIW, the ukmet looks slightly better than the GFS in terms of the longwave trough across the neconus. More amplified/positive.

UKMET:
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GFS:

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Six Mile Wx said:
There are some highly anomalous events going on right now and the models may have to sort out some of those before we get our best look. Just look at what’s in the North Atlantic!
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I was wondering that too -- part of the energy in our system is coming from this group of vortices and it seems like something that would be somewhat unstable and sensitive to input conditions

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ForsythSnow said:
It's not all about temps. We need the moisture and it'll drop the temps as the air is really dry at the time the event should be happening. Temps if wetbulbed did go up partially because there's no moisture or cloud cover to lock in the cooler temps. Ne need to lose this suppressed look or else it's gone.
Click to expand...


DPs across North Georgia are in the mid to upper 30s at 12z Thursday. Temps in the low to mid 50s. Heavy precip in that environment will fall as all rain.
 
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