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Wintry Feb 19-20 Possible Front-End Snow/Ice Thump

Not sure how some folks can speak in absolute terms with this. We are seeing frozen precip already in places that were not forecasted to really get any. The models can be off both ways when it comes to winter precip here. We have seen it both ways plenty of times.
 
Webberweather53 said:
Precipitation during large-scale overrunning events like this where warm moist air from the Gulf of Mexico is gliding up isentropic surfaces (areas of equal temperature) (i.e. isentropic upglide) is usually more widespread & intense than forecast especially on the northern fringes of where its forecast to occur and its not uncommon to see extra sleet or snow (if it's cold enough) on the front-end.
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Also the band if anyone is watching on radar is not weakening at all ... theres even redevelopment happening near Atlanta and precip rates have looked good too
 

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Nick_boynton_ said:
Also the band if anyone is watching on radar is not weakening at all ... theres even redevelopment happening near Atlanta and precip rates have looked good too
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Keep in mind the reflectivity you're seeing on radar in this case isn't entirely related to precipitation rate, some of the higher values (esp when you're using composite reflectivity that takes the highest dBz value in the entire layer being sampled) are attributable to melting hydrometeors (i.e. sleet) near the ground and/or melting snowflake aggregates aloft.
 
Even FFC said in their midnight update they expected the band to fall apart overnight as models didn't show it lasting... it did the opposite lol. The morning AFD mentioned that it never really died out as forecast thus all the sleet reports across North GA throughout the night and morning. Crazy stuff...this is what makes the weather so dang interesting though.
 
CAD starting to commence

pmsl.gif
 
Fountainguy97 said:
Real timeView attachment 15963
Hrrr initialization.

View attachment 15964


Very close
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Duh, the HRRR is supposed to be close to reality at initialization but the point you're clearly missing here is that the 2-3 hour forecasts this poster is referring to were in fact pretty abysmal w/ this band of precipitation.

9z HRRR 3 hr forecast was a joke.
refcmp.us_se (1).png


Reality:

refcmp.us_se (4).png
 
All in on the HRRRRRRRRR..... man if we could just get precip to over perform early on, this could still be a nice front end thump
ref1km_ptype.us_ma.png
 
Webberweather53 said:
Duh, the HRRR is supposed to be close to reality at initialization but the point you're clearly missing here is that the 2-3 hour forecasts this poster is referring to were in fact pretty abysmal w/ this band of precipitation.

9z HRRR 3 hr forecast was a joke.
View attachment 15967


Reality:

View attachment 15968
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Hrrr this winter has been ---- lol, has done bad with CADs and moisture
 
Myfrotho704_ said:
Yep, can see it with 925mb analysis View attachment 15970
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Notice how much stronger the CAD has become esp in NE GA & upstate SC following this band of precipitation, that's not a coincidence as many of these areas cool to their wet bulb temperature leading to surface MSLP rises. This is effectively the in-situ contribution to this CAD dome
 
Nick_boynton_ said:
What is still crazy to me is the models haven’t picked up on this band of precip that’s still moving in ... they don’t have widespread precip like that over spreading until later this afternoon... biggest wildcard imo
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Here was his first post that I commented on.

Clearly the hrrr initialized with the band so it is picking it up.

Lol
 
Let's keep the discussion moving forward folks. That's enough debate about the hrrr for now. Thanks!
 
It's been my experience over the years that weak overrunning events like this are often poorly modeled in regards to qpf placement and strength. This looks like it may be a similar scenario where models aren't handling the precip all that well. This is key because if the initial band is stronger/heavier than modeled in places like NC there might be a quick burst of snow/sleet whereas the models that form the band to the north of NC delay the precip too long. Based on ground observations and radar I would lean right now to the idea of a quicker arrival of precip with a better chance for some brief snow/ice before WAA takes over and changes areas to rain or zr in the CAD areas.
 
snowlover91 said:
It's been my experience over the years that weak overrunning events like this are often poorly modeled in regards to qpf placement and strength. This looks like it may be a similar scenario where models aren't handling the precip all that well. This is key because if the initial band is stronger/heavier than modeled in places like NC there might be a quick burst of snow/sleet whereas the models that form the band to the north of NC delay the precip too long. Based on ground observations and radar I would lean right now to the idea of a quicker arrival of precip with a better chance for some brief snow/ice before WAA takes over and changes areas to rain or zr in the CAD areas.
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I truly believe there may be more frozen precip with this in NC than originally forecasted, including the Triangle area. I can see the frozen precip holding on longer because of CAD. It's been a while, but it has happened here before.
 
Models underperforming on the warm nose esp in CAD events and tending to miss out on the initial precipitation in overrunning events esp for areas further north likely aren't unrelated in terms of the sources of both of these errors. Model vertical resolution is partially to blame imo.

The HRRR for example over northern Alabama hints there's some weak warm air advection (WAA) near 600-700 hPa just below the dendritic growth zone (DGZ) (notice the winds veering slightly in this layer from W near 700 hPa to SW a little higher up in the forecast sounding). This weak WAA is probably a bit stronger than currently modeled (as usual) which would partially explain the larger expanse of precipitation here and into N GA, and the Carolinas.

download.png
 
We can’t speak in absolutes but we can speak truth. This is a novelty event for the bulk of this board. Everyone enjoy your sleet. Nice little change up from the 80’s we had last week
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#Crushed
 
A useful resource for tracking this storm is the SPC mesoscale analysis page. For this storm the 850mb and 925mb layers will be useful in tracking things in NC. I find the 925mb layer usually shows up the CAD pretty well and you can already see the beginning stages of it forming in Western NC. The 700mb layer is a good one to look at as sometimes a warm nose can show up here and also to see what the RH is.
 
Pouring rain here now. Take lots of pictures when the sleet starts to fall. It doesn’t last long
 
snowlover91 said:
A useful resource for tracking this storm is the SPC mesoscale analysis page. For this storm the 850mb and 925mb layers will be useful in tracking things in NC. I find the 925mb layer usually shows up the CAD pretty well and you can already see the beginning stages of it forming in Western NC. The 700mb layer is a good one to look at as sometimes a warm nose can show up here and also to see what the RH is.
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Agree.... like the images posting earlier. ;)
 
Jimmy Hypocracy said:
Pouring rain here now. Take lots of pictures when the sleet starts to fall. It doesn’t last long
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Were you forecast to get rain today or was it supposed to hold off until tonight? We are supposed to be dry until after 8:00 pm. There's that little batch to the south, but I'm not sure it holds together long enough to move in here.
 
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