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Winter threat: 1/9-12/ 25

brianc33710 said:
Do models still indicate temps will rise b/c ice storms can feed themselves once they get started. If temps are only climbing to 33/4 that might not happen. But I'm not a met either. I just remember some past ice storms from across N America.
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Yes, it's close. Highest 0Z HRRR gets for BHM is 35.
 
I can't remember the exact year, Jan 85 or 86, but we had a massive sleet storm in north Mississippi. I was around 15 or 16 at the time.

It was supposed to have been mostly snow but it was all sleet, and we Had thunder and lightning with it.
It was like watching a downpour from a thunderstorm but it was all sleet. Just pouring down for hours and hours.
We ended up with over 6".
Roofs collapsed everywhere from the weight of the ice. Mostly chicken houses and similarly built structures.

Then it turned extremely cold after. We had several days of single digit highs. Luckily, we didn't lose power.
Schools closed for nearly two weeks
because of the roads. It just wouldn't melt.

When the thaw finally started, water mains and service lines were breaking everywhere.

Best time I ever had as a kid. I did more sledding in those two weeks than I have my entire life combined, but being older now, I'd say bah humbug to such a scenario again.
 
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cyelle21 said:
This is probably a stupid question, so pardon my lack of knowledge. Are the time on the models in real time? For instance, if I am looking at "Friday 3z", does that correlate to Friday 3:00am?
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No, it's Zulu time, so subtract 6 hours. 03z is 9pm. 0z is 6pm, 12z is 6am, 18z is Noon.....etc assuming you are in central time zone
 
UncleJuJu98 said:
I've heard that temperatures are running a degree or two colder than models have forecasted, not sure how true that is. I woke up to 22 degrees this morning. Was very chilly.
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I’m seeing posts indicating temps in Tennessee are lower than forecasted this morning. Also looks like the Hrrr is running warmer than actual temps back West
 
Thanksgivingbrown said:
I’m seeing posts indicating temps in Tennessee are lower than forecasted this morning. Also looks like the Hrrr is running warmer than actual temps back West
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I'm guessing it's cause the cold air is more shallower? No clue. Something the experts could probably tell us. Or just weather model error.
 
UncleJuJu98 said:
I'm guessing it's cause the cold air is more shallower? No clue. Something the experts could probably tell us. Or just weather model error.
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Models do a crappy job of handling Appalachian cold air damming, yes. There are ways to tweak the models to compensate using Model Output Statistics (MOS) to adjust for biases, but they do have an issue with it by default.

Some "light" reading.
journals.ametsoc.org

An Analysis of the Impact of a Split-Front Rainband on Appalachian Cold-Air Damming

Abstract Appalachian cold-air damming (CAD) is characterized by the development of a cool, stable air mass that is advected southwestward along the eastern slopes of the Appalachian Mountains by low-level ageostrophic flow. Operational forecasters have identified the demise of CAD as a major...
journals.ametsoc.org journals.ametsoc.org
 
OK, since we are in nowcasting range, I'm going to Forecasted Convective Amplification Deficiency out one of my favorite old-school tools for watching winter weather, WeatherScope, from Mesonet. It's old - but it lets me load observation data for display. This lets me plot the freezing line for temp, dewpoint, and wet-bulb, and overlay Nexrad radar data from sites I choose. Very handy. Old as dirt - requirements are Windows 98 and 512 MB of RAM, I kid you not. Still runs like a champ.
https://okfirst.mesonet.org/train/WeatherScopeHelpPC/Extra/Main.html
1736432988841.png
 
As my forecasting instructors taught me, models are useful, but at some point you have to throw them away and actually look and see what's happening.

Blountwolf said:
OK, since we are in nowcasting range, I'm going to Forecasted Convective Amplification Deficiency out one of my favorite old-school tools for watching winter weather, WeatherScope, from Mesonet. It's old - but it lets me load observation data for display. This lets me plot the freezing line for temp, dewpoint, and wet-bulb, and overlay Nexrad radar data from sites I choose. Very handy. Old as dirt - requirements are Windows 98 and 512 MB of RAM, I kid you not. Still runs like a champ.
https://okfirst.mesonet.org/train/WeatherScopeHelpPC/Extra/Main.html
View attachment 32783
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Will y'all quit sending your wonky weather up to SC please? :p

Lower than expected temps here too, and that's now forecast to continue. HRRR showing higher totals but steadying at ~4" for me in the foothills. And the wonky CAD is not giving clear indications of what part will be snow and what part will be sleet or where the line between the two will land. At least the timing has settled down to a mid-morning start for me. And as usual the NWS is being vague on predictions but we've got Chris Justus like y'all have James Spann to better analyze it all and narrow it down more accurately. Sometimes it's as hard to forecast weather here as it s in AL.

Y'all stay warm ;)
 
Jenifer Jerri said:
Wolf, I think you are the poster I look for to update where that low is in the Gulf - do you have the latest on that?
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So far? It's not...lol. Not much cyclogenesis going on, as the ULL hasn't moved east much. Western gulf around Brownsville is where we'll be watching to start - and then it will roll north and east, but no way yet to tell exactly where. I really do think the upper level dynamics may throw us a bit of a curve ball there.

Pressure is falling at Brownsville.
1736435684281.png
 
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