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Learning Sun angle and other factors

SD

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Every year we rehash this same thing so let's have a thread about it. I have no doubt there are negative impacts from sun angle as you get toward and into March but there are plenty of examples to argue it's not the end all. I think that surface temp and ground temp play just as much of a role. Let's be honest, we live in the South and it's not that common to get snow with surface temps well below freezing and have frozen ground.



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Every year we rehash this same thing so let's have a thread about it. I have no doubt there are negative impacts from sun angle as you get toward and into March but there are plenty of examples to argue it's not the end all. I think that surface temp and ground temp play just as much of a role. Let's be honest, we live in the South and it's not that common to get snow with surface temps well below freezing and have frozen ground.

This calls again for March of 1960 to be mentioned as there was almost unprecedented very persistent snow-cover for very long periods in many areas.
 
Let's be honest, we live in the South and it's not that common to get snow with surface temps well below freezing and have frozen ground.

Which is what made 1/28/14 so special for me in NW GA (and why I would have really liked to be somewhere else with the dry and very cold snow that some areas northwest of me was experiencing last week). It was simply unreal to experience snow with it in the teens, how dry that snow was, the blowing snow I saw the day after...

But that's not the point of this thread. I have one rule with snow, and it seems to work out that way, it's that it needs to get down to freezing to pack a punch during the event (not that it can't accumulate above it though). It doesn't matter if it's in the mid 60s not long before the event if you have a temp of 32 and mod-heavy snow during an event later.

Here's one snow, although I'm not exactly sure about the accumulation here. 3/2/80. It was 72 a few days before and yet I think this was a snow event that gave this area two inches. I'd have to do more looking, as this is going off of my dad's "high school junior journal".
 
In all my experience, what you said there really is the key 9/10 times. Even in our last event, where I got 6" of snow on the ground, we struggled like mad to accumulate through about 4:00pm (maybe 1.5" by then) as our surface temp sat at 33F up until that point. I know I was pounding on ptype can be snow at 40F, and it can and my thoughts on ptype worked out just fine with the last event, but accumulation is a different thing. Unless you are getting moderate to heavy snow, it really is difficult to accumulate efficiently above 32F. It'll come in bits and spurts if precip rate increases, but then it melts.

Conversely, even if ground temps are above 40F and the surface temp falls into the 20s, it doesn't take long to start accumulating that way. If I had to choose between a prolonged cold snap with frozen ground and on event day the temps are 32-33F or a prolonged warm spell with ground temps in the mid to upper 40s but on event day surface temps fall into the low to mid 20s I'd choose the later option all other things being equal every time.
I agree. Really struggled here while we were around 34 didn't get a ton of accumulation until late afternoon when temps fell closer to 32.



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Rates overcome ground temps , always! 3/1/09 is my best example. Rained all morning, hard even thunderstorms, about 3 pm switched to snow, got 8" accumulated snow with temps 33/34 or higher
 
Sun angle: it's a lie. That simple.

Ground temps: Can be applicable, but heavy or moderate snow usually overcomes it if rates are constant. Probably would be nice to see a graph of snow rate and ground temp over time it takes for accumulation to occur.

Heat Islands: They are a thing. If you live in a big city, hope temps aren't marginal, or you could likely be screwed.

Downsloping & snow holes: It's also real. You don't want to end up in a snow hole due to downsloping.
 
I prefer heavy snow falling through temps in the teens landing on a frozen ground at night. Just go ahead and eliminate all worries. :)

Seriously, I don't care about the sun angle one bit. Rates + temps aob freezing is the key to accums.
 
Sun angle plays a huge role if the precip is light and the temps are marginal IMO.
Sun angle isn't what causes melting or prevents snow from accumulating, it's the temps. It's not like the angle of the sun has any difference at a given moment. The whole base of sun angle is built around the time argument of sun per day. It really comes down to timing of an event, not the angle of the sun. In fact, if it's cloudy all day, the sun could be at the summer time angle and we would still have the same accumulation chance if the temps were the same.
 
In all my experience, what you said there really is the key 9/10 times. Even in our last event, where I got 6" of snow on the ground, we struggled like mad to accumulate through about 4:00pm (maybe 1.5" by then) as our surface temp sat at 33F up until that point. I know I was pounding on ptype can be snow at 40F, and it can and my thoughts on ptype worked out just fine with the last event, but accumulation is a different thing. Unless you are getting moderate to heavy snow, it really is difficult to accumulate efficiently above 32F. It'll come in bits and spurts if precip rate increases, but then it melts.

Conversely, even if ground temps are above 40F and the surface temp falls into the 20s, it doesn't take long to start accumulating that way. If I had to choose between a prolonged cold snap with frozen ground and on event day the temps are 32-33F or a prolonged warm spell with ground temps in the mid to upper 40s but on event day surface temps fall into the low to mid 20s I'd choose the later option all other things being equal every time.

I'm only bringing this up because I got hounded by friends and family in the area. In Fayetteville, they remained solidly in the upper 30s to near 40F most of the day with cold mid-upper level temps to support all frozen but actually saw no snow until the very end. The QPF was pretty respectable there as well
 
You want to talk about warm ground temps, how about March 1927 coming off what was the warmest February on record for almost all of the SE US til last year yet almost all of central NC observed 1-2 (or more) feet of snow or better yet, February 1989 where Henderson for example was at 80F and less than 36-48 hours later, heavy-very heavy snow moved in and 15" accumulated. In Raleigh it was 82F about 36 hours before 6 inches of snow mixed w/ sleet fell. A second major winter storm followed on the 23rd-24th dropping up to 11" of snow in Greenville, NC. I reconstructed some of the other observations that were available at the time (as long as they provided QPF) & interpolated SLRs & rounded the values to the nearest inch based on nearby stations.

Screen Shot 2018-01-25 at 5.39.03 PM.png

February 17-19 1989 NC Snowmap.png
February 23-24 1989 NC Snowmap.png
 
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That's not a surprise as the system continued to trend more neutrally tilted that the colder lower-layer (925 et al) temps were delayed making it further south and east. That's a different scenario than what was depicted by the Euro several days out.

The low level temps at 925 hPa were actually similar in Fayetteville vs areas just east of Raleigh in Edgecombe & Wilson counties where 1-3" of snow fell, and where surface temps dipped into the mid 30s when precipitation changed over to snow. Even in portions of Robeson county, ala Red Springs, where surface temps were a few degrees cooler, it started snowing earlier than in Fayetteville where temps were stuck around 37-38F, and they received an inch of snow there as well as in Tar Heel in northern Bladen.
 
Then why did temps drop lower in those other regions more quickly? Fayetteville rained for several hours after onset, as expected, cutting down on their totals, as expected. I forecast 1-3" there, and they received around 1". Were you expecting them to be snow from the onset?
Absolutely not I expected them to mix or start as all liquid but even as the precipitation was ending where the low level temps just off the surface were certainly more than cold enough it was still mostly liquid in Cumberland County minus those bordering Sampson that got super lucky with a band that developed at the last possible second and gave them nearly 2". Urban heat island could have certainly played some role, it's just strange areas to their south received significantly more snow than they did where 925 hPa temps were in fact warmer.
 
KFAY only reported 0.23" QPF total, with only 0.05" liquid equivalent falling as snow (with surface temp of 33F) based on the hourly obs so no surprise they didn't accumulate much.
The QPF was more skimpy than I would have expected in Fayetteville sure but that still doesn't explain how areas further south and east with warmer low-mid level temps changed over to snow more quickly and observed more snow
 
Local variations occur with any storm. More QPF when it was colder? I really don't see anything that stands out as all that atypical or unexpected. There were even reports of 1-2" in eastern Fayetteville and western Sampson Counties so perhaps the real issue is in the accumulation maps.
The accumulation maps are in fact pretty accurate at least the one I made. Visible satellite early the next morning showed a sliver of deeper snow cover exclusive to extreme eastern Cumberland and western Sampson Counties only and surface observations in the area supported 1-2" there with lower totals over the rest of Fayetteville. The point of me bringing this up is to show that I didn't see any observations that supported the notion of it being 40F and snowing during this event and that Fayetteville being just a little warmer (even a degree or so) than those around them actually mattered and delayed the change over to all frozen that occurred sooner in virtually every direction surrounding the city. Those that had cold low-mid level temps even near the end didn't change over to all snow til the surface temps fell to about 35-36F or so.

January 16-18 2018 NC Snow map.png

Visible-Satellite-January-18-2018-1024x573.png
 
I suppose this should be more of a me vs my dad thing but (and I didn’t see any accumulation fwiw because of my being above freezing) but if you go by my dad, it was 38-39 and snowing in the morning here on that day lol. I doubt that’s actually true, as I’ve called him out multiple times for having his thermometer in a place where it’s almost for sure going to be inaccurate (it’s not taped to the house, but it’s taped on a pole on the front porch and our heat pump might make that area a few degrees warmer and yet my dad fires back at me that the reason the NWS station is cooler is because it's in a bit of a valley and we're not) but still, lol.

(I didn’t actually stay all snow but after the cold front got me I was never fully liquid, I was either micro sleet or snow until it ended)
 
I gave you one. Someone deleted it. I'm not wasting my time on you again.

It's a waste of time to explain where you went wrong? I think it's very worth while to delve into where the discrepancy occurred so neither me or you make the same mistake again. You know it is okay to admit you're wrong sometimes.
 
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