GaWx link said:
[quote author=GaWx link=topic=2.msg2483#msg2483 date=1481991446]
I don't know about your area but I do know that single digits would much more often than mean no significant winter storm for a place like ATL though that may give places much further south/east a better chance. ATL has a much better chance when it gets a day or two of lows in the 20's vs singles in advance of any precip. This is based on going through all of the major storms going back to the late 1800's. I may need to go through the #'s & present them here if I ever get time.
For the 38 major SN/IP's at ATL since 1879, here are the lowest lows for the three prior days and including the morning low of the day the storm starts if that was prior to the start like in 1979:
46 (this was the March 2009 upper low), 41 (Blizzard of Mar 1993), 37, 35 (Feb of 2014), 33 (Mar 24, 1983), 32, 32, 30, 29, 29, 29, 28, 28, 27, 25, 24, 23, 23, 23, 22, 21, 20, 19 (Jan 2011), 18, 17, 15, 15, 13, 11, 11, 9, 8, 8, 8, 8, 0, -1, -5 (Snowjam Jan 1982)
Though there are many in the 20's+ (22), there are actually more singles or colder, 8, than I had recalled. That may be because 7 of these 8 were 1940 and earlier. In reverse chron order: 35, 19, 23, 46, 22, 41, 18, 24, 32, 33, -5, 28, 29, 23, 21, 37, 28, 8, 11, 13, 23, 8, 27, 15, 15, 20, 11, 30, 9, 0, 32, 8, 29, 25, 8, 17, -1, 29
Since 1942, avg 27. Before 1942, avg only 16!
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Just to follow up on the stats above, I counted 8 major Atlanta SN/IP storms since 1879 that immediately followed airmasses with the coldest in the single digits or lower. I counted 66 airmasses since 1879 giving ATL single digits or colder. That means that 8 of 66 or 12%/about 1 in 8 of these extreme airmasses gave ATL a major SN or IP immediately following it. To be fair, however, there have been very roughly 1,500 airmasses bringing coldest lows of teens to 20's (average roughly 12/year). They had 22 major SN/IP follow them or only about 1.5 for every hundred of them.
So, even though the number of major SN/IP following airmasses with coldest of teens-20's has been 22 vs only 8 after coldest in the single digits or colder, that is deceiving because the % of the single digits or colder airmasses having a major SN/IP immediately following them has been about 8 times as high as those with teens-20s for coldest.
In summary, I have to say I learned something new today. The chances of a major SN/IP at ATL immediately following a single digit or colder airmass are actually much higher (by a factor of about eight) than an airmass with coldest of 10-29 even though only about 1 in 8 of these extreme cold airmasses lead to one (since they are usually too overpoweringly dry at first and then they warm too fast later) and even though there have been roughly three times as many of them following airmasses with 10-29 for the coldest.
Edit: I want to add a couple more things. I'm lumping together the teens-20's airmasses in saying that they've gotten major SN/IP after only 1.5% of them. Had I separated out the teens airmasses from the 20's airmasses, the % following the teens airmasses would have been a good bit than the 1.5% (probably near 2.5-3%) and those following the 20's airmasses would have been lower (probably near 1%).
So, at ATL a major SN/IP followed ~1 in 8 of airmasses with 9 F or colder, ~1 in 35-40 of those with teens for coldest , and ~1 in 100 of those with 20's for coldest.
Another thing: these don’t include nonmajor SN/IP, which are way more common than major, of course. In addition, I haven't analyzed ZR's yet.
