I had this thought last week, and I sort of thinly speculated about it when I was talking about the upcoming cold weather (that’s certainly here now) and showing the temperatures at about the 5,000 ft level and seeing how cold the models were projecting. If you remember some model data was portraying the potential of those temperatures down to about -20°C which doesn’t happen all that often around here. For the record this AM the sounding from Topeka indicated the temperature at that level was around about -9C and the RAP model is projecting that temperature to hold pretty steady through tomorrow. Since Topeka is even more on the edge of the arctic air compared to KC, those temperatures do drop off more as you get into the metro, we’re probably a -12 to -14°C at about 5K feet.
The reason I bring all this up is that I was wondering about the correlation to -20°C temperatures at that level of the atmosphere and our potential to get to 0°F (if not below) here at the surface. Since we weren’t going to have snow on the ground I was curious what the correlation was, and whether even colder air at that level like -25C or -30C had happened in the past and what were the temperatures when it did.
Well from my blog to the NWS ear’s. Actually they had already worked up some preliminary research which they shared with me when they read my blog as I was wondering about our 0° climatology. So the following is really all courtesy of my friend and colleague Matthew Dux from Pleasant Hill. He sent me his preliminary work on this stuff and I’ll share it with you. This is the stuff that I love to look at and wish I had an easier way of procuring it here at the station.
So here is what he has come up with that I think is fascinating…and I was surprised by some of it. KC weather records go all the way back to 1888. Through 2012 (really 2011 since there were no sub-zero days last winter) we’ve had 453 days with low temperatures below 0°. So essentially -1° and below. Of those days, 231 were -5° and below. Of that subset, 85 were -10° or below and of that small subset, 22 were -15° or below.
OK…now while he didn’t specifically break down each occurrence and find the 850 mb temp (5K feet), he did further research into the role that snow cover played in all those values and it was certainly interesting as this next image shows.
Click on that image to make it larger.
What it reveals is that snowcover absolutely plays a role in the potential of sub-zero temperatures. Of the 453 times we were below 0°, only 6% occurred when there was NO snow on the ground. So what do we take away from that as meteorologists and weather lovers, odds HEAVILY favor that despite a cold airmass IF there is no snow on the ground a forecaster should think VERY hard about forecasting sub-zero temperatures. Now if you have under 1″ on the ground…then the odds are definitely better!
I think that idea of having snow on the ground being a big help to getting sub-zero temperatures is pretty understood already but what fascinated me was 1) just how many times we’ve been sub zero in KC and 2) how FEW times it occurred without having at least some snow on the ground.
OK so let’s run with that 453 events in our weather history and compare that number to some other cities. The other day Chicago released some information concerning their sub-zero climatology. They did a research project going back to 1960 (Matt’s went back to 1888). Their research indicates that out of a total of 469 days of sub-zero lows only 16 occurred when there was NO snow on the ground! That’s less than 4% compared to our 6%. Again it just points out how important snow cover is in forecasting those extreme lows. Also interesting to note that their case study included 52 years while Matt’s study for KC included almost 125 years. So we had more than double the years available and had about the same number as Chicago did for sub-zero lows in their shorter time frame.
Just for the heck of it, I checked to see the sub-zero climatology for New York City. I wasn’t sure what I would find there concerning sub-zero lows because 1) the urban heat island effect and 2) the proximity to warmer ocean waters. So they have information going back to 1870 and from that data they’ve been sub-zero 58 times.
So let’s recap…we’ve had 453 sub-zero days since 1888. Chicago has had 469 days since 1960 and NYC has had 58 days since 1870.
So there you have it…a BIG h/t to Matt for digging through the data for me…that’s the type of information that I love to research because it makes my day! I know I’m weird.