Archives for 2009

Christmas Eve, here in Norman, we had a rare event for these parts — a genuine blizzard. An event of perhaps greater rarity has ensued: a white Christmas!

The “official” NWS blizzard requires sustained 35 mph winds accompanied by visibilities at or below 1/4 mile, with blowing snow, all of which lasts for at least 3 hours. And so it was, for the first time in my experience here since March 1989 — over two decades. The storm closed all interstate highways in the OKC area, stranded dozens of motorists, caused countless crashes, and prompted a declared “state of emergency“.

Some sort of heavy snow band and blizzard-criteria winds had been forecast for days somewhere in Oklahoma, the question being precisely where. That’s a mesoscale uncertainty, as with severe storms, very difficult to predict days and sometimes even hours out. In many ways, forecasting such an event is more challenging than severe storms because it involves phase changes from liquid to ice — and two shapes of ice: sleet, which is frozen rain, versus dendritic crystals we know as snow). Last-minute shifts in weather patterns on scales smaller than states, and above the surface where measurements are sparse, can make huge differences. Asking a forecaster precisely where the snow will change to sleet or rain, or how much snow will fall, is asking too much. The best that can be done is to give ranges and estimates.

All in all, most of the forecast ranges for this system weren’t too bad. Model guidance varied in the position of the heaviest bands of precipitation, but not much in its shape, size or orientation. That was helpful. The largest snow amounts occurred not where the heaviest precipitation band was for the greatest time (generally south through east of Norman), but instead, right at the OKC (Will Rogers) airport, where the change to snow occurred soonest on the western fringe of the heavy band. [UPDATE: The 14.1 inch snow depth at OKC set a new storm-total record for OKC for any event, breaking the previous record of 15-17 January 1988, which I also witnessed. We did have a couple of heavier snowfalls than that in Norman in the late 1980s, near 14 inches.] Here in Norman, the consensus among various meteorologists whose measurements I’ve head so far (including mine) was about 6-7 inches, with drifts 2-3 feet around leeward sides of buildings, slopes and walls. Liquid (melted) equivalents actually were heavier south and southeast of the OKC airport, where more rain and sleet fell before the snow blizzard. Liquid equivalent is what really matters, far more than snow depth, which can be arbitrary when it varies so much with local airflow patterns. My liquid equivalent was 1.68 inches.

At the bottom of this post, I’ve placed a map of peak gust (in MPH) supplied by Oklahoma Climatological Survey. I’ve circled Norman for those not familiar with our geography.

For this meteorologist, born and raised of lower latitude, this was a simultaneously fascinating and agonizing experience. See, I get amped by extreme weather, but hate cold passionately. I would be happy never to see another freezing temperature; but I live here in order to have the chance to be in position to observe severe storms for a nontrivial fraction of the year. That requires baroclinicity (not “baroclinity“, but baroclinicity!), which places that I tend to prefer do not have in enough abundance. Today’s weather won’t happen in the Florida Keys; but neither will multiple supercell intercept opportunities every springtime.

Sometimes this location and its access to violent spring weather means sacrifices elsewhere across the calendar. Yesterday, those sacrifices took the form of several dollars of a heating bill, episodic power outages, staying up all day after being awake all night (for my last overnight shift of a set), and a cold-weather photographer’s stinging to numb fingers. Rain at 8 a.m. gave way to sleet in under an hour, and as the cyclone pivoted northeast from east of the Metroplex across southeast Oklahoma, the wind here picked up to above 35 mph, gusts near 50. The Christmas Eve segment of the system ended up leaving a wide snow swath from New Mexico across NW Texas and much of OK, then over Eastern Kansas.

Being sleet-blasted in such wind was a new experience for me, much like being sandblasted on a beach during a strong tropical storm — but far colder and without the salt spray. The numerous electricity losses kept us from cooking Christmas Eve dinner at home as planned, so we went to the nearest restaurant for lunch. While there, sleet changed to snow, as expected; and the event truly formed a blizzard. The drive back necessarily was slow, with visibility often no more than 50 feet. Intense gusts carried true white-out conditions.

We got back in time to see the snow begin to drift, and for me to get outside for a few minutes at a time to observe and photograph the snow.

One of the most entertaining parts was right down at ground level — streamers of snow howling across near-bare ground from adjacent areas where some snow had accumulated, a fluid multitude of airborne crystals destined for re-accumulation in some drift, somewhere. It’s the classic stuff of grainy old movie films from desolate Wyoming or Dakotas highways in some horrifying wintertime maelstrom, except rendered true much farther south today.

I plan to get out some more this weekend and document some of the snowfall in pictures, and will post more images from the blizzard and its aftermath next week. In the meantime, though it may not be easy…stay warm. And most importantly, merry Christmas to all, from the snowy Edwards household.

[LATE EDIT] As of Dec. 30, I have posted select photography from the event here, in this online gallery. Enjoy!