>> Thursday, February 26, 2015
The good, the bad, and the ugly of the winter storm forecast:
If you watched my video yesterday morning, I went into how the forecast was going to be very tricky for eastern sides of the Charlotte metro up into southern parts of the RDU metro. This was due to a pronounced layer of warm air aloft causing mixing of precip types.
Well, that warm nose aloft was even more pronounced and more north than expected, and that really sullied my snow amount forecast around the Charlotte area and Upstate. Now for the Triad area, the forecast panned out very nicely with many folks in many counties reporting 6-8". So that area did fine. The problem was southern NC and Upstate SC.
Remember those RPM (Futurecast) runs that looked somewhat absurd with the rain/ snow line so far north? Yeah, it was pretty darn accurate in retrospect. It won the model day. For instance, looking at sounding data yesterday, the GFS never got Charlotte out of a snow sounding. The NAM, while much more pronounced with the warm nose, kept CLT at a snow sounding deep into the night, and even then, it was close to isothermal snow soundings. There was nothing on those models that indicated sleet and rain taking over so early in the evening. Some of the high-res short-term models were indicting warming aloft, but it was difficult to take them too seriously while there were spitting out 20" snow products.
The first warning shots to me were fired when a buddy of mine near Anderson, SC let me know he was in a sleet/ snow/ rain war zone early in the evening. I knew we were in trouble then.
So what exactly went wrong with that aspect of the forecast? Again, I thought the area just east of CLT and down into northern SC was going to be trouble. But I thought most of CLT, and certainly areas north and west of Charlotte, would stay primarily snow. They did not, until you went north of the whole metro. The warm nose aloft won out, and a whole lot of the precipitation fell as sleet and rain, especially CLT and points south and east.
The problem had little to nothing to do with ground temps or surface temps. Look at how quickly snow stacked up while precip remained all snow, and look how quickly snow accumulated Tuesday morning with ground temps warmer than last night.
There was always going to be a tight gradient with this system...it just set up further north than expected. Lesson learned. Never, ever, underestimate the warm nose.