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verification

Winter 2011-2012 forecast verification

This was an ugly forecast… pretty much the exact opposite of what actually happened. There was virtually no blocking this year (I was relying on blocking for the cold pattern), and a fairly persistent and strong trough over Alaska prevented any sort of real, long-lasting cold from entering the U.S.

DJF temperature forecast: F

December 2011: F

January 2012: F

February 2012: D-

DJF precipitation forecast: D

Snowfall Verification for Feb 19

While my first two maps left much to be desired, I finally got the storm zoned in on my final forecast:

The southern edge of the system did a bit better than expected east of the mountains as the snowfall rates were able to overcome the above freezing surface temperatures. The northern edge of the 4-8 inch contour also did better than expected in central VA, with spotty 8-10 inch reports in the higher elevations. I also overdid some of the snow in the far southern Appalachians.

A solid B+ forecast overall.

Snowfall Verification for Feb 10-11

What a strange storm this was…

The three-part storm that I was expecting to be a two-parter. First, the snow in central MD over-performed Friday night as temperatures were just cool enough to allow snow to accumulate more quickly. The second part, the squall line, went as expected as accumulations of a dusting to a quarter inch (possibly a half inch in a few spots) were reported from that.

The third part that was enhanced by the inverted trough is what really got me. That produced a good 1-2 inches of snow over a good portion of the Delmarva Peninsula and in extreme eastern VA.

Another major failure in the forecast came in eastern PA and NJ as the coastal low and associated precipitation did not come as close to the coast as I had anticipated. Instead, it took a track similar to what the GFS showed and limited most of eastern PA and NJ to under an inch of snow during the first part of the storm. I also missed some of the higher lake-effect totals in northeast OH and northwest PA.

Weighing in the fact that I missed big in some areas, did fairly well in the mountains and the difficulty of the forecast, this was a D+.

Snowfall Verification for Feb 8

Another headache-inducing storm with poor rates, boundary layer issues and overdone QPF amounts:

The verification wasn’t as bad as I thought it would be. I still got the general idea right, but was off in some key areas east of the mountains. The northern extent of 1+ inch accumulation in NJ was a bit surprising, and the OH snow and southern WV/VA snow was a bit lacking compared to my forecast. The southern edge did go down along the mountain ridges a bit more than I expected.

I’m going to give myself another B- for this event. I bit into the hype east of the mountains in VA/MD and put the one inch line further south than I felt comfortable doing, and that backfired. Going conservative is definitely the best option with the snowfall forecasts this winter.

Snowfall Verification for Feb 4-5

The verification on this one was rather interesting… some odd shapes/placements of the snow totals:

The front-end of the system over-produced and the back edge under-produced, with some front-end banding boosting totals in central MD. Lighter rates and above-freezing temperatures kept the totals down elsewhere. Overall, I had the right idea, but with a warm boundary layer and a weak system it’s always difficult to nail the accumulations. I’d give this forecast a B- for getting the general theme right within the oddly-placed snow totals.

Snowfall Verification for Jan 21

This was an interesting one to watch unfold…

 
Cold air damming allowed for more snow at the onset of the storm than what I was expecting, which resulted in broader 1-2 inch coverage east of the mountains in central VA, MD, DC and southern NJ. This also allowed the freezing rain and sleet to work a bit further south. The back end of the system also had a surprise up its sleeve, bringing up to seven inches of snow to the Pittsburgh area. The snow underperformed a bit along the southern edge in the mountains where warmer temperatures led to more mixing and plain old rain.

The higher snow totals were captured pretty well for the most part, especially along the southern edges of the 2-4 inch and 4-8 inch contours. The pink indicates areas that received 0.1-0.25+ inches of sleet and/or freezing rain (which was a bit trickier to contour due to the nature of the reports).

I knew the snow was a bit of a risk in the CAD region, but I didn’t pull the trigger on it and ended up paying for it. I’m going to give this forecast a grade of B-… the northern areas were quite good, but the southern areas suffered a bit.

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I have a new map design that I will roll out during the next snow event. On top of being a larger image, it also has county lines and interstates for easier interpretation.

Snowfall Verification for Dec 7-8

 
Quite a trying forecast, but overall it wasn’t a complete loss. Verified the mountain areas and highest totals fairly well, but the more heavily populated areas left much to be desired. Looking back, I could have been less generous with the 2-4 inch range in northern MD and southeastern PA, but other than that and bringing the 1 inch cut-off further north in MD I don’t see much that I could have done to change my overall thinking for this event.

The changeover from rain to snow was fairly messy east of the mountains, and most did not even transition to 100% snow. On top of that, the snowfall ended more abruptly and sooner than I had expected, which prevented the stronger cooling to make it to the surface in tandem with the back edge of the heavier precipitation. That slightly warmer boundary layer is what turned 1-4 inches into little to no accumulation.

Going to be a little generous and give myself a C- overall, though it wouldn’t take much convincing to push that to a D+ considering the bust in south-central/southeastern PA and MD and the western edge of the snowfall.

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