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.
Winter Storm Threat: Feb 19 (final call)
Following the latest model trends, it looks like another bust for the DC folks:
Finally a decent snow storm for the southern areas, but the DC region will miss out on the good totals once again. A coating to an inch seems like the best forecast for DCA at this time.
Winter Storm Threat: Feb 18-19 (second call)
Everything trended south in the last 24 hours…
So what happened? The main northern stream energy that was supposed to interact/guide the southern energy creating the snow storm has actually moved out ahead of the storm. This changes a few things…
1. The boundary layer will be able to get cooler and drier ahead of the system.
2. The storm itself (the southern stream energy) has slowed a bit and is allowed to stay further south.
3. Less phasing/interaction with the northern stream leads to a weaker, less amplified system.
There will still be some boundary layer issues along the southern line of the snowfall area, but the boundary layer impact on accumulation is significantly less than what we were looking at a day ago.
Many risks still plague this forecast, and they are
1. The storm could be even more suppressed, which would shift the snow further south.
2. Some models still show a more amplified solution, expanding the precipitation northward.
3. Convection in Alabama and Georgia cutting off some of the moisture feed from the Gulf, which would result in lower QPF and lower snow totals.
I will probably make my final snowfall forecast late tomorrow after the 18z models come out. There are still some big differences between the models, but the trends have been hard not to notice. The most likely change would be shifting the whole thing south.
Winter Storm Threat: Feb 18-19 (first call)
What a nightmare of a forecast…
If I didn’t already say I was going to put out a snow map today I would probably have waited until tomorrow for a first call. As it is, I might do a second update before my final call on Saturday if the forecast seems to converge well over the next 24 hours.
As has been the case all winter, the boundary layer temperatures are going to be a big issue with this event. Most (if not all) of the snow will be on the back end of the system, which doesn’t help matters, either. The latest models would suggest pulling the QPF further south and maybe some of the snow totals along with it, but it wouldn’t be much further south than what I currently have depicted. With high enough snow rates being depicted by the models on the back edge of the system, I think the snow will be able to stick eventually despite the surface temperatures being in the 33-36 range in the lower elevations. Localized 8-12 inch accumulations will be possible in the mountains that get the higher QPF totals.
I believe that the 4-8 inch snow contour could/should extend east of the mountains at some point, but with the discrepancies between the models at 12z and the inconsistency in the run-to-run storm evolution it would be difficult if not impossible to accurately place it east of the mountains.
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+.
Snow squall pushes through the Mid-Atlantic
A snow squall developed ahead of a cold front this afternoon, kicking up winds and bringing a short burst of heavy snow (and thundersnow).
Here’s a video I took of the snow squall as it passed through Gaithersburg, MD:
And here’s the radar for the squall:
Winter Storm Threat: Feb 10-11 (only/final call)
Here’s my snow map for now through Sunday morning 7am:
Above normal boundary layer temperatures are going to hurt totals again for those east of the mountains. The main batch of precipitation will work through tonight and will start off as rain. It should change over to snow by the early morning hours in the DC/MD region, but it will take longer to try to accumulate (if at all). A quick burst of snow is expected in the region during Saturday afternoon/evening as the upper-level energy pushes through. This snow could accumulate up to about a half inch in spots (mostly south-central PA through most of MD and DC), but shouldn’t be much to worry about. Lake-effect and lake-enhanced snow will bring the higher 2-4 inch and 4-8 inch totals to the mountains.