Snow Problem: Snow Ratios and Radar Coverage
UPDATE: Thanks for the Comments below, I'm glad I was able to strike an educational chord. Erie does in fact suffer the same problem (even being too far east of the nearest Canadian Radar in Exeter, Ontario). Over the years the subject of an Erie NWS radar comes up from time to time but I haven't heard much in the last several. As one of you pointed out, you can use the Erie TV radar, which is independently owned. To further illustrate how the radar beam overshoots snow I have posted a NWS image below. Also check out Ron's webcam comparison below showing additional accumulation on his roof overnight -- he posted new photos and videos too.
You may have heard the term "high snow ratios" in regards to this week's storm. What this means is, essentially, that the same amount of liquid will produce "fluffier" snow which will pile up quickly. Snow ratios are not determined only by the temperature at ground level (a popular misconception) but rather by the temperature in the clouds where they are produced and the air that the flakes fall into. Colder temperatures don't necessarily make for higher snow ratio -- there's a "sweet spot" and we'll be in it for this next storm (despite what this TV station chart says, it can be too cold for high ratios according to NOAA's HPC). Bernie Rayno and Maria Molina explain more in this video:
(The video appears to cut off at the end; the rest was removed due to an outdated snow accumulation map for the storm, a newer version of which is available here - see more current videos about the storm on our front page).
Because snow ratios will vary during this week's storm, it's going to be tough to forecast this next one, and will make for widely varying snow amounts.
There was a great example of this today in Vinco, Pennsylvania (in the mountains above Johnstown). Ron sent in these pictures this afternoon. Notice how fluffy the snow looks:
In fact it's so light that it's been pushed out between the rails of his porch:
Snow Ratio Geek Tips: The HPC has some hints for budding forecasters, the NWS has a comprehensive guide to how the atmosphere's profile predicts winter precipitation type, and there is actually a website that predicts the ratio based on forecast model data.
If you look at Ron's webcam you'll notice the snow accumulating on his roof at the bottom, something I've never noticed before (and I keep a pretty close eye on this cam during the winter.)
Ron got about a foot of this stuff between noon yesterday and today - mainly overnight (this photo shows only what fell during that time period) and now has more than two feet on the ground, with drifts above three. In nearby Altoona and here in State College, there is almost nothing on the ground and we haven't seen accumulation in 2010.
Why is this? Three reasons. One, he's in the Laurel Highlands of southwest PA, the highest mountains in the state. Two, he's a little closer to Lake Erie and gets his best snows during a southeast flow like we're having today. But third, and perhaps most importantly, the air moves up the western slopes of the Laurel Highlands and upsloping winds become more humid (meteorological principle: air becomes more humid as it rises).
The funny thing through all of this is that: He can't even see it coming. Ron relies on weather radar to tell when storms are approaching, but lake-effect snowfall is at such a low level that both nearby radar sites are looking up above most of the snow (the lowest radar beam points upward from the tower itself) by the time it gets near his area. The map below shows the approximate range of most snow coverage from the Pittsburgh & State College radars.
Comments (7):
Lee:
We just moved to Morgantown, WV and bought a house on the edge of Coopers Rock forest. We are at about 1800ft and I was wondering what the heck was up with the radar since we have at least a foot on the ground (will measure later today) and I could see the bands of snow on the Pittsburgh and Charleston radar, but it always looks like it isn't snowing where we live. Looked like a dry slot over Morgantown, but it was snowing. Well we have over a foot and at least 6-8" still on our road so I know it snowed!
thanks for this - I thought it was just poor radar coverage, but I can see severe storms in the summer on the Pittsburgh Radar around Morgantown.
Looks like another 6-12 for us with the next system :)
Posted by Lee | January 6, 2010 9:00 AM
Dave Hartland:
Jason said what I was going to say about our region on NW PA here in Erie. The Pittsburgh/Buffalo/Cleveland radars do not reach us here - especially during times of lake effect snow. Indeed, as you've probably noticed during this most recent lake effect event, it's been almost blank in our little corner of NW PA. But I can look out my window and tell you that that is most definitely not the case. In fact, on the Cleveland NWS page, they are reporting a snow depth of 57" in Crossingville, about 20 miles south of Erie. This event has been epic, but you'd never know it by looking at the radars!! During the winter months, I rely on our local ABC affiliate to provide me with the best radar in our area. http://yourerie.com/content/weather
The NWS radars are useless.
Interestingly, this was the topic of debate back in the late 1980s when the Erie NWS station was slated for closure. THe argument was that the PIT/BUF/CLE radars would not be able to provide adequate coverage in our area. Then, the 1985 tornado outbreak was fresh on our minds and became a hot button issue regarding the possible closure. In the end, the station was closed...and we have not had nearly the same amount of radar coverage as we once did - most noticeably during winter storm events and especially lake effect.
Thanks for this post, Jesse! Really interesting!
Posted by Dave Hartland | January 5, 2010 11:40 PM
Justin:
Just wanted to say awesome post. I'm from Williamsburg (east of Altoona about 15 miles) and went to Johnstown tonight for a basketball game. Barely any snow in Blair county but once you get to the mountain they got over a foot with 2 to 3 feet snow drifts. A complete different world on top of the mountain.
Posted by Justin | January 5, 2010 10:48 PM
bart:
thanks J really interesting stuff. was not aware of the point you made about the radar not being able to pick up these snows
Posted by bart | January 5, 2010 9:47 PM
deltaqueen:
This is why I love accuweather. I am not talked down to AND given an education
Posted by deltaqueen | January 5, 2010 8:25 PM
Jason Warren:
Hi,
I am glad you touched on this radar phenomenon. The same thing happens where I am and it impacts the forecast significantly. I live in Trumbull County, Ohio to the SE of Cleveland. Many times, especially during lake effect events the radar shows the snow simply vanishing before it reaches me. But I look outside and it is snowing like crazy. Often times, the NWS misses the mark on their snow forecast for our area. They predict amounts that wind up being much lower than what actually happens.
Posted by Jason Warren | January 5, 2010 7:12 PM
Dave O'Neil:
I recorded 7 inches of snow yesterday with only .12 inch of water. We had 15" on the ground this morning and another 6" has fallen by 6PM today yet I only measure 18" on the ground. We've had over 21" of lake effect here at the Chalk Hill Pa station since New Years Day and it's still coming.
Posted by Dave O'Neil | January 5, 2010 6:17 PM
