A blog about a first-time house owner learning to maintain his backyard, and thoughts about nature, science, history, and life.

Saturday, February 9, 2013

February 2013 Nor'easter: A Meteorologist's View

The blizzard of February 8-9 2013 will be remembered differently depending on where it was experienced.  My many friends in the Philadelphia region saw it largely as an over-hyped dud, with just a few inches of snow that fell mostly overnight, barely affecting their lives.  But for some of my friends in Connecticut and Massachusetts, who are faced with snow drifts up to three or four feet - and I've seen pictures of drifts up to five feet - it's a storm that they'll spend hours digging out of, a storm that they'll remember for a long time.

Here in central New York, it was just another winter snowstorm, as nor'easters typically are for us.  We tend to be on the fringe of the storm (as we were with this one), so we tend to avoid the strongest winds and the heaviest snowbands.  In this post, I'll share some images of the storm from a meteorologist's point of view, and tomorrow, I'll be sharing some of my own photos and experiences of the storm. 

The above image, and the few like it that follow, was produced by a meteorological model.  I'll probably post more extensively on these models at some point in the future, but for now, you should just know that models are the key to the improvements in forecasting over the past few decades.  Forecasters rely on a combination of models, current and past observations of atmospheric conditions, and their own past experience and insights to put together a forecast.  These images all show simulated (or predicted) radar reflectivity: the bluer colors show lighter precipitation (pretty much all snow for this storm), and the yellow-to-orange colors show heavier precipitation.  The green colors represent moderate precipitation.  The above image is for 1:00 pm local time on Friday.

These images are all three hours apart, so this one shows the same thing as above - radar reflectivity - except three hours later.  Can you see how the storm is evolving?  In the first image, there were two relatively distinct areas of green, one pivoting around the eastern Great Lakes (Lake Ontario and Lake Erie) and the other has the highest precipitation intensity off of the southern Delaware coast.  In the image here, the first area is sliding to the east, while the second area is working its way north.  The coastal storm - the nor'easter - is the stronger of the two, and eventually the energy of the weaker storm coming from the Great Lakes will be absorbed into the coastal storm, making it that much stronger.

Here we are three hours later, and now it's much harder to tell that this was originally two storms.  The coastal storm has strengthened, for a number of reasons - which I won't get into here, because they aren't apparent in this image.  But what is apparent in this image is the greater intensity of the snow, which you can see in the ribbon of orange extending across parts of Massachusetts, Rhode Island, and Connecticut.  Snowstorms tend to form bands of heavier snow, and you can see that the model is simulating a couple of bands: the stripes of orange and yellow.  There's also a weaker north-to-south band of darker green extending across central New York, right along the Interstate 81 corridor...this is a little bit east of Freeville.

Now we're getting into Friday night - 10 pm to be exact - and snowfall is expected to be kicking in for my friends in the Philadelphia area.  Meanwhile, the heavier snow in New York State is slowly migrating east, and the band that had been over southern New England a few hours ago is slowly migrating north.  Overall, the snow is in one continuous shield extending from western New York, south to southern New Jersey, north to southern Maine, and east well out into the Atlantic Ocean, where winds are certainly howling by this point.  According to the model, this is about when the storm, as a whole, was expected to be at its peak.

Three hours later, at 1:00 am, when most have gone to bed but the weather weenies are still awake following the storm, it continues to slide off to the northeast.  Nor'easters, by the way, are named for the winds that blow from the northeast when the storm is off the coast.  You can see this, in a roundabout way, in the north-northeast-to-south-southwest orientation of the thin orange snowband around the Boston area in this image.  Here in central New York, as well as for my friends in the Philadelphia area, the storm was expected to be winding down by now, though it is still raging over much of New England.

And finally, at 4 am, central New York is cleared of the snow (the blue colors indicate snow that isn't reaching the ground or possibly flurries), while the heaviest snow is slowly exiting New England.  The model expected the heaviest snow, overall, to fall around the Boston area, with quite a bit for parts of southern New England - Connecticut, Rhode Island, southeastern Massachusetts - as well.

Here's a picture that I nabbed off of Facebook from a friend who works for the National Weather Service office in Gray, ME (near Portland).  NWS employees know how to prepare for this kind of weather - the offices usually have extra staffing, and they may well have to spend the night.

Here's a forecast graphic provided by the Binghamton NWS office on Friday morning.  Notice how the map shows the two storms converging - the western storm is sliding from the western edge of the map toward the east, and the eastern storm will be growing in intensity and size as it slides roughly from south to north, so snow also moves from the eastern edge of the map towards the center.

A few hours later, in the early afternoon, they provided an update to the earlier graphic.  You can see some updates to the map, but perhaps more importantly, they've better pinned down the timing of the snowfall, as you can see in the text to the left.  Now that the storm is in progress, the forecasters can see how well reality is (or isn't) matching the models, and they can better pin down the timing and locations where they expect the heaviest snow.    To me, the bottom point is most important.  During snowstorms, it's not the total snowfall that's most important, but the snowfall rates - how fast the snow is falling....where and when.  If it falls too fast, the plows can't keep up.

I've got a couple of radar images here, just to show some differences between the model and reality.  You can see that the real radar is a lot "messier" than the model radar.  This is partly because the real radar shows a pixel - a point - every 1 km, while the model's pixel is much larger (I don't know exactly what it was, though).  This image is from 8:38 am local time, before any of the model images above, but you can still clearly see the two storms.

Here's the radar a few hours later, as of 12:18 pm local time.  The storms are moving ever so slightly closer together.  Going back to my point from above, another reason that model isn't as messy as reality is that it's designed to be that way.  Models can't calculate the movement of every molecule in the air, so they have to assume that the air over a certain "box "- anywhere from 1 km to 32 km or more - is more or less constant.  The models calculate the interactions between adjacent boxes, and they use approximations to simulate the processes that happen on smaller scales, within the box.  The result of this is that the model tends to smooth things out.  Just compare the yellow bands in this image to the yellow bands in the model-simulated radar above.  There's a lot more variation in color within the bands, and their edges are more ragged.  The models can simulate this kind of complexity, but for a storm like this, it's more important to focus on the bigger picture, so it's ok that the model looks smoother.

Here's the snowfall forecast from NWS Binghamton from 4 am on Friday.  For Ithaca, Freeville, and most of Tompkins county, we were expected to pick up about 6-8" from the storm, most of it coming late afternoon Friday through about 1 am Saturday.  Because the eastern storm was expected to ramp up in intensity and become dominant, the snowfall forecast increased from west to east.

Here's another picture I shamelessly grabbed from Facebook.  The caption: "Impressive features developing from the rapidly intensifying Nor'easter. The pressure has dropped 27.5 mb in less than 10 hours which classifies as bombogenesis. These look like gravity waves or internal atmospheric waves of some kind."  This happened early in the storm, when it was located off the coast near the Virginia/North Carolina border...well before it impacted New England.  It was originally posted by Brad Panovich, aTV meteorologist in Charlotte, NC.  

"Bombogenesis" is a rapid intensification of a storm.  It happens occasionally in really strong nor'easters, and it can result in some really high snowfall rates, lots of wind (there was a gust reported at Boston's Logan Airport of, I believe, 76 mph), and some really miserable people (as well as some very excited weather weenies).  Models, if they're running at high enough resolution (that is, with "boxes" small enough), can produce features like the gravity waves pointed out in this image, but the value is more in showing that they're possible, rather than making meteorologists overly concerned with their exact location and timing. 

And finally, now that you've probably had more than your fill of meteorology for one day, here's a look at some snowfall totals from the storm.  Guess whose snowfall report from 12:50 am was included in the list?

And here are some more snowfall totals!

In case you like maps better than numbers, here's a map of observed snowfall totals, from the Gray, ME NWS office.  You can see that the heaviest snowband set up just inland of the coast across southern Maine, then bent over towards central Massachusetts.  The heaviest snows from the storm, though, were in central Connecticut, where snowfall rates peaked around a ridiculous 6 inches per hour...I don't think the plows had any chance of keeping up with that!

   GROTON                 9.8   715 AM  2/09  TRAINED SPOTTER
   ETNA                   9.5   430 AM  2/09  FACEBOOK
   DRYDEN                 9.0   730 AM  2/09  NWS FACEBOOK
   FREEVILLE              8.5   208 AM  2/09  FACEBOOK
   LANSING                8.2   800 AM  2/09  NWS FACEBOOK
   3 N FREEVILLE          8.0   740 AM  2/09  COCORAHS
   CAROLINE CENTER        7.3   732 AM  2/09  TRAINED SPOTTER
   DANBY                  6.8   819 AM  2/09  2.3 SINCE LAST EVE
   ITHACA                 5.5   930 AM  2/09  TRAINED SPOTTER
And finally, closer to home, here's a look at snowfall totals across the county. It snowed the most in the northeastern part of the county - Groton is 5.5 miles north of Freeville, Etna is a couple of 
miles south, and Dryden a couple of miles east. It snowed less in the southern part of the county (Caroline, Danby), but it snowed least in Ithaca, where the elevation is lowest. Elevation often has a big impact on snow totals, with higher elevations usually seeing more and lower elevations seeing less.

I hope you've enjoyed this look at the storm...come back tomorrow for photos from Freeville and a completely different perspective.

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