Friday, January 18, 2013

The Different "Flavors" of Lake Erie Lake Effect Snow

Totally Ice Covered Lake Erie in Cleveland in early 2011

A survey was done a few years ago about what weather words people latch onto when they heard them on television. The first was the word FORECAST, close to the top were the words LAKE EFFECT.  Yet lake effect isn't a "one-size-fits-all" type of meteorological phenomena.

I wrote about some actual lake effect examples from the 1960s and 1970s in a post from late 2011.

First the variables that go into a lake effect event. Some are independent of the lake (2 and 5 specifically) but work in concert with it.

1. Temperature difference between the lake and the air aloft (5000 feet) has to be at least 13 degrees celsius. The more, the better.
2. Abundant atmospheric moisture independent of the lake
3. Wind speed
4. Wind direction
5. Fetch Length (How far does the wind blow over the lake)
6. Instability and instability depth (Usually driven by a cold front/trough and/or the lake temperature difference) Deeper the instability, the deeper the snow growth
7. Orographic lift (elevation differences between Cleveland and the snowbelt. 1200 feet in portions of Geauga county)

Even if #1, 3, 4, 5 and 6 are present (the most common variables), subtract any one of these variables especially 2 and 5--sometimes 7 if the wind direction shifts) and snowfall forecasts can turn out much different than anticipated.

What are the different "flavors" of lake effect here in northern Ohio? Why does the secondary snowbelt vary so much?  How can some areas like Akron get significant lake effect while the traditional snowbelt receives minimal amount? The differences lie in the wind direction.

The first example is what I like to call: CLASSIC LAKE EFFECT EFFECT SNOW.

Winds are primarily out of the northwest, usually behind an Alberta Clipper type cold front. The higher elevations east of Cleveland (Geauga, Lake and Ashtabula counties) AND SOUTHWEST OF CLEVELAND enhance the snowfall due to the lifting of the moist air. The secondary snowbelt in this example would include northern Medina, Summit and Portage counties. This lake effect snowfall map is the one that you're probably the most familiar.

CLASSIC Lake Effect Snowfall Map
The second example is LAKE EFFECT with a WEST WIND

Band or pockets of lake effect snow in this example usually hug the shoreline and are partially enhanced by the elevation. The fetch off of the lake is more significant for eastern areas.  The secondary snowbelt usually doesn't push as far south.

NORTHWEST WIND: Lake Effect Snow Map
The third example is LAKE EFFECT with a NORTH WIND

This example can be very tricky because not only are you forecasting snowfall from the moisture in Lake Erie, north winds will carry moisture from LAKE HURON too! The Lake Huron component isn't as large as Lake Erie but it can be significant. The fetch isn't as far (distance from Canadian shoreline is ~50 miles) Yet with some instability created by BOTH lakes due to the cold air/milder lake, snow bands/pockets can stretch into Akron, Canton and even northern Tuscarawas county.

This example seems like a bit of a stretch as there are many components necessary for this to happen. Back in the winter of 2009-2010, we had several lake events that mirrored this example exactly.

Its easy to see how lake effect can and does change on a moments notice as the winds shift. A good understanding of the wind component is essential in forecasting lake effect. Yet even the most comprehensive high resolution data from the surface and aloft plugged into a very high resolution computer model projection will never be exact.

No wonder we can have one location with 2 inches of snow and a few miles down the road, the amounts can reach 15"! That's why we use snowfall ranges.

Tuesday, January 15, 2013

Why I Enjoy Broadcast Meteorology

I take pride in several things during an on air weather cast. The first is explaining the forecast in easy-to-understand points.  The second is explaining why the weather is happening in basic scientific terms when applicable.  Yet most viewers view the current state of the weather (whether its winter or summer, etc) here in northern Ohio as a chaotic, random system incapable of being projected more than 6 hours ahead of time. Many times, this is not far from the truth.  Yet by throwing in some local historic weather events as a good reference frame with the science and a narrative cocktail can be created which most people can drink without too many problems. Next week might be one of those instances where understanding the weather along with some history might make the colder weather a bit easier to mentally digest when it arrives. Note I said mentally.  I can only hope :)

Now the situation at hand: One of the main factors in predicting LAKE EFFECT SNOW is how cold the air is (5000 feet) above the lake. More importantly, its the temperature DIFFERENCE between the lake and the 5000ft level. As long as the difference is greater than 13 degree Celsius, lake effect has a very good chance of developing (among other factors too). Greater the difference, the greater the potential for snow development.  Usually the 5000ft temp has to be at least -5 to -7 in NOV for snow to get going (given the mild lake). -10 to -15 is ideal this time of year given the water temps at 39 degrees F(4 degrees Celsius). Sometimes, we get temperatures at -20 or colder at 5000ft which is super cold! Curiosity got the better of me over the last few days so I checked the 5000 ft temperatures each day over the last 4 winters including this one here in northern Ohio. There was only one time in the last 4 winter when we had a 5000ft temp at -20. That was JANUARY 29, 2009.

Guess what the long range projections have been saying since the weekend about how cold the 5000ft level would drop to next week? You guessed it. -20!  This could mean some LAKE EFFECT SNOW and daytime highs in the teens.

Monday, January 14, 2013

What Does Lake Erie Look Like From Space?

The top image is a high resolution satellite photo of Lake Erie last week as the snow began to melt and temperatures started to climb. The lower photo is a satellite photo take in Feb 2010 showing the heavy ice cover in the lake effect areas north of Cleveland. Notice the cracks in the ice and the open water near New York. The detail on both is amazing.The red dots represent the cities of Cleveland, Lorain and Conneaut

The next two weeks will be critical in determining whether or not conditions will be cold enough for ice to form on Lake Erie. We really need about a solid week to ten days of below normal temperature to get the process started. The front coming through Sunday might set the stage for this but there is no guarantee that it will be long enough for ice to form; maybe some partial ice in the western basin.

 Will this arctic air now in eastern Canada slide further south next week?