U.S. Snow Cover

Well Happy New Year -- it is 2008. The first of a new year can be an exciting time. It is a fresh start for any and all situations. I wish you the best of the best this year.

On to the weather...

Click this link and it will bring up the National Operational Hydrologic Remote Sensing Center (NOHRSC).

Scroll down just a little bit and you will see several thumbnails. Look at the middle one on the top row called Snow Depth. Click it to view larger in a new window.

Just look at how much of the country is covered in snow!! The deepest snow outside of the mountains of the west is across northern New England and around Lake Superior.

Despite all the numerical weather forecast models out there, a forecaster must take information like this into account when making a temperature forecast.

For instance -- the ETA/NAM model has Denver with a high of 53 degrees on Wednesday, Jan 2.

We are projected to have a south/southwest wind so I can definitely believe warmer air will be advecting into the state -- but with that large of a snowfield on the ground across the region, I doubt we will hit the 50s.

A large portions of the sun's energy will be used by the snowpack to melt versus warming the air that much.

Now if we didn't have snow on the ground -- then yes, we could hit the lower 50s.

As you can see, there is a lot of things to consider for something as simple as making a temperature forecast.

On the flip side, it works the opposite for overnight lows. One model may be predicting 4 degrees for a low -- but if a location had clear skies, no wind and a large, deep snowpack -- the actual overnight low could easily drop 5 to 10 degrees lower than the model predicts.

A beauty of technology is we can see from space just how much snow is out there, the amount of real estate it covers -- and therefore, take it into account as we forecast high and low temperatures.

If a forecaster is really on his game and knows local variability, then even better. A good example is a town here in Colorado called Greeley, just a county away to the northeast of Denver. In some respects, it could be considered a distant suburb.

Last week we had some very cold air move into the state. Cold air is heavy and dense -- and the weather station in Greeley happens to sit in the South Platte River Valley.

As with most winter mornings in the Front Range, we woke up to an atmospheric inversion -- that is where the temperature actually warms with height as you go up from the surface.

So the inversion trapped that cold air down in the river valley -- and let them cool much more than nearby locations just up from the river.

So on a weather map -- it looked like a mistake that Denver and locations in northeast Colorado were in the single digits above zero for overnight lows and Greeley was 18 degrees below zero. By that afternoon, most locations were in the upper teens and lower 20s and Greeley had only struggled to 3 above zero.

It is that small detail of forecasting and knowing your area that makes a meteorologist shine.