Welcome back to the world of weather forecasting. In the last article, I covered temperature and pressure; in this one, I will talk about moisture and precipitation. As mentioned before, you need favorable air temperatures, snow levels, and precipitation to create snow.
The following is a very widely used weather chart. I personally use this one the most to map out where it is going to rain and snow. It is an MSLP chart, which shows precipitation and the 500-1000mb dam level (explained in the previous article). MSLP stands for mean sea level pressure and shows surface air pressure, which you can measure using a barometer. The black lines around the lows (L) and highs (H) are called isobars and show wind direction and speed. Tight isobars mean it's windy, and isobars that are far apart mean it’s calm. The red and blue lines show the 500-1000 dam height with their corresponding numbers on the line.
The other major part of the chart is precipitation, which is measured according to the scale on the right of the map.
Green = rain
Yellow and orange = heavy rain
Blue = snow
Darker blues = heavier snow
Pink = freezing rain
Purple = sleet
But what drives this rainfall? Lows are generally associated with the most precipitation because the winds around a low come toward the middle, bringing in moisture, much like a tropical cyclone. In fact, the technical term for a low is a cyclone.
This picture is a satellite image of a “Nor’easter," which is a deep low affecting the Eastern United States. You can see the clouds coiling around the low, which keeps the moisture together and then pushes it upward to condense into clouds. Highs are dry because the moisture is pushed away.
When all the factors add up, you get snow. This map shows how much snowfall in inches, according to the scale to the right, will occur over the next five days (120 hours).
Here is what to look out for when forecasting snow:
You might have noticed “GFS” in the map titles. The Global Forecast System is the particular weather model that produced the chart; the most widely available weather model, the GFS is run by the American NOAA. Other weather models of note are the Euro model, produced by the European Center for Medium-Range Weather Forecasts (ECMWF), and the Canadian model known as GEM (Global Environmental Multiscale), which comes from the Canadian Meteorological Center.
I hope these two articles have helped you understand the weather charts a bit more and will allow you to engage with weather forecasters like me. Most of all, I hope they help you know when the powder is falling! I am more than happy to answer any questions in the forums.
[All weather forecast charts are created by Levi Cowan, a graduate PhD student at Florida State University: http://www.tropicaltidbits.com/analysis/models/.]
I also need to acknowledge the assistance of @SBrown for editing this article, and @Tricia and @Philpug for helping me to make this happen. Thanks all.
The following is a very widely used weather chart. I personally use this one the most to map out where it is going to rain and snow. It is an MSLP chart, which shows precipitation and the 500-1000mb dam level (explained in the previous article). MSLP stands for mean sea level pressure and shows surface air pressure, which you can measure using a barometer. The black lines around the lows (L) and highs (H) are called isobars and show wind direction and speed. Tight isobars mean it's windy, and isobars that are far apart mean it’s calm. The red and blue lines show the 500-1000 dam height with their corresponding numbers on the line.
The other major part of the chart is precipitation, which is measured according to the scale on the right of the map.
Green = rain
Yellow and orange = heavy rain
Blue = snow
Darker blues = heavier snow
Pink = freezing rain
Purple = sleet
But what drives this rainfall? Lows are generally associated with the most precipitation because the winds around a low come toward the middle, bringing in moisture, much like a tropical cyclone. In fact, the technical term for a low is a cyclone.
This picture is a satellite image of a “Nor’easter," which is a deep low affecting the Eastern United States. You can see the clouds coiling around the low, which keeps the moisture together and then pushes it upward to condense into clouds. Highs are dry because the moisture is pushed away.
When all the factors add up, you get snow. This map shows how much snowfall in inches, according to the scale to the right, will occur over the next five days (120 hours).
Here is what to look out for when forecasting snow:
- A snow level below the height of the resort you ski,
- Lots of precipitation, and
- A deep low and a 1000-500mb dam height level of 552 and below.
You might have noticed “GFS” in the map titles. The Global Forecast System is the particular weather model that produced the chart; the most widely available weather model, the GFS is run by the American NOAA. Other weather models of note are the Euro model, produced by the European Center for Medium-Range Weather Forecasts (ECMWF), and the Canadian model known as GEM (Global Environmental Multiscale), which comes from the Canadian Meteorological Center.
I hope these two articles have helped you understand the weather charts a bit more and will allow you to engage with weather forecasters like me. Most of all, I hope they help you know when the powder is falling! I am more than happy to answer any questions in the forums.
[All weather forecast charts are created by Levi Cowan, a graduate PhD student at Florida State University: http://www.tropicaltidbits.com/analysis/models/.]
I also need to acknowledge the assistance of @SBrown for editing this article, and @Tricia and @Philpug for helping me to make this happen. Thanks all.
Last edited:
