Colors, shapes indicate fronts, directions on map

For the past couple of columns, I have been covering Meteorology 101. I wrote about the meaning and significance of high and low pressure, and covered the basics of cold fronts, warm fronts and stationary fronts. I ran out of space last week before I had a chance to describe how the fronts are symbolized on a weather map, so let me tie up those loose ends.

When you are looking at a weather map with fronts on it, either on television, in your local newspaper, or on the Internet, the cold front appears as a blue line with triangles attached to it. The triangles are all pointed in one direction, and that direction tells you which way the colder air is advancing. If you ever see a cold front in which the triangles are pointing north, it is likely a mistake. Colder air will almost always originate from the north – or at least in a direction with a northward component such as northwest or northeast. The movement will then be southward, southeasterly, or southwesterly with the triangles pointed in that direction. In our neck of the woods, the colder air source is usually Canada or the Gulf of Alaska.

Warm fronts are designated by red lines with attached semicircles. Using the same reasoning as with the cold fronts, the semicircles are poking out in the direction that the warmer air is advancing. This warmer air will most likely originate from somewhere farther south, with some sort of northward movement.

The stationary front will look like a combination of the warm and cold fronts. It will have blue triangles pointed in one direction, and alternate with red semicircles pointed in the opposite direction. Again, a stationary front stays true to its name by not moving at all – or moving very little. As the focus for precipitation, a stationary front can bring flooding conditions to an area as storms reform over the same location several days in a row.

One final type of front that is not commonly seen is called an occluded front. It occurs when the faster moving cold front overtakes the advancing warmer air. You can visualize it by imagining a cold front rotating around a low pressure system and catching up to the warm front. The occluded front is drawn in all purple and has alternating triangles and semicircles pointed in the same direction. This type of front usually indicates a weakening or dying storm system.

Apparently, Mother Nature has not checked the calendar lately. Though spring officially began March 19, we have had a hard time seeing any signs of a changing weather regime. Normal daytime highs are in the low 50s now, though that type of warmth has not been seen for more than three weeks in the Spokane/Coeur d’Alene region. Though snowpack is above normal across most of the Inland Northwest, short-term flooding potential has been minimal due to continued below normal temperatures and generally light amounts of precipitation. Spring is the season when flood potential is most closely monitored, and heavy precipitation combined with abrupt warming this time of year can lead to flooding of local rivers and streams.

It does look like we will have to deal with unsettled weather through the end of the month and going into April, with temperatures trending toward the cooler side of normal. We’re still adding to those seasonal snowfall totals. As of March 26, Spokane International has seen more than 75 inches of snow, while Coeur d’Alene has seen a whopping 147.5 inches.