Going Down!

A large storm is forming along the eastern slope of the Rockies this morning. The first sign has just raised its head at Cedar Falls, Iowa. That sign is found in the barometric pressure trace.

Look at the chart below. Beginning on the far left side lets follow the trace. The pressure decreased until 2:00 p.m. on Christmas Day when it reached a low of 1004.0 millibars. At that point you will notice a small jump that began a small unsteady rise into the early hours of the 26th. At just after midnight (12:50 a.m.) on the 26th a steeper climb began. It continued until 10:20 a.m. this morning when the peak of 1024.2 millibars was reached. Then the pressure trend reversed itself. It is now decreasing. This marks the beginning of an expected sharp fall in pressure as a storm center deepens over SE Colorado and moves toward Iowa.

The weather map below is at 10:00 CST this morning. High pressure is centered along the Iowa-Missouri border. As the high moved across the Midwest the pressure at Cedar Falls increased - as shown on the graph above. Notice the calm winds under the high center. Winds are from the NW to NE to the south and east of the center and west to southwest to the north. High pressure rotates clockwise in the northern hemisphere. Further west winds are from the east in Kansas, western Oklahoma and western Texas as air moves toward the low pressure center forming just off the SW edge of the map. Air is descending out of the high and rising into the low.

The air pressure will go down (decrease) as the low intensifies and begins its trek to the northeast. Look for a major snowstorm to develop to the left of the storm center track and heavy rain to fall to the right of the path. Thunderstorms will likely develop east of the storm center.

By the way, the first sign of a storm at Cedar Falls appeared in the change in barometric pressure. Looking out the window the sky is sunny! It’s a beautiful day! There are no signs in the sky yet but they are coming. There are no signs in the wind yet either - but those signs are coming too!

If the data plots on this map are new to you go to the Station Model Plot section on this web site to learn how to read them. There is a lot of information available in each station plot.