Past IEM Features tagged: pressure
If you have sensitive sinuses, yesterday was probably not a very pleasant day for you as air pressures were near the largest values ever recorded in the state. The featured table displays IEM computed pressure records (as expressed by the pressure altimeter reading). There are a number of caveats to this chart as locations in the state have different periods of record and the maximum daily high pressure is something not commonly reported, so this table simply lists out the maximum hourly value reported. Extreme high pressures like this are found with dense areas of very cold air during the winter time.
Tags: pressure altimeter
Are you old like me and do not enjoy it when the pressure changes as various parts of the body start to ache? The featured map displays the total amount of pressure change for the year to date. This value represents the amount the mean sea level pressure observation has changed hour to hour for the year. The largest values (most change) are in southeastern Colorado / northeastern New Mexico while the lowest values (least change) are along the coast in southern California. The maximum area is the preferred location for low pressure systems to develop thanks to geography and the jet stream. If you are bothered by pressure changes, you may wish to move to Florida or the coast of California!
Tags: mslp pressure
After a windy Tuesday, winds are on the increase today and expected to gust upwards of 50 mph. These strong winds are forced by horizontal differences in pressure as air moves from areas of higher pressure to areas of lower pressure. The featured chart presents the combination of an approximate pressure difference over the state to the observed wind speed for Des Moines. An informal forecasting rule of thumb is that for every 4 millibars difference in pressure over Iowa leads to a wind of 10 more miles per hour. For example, a 12 millibar difference should support a 30 mph wind speed. The chart would indicate that this is a fair approximation with most of the distribution near the theoretical line.
Tags: forecasting wind pressure
Low pressure systems get all the publicity as they are the ones that bring the precipitating weather and are called storm systems. On Wednesday, such a system rapidly deepened over the Midwest before departing to our north early this morning. The featured chart displays the reported mean sea level pressure values from the airport weather stations over the Midwest since Tuesday. It is interesting to notice that while pressure was dropping over some sites, other sites were experiencing an increase in pressure as the high pressure system moved in from our west and strengthened as well. We typically do not think of high pressure systems strengthening at the same time the low pressure system is deepening as well. These changes help to increase pressure gradients, which ultimately drive increased wind speeds.
Tags: mslp pressure
A strong fall storm system is currently providing Iowa with plenty of wind and severe weather over the southern plains. Our sea level pressure has dropped below 1000 mb for the first time since May. The featured chart looks at some climatological aspects to the mean sea level pressure (MSLP) reading for Des Moines. The top chart presents the range of observations for each day of the year since 1960. The range in pressure is much smaller during the summer time due to the strong storm system tracks being further north and the air mass dominance of warm air. The bottom chart is an attempt at showing the relative frequency of pressure readings and the variability of the fall, winter, and spring months can clearly be seen. These larger differences in pressure help to drive stronger winds as will be the case for today!
Tags: mslp pressure
Very cold air has settled into the state thanks to a robust area of high pressure. The altimeter reading (a measure of pressure) yesterday morning was a few hundredths of an inch below the highest value reported so far this year. The featured chart presents the yearly events of when the highest and lowest altimeter readings were observed. The first chart compares the air temperature against the day of the year for the observation. The highest pressure events are associated with colder temperatures than low pressure events as confirmed by the second chart. Low pressure events tend to be with dynamic storm systems (upward motion) that are windier than high pressure events (downward motion). The last chart shows the time of day that each event type occurs. High pressure events mostly occur during the morning hours when the atmosphere is still cooling, while low pressure events happen about any time of day.
Tags: climate pressure
An epic winter storm has most of Iowa shut down this Wednesday morning with snowfall amounts approaching a foot and a half in areas. The big story now is the blowing snow thanks to strong winds blowing over 30 mph sustained. These winds are due to a tremendous pressure gradient over the state. The featured image shows the pressure drop yesterday for the Des Moines ASOS at 34 millibar in a 24 hour period. This rapid change, perhaps unprecedented, in pressure will help keep winds strong today and roads in Iowa impassable.
Tags: blizzard bomb pressure
When you get old like me, your bones and joints become the best predictor of the weather. The development of powerful storm system yesterday and today has dropped our surface pressure by around 0.7 inches of mercury (~ 24 millibars) in just over 24 hours. This is close to the "bombogenesis" criteria (24 mb in 24 hrs), which is just a cool sounding term to describe another cool sounding term, rapid cyclogenesis.
Tags: bomb pressure