General Weather/Earth Sciences Topics > Weather Conditions Discussion

Rain vs Pressure

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Stryder87:
Hi All

Because I've always been fascinated by the weather, I finally indulged myself and bought my first weather station a few weeks ago and have been doing a lot of reading on the different aspects of the weather, how things fit together, forecasting etc.

From what I've read and what I've been observing with my station, I'm seeing something that doesn't make sense and I was hoping you folks could help me understand it a bit more.  Everything I've read says that rain is usually preceded by a low-pressure system.  However, what I see in the attached screenshot from my station, there seem to be a couple oddities in the last three weeks that are making me scratch my head.

Box 1 is the first one that doesn't seem to match.  The pressure went up and then it rained, the rain stopped/paused, the pressure dropped and it continued to rain.  Box 2 is the opposite, as expected, the pressure dropped first then it rained, but the pressure rose and it rained again.  Box 3 matches everything I've read, the pressure dropped and it rained.

The pressure rising before it rained in box 1 & 2 seem to contradict everything I've read.  Since I've only really gotten through the basics, is there something that I'm missing that would explain this?  It doesn't make sense and I'm really puzzled by this.   :?

Thanks.
Ray

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VaJim:
Nice chart

I think what you'll find is that no one system is like the one that just left.  Each low pressure will vary.  The deeper the low the more obvious it will appear on a chart.  I've seen cases such as what you show, where the pressure either remained steady or rose slightly.  The other factor our chart doesn't really display is distance of the low center to your station.

You may want to take a look at any other stations in your area to see how their pressure tracked during the same time frame.

Mattk:
Weather is not all controlled by surface systems which can be seen on surface charts etc Upper level systems control a lot of the weather which isn't going to show on ground based pressure instrumentation but these types of systems bring much of the rain in many places. 

floodcaster:
You can also experience pressure jumps just before/during passage of outflow boundaries or gust fronts.

BeaverMeadow:
You may find this page of interest--

http://www.islandnet.com/~see/weather/eyes/barometer3.htm

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