Saturday, January 23, 2010

Record Low Pressure


As readers of this blog can attest, I enjoy talking about record-breaking weather...and during the past several days records have been broken in spades with one of the most unusual West Coast weather situations in years.

I have talked about our torrid month here in the NW, with April temperatures in January. But even more amazing have been the extraordinary low pressures over the western U.S. and particularly the U.S. SW. Here is a sample from the National Weather Service:

...THE LOWEST PRESSURE EVER RECORDED AT PHOENIX SKY HARBOR OCCURRED AT 644 PM MST THURSDAY EVENING WITH A READING OF 29.20 INCHES OF MERCURY. THIS BREAKS THE PREVIOUS RECORD BY A FULL TENTH OF AN INCH.

Other ALL TIME RECORD low pressures:

LINDBERGH FIELD IN SAN DIEGO WITH 29.15 INCHES OF MERCURY AT 1222 PM PST...
LOS ANGELES INTERNATIONAL AIRPORT WITH 29.07 INCHES OF MERCURY AT 121 PM PST...
LAS VEGAS MCCARRAN AIRPORT WITH 29.03 INCHES OF MERCURY AT 514 PM PST.
YUMA WAS 29.12 INCHES OF MERCURY AT 259 PM MST

.Medford, San Francisco,and many others, also had record low sea level pressures.

I mean...this is really historic stuff. Perhaps your grandchildren will ask you about it someday....(maybe not).

The origin of these record low barometric readings? An extensive, very deep low over the western U.S. Below I have a sea level pressure map for Thursday afternoon...you can see this massive low. And also I have an upper level chart for the same...a massive trough over the West Coast with a strong jetstream (where the lines are close together) headed straight into the southwest.

The impact of this jet was profound: record precipitation into southern CA, Nevada, and Arizona. Heavy snow in Flagstaff and northern AZ.

Although we did not set pressure records in Washington in terms of the minimum, we did have very low pressure for an amazing length of time. Check out the plot of pressure at Sea Tac. I cannot remember an event in which our pressure stayed so low for so long (days below 990 mb).

I sometimes get calls from people suffering from arthritis, wanting to know about low pressure and big pressure falls--which they feel worsens their condition. I wonder if anyone noticed anything?
Finally, today will have a few showers and plenty of clouds....and a more serious system comes in tomorrow afternoon (Sunday). But absolutely nothing major happening. No threat of flooding in the Cascades as far as the models can predict. I think those worried about the Green River and Howard Hansen Dam can relax and go on vacation soon. After Jan 1 El Nino years rarely have major flooding and in any case, floods are very rare on west side rivers after Feb 20th...and our computer models show nothing significant for the next week. Plus, the dam water level is way low and there is room for a fairly major storm.

15 comments:

Michael Raveneye said...

Thanks for the low pressure info Cliff. Over here in Sequim we have the great weather site at the Dungeness Light House. I noticed the very low pressure readings and that it stayed that way and was wondering if it wasn't unusual. Also, watching that jet stream and storm action hit So. Cal and AZ has been very interesting. Historic!
For those interested here is the site:
http://www.olypen.com/dungenesslight/DungenessLightWeather.htm

Mark said...

Typhoon Tip recorded 25.69 (http://www.srh.noaa.gov/jetstream//tropics/tc_notable.htm). Not necessarily the Northwest, but this is the lowest low on record.

James Lupori said...

Dr. Mass,

I really enjoy your blog but sometimes I think you assume your audience (those of us with a marginal level of meteorological knowledge) knows enough to truly understand the weather you describe.

This last week you have been discussing the historically low pressure even in the Pacific and I sort of understand what low pressure does (sort of). It would be helpful if you might give us notion of what low pressure is and what conditions low pressure creates in different situations. For example, does a low pressure in TX cause a different array of weather in that region?

Thanks for a great blog!

Must read blogs said...

i have to wonder how many women went into labor because of the low pressure. There is a strong correaltion btw pressure change and rates of women going into labor.

Dawn said...

Cliff,I've got a theory about low pressure and arthritis. I'm fairly new to this phenomenon, but I've noticed is that achy fingers are associated with the type of pattern we usually have in November, when lows move through quickly, and are interspersed with higher pressure. This recent situation of extended, stable low pressure hasn't resulted in sore fingers for me.
I've always figured that the symptoms are the result of the expansion of the fluids (like a balloon) in the joints in relation to the atmospheric pressure, so it makes sense that when there is extended low pressure, the relative pressures even out, and the ache dissipates.
I'd be interested to know if this has been experienced by others.
Thank you for sharing your wit and wisdom.♦

Josh said...

must read blogs

Funny you say that. I am in the process of research for labor rate and connection to moon phase and pressure tendencies. It will be a wile (lots of data to sort through) before any true frequency shows. Though with the data I have populated so far, full moons seem to be popular with births.

Jim said...

We sure noticed. Even after the predicted fairly high tides of the past weekend, the effect of the low pressure was noticeable. In 30 years living here I don't remember this many "over the top" tides occurring in one cycle. Day after day starting last weekend the tide covered the sand spits here in Dutcher Cove as well as Vaughn Bay here on the far south end of the Salish Sea. Drift logs are floating all around the Sound as a result of the high tides. And there was little wind to cause the effect, either.

JewelyaZ said...

Cliff,

Thanks for this great info... I too noticed the length of time below 990 mb... so much so that I changed the batteries in my sensor, thinking it must be out of whack... such low pressure AND sunshine didn't really add up!

Glad we're in the clear most likely on the Green River... times are hard enough, it's good to catch a lucky break once in a while. :-)

Those of you wondering about birth rates in connection with the moon and with the low pressure cycle we're going through would do well to contact the midwives at Puget Sound Birth Center in Kirkland. They don't do any labor induction and they have over ten years of historical data to draw on. Puget Sound Birth Center I gave birth to two of my three children at home with midwives from the Birth Center.

Roberto said...

So Jim, and Cliff of course, does the extreme low pressure, coupled with winter high tides, pull in ocean water like a storm surge. The high tides are substantially higher that the tidal charts are indicating- witness the enormous amount of drift on the Sound.

Cliff Mass Weather Blog said...

FYI from a wiki on sea levelheight:

The rising water level will counteract the low atmospheric pressure such that the total pressure at some plane beneath the water surface remains constant. This effect is estimated at a 10 mm (0.39 in) increase in sea level for every millibar drop in atmospheric pressure.


In our case the pressure was about .6 inches below normal...cliff

tchedoen said...

I live in Port Townsend, and for the last couple of weeks, many people I know have commented on restless sleep, lack of sleep, weird dreams, unsettling moods, and general depression and uneasiness. Some of us had wondered if low pressure might be the culprit (it made more sense than a town-wide demonic presence, which was the other popular theory). The historic dimensions of the low might well account for such a wide-spread reaction.
(Personally, I have also experienced a sharp flare-up of fibromyalgia symptoms. It stinks.)

Emily said...

I had plantar fasciitis and thought I had been cured last summer, but my foot pain returned over the last week. I'm glad to know I can blame it on the weather...although I'd rather just not have the pain.

Wendy said...

I'd heard about arthritis and bone aches with barometric changes, but I too wondered about other symptoms, like tchedoen said. Any data out on that?

Martha said...

I'm a Seattleite living temporarily in Tucson. I felt increased pain and achiness right before the big storm passed through Tucson. I felt much better the next day. Another person here mentioned having cardiac problems before the storm and felt fine after the storm passed. We really rocked and rolled in that storm. Felt like home.

Christy said...

I have no idea if there is truly an correlation to migraine headaches and barometric pressure. However, when the pressure is low and stays low, I seem to have fewer (or no) migraines. Has anyone else ever noticed this?