Most Humid of the Summer

September 17, 2010

This 2-3 day stretch of warm and humid weather is unprecedented this summer.  Yes, I know, most of us would agree that summer ended a few weeks ago weatherwise…we’ve only had two days above 80 this whole month, with none above 75 in sight.  Here’s a nice graph (click on it for a good view) showing dewpoint at PDX for the last 3 months.  The last few hours are not plotted on it, but you can see only one other time we’ve reached a dewpoint above 63 degrees.  And that was only for a few hours.  We’ve had a dewpoint near or above 60 degrees for just about all of the last 48 hours.  And this evening it’s been up to 65 degrees at times.

Dewpoint is the direct measure of the amount of moisture in the air; technically it’s  “the temperature to which a given air parcel must be cooled at constant pressure and constant water vapor content in order for saturation to occur”.   Warmer air can hold more moisture than cooler air before it saturates.  Ever been to Florida, the USA Southeast, New Orleans, or Central America?  How about a Turkish Prison?  (that last one was a joke, no need to ask about gladiator movies either).  All those places are pretty disgustingly humid during the warm season.  And when it rains it REALLY rains!

The main band of rain has passed on to the east this evening, with almost constant lightning from storms in north-central Oregon lighting up the radar screen.    One particularly strong cell around 9:30pm has produced 150-200 lightning strikes in a 10×10 mile square in 15 minutes!  Right around Antelope/Shaniko.  It’s going to be a wild few hours across the wheat fields of north-central Oregon.

Humidity stays high tomorrow as another wave of rain moves in during the afternoon/evening.  Flow direction is from the south-southwest again.  Then drier air (more typical cooler showers) for Sunday means an end to the very high humidity.

A brief break the middle of next week and then we appear to get our first strong westerly jet of the season…very wet beyond Thursday!

Chief Meteorologist Mark Nelsen

 

 


Thunderstorms Popping Up

September 17, 2010

Some thunderstorms right around Multnomah Falls, east of Sandy and headed towards the Central Columbia River Gorge at this hour.  There are more storms down around Detroit Lake, also headed north.  Another warm and humid day out there with temps right around 70 even with the thick cloud cover.  A good soaking coming up the next few hours.  Thunderstorm chance not real great down here in the lowlands with no sunbreaks, but a moist southerly flow can always surprise us (in a nice way!).

12z WRF-GFS showed some very heavy rain this evening; we’ll see if that comes to fruition.  Our RPM model showed more of the scattered showers that we are seeing now.

Chief Meteorologist Mark Nelsen