Friday, July 29, 2016

The Upcoming Cool Down

During the past week we have experienced a few warmer than average days, although none pushed temperatures into the 90s over the Puget Sound region (see Sea Tac temperatures below, with average max and min values in red and blue).
The recent warmth has been associated with a broad upper level ridge of high pressure over the West Coast and eastern Pacific, as illustrated by the upper level map at 5 PM Thursday below.

However, the hallmark of this summer has been the transient nature of West Coast high pressure, with the tendency to have periods in which troughing (low pressure) has developed over the region.    Such troughing will be happening in spades during the next week, as illustrated by the upper level map for Saturday at 5 PM:  a low is centered over British Columbia, with a trough over the Northwest.

 Subsequently, the trough moves out and is replaced by a strong, small-scale, low centered over NW Washington (see below for 11 PM on Monday).  This will bring both cooler temperatures and some precipitation.

 Fast forward to Thursday at 5 PM. Another low is moving into our area.

This time of the year it is hard to get heavy rain even with weak troughing.   Thus, the 24-h precipitation forecast ending 4 PM on Tuesday shows some light rain over western WA, but modest wetting over British Columbia.

Turning the National Weather Service GFS model, here is the accumulated forecast precipitation over the next 10 days.  The West Coast is starkly drier than the rest of the continent, with Oregon and coastal CA being dry.  In contrast, the East Coast is soaked.

With much cooler and wetter conditions over the Northwest, the number of wildfires has been minimal.  With the upcoming cooling, one should expect the continuation of the benign fire season.


richard583 said...

.. As I see things professor, things cold (i.e. whatever colder air remaining more northward at this seasonal point. / North of the Jet.), have been in consolidation mode for the past 10 to 14 days. And with this, their being about to spread a bit more southward where looking ahead more, to contribute to some amount of moderation of the higher temperatures that we've been seeing (Certainly here more south, in CA.) downward.

Buddy said...

"With much cooler and wetter conditions in the Northwest.." As compared to last year, or the summer before or summer before that? Sure but temperatures are still running above normal and rainfall hasn't been great (normal).

Never the less it was a very pleasant July in Eastern Washington. But a late month rally is going to push us above average for the month in KYKM. Thought the streak was over but we're going to continue the 29th consecutive month of above average temperatures. Truly remarkable stretch.

Bryan Black said...

If this strong through pattern continues into the winter, then cold temps in the lowlands are more likely to happen, right? Especially if the polar vortex buckles and sags south into North America again

John Marshall said...

I notice that Chile and adjacent areas of western South America are having a REALLY cold winter. Report yesterday of 50,000 Alpacas freezing to death and another 300,000 threatened, with weather predictions saying more of the same bitter cold weather coming.

I've tried to Google info on a correlation between western S America and N America when it comes to winter, but I can't find anything authoritative. Not sure if our shared El Nino/La Nina cycle is significant, or if northern and southern polar weather patterns fundamentally differ enough to decouple our winters.

Because if there is correlation, we could be looking at a very cold winter.

Michael DeMarco said...

Sure got hot today in the Puget Sound region as well as the Olympic Peninsula. Around Sequim it hit the low 80s then dropped dramatically after 3PM into the 60s. We will enjoy the 60s with a little precip since there are three wildfires in the Park and they were really cooking today.

MRT said...

Buddy: That is scary that 29 months in a row of above average temps. Although as somebody who lives in Central Washington, the last week has been on fire, though a cool down is also going to hit here starting tomorrow I think. Been liking this summer better than last year.

Jan Rolstad said...

Looking at the graph today ( 7/ 30) on Weather Underground I see that the expected cool down over the next few days is accompanied by rising barometric pressure, after which the the temps are expected to rise, the skies clear, and the pressure drop, so good weather and barometric pressure seem to be inversely correlated. Isn't this counter to what is normal? I've always understood higher barometric pressure to be correlated with clear and warmer weather at least in the summer and clear colder weather in the winter. What am I missing?

Nanoo Visotor said...

Last year in Aug, an image of smoke from wildfires was posted: . This year has seen at least three large wildfires in North Central to Central OR. InciWeb did Not report them, possibly because much of what was burned was grass and sagebrush.

There also seems to be a spate of reports about railroad tie fires. Whether arson, or just a kind of fire that was not reported on in the past, conditions suggest quite risk of conflagration in the areas east of the Cascades where drought conditions continue.

Rod said...

Thanks for the information, Cliff. Great news for my vegetable garden and me. Less watering equals less work. But, it will still be plenty warm enough for a healthy, ripening garden.

sunsnow12 said...

"...and rainfall hasn't been great (normal)."

Yakima is at 138% of precip for the 15-16 water year according to Weather Underground. That is substantially above normal.

Buddy said...

Cliffs statement was directly related to this summers condition. It has not been wetter or cooler than normal since April in the PNW. It's been perfectly normal. And the post was a forecast, not what it has been. Thank you. Cliff called it a couple months ago. But let's not forget what normal is compared to short term memories of our past summers.

Rod said...

RIP Dave Schwartz, my favorite Weather Channel meteorologist. I loved his voice, his manner, and his looks. He was a weatherman, through and through.

Gosh, that one hurts.


MRT said...

Sunsnow21: Is that figure of 138% of normal for just Yakima County/Valley, or does it include Kittitas Valley as well? Also, I know that because of freak thunderstorms in both June and July, the precip in Kittitas was sitting at 150% or so of normal, for those two months, but April and May were very dry if I remember correctly. This has to be the best summer in years; some hot spells but nice cools downs, and the next week is only supposed to be in the 80s, maybe 70s for one of two days as well. Gotta say I love the low 80s best for a summer temp anymore, the 90s just fry me bad anymore.

Ann M said...

The first Tuesday of August is Neighbors Night Out /Blockwatch Parties. Once again, we appear to be headed to a cool/cloudy evening. Is it just my imagination or is the first Tuesday of August generally a below average temperature day. At least it sure seems to be the case for the quarter century or so.

David E. Ortman in Ballard