Sage Bret B.
Posted by Mark S.  on July 24, 2014, 9:23 am
187.146.137.219
Yesterday was hotter than the day before and then, in the evening, it was like God turned on the celestial air conditioner.
What was the science behind this?
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-----------------------------Re: Sage Bret B.
Posted by Bret B on July 24, 2014, 6:42 pm, in reply to "Sage Bret B."
187.148.186.101
Some odd things have been happening the last couple days, weather-wise:
1. Yer not kidding yesterday was even hotter. Back up to 95.9°F / 35.5°C, but the humidity at the same time was even higher than the previous day (63%.) That works out to a heat index of 119°F / 48°C. That's the highest HI all summer! (Heatstroke high-five!)
2. Then around 8PM a huge area of thunderstorms came from inland bringing us windy/gusty/dusty conditions for a while, but not much thunder and NO rain here at my place.
3. Then again around 1AM more of the same, with even less thunder and NO rain.
But even without the cooling rains, the winds did a great job cooling it down quickly. You could feel (and smell) that the winds had travelled through some rains on their way to us. We were able to turn off most of our fans for the rest of the night. Amazing! (PS, the Melaque/Barra guys reported 2" from the first set of storms.)
4. Now today the afternoon max temperature was only a little lower (94.5°F / 34.7°C), but the humidity was MUCH lower (48%), for a much less sweaty heat index of 102°F / 39°C. Does today feel different, Mark? It does to me, based on fan count divided by sweat drops.
I think some of our surface-level air has been coming from the east off the land the last day or so, possibly explaining the lower humidity. It might be a sporadic and localized effect, because I can't find much evidence in any of my sources.
As far as the cause of the huge thunderstorm complex last night, all I can find is this excerpt from the NHC East Pacific Tropical Discussion ( http://www.nhc.noaa.gov/text/refresh/MIATWDEP+shtml/ ):
"...AN UPPER CYCLONIC CIRCULATION IS CENTERED NEAR 17N105W (200 mi south of us) WITH A TROUGH EXTENDING SW TO NEAR 11N112W. A DIFFLUENT PATTERN ALOFT AHEAD OF THE TROUGH AXIS IS HELPING TO INDUCE CONVECTION E OF 110W..."
Also, the surface trough that usually resides over the Sierra Madre this time of year has migrated out into the Gulf of California. And a tropical wave passed by us last night.
This all can help to develop thunderstorms, especially when there is so much moisture in the air. It doesn't take much to trigger it...
Who knows what's next? Not me, but it's fun to watch it happen!
(PS, no tropical storm development expected for the next couple days, but maybe something will develop later in the weekend down south of us.)
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-----------------------------Re: Sage Bret B.
Posted by Bret B on July 24, 2014, 7:00 pm, in reply to "Sage Bret B."
187.148.186.101
Oops, I forgot to answer your question:
I think the cool air coming out of the thunderstorms probably started as a downdraft though the core of the storm where it was cooled by lots of rain (and maybe some hail). When this downdraft fell out of the bottom of the storm it hit the ground and fanned out in all directions, leaving the rain behind in some directions, like ours.
If the downdraft just fell though non-rainy air it would actually heat up from compression as it fell into the higher pressures at ground level (called a heat burst.) It's the cooling rain that's the key to getting cool air out of a storm.
Plus some of that air started out at high altitudes where it was already quite cool. Not all of it, though; a lot was pulled up from the lower altitudes by the convection that caused the storm in the first place. We know THAT air is warm and humid because we live in it.
Check out the Wikipedia article discussing downdrafts, downbursts, microbursts, derechos, heat bursts, etc: http://en.wikipedia.org/wiki/Downburst
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-----------------------------Re: Sage Bret B.
Posted by Mark S. on July 25, 2014, 7:45 am, in reply to "Re: Sage Bret B."
187.146.137.219
Yes, yesterday definitely felt cooler, perhaps due to the wind coming off the ocean.
Thanks for the scientific information and confirmation that I was not imaging things.
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