Many of you may have taken a step outside this morning, only to notice that the humidity was sky high again. So what happened?

We had a classic "GULF SURGE" event this morning, whose humidity originates from decaying thunderstorms and a shallow humid airmass from the Gulf of California. Let me explain below.

Screen Shot 2018-08-07 at 9.30.30 AM.png

Late last night, a huge thunderstorm complex formed south of Arizona. This is a common place for storms to form this time of year, as very humid air clashes with instability formed by the mountains to provide the perfect breeding grounds for thunderstorms. A light easterly flow allows these thunderstorms to drift west off the mountains into the lower deserts of Western Sonora. They encounter hot temperatures and a shallow moist layer of humid air generated from the Gulf of California, and as they move west toward the gulf, they generally begin to lose their strength for a number of reasons, including the flatter topography the further west the storms navigate, which reduces instability. 

As the thunderstorms collapse, strong downdrafts accompany the decay of the storms. The damp air is heavier than the warmer drier air, so density helps accelerate the moist air outward away from the decaying storms. The result is a gust of wind that accelerates far out in front of the original storm system... much like what causes our famous "haboobs." 

Last night, this shallow gust moved northwest from the Gulf, and continued up into the Imperial and Coachella Valleys. It was carrying the hot humid airmass from the northern Gulf of California... which has water temperatures up over 90 degrees this time of year. That extremely humid airmass easily moves along the mostly flat terrain from near the mouth of the Colorado River, all the way up into our area.

Notice the jump in the dew point and humidity at Palm Springs Airport (below) between 4:53 am and 5:53 am....

Screen Shot 2018-08-07 at 9.59.36 AM.png

The humidity increased from 26% to 57% in one hour. For those that track by the more accurate "dew point" temperature, the dew point went from 50 degrees up to 72 degrees in one hour.

I took a look at communities to our south, and discovered the northwest movement of this humid airmass from late last night. It moved north of the US/Mexico border around 1:30-2:00 am, hitting the Thermal area a few hours later around 4:00 am, and finally moving up into the Palm Springs area around 6:00 am. 

The airmass change was accompanied by a brief wind shift to the southeast, and greatly increased humidity levels. The air is also quite hazy from both the lower level humidity, and the smoke that blew into the valley last night from nearby fires. 

Screen Shot 2018-08-07 at 9.42.13 AM.png

This came in a day earlier than was anticipated. The good news is the humidity layer is quite shallow, so as the day heats up, the humidity will evaporate away as the day progresses. Dewpoints will fall back into the 60's and perhaps back down to the 50's later in the afternoon.

However, we will be increasingly influenced by southeast weather patterns and increasing humidity as the week progresses. Hurricane activity off the Baja coast will also add to the uncertainty. Hope you all enjoyed the brief spell of no humidity while it lasted!