Radar showed rain showers in the area, but most Sacramento-area residents received only a few splashes due to dry air in the lower atmosphere.
SACRAMENTO, Calif. — Many in the area might have been surprised to wake up to gray skies, cooler temperatures and even a few drops of rain. It was like a cool fall morning, with almost overcast skies and temperatures of 63 degrees at 9am.
Minute precipitation readings (less than 0.01″ of rain) were all the Sacramento area received the most. Most of the rain that fell evaporated before hitting the ground due to the extremely dry air in the lower atmosphere.
Meteorologists use sounding data, a method of obtaining a vertical profile of the atmosphere via weather balloons, to forecast rainfall for events like this.
Below is a poll of the 9-hour model run from the High Resolution Rapid Refresh (HRRR) forecast model obtained from pivotalweather.com. The survey data may be intimidating at first glance, but it paints an extremely valuable picture of the atmosphere.
The lime green line on the left represents the dew point (the temperature at which water droplets condense) and the red line represents the atmospheric temperature. The points where the lines overlap mean that the air is saturated, while the further apart they are, the drier the air in that layer. Areas of saturated air are likely locations for rain.
Using the data above, we can see that the rain-producing clouds were located about 6 km (3.7 mi) above the valley floor. As we descend back to the surface, the lines recede, which means low relative humidity values. When raindrops penetrate this drier layer, they evaporate and do not reach the surface. This is called the virga.
The Sacramento National Weather Service described the situation this morning.
“There were lots of showers on the radar today, but little rain with these made it to the ground. You may also have noticed streaks or streaks coming from the clouds. This is considered Virga “, said an official in a tweet.
A rotating low-pressure system on the state is to thank for the brief relief from above-average temperatures. As the storm system moves northeast, high pressures and warmer temperatures will return to the area. Thunderstorms are expected to persist in the Sierra for the remainder of the afternoon, primarily south of Highway 50.
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