Ground and Sky Thermal Observation during an Inversion, 27 December 2017

At 8:10 AM MST this morning, I made a thermal observation of the sky and ground at NearSys Station. Currently, the Treasure Valley, especially the lower or western valley is under an inversion. Our sky is completely overcast and we have mild fog.

Interesting how the featureless sky above is not featureless in thermal infrared. The coldest ground temperature is 5 degrees F. The sky is 8 degrees, except in patches that are 3 degrees colder. I believe these are cloud regions that are hanging lower that our overcast.

The sky looks featureless in visible light.

The overhead stratus clouds are 3 degrees warmer than the ground.

Except in patches that are as cold as the ground.

Ground and Sky Thermal Observation for NearSys Station, 25 December 2017

With snowfall in the ground, the coldest ground temperature was 6 degrees F. The overhead stratocumulus had a temperature of 1 degree F. Assuming a dry adiabatic lapse rate of 5.4 degrees per thousand feet, the cloud base has an altitude of 900 feet.

Furthermore, the clouds drifted 10 degrees towards the east in 31 seconds. The estimate of 10 degrees was made by looking at the width of my fist from my extended arm. Using the definition of the tangent, I calculated that the clouds drifted 0.176 of their 900 foot altitude in 31 seconds.

Assuming an altitude of 900 feet, the wind speed is 3.5 miles per hour towards the east at that altitude.

Thermal infrared image of the overhead stratocumulus.

Visible image of the overhead straticumulus clouds.

Visibility for NearSys Station, 25 December 2017

Three inches of snow fell at NearSys Station in the last 24 hours. At 10:45 AM MST, measurements from the UAVSonde indicate the visibility is 30 about miles.

Looking East.

Looking North.

Looking South.

Looking West.

Sunspots for NearSys Station, 23 December 2017

NearSys Station briefly experienced mostly clear skies. Not bad after one inch of snowfall. Three tiny sunspots were visible. However, their small size and the partial cloudiness covering the sun made impossible to photograph them with a call phone camera.

The three sunspots are located close to each other in the lower left quadrant.

Visibility for NearSys Station, 23 December 2017

It snowed last night and this morning. So after shoveling snow, I sent the UAVSonde up to collect images. Visibility was good and there was no air traffic.

Based on the images returned by the UAVSonde, the visibility is on the order of 15 miles.

Looking East.

Looking North.

Looking South.

Looking West.

Ground and Sky Thermal Observations for NearSys Station, 22 December 2017

According to readings from the Seek Reveal, the ground temperature was 13 degrees F. Below are two images of the sky recorded at 4:30 PM MST and 5:15 PM MST. Snowfall began shortly before the second image was recorded.

At 4:30 PM, the stratus clouds over NearSys Station were 9 degrees colder than the ground. Assuming a dry adiobatic lapse rate of 5.4 degrees per thousand feet, the clouds were 1,600 feet above NearSys Station.

Forty-five minutes later, the clouds were 5 degrees warmer. Therefore, the cloud height deceased to 700 feet above NearSys Station. That's a decrease of 900 feet in 45 minutes or 20 feet per minute. Is it normal for clouds to decrease their height before precipitation begins? More testing is called for.

All Sky Photometer Data for NearSys Station, 22 December 2017

It remained overcast all day long at NearSys Station. Then finally around 5:15 PM MST it started to snow lightly. Below is the chart of the all sky photometry data.

The sky became too dark to any effects of the snowfall appropriately 10 minutes before the snow began falling.