PORTLAND, Ore. (KOIN) — You can count on one hand the number of mostly sunny days in the forecast this week: two! First, we must break through the morning fog. There will be plenty of moisture looming in the air after several days of rain. Winds have died down. As the sky cleared, that allowed temperatures this morning to drop in a big way, and for most locations in the valley, that brings temperatures to near the dew points. So, our moment of clarity was brief.
For instance at Hillsboro airport early this morning we had a temperature of 35 °F and dew point of 35 °F. That gives us a relative humidity of 100%. The air is saturated, and if you were over there at the airport you would have been sitting in the fog. It’s called radiational cooling.
The cooling of the Earth’s surface. At night, the Earth suffers a net heat loss to space due to terrestrial cooling. This is more pronounced when you have a clear sky.https://w1.weather.gov/glossary/index.php?word=RADIATIONAL+COOLING
So, how about those meteors?
Once we break away from the morning fog sunshine enters the picture and daytime highs will be in the low 50’s. Great! Now how about those meteor showers? Does this mean we’ll have a clear evening view? Yes and no. High pressure is attempting a takeover, at least through Saturday. You can expect mostly clear conditions tonight, with fog returning late, closer to midnight as temperatures drop.
The second part to that answer has to do with the timing of the Leonid meteor shower. You see, we already passed the peak viewing a few days ago. That’s okay, you could still see a few bright streaks across the sky. It will be cold tonight in the mid 30’s in the valley, so bundle up!
The Leonids are active all of November but only produce strong rates near the date of maximum activity. In 2020, that date will be the night of November 16-17. No major outbursts are predicted this year but the Leonids are impressive meteors regardless of the numbers seen. Many Leonids meteors are bright and colorful, often leaving long-lasting persistent trains visible in the sky after the meteor has disappeared. Realistic hourly rates at maximum are probably near 10. Expect to see the highest activity only during the last couple of hours prior to dawn on November 17th. Should this morning be overcast, the morning of the 18th should present nearly as much activity.
The Leonids are remnants of comet 55P Tempel-Tuttle, which last passed through the inner solar system in 1998. The comet has just passed its farthest point from the sun and is now on its inbound leg of its journey around the sun. It is expected to be closest to the sun again in 2031. The comet has completed so many trips around the sun that remnants are encountered on Earth every November, regardless of the position of the comet. Each journey around the sun produces its own unique path and the Earth often passes close to this paths each year.https://www.amsmeteors.org/2020/11/viewing-the-leonids-in-2020/