Weather of the Day - Cold Advection & Clouds of the Day - - Friday, October 6, 2023
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A solid Stratocumulus Cloud deck that formed near the top of the colder layer of air. light rain fell from showers that formed within the stratocumulus layer as Nimbostratus or cumulus congestus. The sky was blue on top. Photo copyright by Craig Johnson, Weather Briefing LC October 2023
Colder air continues to spread south and east across much the country today. The first map shows the station model plots for select cities at 11:00 a.m. CDT. The second map shows the surface wind streamlines for the same time. Streamlines are snapshot of the wind direction at the observation. The station model plots show the current weather observation at the same time.
Colder air was being advected (moved) from Canada into the central and eastern United States. Cold advection is the movement of colder air from one place to another by the wind. The Stratocumulus in the photo above formed in the lower levels of the atmosphere of the cold air mass. Cloud ceilings (the bases of the clouds) were between 1,000 and 3,500 feet above sea level. Moisture in the air was condensing as clouds. The coldest air was shallow and the clouds formed near the top of the cold layer. Light rain fell as the cold air arrived and deepened but we only received .04 inches of rain. Stratocumulus clouds do not produce rain so the rain received came from either Nimbostratus or cumulus congestus clouds that were embedded withing the cloud deck. Skies began to clear during the evening as shown is the cloud photos below.
Temperatures werein the 60s east of the leading cold front and drop to the 20s in northern Montana. Follow the streamlines to see the trajectories of the air. Learn to decode the station model plots by scrolling down the home page to the Station Model Tutorial.
Map plotted using Digital Atmosphere available from Weathergraphics.com.
Map plotted using Digital Atmosphere available from Weathergraphics.com.
Photo copyright by Craig Johnson, Weather Briefing LC October 2023
Photo copyright by Craig Johnson, Weather Briefing LC October 2023
Stratocumulus turned into these cumulus clouds as evening approached and daytime heating waned. There was a definite chill in the air with temperature in the 40s and lower 50s all day.
The barometric pressure trace below shows the first cold front passage at about 5:00 a.m. and the rising pressure through 9:15 p.m. It also shows the gusty winds that accompanied the colder air with gusts over 15 to 20 mph from after 5:00 a.m. into the mid-afternoon. Wind gusts at the airport exceeded 35 mph. Our winds were not as strong because we are in an urban area with large numbers of close-by trees and buildings that slow the wind speed.
