Ocean currents rotate clockwise in the Northern Hemisphere, but there are also counterclockwise winds. Is the difference caused by the Coriolis force?
The terms “clockwise” and “counterclockwise” refer to the sense of rotation around a center, when viewed from above. Do not confuse those terms with the Coriolis deflection which, in the Northern Hemisphere, is always directed to the right of the motion — for water, air and for anything that moves.
When air blows inward toward a central point (toward a low pressure center, for example), the rightward Coriolis deflection causes a counterclockwise inward spiral. When air blows out from a central point (from a high pressure center), the rightward Coriolis deflection causes a clockwise spiral outward.
Ocean currents, driven by wind and density differences, experience the same deflections.
In recent days, some of our blog readers have sent us some pretty amazing photos of morning fog as seen across the Chicago area. We’d like to share a few of them with you:
Nicholas Andrews sent us this image of fog draping Lake Point Tower (near Navy Pier) on Sunday.
Mike and Candi Straub sent these beautiful images from their farm in Harvard. The pictures were taken last Friday morning between 6 and 6:20 a.m.
Jeremy Draftz sent this picture of fog seen over the Lake in the Hills Airport early Friday morning.
Finally, Lisa Histrom of Hebron took this picture while driving in Lake Geneva area, also on Friday morning.
Thanks to everyone for sharing their pictures with us!
The upper-air pattern remains relatively unchanged with the stronger northern jet stream winds well to the north in Canada and the southern jet running from the Gulf of Mexico up the eastern seaboard. The light winds aloft leave little opportunity for any significant air mass changes here in the Midwest or western Great Lakes. As a result, the light easterly flow continues to allow fine particulate concentration to slowly increase, and hazy conditions will persist. In Wisconsin the Department of Natural Resources has continued an Air Quality Watch through Monday over southern and central portions of that state with concern that particle pollution and ozone concentrations might reach unhealthy levels for people in sensitive groups.
Rain/cooler conditions possible next weekend
Computer models indicate a cold front accompanied by showers and thunderstorms could bring cooler Canadian air into northern Illinois next weekend. Chicagoans may be in store for highs in the 60s, more like late September and early October.
Why is it that we get storms when a cold front arrives but not when a warm front arrives?
It’s true that the weather in advance of a cold front is more turbulent and more likely to erupt into thunderstorms than warm frontal weather, but warm fronts do sometimes generate precipitation.
A front is the boundary between air masses of differing characteristics, most notably temperature. We call it a cold front when cooler air is advancing, and similarly for a warm front.
Stormy weather develops when air is lifted, but cold fronts are far better lifting mechanisms than warm fronts. Advancing cold air, heavier and more dense, turbulently forces its way under warmer air, thrusting it up and thereby triggering stormy conditions. Advancing warm air, lighter and less dense, glides gently over cool air, usually generating little more than clouds and steady rain.
Under the influence of cool dry high pressure, It’s been a week (Aug. 29) since rain was last measured at the official O’Hare airport observation site. The rainless streak could well continue at O’Hare Sunday, but showers are becoming more and more likely, especially in southern portions of the metro area and in northwest Indiana. Low pressure has moved into western Illinois. Showers that fell over central and southern sections of the state Saturday and Saturday night have been working their way east and north, ever closer to Interstate-80. The Chicago area will again on the borderline for showers Labor Day into Tuesday.
Warm-up Wednesday, then turning cloudy/cooler
As the low moves east and weakens over Indiana, clouds will thin allowing the sun to warm readings into the lower 80s Wednesday. However a cold front will approach from the northwest and even though it’s movement through the Midwest will be slow, associated clouds and showers/thunderstorms along with cooler air behind the front will lead to a return to sub-normal temperatures later in the week.