Weather in the Northern Temperate Zones

     The chart below shows a more accurate scheme than the usual solstice-equinox model, of how the weather in the northern temperate zones actually tends to behave, relative to the calendar (note that spring and fall are only one month long).

Seasons and the calendar
season date
spring, April 6 - May 6
heat mean, April 6
summer, May 6 - October 6
storminess mean, May 6
hottest month, June 21 - July 21
muggiest month, July 21 - August 21
autumn, October 6 - November 6
heat mean, October 6
winter, November 6 - April 6
storminess mean, November 6
coldest month, December 21 - January 21
stormiest month, January 21 - February 21

     (These 6th- and 21st-of-the-month dates may be more accurately changed to the 7th and 22nd, if the nearest solstice or equinox is on the 22nd, instead of the 21st.)

     Description of a typical winter storm in western North America:   There is a "low pressure" center, and, as the winds blow toward it to fill it, they spiral counter-clockwise around it (in the northern temperate zones, wind blowing north is deflected to the northeast, because, as it goes north, the surface of the earth moves east more and more slowly under it, so its higher eastward momentum, from when it was further south, deflects it that way -- conversely, wind blowing south is deflected southwest).
     Frontal systems, which are usually shaped like spokes of a wheel bent around backwards, develop in these spiraling winds, usually coming southward from the low, and rotating with the spiraling winds.
     Typically, there are two of these fronts: a warm front, and, some 90 degrees behind it, a cold front. The cold front tends to move faster than the warm front, so that they eventually merge into an occluded, or stationary, front.
     The warm front consists of warm air on the surface being pushed up over colder air (typically causing light, steady precipitation as the warm air cools as it gains altitude, and its moisture condenses).
     Cold fronts are the usual sources of most precipitation in the western North America.
     In cross-section, they are a mass of cold air moving along the surface (typically from the northwest), but they have a strange wind circulation around them -- the wind above them blows to the southeast faster than they move, causing high clouds to precede them; at the surface, the wind blows from the southeast (back against the front), and when this warmer, opposing air hits the front, it goes up over it (being warmer and less dense), and its moisture condenses into precipitation as it cools and rises; as the cold front passes, during the rain, the surface winds veer clockwise, from southeast to southwest, then northwest (usually, with broken clouds, by then).
     Thunderstorms: These are more common in the US Midwest during the springtime or early summer (after May 6), and often result when cold winds from the north or northwest (which prevail during the winter) clash with warm, moist air from the Gulf of Mexico.
     These storms have strong internal winds, typically shearing past each other, as they go up and down -- this generates the lightening, and can cause destructive hail, as ice balls are circulated up and down repeatedly -- they can form into "squall lines" (systems of thunderstorms hundreds of km long), and tornadoes can result when the clashing air masses involved do a swirling dance around each other. (Tornadoes often start as air swirling around a horizontal axis, as warm, moist air goes up over colder, drier air, and then get raised up more vertically.)

Seven-day forecasts for US zip codes

US weather map (expands if you click on it) -- US National Weather Service

Soda Springs, California (Donner Pass, on Interstate 80) forecast

Loveland Pass, Colorado (on the continental divide, on US 6, south of Interstate 70, 3.655 km [11,992'] elevation) forecast

Complete Sun and Moon Data for One Day (US Naval Observatory)


Dave's Home Page