This begins with the Vernal Equinox (around March 20 in the Northern Hemisphere), when day and night are roughly equal in length.
When warm, moist air from the Gulf of Mexico clashes with lingering cold, dry air from Canada, the result is atmospheric instability. spring season weather
The polar jet stream, a river of strong winds at 30,000–40,000 feet, weakens but becomes wavier in spring. Instead of a smooth west-to-east flow, it develops deep troughs (dips) and ridges (bulges). A trough allows Arctic air to plunge south; a ridge allows tropical air to surge north. These sharp contrasts generate intense low-pressure systems. This begins with the Vernal Equinox (around March
Plants respond to the warming soil and increased daylight. This "green-up" can be seen from space as a wave of color moving northward. Instead of a smooth west-to-east flow, it develops
Spring is the season of "mud season" and snowmelt, where warming temperatures can lead to rapid runoff and river flooding.
But spring is a fickle director, and the script was not finished.
As weather warms, plants reproduce. Tree pollen (oak, birch, cedar) explodes in early spring, followed by grass pollen in late spring. The alternating dry winds and humid rain create a perfect storm for allergy sufferers—rain washes pollen away temporarily, but dry, breezy days send concentrations soaring. This is often called "spring asthma" or "hay fever season," affecting millions.