Today's forecast: Partly crabby, sneezy and painful this morning, followed by scattered ennui this afternoon and a strong chance of sleep disturbances tonight. Tomorrow: Possible aches in outlying suburbs, clearing to general feeling of well-being late in the day.

While Americans may feel "under the weather," West Germans expound on the phenomenon through "biometeorological advisories" (similar to the above) that explain how the weather may make people feel.

"Since 1952, West German law has required that weather reports not only forecast the weather but also personalize it," says physicist Stephen Rosen, author of Weathering: How the Atmosphere Conditions Your Body, Your Mind, Your Moods--and Your Health.

"This recognizes a traditional belief, supported by extensive European research, that weather affects health, well-being, behavior and moods of most people every day."

Americans are expressing a new interest in "the age-old questions about how weather and climate affect human beings," says meteorologist Helmut Landsberg, president of the American Institute of Medical Climatology. (The Minneapolis-based Med-Weather Forecast Service now offers "bio-prognosis" reports, adapted from the West German system, to TV and radio stations and plans to market the service to newspapers and health care facilities.)

While Landsberg stresses that "no two human beings react in the same way with respect to the weather," studies show that weather can affect everything from test scores to sex drive.

"Most weather reactions--such as sneezing, headaches, painful joints--are discomfort reactions. If you're not in equilibrium with your environment, you experience stress."

Spring and fall are particularly stressful times, notes Landsberg, "since the weather fluctuates greatly." The restless, daydreamy condition known as Spring Fever is "likely linked," he says, to physiological reactions to these climatic changes.

(Suicide rates and hospital admissions for depression peak in the spring and fall.)

Among other preliminary findings of biometeorological studies:

* Our metabolic mechanism is in best harmony with air temperatures around 77 degrees.

* Temperatures of about 65 degrees most favor fertility and sexual vitality.

* People are more alert and have fewer accidents on dry, cool days with little wind and a steady barometer.

* Male hormonal levels peak in mid- to late September.

* Ideal work conditions are 64 degrees with 65 percent humidity.

* Falling pressure causes body tissues to swell and prompts susceptible people to behave peculiarly, with symptoms including drowsiness, agitation or migraine headaches.

* Extremely hot weather dulls the intellect. (More people flunk Civil Service exams in July and August than any other time of year.)

* A lengthy stretch of bright weather reduces productivity.