It's going to rain (snow, get cold, get hot, get humid, get dry).

How do I know? Willard? Gordon? The groundhog? (What a fraud he turned out to be. You know he couldn't have seen his shadow Monday in all that rain.) No, it's none of them.

It's my aching bones.

I've always known about the bone (or joint) connection. I remember my mother, back in the days when snow meant sleds and no school instead of skids and slick driving, promising a day of snow with "I feel it in my bones." (Her corns told her, too.) She was always right and now so am I.

It's nothing to shake a leg at. Dr. Joseph Hollander, a rheumotologist at the University of Pennsylvania medical school, did some controlled tests in the mid '60s which, as he puts it, "corroborated the old wives."

The study was done with a group of arthritis patients placed in a controlled climate chamber where humidity and barometric pressure were raised and lowered. When the humidity went up and the pressure went down, recalls Dr. Hollander, "73 percent of the patients were definitely worse." Likewise, when the latter went up and the former went down.But, to get a rise out of the bones, both pressure and humidity had to change.

The theory the doctors evolved from this -- old wives never needed theories -- was this: "Adjustments to changes in humidity and pressure which are automatic and prompt in normal tissue tend to lag where there is inflammation (as in arthritis) or scarring" (from old fractures or amputations, for example).

Funds for the research, recalls Hollander, who included the results in his textbook on arthritis, were provided by the duPont organization. The late Irenee duPont, when apprised of the results, was something less than delighted, the rheumotologist remembers. "He said, 'Is that what you did with my money? I could have told you that years ago.'"

Me too.

Now somebody ought to tell Willard and Gordon.

KEEP IT (not so) Cool: It's hypothermia time again and a good time to warn people that energy saving is all well and good, but when thermostats stay under 70 degrees some people may be flirting with dangerous consequences.

Hypothermia is a condition in which the body's temperature regulator cannot handle the continued cold. Old people are particularly sensitive to the disorder, although it can affect young people engaged in hiking, mountain climbing and other sports, even in the summer.

It is insidious because the victim may not feel ill or even cold in the later stages. Studies have suggested that many deaths in elderly people attributed to other causes, such as strokes or heart attacks, may actually have been caused by hypothermia.

Even worse, many American hospital emergency rooms are not equipped with thermometers that register at low temperatures so that possible victims may not even be properly diagnosed. A survey of 243 hospitals in New York state, reported recently in Medical World News, found only one of six hospital emergency rooms had low-registering thermometers, needed to distinguish between hypothermia and stroke.

Dr. Michael Rolnick, director of emergency services at Georgetown University Medical Center, says that anesthesiology departments often have the proper thermometers when emergency rooms don't, but not enough doctors are aware even of the need to get measurements at the lower levels.

In addition to the elderly and athletes, people may be sensitive to hypothermia risks if they are on certain drugs, such as major tranquilizers, which suppress shivering, or vasodilators or if they are drug abusers, handicapped, or have burns or skin diseases.

Early symptoms include clumsiness, slowed responses and shivering. In later stages there may be delirium, stupor or, finally, coma.

A good rule of thumb says Dr. Rolnick: If you're shivering, you're too cold. Turn up the heat. If that doesn't help, call a doctor at once.

Hypothermia is a medical emergency. Get a suspected victim to the hospital at once and make certain a low-registering thermometer is used in the diagnosis.

PEANUT BUTTER AND JELLY BEANS. With the price of peanut butter soaring, this may be moot, but eating peanut butter out of the jar, whether by the spoonful or the fingerful, is not only uncouth, but positively life threatening.

And no greater authority on the dangers inherent in the mechanism of eating than Dr. Henry Heimlich (he of the anti-choking maneuver) has warned that choking on peanut butter is no joke. Unless it is spread on bread or cracker, the viscous, stick stuff can stick to the throat and spread through the lungs and no maneuver or back slapping can avail.

On the other hand, the Heimlich maneuver has helped choking victims expel pieces of peanut-buttered bread.

On the jelly-bean front -- currently the Oval Office -- some nutritionists and dentists are shuddering over President Reagan's much-touted predilection for the sweet.

Says the Health Insurance Institute, "They rot your teeth, plain and simple." Nutritionists also note that the jelly bean is a ball of empty calories -- mostly sugar and coloring.

Reportedly the president started popping jelly beans when he stopped smoking.

There's no getting around it. A jelly-bean is better than a cigarette.