This warm stretch of early May is an inviting opportunity to go running. Perhaps you will pass those purple signs of spring, lilacs, whose aroma is as much a part of spring as barbecues are to summer.People seem a little happier that they’re out running. While on a morning dog-walk on the North Cambridge bike path on Tuesday, I spotted two runners going in opposite directions recognize each other and exchange a high-five.If you’re out running, it helps to take precautions in warm weather. Joe Abelon, founder of the Lynn Woods summer cross country race series, has some helpful advice.”Make sure you hydrate,” Abelon said. “Hydrate on a continual basis. Look at your urine; if it’s pale, or light, you’re hydrated. If it’s darker, (you’re) dehydrated. It’s a very simple signal.”As far as what to drink, Abelon had several suggestions.”Drink water constantly; not a lot, just constantly,” he said. “A lot of people drink sports drinks. There’s a certain amount of calories involved, a certain expense to it.”A very simple, inexpensive (alternative) is a combination of equal parts orange juice and water. It’s supposed to give you a carbohydrate ratio that’s easier to absorb. If it’s too acidic, you can make it thinner. It contains far more potassium, a lot more potassium, which is important for muscle contraction and vitamin C, and a healthy thing to have anyway. It provides it a lot cheaper than that Gatorade stuff.”In addition to what to drink, think about what to wear.Abelon recommended a hat for the sun – “a light hat,” he said, “you don’t want to wear a heavy hat.” He also noted the importance of sunglasses and sun/skin protection.Another element is knowing when and where to run.”Especially as it gets warmer, the middle of day is the worst,” Abelon said. “It’s hottest. The sun is at its peak.” He suggested running “either in the morning or evening.”Mother Nature has provided us with havens from the heat.”Luckily around here, the coast is markedly cooler,” Abelon said. “Also, you’ll notice, it’s markedly different when you run in the woods. It’s shady, definitely cooler than out in the sun. At 6 or 7 o’clock at night, it’s cooler.”Speaking of the woods: The 44th installment of the Lynn Woods Summer Cross Country race series starts this month. The first edition of the 2013 series is on Wednesday, the 29th.The May 29 races include two for adults, a 2.3-miler and the Tour de Lynn Woods #1, as well as a 1.59-mile junior high race.Asked about the length of the first Tour, race director Bill Mullen said, “I make up the course usually the day before I get there. Usually somewhere between 5, 6 1/2 miles.”All races are free and begin at 6:30 p.m. at the Great Woods entrance to the reservation.Cross country running in the Woods is much different than a run on a flat bike path or city street. You’ll go up and down hills, like those of the Steel and Stone Towers. If you’re not too winded, the view from Steel Tower Hill (Mt. Gilead, 272 ft.) is a beauty, while the Stone Tower on Burrill Hill (285 ft.) is an intriguing piece of WPA architecture.”I think going up Stone Tower Hill direct from where we start is the most difficult ascent,” Mullen said.Asked whether this had something to do with transitioning from a flat parking lot to an uphill climb, he replied, “That, plus it’s relentless, with only a very short flat area, but for almost a mile you’re pretty much going uphill all the way. It’s a long pull.”The rocky terrain is challenging in general. It helps to have the nimbleness of a mountain goat on the Goat Path.”I think that’s a requirement if you’re going to run trail races in Lynn Woods,” Mullen said. “Some who are particularly nimble can go almost at normal road speed. For most, (they’ll) shorten their stride, look down and hope you avoid rocks, ruts and roots, keep moving forward.”The goal is to stay vertical as opposed to wind up being horizontal.”Yet the rewards of finishing such a race are worth it. Chocolate-chip cookies at the finish l