Eclipse madness is surging across Idaho.

Businesses within the stripe of Idaho cities and towns where the moon will totally block sunlight on Aug. 21 have one eye on the sky and another on the cash register. Hotels are booked. Porta-potty rentals are brisk. Restaurants and grocery stores are packing in extra food. Campsites are filling up. Idaho could have hundreds of thousands of visitors to see the eclipse, although there’s no official estimate. In Oregon, officials predict as many as a million visitors and warn of a possible “cosmic traffic jam.”

Communities are planning eclipse parties and distributing information on the best places to see the eclipse, which comes into Idaho at 10:10 a.m. and leaves the state at 12:48 p.m.

If you’re thinking of driving to Eastern Idaho, be doubly prepared. Crowds of 300,000 to 500,000 are expected, many of them flying to Salt Lake City and then driving to Idaho, said Kerry Hammon, a spokeswoman for the city of Idaho Falls.

If you have not booked a week somewhere to settle in to await the eclipse, there are still ways you can see it. But expect lots of traffic and be prepared for crowds and contingencies, state officials say.

Planning is still being fine-tuned, but here is a day tripper’s guide on what to see and where to see it in Southwest Idaho and eastern Oregon.

Idaho roads

Get ready for traffic: If you have a favorite place where you want to watch the eclipse, double the normal time it would take to get there, says Tim Marsano, Idaho State Police spokesman. That includes routes involving Interstates 84 and 15 and Idaho highways 75, 21, 55 and 20 —“any road that heads north through the optimal viewing area,” Marsano said. State Police will beef up patrols through the eclipse area, pulling troopers from less-traveled parts of the state that weekend, he said. “We are expecting an immense crowd coming into Idaho from other states and throughout the world,” Marsano said

Weiser crunch: Weiser, one of the first places in Idaho to get the full eclipse, has two routes into the city, U.S. 95 from Idaho and Oregon 201. Both are two-lane roads and could easily become congested.

Road construction: The Idaho Department of Transportation is suspending construction Aug. 19-21 in areas where heavy eclipse traffic is anticipated, to help keep traffic moving and crews safe.

No roadside viewing: Use the shoulder only for roadside emergencies, not to gawk at the eclipse, transportation officials say. “We don’t want people stopping in the middle of the road when the eclipse (happens),” said Bill Kotowski, Idaho Department of Transportation spokesman.

The biggest traffic jam: The worst traffic may not be people coming to see the eclipse, but motorists eager to leave all at once afterward, planners say. Some communities are suggesting visitors stay awhile, rather than try to leave immediately.

The numbers

Expect lots of people: No one knows for certain how many people will show up. But the eclipse is a highly publicized event that happens at one specific time, community leaders note. Visitors to specific cities and regions in Idaho could range from 20,000 to hundreds of thousands. The Oregon Department of Transportation is projecting a million visitors and warns of a “cosmic traffic jam” if people don’t plan ahead.

Traveling

Gas: Leave home with a full tank of gas. Some of the communities where you can view the eclipse, such as Crouch, have just a couple of gas stations.

Provisions: Bring food, water and other stuff you might need. Stores and restaurants could easily be overrun with people who don’t prepare ahead. Don’t leave trash: Pack out what you pack in. Make sure you have enough cash or credit cards. ATM machines hold only so much cash, say Idaho tourism officials.

What to see, and where

Baker City, Ore: Most of Baker County is in the path of totality for the eclipse. No special viewing areas are being set aside and no shuttles are planned, says Jason Yencopal, Baker County Emergency Management manager. As eclipse viewers spread out, Yancopal reminds visitors to stay off private property. Planners are encouraging restaurants to simplify menus to about three items to accommodate crowds, Yancopal said. Baker County Tourism has an online list of recommended places to see the eclipse. The rest of Oregon does, too.

Weiser hosts Eclipse Fest 2017: The town will wrap up its four-day festival on Monday, Aug. 21, with a pre-eclipse pancake breakfast sponsored by the FFA from 6 to 10 a.m. on State Street between Idaho and Commercial streets. Eclipse Fest 2017 will include a fun run, car show, wine-tasting, barbecue competition and concert. Eclipse viewing areas are planned at Weiser schools and Memorial Park. (No details were available on Payette’s plans.)

Garden Valley: Idaho X Sports adventure park is taking the lead in publicizing places to stay and view the eclipse. Plans are in the works to open 40 acres for eclipse viewing, said Jason Sawin, who owns the park with his wife, Kelly. Details will be available at the X Sports business website. A pre-eclipse country music concert is set for Crouch at noon Sunday, Aug. 20. Performers include honky-tonk and rock pianist Bobby Dee Keys and Dustin Isaac, lead singer for The Tumbleweeds. The $10 admission includes the adventure park. The Idaho X Sports website lists available camping and other viewing sites.

Stanley: Stanley’s biggest event each summer is the Mountain Mamas’ Arts and Crafts Festival in mid-July, which draws 8,000 to 10,000 people. For the eclipse, Stanley is bracing for 20,000. Undoubtedly people coming to Stanley are lured to all that open land along Idaho 21 between Banner Summit and the town as a great place to view the eclipse. But Stanley Mayor Herb Mumford cautions that a lot of that land is private, not government property.

Pioneer Park, the city park overlooking Stanley, will be closed to vehicle traffic, with only foot traffic allowed, Mumford said. On Aug. 19 and 20, the Boise Astronomical Society will put up telescopes in the park for public star viewing; the same two days, the club also will have a solar telescope available from noon to sunset and will host a laser-guided tour of the stars at 10:30 p.m.

Woody Sullivan, an astronomy professor at the University of Washington, will give a public lecture on “Awesome Solar Eclipses from Ancient Time Until Tomorrow” at 3 p.m. Aug. 20 in the Community Building.

Restaurants and stores are stocking up for huge crowds. You may see some semi-trailers parked near businesses to hold all the extra provisions they are stocking up on, Mumford said.

Stanley has not set aside a public viewing area. But the Sawtooth National Forest is working on a couple of places. One will be a fire base camp off Idaho 75 south of the Redfish Lake turnoff. Watch for signs. Forest officials are working on another venue, but details are not set. Check the Sawtooth National Forest website closer to eclipse day for more information.

Redfish Lake Lodge and the reserved campgrounds at the lake are booked. First-come, first-serve campsites are expected to go quickly. But people can view the eclipse at the beach and at places around the lake.

Cascade: Visitors to Cascade can view the eclipse at Kelly’s Whitewater Park. Parking will be available at: Cascade Community Center, 409 N. School St.; city parking area across from Cascade Rural Fire and EMS Station, 109 E. Pine; Valley County Fairgrounds, 520 S. Front St.; Cascade Sports Park; and Cascade School District, 209 N. School St.

Donnelly: View the eclipse at the Donnelly Elementary School field, 327 E. Roseberry Road. Park at Donnelly Elementary and Donnelly tennis courts, near the school.

Tamarack Resort: About 400 people already have booked a sold-out ski-lift trip up the mountain, elevation 7,700 feet, to get a little closer to the eclipse. But the resort’s amphitheater will be open for viewing, as will the beach on Cascade Reservoir near the resort. Kayaks will be available for rent. Reservations are suggested, said Wolfe Ashcraft, Tamarack director of base operations. Go to Tamarack’s website for more information and reservations.

Idaho Falls: Eastern Idaho’s regional website on the eclipse, eieclipse.com, is packed with information, including camping and viewing areas.

Idaho City: Phoenix Hobbs, a 16-year-old who will be a junior at Idaho City High School this fall, is getting a jump on her required senior project by planning her own eclipse festival. Hobbs’ festival will be at the Idaho Center for Outdoor Education, an 87-acre forested area not far from the high school. On top of a hill, away from trees, folks will be able to watch the eclipse, get face-painting for the kids and grab a bite to eat. Hobbs has arranged for permits and is working on parking for the 500 people she expects to come. The festival starts at 9 a.m. on eclipse day.

“There will be a hike up to the top where my event will be, there will be glasses being sold, special T-shirts supporting the event — basically just a fun day of activities,” she said.

Hobbs is volunteering this summer helping Idaho City elementary kids learn about the outdoors, and she hopes to major in environmental sciences at the University of Washington or Gonzaga University. “I have always had a love for the outdoors,” she said. “I absolutely love the idea of introducing outdoor education” to other kids.

Details are being worked out. Check the Idaho Center for Outdoor Education Facebook page or the Idaho City Schools website for more information on parking and the event.