The long fetch coming from the northwest can provide downwind waves with a wind that does not have to be as high as the wind sometimes needed in Bellingham Bay. Look here on days with a WNW, NW or NNW wind starting in the mid-low teens for downwind laps. Of course if the wind and waves are cranking up in the Strait of Georgia then the swell going south can be quite sizable and you can use the north land arm of the Bay for protection going upwind before you decide how far to venture into the waves for going downwind. Most of the time when there is much west component at all to the wind, big waves will be coming at you very soon after launch and you will be able to paddle more or less straight out until you are ready to turn for a downwind lap. This can be a real ocean swell with separate wind waves - just like ocean conditions in other popular destinations around the world. You can't judge the swell size from shore, but you will get to large swell soon once you paddle away from shore. A great opportunity to practice ocean downwinding when Bellingham Bay does not have its usual variations of south wind that work well there.
Bellingham boaters hardly ever look farther than Bellingham Bay when south winds are blowing. But Alan Lipp reports you can also catch larger swell in Birch Bay on a south wind with a west component. You use Point Whitehorn at the south end of the bay as protection for going upwind then paddle out and catch downwind laps back into the bay on WSW, SW, SSW winds. The longest line you can take from Point Whitehorn back to the Bay shoreline is over 3 miles.
Good swell and waves may be farther out in the channel if there is little west component in the wind/waves BUT you really do NOT want to be blown too far into or across the Strait of Georgia toward the San Juans or Vancouver Island whether you are going north or south. You need to be even more sure of your abilities and safety precautions (radio, leash, buddy, etc.) if you venture into bigger water that is not clearly aiming you back into the bay. Be aware of any forecast wind direction or strength changes and likewise pay attention to any changes on the water. You can hedge your risk by keeping more inside the bay and catching a level of waves where you can still feel comfortable or you are able to practice stretching your skills while you will clearly be pushed back to the bay shore if you have any trouble. On bigger days with plenty of from the west component in the wind and waves the push back to shore will be a given and your major decisions can be: can you get out (and back in) through the shore break safely and how far can you paddle out against the wind and waves? Far enough to get decent downwind laps or not at all? Significant local wind in the bay can add considerable side wave action on the water as well as daunting wind resistance that makes everything more difficult, particularly getting in and out of the water.
Some sort of paddle shoe is highly recommended for walking in and out. The shoreline bottom is mostly shells and small, barnacle encrusted cobbles.
Ebb tide helps build the waves in the bay but can make for walks across the shallow shoreline flats particularly at max low tide. Well worth it if the waves are good. Launch from the pavillion (BP Heron Center) area can have a little more protection from shore break sometimes - depends on wave direction. There are also hot showers in the pavillion area that take $quarters.
To get better surfing waves all the way to the shore you may need somewhat higher northwest winds. Since it's a point break at Birch Bay State Park, the wave tends to peel so you can find a spot for a SUP in the pocket or for a surfski out on the shoulder. The long fetch makes for much longer period waves as long as the winds at Birch Bay aren't nuking.
If it's cool weather it will almost always seem colder at Birch Bay as soon as you get out of your car and get hit by that steady, unimpeded onshore wind.
Parking in Birch Bay State Park requires a day fee$ or Discover Pass. There is parking at numerous spots along the main shoreline drive and there is a boat ramp at the park's south entrance. At low tide park closer to the Pavillion. At high tide you may want to park close to the boat ramp.