I'm not going to break any laws by attempting to get on the roof of the China Panda building there now (same as Imperial Hotel), but here's what it looks like today:
And looking north, from about the same place today as the 1915 picture:
The "Woelz" store that you see on the east side of Main Street was likely at 315 Main Street, as per this advertisement from the Longmont Ledger in 1907. I say "likely" because another report below lists the store at 331 Main. This is not unusual, as stores tended to move to nearby locations as they outgrew their space. The Woelz Brothers store was a Men's clothing store.
A google search for the Woelz Brothers dug up some history about them, from a City of Longmont historical architecture report of Herman Woelz's house at 342 Pratt Street:
By the early 1920s, this Pratt Street home belonged to Herman H. and Grace W. Woelz. Herman Woelz was born on September 8, 1879, in Germany. His parents immigrated to the United States when he was two. Grace was born in Kingsville, Ontario, Canada on November 1, 1879. Following their marriage, the couple moved to Fort Collins in 1903, where Herman and his brother Christian established a clothing store. In 1913, the couple moved to Longmont, where Herman was associated with another brother, Gotlieb, in the Woelz Brothers Clothing Store at 331 Main Street.. Following the death of his brother, Herman became sole owner of the business, which he operated until his retirement in the late 1940s. Herman and Grace Woelz made the dwelling at 342 Pratt Street their home until their deaths. Herman Woelz passed away on August 16, 1951, at 71 years of age. Grace Woelz followed him in death on May 3, 1958, having lived to be 78.The 315 Main Street location is unoccupied today:
Or, as seen from the other side of the street with the obligatory Sunday afternoon motorcyclist:
Back to the original picture, you'll see the Carlton Hotel ("Rooms") up the road, on the east side. Opened in 1905 (the City of Longmont link above says 1906 but the Longmont Ledger mentions the opening a year earlier), the builder C. C. Caulkins named it after his first name, Carlton. The upper floor had fifteen rooms, that could be used by either long-term boarders or as hotel rooms. The rooms shared two baths, and a toilet room. The downstairs was leased to a business, which in 1905, was a dry goods store owned by G. V. Booth.
Noah's Ark was a general goods store.