I am of the opinion that there is no place, at least in the USA, that has ideal weather. Here in the Southeast, we have to deal with the heat and humidity in the summer with pop up storms as well as tornado threats in the Spring. The Northeast and upper Midwest can have cold snaps in which the high temperatures do not climb above freezing for entire month or more. The Pacific Northwest is chilly and grey for much of the year. Even Southern California has to deal with the threat of earthquakes and wildfires.
What are my thoughts on Birmingham's weather? Overall, not too bad. Not the best but certainly far from the worst. Let's break it down by season:
Winter: We'll see measurable snow maybe 1-2 times per year and yes, panic may set in when it does. You had best stay off the roads if it does snow. We only see 4-5 days in which temps do not make it out of the 30s. A typical day will dawn chilly with low temp near freezing but by the afternoon, it will warm to the low-mid 50s. If you can wait until noon to run, that's pretty favorable conditions for a long run. We'll get maybe 2-3 rain all days per month but a lot of bright and sunny days as well.
Spring: Trees begin to bloom in early March most years and it sure is a pretty sight. As an aside, my allergies have been almost non-existent since starting on the magnesium. Again, we get a few rainy days every month and this is the time of year in which the tornado threat is the greatest. That said, the perfect "sunny and 75" weather days will outnumber the bad ones.
Summer: If you want to run long distance here, you had better be done before 8 AM or start after 5 PM or it will be a very slow and painful affair. It is no unusual to see severe storms on one side of town with no sign of rain only 5 miles down the road so you've got to be careful checking the weather. There are basically 2 weather patterns here. Upper 80s and sticky with a 50/50 chance of storms OR 95+ and dry. I, along with most other runners would prefer the latter. If you can wait until after 6:30 to run, it's fairly comfortable. There are really only about 8 weeks (mid-June through mid-August) that are really tough. Speed workouts are manageable at dewpoints under 75 and short tempos can be done at near 70. They say that you need to scale back if dew point + temp exceed 150 but you also need to consider the humidity. I prefer evenings to mornings in the summer. Although the temps are higher, humidity is only 50% compared to 90% in the morning and IMO, it is more comfortable. I have been known to stay inside when the weather is iffy.
Fall: This is by far the nicest time of the year, especially between about Labor Day and Veteran's Day. It may remain warm but the humidity has gone down and the rainfall is the lowest of the year. Severe weather is also very rare this time of year. High temps are often in the 80s in October but in the mornings and evenings when it's time to run, conditions are usually near perfect.
Worst weather in the country:
I've chosen 4 cities in different parts of the country that would be brutal for runners:
-Buffalo, New York- 100+ inches of snow per year piled high on the sidewalks. 'Nuff said.
-New Orleans, Louisiana- Not a fan of this city for other reasons but the humidity is absolutely brutal in the summer. Birmingham is dry by comparison. Low temps are often about 80 degrees with 100% humidity. Temps will climb to 95 and the humidity remains quite high. 65 inches of rain per year with hurricane threats.
-Phoenix, Arizona/Las Vegas, Nevada- It may be a "dry heat" but 110 and dry cannot be preferable to 90 and humid. The running group usually starts at 3 AM and you had better be done by 6 AM.
Fargo, North Dakota- Not as snowy as Buffalo but the sub-zero cold and wind more than makes up for it. When the snow melts in May, flooding is always a concern.
Best weather for runners:
San Diego, California- I've heard others refer to this city as a "runner's paradise" as temps rarely fall below 50 or rise above 80 and it almost never rains. Beware of the wildfires.
Denver, Colorado- This may be a surprise pick but winters are not as severe as you might expect. The major downside is that it is very cold in the mornings but again, if you can wait until afternoon, it's not so bad. 300 sunny days per year with very little humidity in the summer. Lots of great trails too.
Asheville, North Carolina- Winters can be chilly here in the mountains but humidity is noticeably less severe in the summer. You can expect about 10 degrees cooler than Birmingham throughout the year. I also thought about Richmond, Virginia. I know there will be some cold snaps and heat waves there but neither will be constant or extreme for very long.