School transmutation [air]; Level druid 1, sorcerer/wizard 1
CASTING
Casting Time 1 minute
Components V, S
EFFECT
Range touch
Area immobile 10-ft.-radius emanation
Duration 1 hour/level
Saving Throw Will negates; Spell Resistance yes
[This content was created for the Pathfinder rules by Paizo Publishing LLC and is part of the Pathfinder RPG product line.]
DESCRIPTION
You subtly enhance or diminish the effects of natural winds within the spell's area, which is an immobile emanation around a point touched by you as the spell is cast. Within the area, natural (but not magical) wind effects are either increased or decreased by one step in intensity. The maximum wind force you can affect with this spell is based on your caster level, as shown on the table below. Alter winds has no effect on magical wind effects.
Caster Level Wind Force
1st-3rd Light
4th-9th Moderate
10th-15th Strong
16th or higher Severe
Section 15: Copyright Notice - Advanced Player's Guide
Advanced Player's Guide. Copyright 2010, Paizo Publishing, LLC; Author: Jason Bulmahn.
Example use case:
Enemy caster puts up Obsuring Mist in an area with no wind. You cast Alter Winds so as to reveal a 10-foot radius of it.
"Calm" is a wind state, so yes. It's a step less than "light". Obviously, you can't make "calm" any calmer, so you will only be able to increase the wind effect up to the maximum allowed by your caster level.
EDIT: Abraham has the better information.
Light 0–10 mph
Moderate 11–20 mph
Strong 21–30 mph
Severe 31–50 mph
Windstorm 51–74 mph
Hurricane 75–174 mph
Tornado 175–300 mph
As you can see a wind of 0 mph is a light wind, and therefore can be altered to a moderate wind.
Ah thanks guys for clearing that up. I bet that was in the Gamemastery Guide somewhere.
There's always air around (unless you're in a vacuum, in which case, you've got bigger things to worry about than a first-level spell), and it's always in motion, even if we don't really notice. It seems reasonable to me to say that you can increase stagnant-feeling air by one step to a light breeze.
Well it was in the gamemaster's section of the core rulebook so you are close.