The National Weather Service has added an
"Experimental Weather Safety Planner" to their Web site. You can select up to six parameters, enter acceptable numerical values, and then either click the map or enter a latitude and longitude and click "submit": "This will query the forecast grids to find when your weather requirements will be met at the nearest grid point over the next 7 days."
The available parameters are temperature, relative humidity, surface wind speed (mph), surface wind direction, sky cover, precipitation potential (those six are filled in by default), "temperature >=100," "temperature <=32", dewpoint, heat index, and surface wind speed (in knots).
The output is a chart, with colored bars highlighting the times in the upcoming week that each of your requirements is expected to be satisfied; it seems simple enough to find times (if any) that meet all one's requirements.
I'm assuming this is US-only, and haven't tested it beyond playing with my own location and a couple of simple parameters that seem possible for this time of year (nothing below freezing, for example). But it might be useful, fun, or both.