A number of municipalities and businesses have experimented with outdoor Wi-Fi installations that have yielded mixed results. One example is Google's community Wi-Fi in the Palo Alto region of the San Francisco Bay Area. While a number of factors have slowed the roll-out of community based Wi-Fi, one of the ongoing questions is how weather impacts Wi-Fi signal reception and equipment.
Rain and Radio Signals
The weather condition that has the greatest effect on a Wi-Fi signal is rainfall, particularly for wireless setups using the 2.4-GHz radio frequency. Water droplets absorb this radio frequency and partially block the signal. Anecdotal evidence from communities with light-pole-based public Wi-Fi suggest that rainy days had an impact on signal strength. Even so, Wi-Fi signals are short range and usually deployed indoors. While rainfall can create interference -- in much the same way that it limits visibility for human eyes -- attenuation due to distance from the router is a much likelier culprit for low signal strength.
Temperature and Radio Signals
Wi-Fi signals themselves ignore temperature in a given environment. While there's a great deal of anecdotal evidence that community Wi-Fi services work less well on hot days, when the temperature exceeds 90 degrees Fahrenheit, the explanation has less to do with the signal strength and more to do with equipment overheating. Wi-Fi devices, like all electronic equipment, are built for working within a limited temperature range. While it's possible to heat wireless equipment in the winter, because of the need for exposed antennas, it's not feasible to cool an outdoor Wi-Fi system in the summer.
Weather and Power Outages
The other major impact on outdoor Wi-Fi infrastructure – as well as cellular phone services – is wind damage to broadcast towers, falling trees and similar hazards. These secondary effects from extreme weather can be caused by windstorms, blizzards, hurricanes and tornadoes. Power outages caused by extreme weather interfere with outdoor Wi-Fi and cellular system services. It is even theoretically possible for a sufficiently powerful coronal mass ejection -- a blob of electrically charged plasma from the sun that interacts with the Earth's magnetic field -- to knock out outdoor Wi-Fi infrastructure. That sort of phenomenon would also damage most communications satellites, causing power outages across a large geographical area.
Indoor Wi-Fi and Weather
Wi-Fi in its most common form – a wireless router used in an office, apartment or home – is largely immune to weather effects. Weather can affect Wi-Fi reception if you're trying to get a signal across an open outdoor space; for example, in your detached garage converted into an office. Wi-Fi has only limited interaction with weather under normal circumstances -- about the same degree of interaction you would experience using a cellular phone.