From a fire containment standpoint, temperature is not as critical as compared to relative humidity and wind speed. As rule of thumb, remember that as temperature increases by 20°F, relative humidity decreases by about 50%, and vice versa. However, (high) temperatures should be considered in regards to how it might affect crew stress and safety. Likewise, prescribed fires conducted above 32°F avoid challenges of freezing water tanks and sprayers.
For more information about weather and prescribed burning refer to Fire Prescriptions for Maintenance and Restoration of Native Plant Communities.