Winters are normally mild but subfreezing temperatures occasionally occur. In the northwest, winters are cold with heavy snowfall and subfreezing temperatures. Saguaros can handle higher temperatures but are susceptible to subfreezing temperatures. During spring temperatures warm steadily, although 2.7 mornings in May still expect subfreezing minima. During a cold winter, however, tongues of Antarctic air bring subfreezing temperatures to all areas. Under the water many benthic invertebrates will experience some subfreezing temperatures, especially in small streams. The remainder (dry permafrost) is simply soil or rock at subfreezing temperatures. The venom even works at subfreezing temperatures. Snowflakes nucleate around mineral or organic particles in moisture-saturated, subfreezing air masses. Subfreezing lows are common in the winter, providing some frost. Species of "Drosera" and "Pinguicula" also tolerate subfreezing temperatures. Subfreezing highs are very common in the winter, which would present frost. Subfreezing conditions have significant implications for naval operations.