Near record high temperatures will be with us through the weekend in spite of the fact we should see considerable cloudiness. A warm tropical flow will bring both the warmth and the clouds across western Nevada and the Sierra, but the core of the moisture and any dynamics which is needed to shake any out of the skies is likely to stay offshore, so in all likelihood we will stay dry through the weekend. Temperatures remain high and the skies will remain cloudy well into next week with only slight chances of any showers.
The warm temperatures have brought out various iterations of the following question: “I have been advised that I should not prune my roses until after the danger of the last frost has passed. However, I don’t know exactly when that would be here in Hidden Valley. Last year they started blooming before I could get them pruned. Can you help me out?”
You ask the question that has plagued gardeners and meteorologists throughout the ages. Trees, roses or shrubs will often bloom during a warm spell, only to be followed days, weeks or even months later by a peach-killing frost. 
The best way to answer is just to give you some historical averages, and you can do with them what you will. May 15th is the average date of the last killing frost here in the Truckee Meadows. Sometimes you will get the last frost in early April; sometimes you get nailed with a cold snap in June. May 15 is just the average.
Keep in mind; it can change drastically from one location to another. Microclimates within the Truckee Meadows (and in the outlying valleys) can make a huge difference on the overnight low temperature. So you might want to wait a little longer if you live in Dayton or Smith Valley than you would if you live in Fallon or Hawthorne.
In a word… know thy microclimate.
Lloyd also asked when it was safe to plant his tomatoes. Now he’s really trying to get me into trouble. For one thing, I can kill silk flowers, so I would take any agronomic advice from me with a grain of salt.
Wall O Water
That said, the old saying “Don’t plant your tomatoes until the snow is off of Peavine Mountain” has had questionable success. But if you use the “Walls O Water” protection method, you can usually take a chance in late April or early May. The “Wall of Water” is a circular wall of water filled tubes that will release heat as they begin to freeze, which protects the plants inside to temperatures well down into the 20s.
Unless of course unless I use them.
A Word of Weather 