It looks like our very dry summer will finish out on a very dry note, with no real chance of any rainfall on the immediate horizon. Temperatures will warm from the low 80s on Thursday to the upper 80s Friday and Saturday. A dry cold front will pass by to our north, kicking up some breezes on Sunday and throwing a few clouds our way, but the dynamics and moisture content will be too weak to give us any real hope for rain down this far to the south.
As we head into next week, after a brief drop to the lower 80s, temperatures will warm back into the mid to upper 80s with sunny skies for the duration of the forecast period.

Temperatures will drop significantly over the next couple of days, and the push of the cooler air into the region will keep our winds at a brisk level, increasing the fire danger in our area. A Red Flag Warning is in effect across northern Nevada and eastern California through Wednesday. High temperatures on Wednesday will drop to the upper 70s, and fall further to the mid-70s on Thursday before recovering back to the 80s by the weekend. A few clouds will pass through the next couple of days, but conditions should remain dry throughout the rest of the week.

While we are still likely to add a few more days onto our streak of 90 degree days, there does appear to be some relief from the heat on the way. Skies will still remain mostly clear through the next week, with occasional haze and smoke drifting into the region from the fires to our west, and temperatures will drop by the weekend to around 90 degrees. As we head into the next week, a trough of low pressure will carve out some cooler air into the west coast, dropping our highs down into the 80s, putting an end to the streak.

I’ve talked about how lightning forms before. Negative charges from the base of thunderstorms clouds induce a positive charge on the ground, and after a “stepped leader” forms out of the clouds, it causes a “return stroke” from the ground once the negatively charged leader gets close enough to the positive charges on the ground. This generally referred to as “negative” lightning, and is the most common kind. But it doesn’t always work that way… lightning can be “positive” as well. Tomorrow, I’ll tell you the difference.

The dry and sunny conditions will continue through the rest of the week, and although the temperatures will still stay slightly on the warm side of average, they won’t be chasing any records. A low pressure center has snuck into the Pacific Northwest, which will cool us slightly into the low 90s and upper 80s in western Nevada, but the westerly flow will keep our skies sunny and will make our afternoons a bit on the breezy side. Temperatures could finally fall out of the 90s by the start of next week.

One reason our low temperature is often higher than the “average” is much of our database occurred when the airport was surrounded by irrigated alfalfa fields. This natural swamp cooler makes a tremendous difference… especially in the night time period. Now the airport is almost entirely surrounded by concrete and asphalt. The amount of warming that it can make can be pretty drastic. Just look at differences in places like the airport (the official Reno location) and outlying areas like Spanish Springs or Washoe Valley. All of them are pretty close in elevation and general geography, but the airport can be 10-15 degrees warmer on a clear and calm night, thanks to the heat island.

Our dry weather will continue for the next week, with some afternoon breezes and warm temperatures throughout. For Monday, some areas of smoke and haze could still pop up off and on through the day, but generally sunny and clear skies will bring a high in the mid-90s, temperatures and conditions that should remain fairly constant through the rest of the work week and into the weekend.

Matt asked: “Why do the nighttime lows (in Reno) seem to be less low than they used to be and, my main question, why does it seem that there is often a smaller difference between the highs and the lows than there used to be? I’ve been pondering this question for some time.” Ponder no more. The reason is almost entirely due to urban heat island effect… especially in the area around the Reno airport, which is where the official temperatures are recorded.

Average temperatures are calculated using a 30 year rolling average, and those averages are updated at the beginning of the decades. So our “average” Reno temperatures were determined using the period from 1980-2010. Tomorrow, I’ll tell you why that is important.