Thunderstorms Could Give Some Relief to the Heat…And Why Thunderstorms Will Increase Over Time.

7dayWest_Sat_Rad_Large_PacWe have another hazy and hot day ahead before we import enough moisture up from the south to bring scattered thundershowers back into the region. For Thursday, highs in the low 100s will help produce some afternoon clouds, but most of any thunderstorms will likely still remain to our south. By Friday clouds will form earlier, and we have a slight chance in the Reno area of getting a thunderstorm, but those chances increase regionally as we go through the weekend as the airmass continues to destabilize. High temperatures drop from 103 on Thursday down into the 90s through the weekend, but could return to the low 100s by the middle of next week.

Thermal Thunderstorms

I mentioned that as time goes by the airmass will continue to stabilize… a very common occurrence. Why would this be? Before the first thunderstorm occurs, the air in the lower part of the atmosphere is generally very dry, which is more stable than moist air. But once you get one thunderstorm to form, any precipitation it produces will evaporate in good part (if not completely) on the way down to the ground. That additional moisture in the lower part of the atmosphere increases the instability of the airmass for the next day, which increase the likelihood of more thunderstorms. This feedback mechanism continues until a front or other weather system comes in to knock the stagnant pool of atmosphere out of the region.

 

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Record Heat and Thunderstorms Coming… And Why Do Thunderstorms Usually Happen in the Afternoons? (Pt 2)

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If we don’t set a new temperature record on Wednesday, we should get close enough for it to really not make a difference. Sunny skies with variable levels of haziness will result in a high around the record of 104 degrees. As we move into Thursday, a lighter southerly flow will allow some afternoon cloudiness to build up, with only an isolated thunderstorm, mainly to our south and east. By Friday, a stronger push of southerly moisture will bring increased thunderstorm activity, as temperatures fall slightly to the upper 90s, and those basic conditions will last through the weekend.

Reno Tstorm

So why are thunderstorms more common in the afternoon? This time of year, this kind of weather pattern occurs because ground temperatures get warmer faster than the temperatures up at about 20,000 feet. This creates instability, and pockets of air will rise during the heat of the day, and that vertical motion creates the thunderstorm cells. And the longer the pattern stays the same, the more likely thunderstorms will form the next day. Why would this be? I’ll tell you tomorrow.

Thermal Thunderstorms

 

Near to Record Heat…And Why Do Thunderstorms Usually Happen in the Afternoons? (Pt 1)

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Heat remains the main noticeable forecast component for the next couple of days, with thunderstorms creeping back into the picture as we head toward the latter half of the work week. A strong, but flat ridge of high pressure will keep our skies mostly sunny through Wednesday, although smoke and haze (mainly from the Ferguson Fire west of Yosemite) will still likely frequent the region for at least the next few days. As the week progresses, an offshore low will dig down out of the north, steering the flow to a more southerly direction toward the end of the week, which will allow those aforementioned thunderstorms to develop, and that should allow high temperatures to drop back a bit into the upper 90s.

Reno Tstorm

Over the last week we’ve seen a lot of thunderstorm pop up in the afternoons, especially in the mountains. This type of weather pattern is always a hard to thing to predict with any real specificity. The reason for that is there isn’t a front moving in or any other defined weather feature that will be the direct cause of storms, so it’s not like you can point to anything on a satellite loop and say “Here it comes.” What causes them to form? I’ll tell you tomorrow.

 

Thunderstorms and Fire Danger… And Why Isn’t the Sun Setting Earlier? (Conclusion)

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The heat will finally start to result in some afternoon cloudiness, and although it has been a slow process, the monsoonal moisture coming up from Arizona will likely make it close to the Lake Tahoe area by Thursday, and should move through the Reno area by Friday. That brings a chance of mainly afternoon thunderstorms with it, while high temperatures will continue to hover around the 100 degree mark through the weekend. We have a Fire Weather Watch posted starting Thursday afternoon as a result of the chance of dry lightning. Conditions do stabilize by the end of the weekend and things should dry out as we start the next work week.

orbit

Finishing up yesterday’s column: Because we are travelling around the sun slower this time of year, we over-rotate just a bit every 24 hours. This effect delays the time that the sun sets each night, offsetting the shortening of the days. Conversely, it takes extra time off the morning, but it takes a while before we take the time off the evening. As we speed up our orbit that offsetting effect evens out, and both sunrises get later and sunsets get earlier.

Now in the winter (late December/early January), the opposite happens… the sunrise stays the same while the sunsets start to get later. Give it six months and you’ll see.

 

The Heat Goes On… And Why Isn’t The Sun Setting Earlier? (Pt. 2)

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The high heat will stick around for the next week, with a subtle shift in the flow allowing some of the monsoonal flow to move up from the south. While Wednesday will likely stay sunny in the Reno area, with high temperatures expected to touch on triple digits, the moist air could get close enough to us by Thursday to allow some scattered afternoon thunderstorms to pop up in the area. That basic pattern will remain unchanged through the weekend.

Sunrise Nevada

So why doesn’t sunset start getting earlier right after the summer solstice? Right now we are just about at the furthest point out from the sun, and as a result we are moving around the sun at the slowest speed. Every day, the earth spins one full rotation PLUS 1/365th of a rotation to make up for how far the earth has orbited the sun (we keep our days straight with respect to the sun’s position relative to the earth). That means that every 24 hour period we over-rotate a bit a bit since we are travelling a little less around the sun during that 24 hours.

orbit

Ponder that for a bit, and tomorrow, I’ll finish up.

 

Hot, With Thunderstorms on the Horizon… And Why Isn’t the Sun Setting Earlier Now?

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A hot week will continue through the next seven days, with mostly sunny skies Tuesday and Wednesday finally giving way to some afternoon clouds and a slight chance of thunderstorms toward the end of the work week through the weekend. High temperatures will flirt with the 100 degree mark in Reno throughout the week, and as the chance of thunderstorms develop, a Fire Weather Watch is in effect for Wednesday and Thursday due to the possibility of dry lightning and strong outflow winds that could develop from any storms that come to fruition.

Sunrise Nevada

Summer has officially been with us for over two weeks, but something about it bothered Tom (who wrote in about a week ago): “Could you please explain why it is that we’ve lost 6 minutes of daylight in the AM yet NONE in the PM since the days began to get shorter last week? Why isn’t it more balanced on each end?”

It’s a little tough to explain without holding a model of the earth and the sun, but I’ll try. Basically the reason is because the earth’s orbit is elliptical. What does that have to do with the price of Tea in China? Nothing. But it has lots to do with his question. And I’ll tackle that tomorrow.

 

 

A Scorcher Coming… And Why Do I Hear So Many More Radio Stations at Night? (Final)

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With clearing skies and a building high pressure ridge, our temperatures will climb rapidly over the weekend, reaching the upper 90s Saturday and Sunday with sunny skies, and then likely topping 100 degrees early next week. Gusty winds in the afternoons have also kicked off another Red Flag Fire Warning from 1 pm to 9 pm Saturday.

As the ridge moves in toward the four-corners area mid-week, a light southerly flow will develop, bringing in a slight chance of afternoon thunderstorms by late in the week.

Radio Dial Night

Normally, AM radio signals are limited to line of sight reception. But the ionosphere can act as a backboard, bouncing the signal back down the earth at a much farther distance, hundreds or even thousands of miles away.  I once picked up a station in Minnesota while driving in Seattle.

radio waves day night

But this bouncing will work more effectively after the sun goes down. Without going into a lot of detail about the various (D, E and F) layers of the ionosphere, the lack of the sun’s rays at night changes the characteristics of the ionosphere, making it much more efficient at creating the “bounce.”  In fact, the extent of nighttime radio station reception increases so much that many stations are forced to lower their power output so they don’t interfere with other stations on similar frequencies that could be hundreds or even thousands of miles away.

 

First 100s?… And Why Do I Hear So Many More Radio Stations at Night? (Pt. 2)

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Our extended sunny streak will get a brief interruption as some moisture thrown off from a dying hurricane Fabio will drift across the region, but it is unlikely it will produce any showers. It will serve to stall any more warming, with Fridays highs still just reaching the low 90s. Once that cloudiness passes through the sun will return on Saturday, and a building ridge of high pressure will send the temperatures soaring into the upper 90s over the weekend, and likely into the low 100s by the first of next week.

Radio Dial Night

So why can you hear so many more radio stations at night than during the day? Actually, you can blame the sun and the ionosphere for the change at night. The ionosphere is that portion of the atmosphere above the stratosphere (about 50 to 600 miles above the earth’s surface) that contains a high concentration of ions. The sun I think you already know about.

radio waves day night

Radio waves can only travel in a straight line, and because the earth is curved, most stations can only be heard about 60 miles away because the earth gradually curves under and away from those signals. Without anything else to help, you would be limited to those kinds of distances. Tomorrow, I’ll tell you how the ionosphere helps out.

 

 

Hot Times Ahead… And Why Do I Hear So Many More Radio Stations at Night?

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We have some “typical” early July days coming our way with seasonably warm temperatures (low 90s) and mostly sunny skies. A trough of low pressure up off the Pacific Northwest coast will keep us in a dry and stable pattern through Friday. As that trough moves out over the weekend, a quick warming trend should send the mercury up to if not over the 100 degree mark by Sunday. The skies will remain mostly clear, with the exception of some mid to high clouds passing over on Friday, but don’t be surprised to see some last afternoon cumulus clouds come in with the high temperatures over the weekend.

Radio Dial Night

A reader asks: “Here’s something that has always puzzled me. How come I can hear so many more radio stations at night than I can during the day time? Are there just a lot more on the air then, or do they turn up their power, or is there some other explanation?”

No, no, and yes to your questions, in that order.  There aren’t more stations on late at night. In fact, many sign off during the late hours. As for power, there are many radio stations that are required to turn DOWN their power at night. I’ll explain what is happening tomorrow.

Smokey 4th

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While the overall forecast calls for mostly clear skies across the region, smoke and haze from a few California fires could settle into the valleys periodically, especially in the late night/early morning hours. An exiting British Columbia trough and an approaching Pacific trough will balance each other out a bit and keep our temperatures within a few degrees of average.

Winds are always at the forefront of many of our minds on the 4th of July. While criteria will vary depending on where the fireworks displays are occurring, generally most pyrotechnicians want the winds to drop to 10 mph or less. Wednesday evening’s winds will likely be in excess of that prior to the sun setting, after which they should ease steadily through the night. While some delays could occur, it’s likely that the displays should be able to eventually get underway.

Temperatures will remain near seasonable through Friday, after which the ridge builds back in, sending the mercury soaring to well above average levels, giving triple digits a scare by the end of the weekend.