The Weather Wire
August 2006 Volume 14 Number 8
Avg High 90.7
Avg Low 61.7
Snow - 0.0"
Season Snow - 30.4"
Precipitation - 1.37"
Avg High 86.0
Avg Low 57.4
Avg Snow - 0.0"
Avg Precip - 1.82"
Terms and Definitions
Sometimes it is good to review some of the terms that we as weathermen use everyday to make sure we are all on the same page, so to speak. Weather in many ways has its own language and we as weathermen know because we use it every day, sometimes we assume everyone understands what we are telling them when we talk weather, but that is not always the case.
Upslope – We hear this term more often in the winter, but we also see it any time of the year. This simply put is when air is forced upward due to rising elevations of the local terrain. For us in northeastern Colorado a northeast or easterly wind direction pushed air from the lower elevations of eastern Colorado and Kansas uphill to the Front Range. The elevation gain can be 2-3000 feet. The reason this is note worthy is that air cools as it rises 5.5 degree per 1000 feet of lift. As air cools it holds less water, when it can hold no more we see clouds develop, rain and or snow for the Front Range. Our heaviest snows are the upslope variety. Now go west to the high country and the upslope winds are generally from a westerly direction forcing the air up and over the mountains. Elevation gain is much more in the high country in the area of 5-10,000 feet. The cooling is greater and the result precipitation is greater, hence the big snows that fall in the high country. Upslope, its all about elevation gain.
Chinook – This is an Indian word meaning snow eater. It gets this name because it is a warming wind coming down off the mountains and can dramatically raise temperatures along the Front Range. Now it is now coincidence that this term follows the term above, ‘upslope’, because this is just the opposite, descending air or “downslope”. Now if air cools when it rises what to you suppose happens when it is forced downward?? Exactly! It warms. Descending air warm 5.5 degrees for every 1000 feet it descends. So if we took air along the continental divide at about 10,000 feet and brought it down to Denver at 5,000 feet the air would warm 27.5 degrees (5000ft X 5.5 degrees) by the time it arrived in Denver. So if the temperature of the air was 40 degrees at 10,000 feet it would be 67.5 degrees by the time it arrived in Denver. You can see that warming like this can melt quite a bit of snow during the winter months. We usually get Chinooks when strong westerly winds set up over the western half of the state forcing the air up and over the mountains and then down to the flat lands.
Doppler Radar – This specialized radar that has replaced all the older radars that were in use 20 years ago. This radar can sense whether the rain drop or snow flake is moving toward or away from the radar by the “Doppler Shift” of the return echo. All radars send out an energy wave and then capture the return wave that has bounced off rain drops or snow flakes. This return wave is analyzed by computers in the radar and then plotted on a computer screen. This is what we see when watching the weather on TV, when they show the radar screen. Doppler shift is easiest to explain, by using the old moving train with its whistle blowing. As the train approaches the pitch of the horn or whistle is higher. This is because the train is actually catching up with the sound waves slightly compressing them. As the train goes by the pitch drops because the train is running away from the waves or stretching them out causing the pitch to drop. Now the words pitch and frequency refer to the same thing, basically pitch is associated with sounds, frequency to waves, in this case radio waves sent out by the radar. The programming in Doppler Radar detects this shift in frequency caused by the motion of the rain or snow. This gives us a much more accurate and more sensitive radar. We are now able to wind flow inside clouds because the radar can see the motion of the rain drops which is caused by the winds inside the storms.
Watch/Warning - Always good to go over these two. They come in a variety of flavors depending on the season. During the summer; severe weather, flash flood, tornado. During the winter; winter storm, high wind, heavy snow. To keep it simple a ‘Watch’ means that conditions are present that could produce those events, but those events are not currently happening. Warning on the other hand means that those conditions are now occurring or will be a very short period of time. For example: Tornado Watch - the weather conditions exist where tornadoes might form during the time period indicated in the watch, but these is no tornado currently being seen. Tornado Warning – A tornado has been spotted on the ground or radar indicates a tornado. The threat is imminent and those in the warning area should take the proper precautions.
That is it for this newsletter, but if you have a term or two of your own that you are hazy on, e-mail it to me and we will cover it in future news letters when we do terms and definitions. My e-mail is Paul@Skyview-wx.com .
Printing Newsletters Now Possible
We have received many requests over the years of how to print this newsletter. Unfortunately, until now, the newsletter has been formatted for online and email viewing, and did not format properly for printing. However, with the release of the new Microsoft Internet Explorer Internet 7 Beta version 2, this is now possible! The new release of Microsoft Internet Explorer reformats the fonts to allow documents to be printed. The latest beta release of Internet Explorer can be found at http://www.microsoft.com/downloads/Browse.aspx?displaylang=en&categoryid=6 . Although a Beta version, we have not had any problems using the new software. Also, remember that older newsletters can be found on the www.skyview-wx.com website under newsletters, so you may print older newsletters!
Little overall or some improvement in drought conditions across Colorado for July.
The map below shows forecasted temperature deviances for August 2006. As can be seen, above normal temperatures are expected for the the eastern half of Colorado for August 2006, with normal to slightly below normal conditions west.
The map below shows forecasted precipitation deviances for August 2006. Normal to above normal precipitation is expected for all of Colorado for August 2006.
As can be seen in the below map, with the some drought improvement is forecast for all of Colorado during August.
It was another hot month for Denver. There were 21 90 degree days which is 6 above normal. Temperatures ranged from 103 degrees (a new record) on July 16th down to 54 degrees on the 10th and the 4th of July. The average temperature was 76.2 degrees which was just 0.1 degree away from registering as the 10th warmest July in Denver. The warmest July in Denver weather history was 77.8 degrees in 1934, which by the way is the hottest Denver month in Denver weather history since 1872. Three records were set or tied during July of 2006.
9th – Tied record low maximum with 62 degrees last set in 1899.
15th- New record high 101 degrees, old record 100 last set in 1902.
16th- New record high 103 degrees, old record 102 last set in 2005
With the 21 90 degree days during July and the 21 90 degree day total for May and June, the total for the season is now at 42, 21 above normal. Still a far cry from the 2000 90 degree total of 61. But getting closer to the 56 in 2002 and the 55 in 2005. And we still have August and even September left to rack up more 90 degree days. August has a normal of 9 and September has a normal of 2 90 degree days respectively.
In spite of getting a couple of good soaking days at DIA, 0.23 on the 8th and 0.75 inch on the 9th, the month still finished below normal. The total of 1.37 inches was 0.79 inch below the normal of 2.16 inches. So far for the year through July 31st only 4.09 inches of rain has fallen. Even though DIA did not receive a normal month’s rainfall, there were numerous locations around the metro area that received their normal and much more as storms produced heavy rains and even flooding in a few spots.
The weather pattern in August is similar to the rest of the summer months, but the severe weather decreases significantly. Temperatures also toward the end of the month begin to decline. Skies are generally clear between midnight and noon, but during the afternoon showers and thunderstorms develop along the foothills during the afternoon and then move eastward across the urban corridor.
The occurrence of severe weather decreases considerably during August compared to the severe weather months of June and July. The typical air mass aloft over Denver is nearly as warm as earlier in the summer, however, the air mass is usually a bit cooler near the surface. As a result, the air mass is more stable and therefore thunderstorms are less intense. Tornadoes and large damaging hail are fairly rare, especially after the middle of August. Because of slow movement, thunderstorms in August are more likely to produce heavy rain then large hail.
By late August, the days become noticeably shorter and an occasional cold front slips across Denver and brings a nip to the air. A reminder that summer is really winding down. There has never been any snowfall recorded in Denver during August. August still brings in some hot days. In fact, the highest temperature ever recorded in Denver was recorded during the month of August, 105 degrees on August 8, 1878. This record was just tied on July 20th 2005.
Sunrise/Sunset (Denver area)
May 2006 to September 2006