The Weather Wire
July 2008 Volume 16 Number 07
Avg High - 83.9
Avg Low - 50.9
Snow - 0.0"
Season Snow - 46.3"
Precipitation - 0.73"
Avg High - 88.0
Avg Low - 58.7
Avg Snow - 0.0"
Avg Precip - 2.16"
The spring and early summer of 2008 has been very dry along Colorado’s Front Range with well below normal precipitation. The dry weather has resulted in fire concerns for many locations. Skyview provides fire weather forecasts and current weather information from local weather stations to help local fire fighters and wish to share some terminology we use in our forecasts and additional information with the rest of you.
Lightning Activity Level or (LAL) Definitions
* = Information from: Intermediate Wildland Fire Behavior: Student Workbook. National Wildfire Coordinating Group, July 1994
Haines Index* - Haines Index combines the effects of instability and dry air to determine conditions in which an existing fire has the potential to spread rapidly. It should not be used to determine if a fire will start. Since wind is not a parameter of the Haines Index, it is best used for plume-dominated fires which can develop extreme surface winds through their own internal heat. The Haines Index is yet to be tested on wind-driven fires… When the value is 5 or 6, the probability of extreme fire behavior, including torching, crowning and spotting is significantly increased. Critical fire behavior is usually low, with minimal fire spread when the values are 4 or less… * = Definition from: http://www.crh.noaa.gov/fsd/firewx/firedef.php
Haines Index values of 4 or higher are days with a dry and unstable air mass, while 4 or lower are typically days with cool/moist and a more stable air mass. A high Haines Index value in tandem with a high LAL value and strong surface winds can combine for disaster. This is the worst type of scenario and the Front Range of Colorado is primed for these types of conditions. Winds have been breezy through the spring and summer so far, fuels for fire are dry due to below normal precipitation, the atmosphere becomes more unstable with the hot temperatures of summer and thunderstorms that do manage to develop produce more lightning than rainfall. Unless changes in the current weather pattern change significantly expect more Red Flag Warnings and the threat for wildland fire to increase further. It’s not all doom and gloom as monsoonal moisture is late to arrive this year, but should return by late July bringing much needed rainfall to the Front Range of Colorado from scattered afternoon thunderstorms.
Some areas of drought are beginning to appear once again across much of eastern Colorado.
The map below shows forecasted temperature deviances for July 2008. As can be seen, it is expected that all of Colorado to have normal temperatures for the month of July 2008.
The map below shows forecasted precipitation deviances for July 2008. Normal precipitation is anticipated across eastern Colorado as well as extreme western Colorado, with above normal precipitation anticipated for the mountain areas of Colorado for July 2008.
Little change in conditions is anticipated over the next 3 months, with most of the state not expected to see drought conditions. Southeastern Colorado is anticipated to experience drought conditions improving over the next 3 months.
June 2008 was a mundane month with no noteworthy weather statistics to mention. Precipitation started off the month like June 2008 might be a record setter. In the first 5 days 0.71 inch of rainfall was measured at DIA. But the rest of June only 0.02 inch additional rainfall occurred. The 24 hour maximum total was 0.70 inch between the 4th and 5th. No precipitations records were set or tied during June 2008.
Temperatures ranged between a high of 95 degrees on the 26th down to a low of 37 degrees on the 12th. The average temperature was 67.4 degrees which was only 0.2 degrees below the normal of 67.6 degrees. Only one record was tied, 47 degrees on the 29th last set in 1995. There were ten 90 degree days which is 4 above normal. Ten is also the total for the year.
There was no snowfall recorded. The most snowfall ever was 0.4 inch in June 1919. There are other reports of snowfall, however, this is actually hail which is sometimes entered into the snowfall column with an asterisk. For June 2008 small hail was reported at DIA but not at the former Stapleton International Airport, which is where official snowfall is measured.
There were 5 thunderstorms recorded at DIA of which only 2 had measurable precipitation. The storm on the 20th produced small hail. Only 4 days recorded light fog but no dense fog was observed. A peak wind gust of 53mph from the southwest was recorded.
Denver’s weather is notorious for being changeable. However this is not the case during July. Most July mornings are sunny with clouds developing during the late morning and early afternoon. By mid-afternoon, thunderstorms develop over the foothills and drift across the Denver metro area and then onto the eastern plains. Some of these storms continue to develop and reach severe status. Severe thunderstorms containing large hail, strong gusty winds and heavy downpours are not uncommon during July for the Denver metro area.
The worst hailstorm on record in Denver history moved across western sections of the city on July 11th 1990. This ferocious storm dropped baseball to softball sized hail and caused millions of dollars worth of property damage. July is the stormiest month of the year with thunderstorms occurring about every third day or usually 11 days per month. Most of the rainfall during the month is the result of slow moving thunderstorms which can cause precipitation to vary tremendously at different locations across the metro area. It is not unusual for some areas of the city to receive two or three times as much precipitation as other areas. Flask flooding is also quite possible during July.
July is also the month that Denver has the most 90 degree consecutive days. There have been 14 times where consecutive streaks of 10 or more 90 degree days have either been entirely in July or at least started in June and finished in July or started in Jusy and finished in August. The highest consecutive streak of 90 degree days is 18 and occurred twice. Once in 1901 from July 6th through July 23rd 1901 and again in 1847 from July 1st to July 18th. More recently we had 17 consecutive 90 degree days in 2000 from June 29th through July 15th.
Sunrise/Sunset (Jul - December Denver area)
May 2008 to September 2008