The Weather Wire
July 2009 Volume 17 Number 07
Avg High - 77.7
Avg Low - 51.1
Snow - 0.0"
Season Snow - 38.1"
Precipitation - 4.86"
Avg High - 88.0
Avg Low - 58.7
Avg Snow - 0.00"
Avg Precip - 2.16"
Wet Weather Pattern?
Although DIA only reported 1.30” of rainfall during the month of May this did not represent the Denver area well as many locations received between 2.0-4.0”. July was very wet all locations along the Front Range from Trinidad through Cheyenne receiving above normal precipitation. Really, ever since the last week of March the weather pattern has been very active with above normal precipitation for many areas in Colorado. Is this wet weather pattern just a short term cycle or is there more to it than that?
NOAA indicated recently that, “monsoon-like weather patterns have been present in Arizona…and that the main monsoon season likely will arrive several weeks early and have a greater impact in eastern Colorado (than the west slope).” The monsoon season typically starts around the 4th of July in recent years, but there is no question that the moisture we have been receiving has been sub-tropical in origin the last month. I believe it is safe to say that the monsoon season has already begun in spurts and will resume by later this month resulting in above normal thunderstorm activity and the potential for above normal rainfall. Remember the term monsoon really just means a seasonal shift in the overall wind pattern, but if those winds carry moisture rich air then rainfall becomes more likely.
NWS/NOAA indicated that, “we appear to be transition from a La Nina to El Nino cycle (though data in the next few weeks will provide greater certainty). This could lead to some substantial rainfall flooding.” The transition from a La Nina to an El Nino cycle will result in warmer ocean temperatures in the eastern Pacific and thus an increase in available moisture for the desert southwest and other areas affected by the summer monsoon. With additional moisture storms may be stronger and produce more rainfall. This could also lead to an above normal snowfall this upcoming winter!
Overall, the number of thunderstorm days will likely be above normal this summer as there will be more moisture available and with more chances for rain our total precipitation amounts will likely be above normal as well as we have already experienced in June. This would be a big change compared to last year as we ended up around 33% below average for the year in precipitation. Already this year DIA has reported over 10.0” of precipitation which is about 2/3 or normal for an entire year and we have more than 5 months to go.
With the widespread precipitation of the last several months, little areas of drought remain in Colorado.
The map below shows forecasted temperature deviances for July 2009. As can be seen, it is expected that much of Colorado to have normal temperatures for the month of July 2009, with far western Colorado expected to have above normal temperatures.
The map below shows forecasted precipitation deviances for July 2009. Most of Colorado is expected to have above normal precipitation for July 2009.
Little in the way of drought remains in Colorado, with no changes expected.
June of 2009 came ever so close to breaking the record precipitation for the month with 4.86" measured at DIA. This was just 0.10" shy of the old record set all the way back in 1882. On the 23rd, 1.64" of rain fell setting the daily record for the date. There were 18 days with thunderstorms in the area with 15 of those day producing measurable precipitation. All of the wet weather led to well below normal temperatures with the monthly mean 3.2 degrees below normal. June is typically the most active weather month when it comes to severe weather and this June did not disappoint. There were numerous tornado reports and funnels reported all along the Front Range with many strong storms producing damaging hail and strong winds. For the year we are currently at 10.38" of precipitation already 2/3 of a years worth of moisture. Normal is 7.07" a far cry from 2008 when Denver only had 3.04" for the entire year and 0.73" for the month of June.
July is typically when the monsoon season gets under way with afternoon thunderstorms 1 out of every 3 days. The storms however have a tendency to be less severe than storms in the month of June as far as tornadoes go. Severe weather is still common with hail being the greatest threat, but the flooding threat increases due to upper level steering winds becoming lighter resulting in slower storm motion. The month is typically very warm with about half of the days reaching 90 degrees or more. This July will likely be slightly below normal in temperatures and at or above normal in precipitation.
Sunrise/Sunset (Jul - December Denver area)
May 2009 to October 2009