July through September Outlook
Area Climate Outlook for Summer/Early Fall
July – September 2008
1. July through September Climatology:
July is on average the warmest month of the year. August tends to be a little cooler with more significant cooling reaching the region in September. Average low temperatures across the region east of the Wyoming mountains are in the mid 50’s to around 60 degrees in July and August, then fall into the mid 40’s for September. Average high temperatures over lower elevations tend to be in the mid 80’s to around 90 degrees in July and August, and in the mid to upper 70’s in September. For locations like Laramie and Rawlins, average lows tend to be in the mid 40’s to lower 50’s in July and August, lowering into the upper 30’s to lower 40’s in September. Average highs are in the upper 70’s to lower 80’s for July and August, then cool to around 70 degrees in September.
Average total rainfall begins declining during this period, especially from about mid-August onward, as drier air masses become more common over the region. There is a bit of an upswing in rainfall during the latter part of July into early August as some monsoonal moisture normally invades the region. Average rainfall east of the mountains ranges from about 2.0 to 2.25 inches in July, then drop off to about 1.2 to 1.6 inches during September. Laramie and Rawlins average about 1.0 to 1.4 inches of rainfall in each of the three months.
2. Current situation:
The event known as La Nina has basically ended and neutral conditions are being observed over most of the tropical Pacific Ocean as depicted in Figure 1 below: Little change is expected during the remainder of the summer.
Figure 1: SST and Anomaly
More information can be found at the Climate Prediction Center’s website here:
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html
Drought Status: Overall drought conditions have changed little across the region with only some minor improvement noted over the northern Nebraska panhandle. Good run off from snowmelt and generous rains in late May into early June has improved area reservoir levels especially over eastern Wyoming. Much of the area’s drought status remained in normal conditions to abnormally dry conditions. A relatively small area of moderate drought condition (primarily hydrologic in nature due to low reservoir levels) is over the northern Nebraska panhandle, as can be seen in Figure 2 below:
The latest drought status and more information can be found at the National Drought Mitigation Centers website here:
July through September Outlook:
The Climate Prediction Center’s three month temperature outlook for this area indicates that there are equal chances that temperatures will be above average, near average, or below average temperatures for the period, as depicted by Figure 3 below.
Figure 3: July – September 2008 Temperature Outlook
The local downscaled temperature outlook, which provides the temperature outlook for more specific sites as opposed to a general area, shows a greater likelihood for above normal temperatures across southern Wyoming, with essentially equal chances over the northern and eastern Nebraska Panhandle. Specific probabilities for selected locations in this area are shown in Table 1:
|
Location |
Probability Above Normal |
Probability Near Normal |
Probability Below Normal |
|
Cheyenne |
33% |
34% |
33% |
|
Laramie |
36% |
34% |
30% |
|
Medicine Bow |
36% |
34% |
30% |
|
Scottsbluff |
33% |
34% |
33% |
|
Sidney |
33% |
33% |
34% |
|
N. Neb. Panh. |
33% |
34% |
33% |
More information on the Local 3 Month Temperature Outlook can be found here:
http://www.weather.gov/climate/calendar_outlook.php?wfo=cys
For precipitation, the latest outlook indicates that there is about a 33 to 35% percent chance that rainfall during the period will turn out below average across much of central and eastern Wyoming. Equal chances for above, near, or below average precipitation is forecast from the Nebraska panhandle into the southeast corner of Wyoming, as depicted in Figure 4 below:
Figure 4: July – September 2008 Precipitation Outlook
The latest drought outlook (see Figure 5 below) indicates that the current drought situation over the region is not expected to change significantly during the remainder of the summer, though some further improvement is expected over the northern Nebraska panhandle.
Figure 5: Seasonal Drought Outlook
Issued July 3, 2008
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