May has featured cooler-than-normal temperatures across all but the Southwest Division, where near-normal temperatures have prevailed. The Climate Prediction Center’s summer outlook favors a continuation of those warmer-than-normal conditions in the southwest, but is neutral for the rest of the state (Figure 1). That means it is equally like to have warmer- or colder-than-normal temperatures for the three-month period of June through August. Remember that this is the average for the three months, a cooler-than-normal June could be countered by a warmer-than-normal July or August.
Figure 1. Summer temperature outlook (NOAA)
Antecedent conditions
Temperatures were cooler than normal in April (Figure 2), creating issues with planting and emergence of summer crops. Several freeze events, including ones in early May, further stressed the winter wheat crop.
Figure 2. Departure from normal April average temperatures. Source: Weather Data Library
Aside from temperature, a major concern is precipitation. Summer precipitation constitutes the majority of the annual precipitation, particularly in the west. Currently, there is a sharp divide of above-normal amounts in the southeastern areas of the state and below-normal amounts in the western third. The southwestern corner of the state has received particularly little amounts. Elkhart, Morton County, has recorded just 2.14 inches for the year-to-date, less than half of the normal 5.25 inches that would be expected. In contrast, Columbus, Cherokee County has recorded 25.20 inches compared to the normal of 16.07 inches.
Precipitation outlooks
The precipitation outlook for summer favors above normal precipitation for much of central and eastern US (Figure 3). This includes much of Kansas except the areas of the state that need it the most.
Figure 3. Summer precipitation outlook (NOAA)
Forecast models provide a wide variance in possible precipitation outcomes for the season and resulting drought impacts. While there are many models, one method is to blend the models together in what is called an “Ensemble Mean.” This provides a quick glimpse in overall trend in all forecast models for the period. The result of the June through August model output is overall moderate confidence in above (green) normal precipitation (Figure 4). This would favor above-average precipitation, however, that can fall all at once or spread out over many days and doesn’t provide further guidance on flood or drought impacts.
The US Drought Monitor favors improvement of drought conditions in some parts of the state. However, persistence is expected along the Colorado border, with intensification in the northwest (Figure 5).
Figure 4. National Model Mean Ensemble forecast into August 2020. Source: Climate Prediction Center
Figure 5. U.S. Drought Outlook. Source: Climate Prediction Center
Some Science Behind the Outlook
Historically, the ENSO (El Niño Southern Oscillation) in the equatorial Pacific has little impact to summer conditions in Kansas. This year, trends are towards either La Niña (colder than normal sea surface temperatures) or neutral conditions (Figure 6). Combined with warmer temperatures in the Atlantic Ocean, tropical activity is often more active than normal to our east/southeast in the oceans. Tropical systems form under high pressure which would infer ridging to our east.
Another concern is the Pacific Ocean off the west coast of the United States. Temperatures are much warmer than normal already and expected to continue (Figure 6). This often develops negative EPO (East Pacific Oscillation) which incurs another ridge of high pressure across the western United States, driving the Jetstream northward.
Figure 6. Sea surface temperature anomalies (red = warmer than normal, blue = colder) with Eastern Pacific Oscillation (red box) and the El Nino Southern Oscillation (purple box) highlighted. Image from Tropicaltidbits.com.
With high pressure often to the west and east, two things can happen. First, we could spend much time in the transition area on either side of the high pressures. This would typically mean impacts from ridge-riding troughs (weak low pressure systems) providing increased amounts of moisture and normal to slightly below-normal temperatures. Another possible, but probably unlikely scenario would be a large scale ridge/high pressure across the entire US. This would likely mean above-normal temperatures and drier conditions. This scenario would have monsoonal influences and rely on its location for any moisture. Should it persistently set up over one location, it would have a resulting impact on temperatures (and increased precipitation).
The resulting expected weather pattern this summer will likely be influenced by the dominant areas of high pressure to the east/west and any associated blocking patterns that develop. Predictability will be limited on the timing and duration of these events. Often, summers get remembered for a short term period that has a high impact (significant rain event or week long heat wave). This summer (as usual) will feature them, but the impacts will be determined by the persistent pattern averaged over the next three months.
Summary
• Temperature outlook is neutral for all but the western third of the state.
• Above normal precipitation is favored in the east.
• Drought is likely to persist in the west and may intensify.
Mary Knapp, Assistant State Climatologist
mknapp@ksu.edu
Christopher “Chip” Redmond, Kansas Mesonet Manager
christopherredmond@k-state.edu
Tags: weather summer outlook