Northwest Outlook September 2017

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Berniece Horton
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Northwest Outlook September 2017 Hot and dry August August 2017 continued with the pattern established in June and July that featured a large, semipermanent ridge in the flow of the jet stream.

1 Northwest Outlook September 2017 Hot and dry August August 2017 continued with the pattern established in June and July that featured a large, semipermanent ridge in the flow of the jet stream. Temperatures routinely soared above 90 F and at times reached into triple digits. This same ridge blocked any chances for rain in most of the Pacific Northwest region, leaving some areas dry for the last 60+ days. Heat throughout the Columbia River Basin has impacted dairy production as dry matter intake is reduced substantially at temperatures above 95 F. Pasture growth across the Northwest has deteriorated, especially in Montana where exceptional drought has gripped the eastern half of the state. While Growing Degree Day units have played catch-up after the slow start in May, research shows that early season heat and late season cool is ideal for potato yields s growing season featured just the opposite. Grass silage yields have been reduced due to the heat and lack of rainfall. Some fields in Washington have set all-time records for the longest stretch of dry days. Spring wheat and other small grains that were planted late due to cool and wet spring weather have had a difficult time with root growth as the water levels receded during the dry season. Figure 1.a. Number of hours during August 2017 with temperatures above 95 F. Data source: RTMA; created by Eric Snodgrass.

2 Figure 1.b. Correlation of May and July temperatures and Idaho potato yields. Data source: NOAA; created by Eric Snodgrass. Wildfires The extremely wet winter and spring led to strong vegetative growth across the Pacific Northwest early in the season. However, as we have been warning, this growth has turned into fuel for fires during the dry season. Here are the impacts: High heat, low humidity, stronger winds at times, and plenty of fuel have led to numerous wildfires across the Northwest. Some locations have not seen rain since May Industrial Fire Precaution Levels across all four states in the Northwest have risen to Partial Hootowl and Partial Shutdown in most regions. Smoke has spread from the Northwest across the U.S. to the Great Lakes, dramatically reducing air quality. Northwest Outlook, September 2017 Page 2

Figure 2. September 4, 2017 MODIS satellite image showing the extent of the smoke plumes from the Northwest extending east to the Great Lakes. Source: NASA WorldView.

3 Figure 2. September 4, 2017 MODIS satellite image showing the extent of the smoke plumes from the Northwest extending east to the Great Lakes. Source: NASA WorldView. Outlook for September 2017 and winter The large ridge in the jet stream that has dominated the weather pattern for the last 60 days will be a persistent feature through most of September. This translates into a higher probability that September finishes with a warm and dry bias. Not every day will be warmer than average, but longrange model guidance consistently keeps the region above average for the next 45 days. Looking longer term toward winter, the lack of a strong El Niño or La Niña signal makes forecasting winter weather challenging several months in advance. Preliminary analysis supports the forecasts shown in Figure 3.c. Temperature patterns from November through January are looking to carry a warm bias across the Southern U.S. while the Pacific Northwest is projected to have near-average temperatures. Longrange model guidance has also trended toward a near-average or wetter-than-average winter. The accuracy of this forecast will depend on the position and intensity of the Pacific branch of the polar jet stream as fall and winter arrive, but as of early September, this is our best guidance. Northwest Outlook, September 2017 Page 3

4 Figure 3.a. ECMWF (European) 32-day temperature anomaly forecast for September Figure 3.b. 32-day precipitation anomaly forecast for September Source: Northwest Outlook, September 2017 Page 4

Figure 3.c. November 2017 - January 2018 temperature and precipitation outlooks.

5 Figure 3.c. November January 2018 temperature and precipitation outlooks. Source: IRI Multi-Model from Columbia University, National Multi-Model Ensemble for the Climate Prediction Center and NCEP. Northwest Outlook, September 2017 Page 5

Northwest Outlook October 2016

Northwest Outlook October 2016 Rainfall Opportunities and Challenges Rainfall over the month of September presented some challenges for the fall harvest while other producers benefitted. Figure 1a shows