Seasonal Climate Forecast August October 2013 Verification (Issued: November 17, 2013) Note: This product is published by the Oregon Department of Agriculture (ODA), in cooperation with the Oregon Department of Forestry (ODF). Contact: Pete Parsons, ODF Meteorologist 503-945-7448 pparsons@odf.state.or.us ODA Production support from Diana Walker and Sean Fornelli
Format and Purpose: n A side-by-side comparison of the Seasonal Climate Forecast vs. what (Actually Occurred) is done for both the 1-month & 3-month forecasts. n To assess the utility of this forecast and form a basis for adjustments to the forecast method*. n Note: 1981-2010 long-term averages are used. * See Forecasting Methods at: http://cms.oregon.gov/oda/nrd/pages/weather.aspx
Verification Updates: n This forecast method verifies best during El Niño (warm) or La Niña (cold) events. ENSO-neutral winters are more varied but do have some climate signatures. n A return to the cool phase of the Pacific Decadal Oscillation (PDO), which occurred no later than 2007, appears to be significantly influencing Oregon s weather. n Using analog years from other cool phase periods should help to limit forecast error. However, most of those years are prior to 1977, which adds another element of error (adjustments are not made for any
August 2013 (Forecast Issued July 23, 2013) Forecast Temperatures Actual Temperatures Data courtesy of the National Climatic Data Center (NCDC)
August 2013 (Forecast Issued July 23, 2013) Forecast Precipitation Actual Precipitation Data courtesy of the National Climatic Data Center (NCDC)
August 2013 (Forecast Issued July 23, 2013)/(Actual) n Weather during the top analog years varied greatly, with the forecast graphics skewed cool by just one of these years. The other top analog years were warmer than average, so confidence in the forecast was low. (Temperatures were above average statewide. Precipitation increased during the second half of the month. Rainfall was above average from southwest to south-central Oregon and near average elsewhere.) n Elevated concern for wildfires due to a dry winter and early spring. (Lightning started numerous wildfires across the state, beginning in late July. SW Oregon was hardest-hit, where several large wildfires remained active through August.)
September 2013 (Forecast Issued August 21, 2013) Forecast Temperatures Actual Temperatures Data courtesy of the National Climatic Data Center (NCDC)
September 2013 (Forecast Issued August 21, 2013) Forecast Precipitation Actual Precipitation Data courtesy of the National Climatic Data Center (NCDC)
September 2013 (Forecast Issued August 21, 2013)/(Actual) n Forecast confidence was low due to a wide variety of weather during the analog years. The one clear signal was that the first half of the month should be relatively warmer and drier than the second half. (It is an understatement to say that the second half of the month was cooler and wetter than the first half! After a quite warm and dry start, mid-month began a transition to cooler and much wetter conditions. Record rains drenched the state during the final few days especially from the Cascades westward. Sections of the northern coastal range received in excess of 10 in just 3 days! )
October 2013 (Forecast Issued September 19, 2013) Forecast Temperatures Actual Temperatures Data courtesy of the National Climatic Data Center (NCDC)
October 2013 (Forecast Issued September 19, 2013) Forecast Precipitation Actual Precipitation Data courtesy of the National Climatic Data Center (NCDC)
October 2013 (Forecast Issued September 19, 2013)/(Actual) n Higher than normal confidence in a colder than average month statewide. (It was an exceptionally cool month statewide. Climate zone averages ranged from 1.6 F to 4.2 F below average.) n Above average precipitation likely, especially across western zones. (Precipitation was below average statewide with the greatest deficits in the west. However, the record rainfall during the last week of September would have skewed October precipitation above average, if it had occurred a week later.)
August October 2013 (Forecast Issued July 23, 2013) Forecast Temperatures Actual Temperatures Data courtesy of the National Climatic Data Center (NCDC)
August October 2013 (Forecast Issued July 23, 2013) Forecast Precipitation Actual Precipitation August 2013 - Data courtesy of the National Climatic Data Center (NCDC)
August October 2013 (Forecast Issued July 23, 2013)/(Actual) n A very cool October skews the 3-month temperature forecast colder than average statewide. The graphic may be overstating the cool anomalies due to a very cool August in 1968 (one of the top analog years). (Above average temperatures in August and September were countered by a very cool October.) n Western zones have the greatest chance of seeing above normal rainfall. (Record rainfall in late September more than offset the near average rainfall in August and below average rainfall in October.)
Updated Monthly (mid-month) Your Feedback is Welcome! Pete Parsons, ODF Meteorologist 503-945-7448 pparsons@odf.state.or.us