Seasonal Climate Forecast September - November 2018 - Oregon.gov

Seasonal Climate Forecast
      September – November 2018
                      Issued: August 16, 2018

           Contact: ODF Meteorologist Pete Parsons
         503-945-7448 or peter.gj.parsons@oregon.gov

Oregon Department of Agriculture (ODA) - Oregon Department of Forestry (ODF)
 ODA Production support from Diana Walker, Jacob Cruser, and Andy Zimmerman

El Niño Southern Oscillation (ENSO)
        Current Status and Forecast
n  The Oceanic Niño Index (ONI) for May – July was 0.1°C, which is in
the ENSO-Neutral (average) range. Note: The ONI lags real-time SSTs.

n Sea-surface temperatures (SSTs) across the equatorial Pacific Ocean
have recently cooled to near average. Subsurface temperatures remain
above normal, which is a key factor in CPC’s ENSO forecast (below).

n  The Climate Prediction Center (CPC) favors El Niño (warm)
development this fall (60% chance) or winter (70% chance). In contrast,
the analogs used here favor a continuation of ENSO-Neutral conditions.

IMPORTANT NOTE: Beginning with the October 2017 update, ONI values use ERSSTv5 data
(Huang et al. 2017, J. Climate, vol. 30, 8179-8205).

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

Forecast Overview
n  2012 replaced 1985, as one of the top analogs this month (1985 SSTs
were trending too cold). The other analog years (1996; 2006) remain
unchanged from last month. 1996 and 2012 stayed ENSO-neutral
through the subsequent winter, with 2006 warming into a weak El Niño.

n Drier-than-average conditions should persist through early October,
with progressively wetter weather after that time. There is a heightened
chance of unusually stormy and wet weather in November.

n Expect mild temperatures, with the warmest readings in September
and November, relative to average. However, Arctic air may push
southward, close to the region, in November and can’t be ruled out.

IMPORTANT NOTE: This forecast is based on past and current weather data and is not
associated with CPC predictions (see “Forecasting Methods…” at: https://oda.direct/Weather)
nor the official CPC “Three-Month Outlooks,” which are available here:
http://www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal.php?lead=1

July SST Anomalies (°C)
                  2018                         Composite: 1996; 2006; 2012
                                         Observed
                                      tropical Pacific
                                      SST anomalies
                                        were slightly
                                          positive

                                      Composite of
                                      analog tropical
                                       Pacific SST
                                      anomalies was
                                       also slightly
                                         positive

n   The July 2018 observed Pacific Basin SST anomaly pattern is similar to the constructed
    July composite of the current analog years (1996; 2006; 2012).
n   Both graphics (above) reveal slightly above-average SSTs in the central and eastern
    tropical Pacific Ocean.

Pacific Ocean
     Animated (PowerPoint only) SSTs (top) / Anomalies (bottom)

                        Central and eastern tropical Pacific SSTs
                       have recently cooled back to near average.

Courtesy: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/gsstanim.shtml

Tropical Pacific Ocean
                            Currently ENSO-neutral

     Central and eastern
    Pacific Ocean SSTs are
     mostly near average

Courtesy: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/sstweek_c.gif

Tropical Pacific Ocean

(1995-96; 2005-06; 2011-12)     May – July
                               ONIs of the
  Strong                       analog years
           El Niño            were all in the
  Moderate                    ENSO-neutral
                                  range
  Weak

      ENSO-neutral

  Weak
  Moderate                    May - July 2018
                              ONI reflected
  Strong   La Niña            ENSO-neutral
                               conditions

Tropical Pacific Ocean

(1995-96; 2005-06; 2011-12)    Analog years
                              had July SOIs
                              ranging from
La Niña                         La Niña to
                              ENSO-neutral

  ENSO-neutral
                              July 2018 SOI
                                was in the
El Niño                       ENSO-neutral
                                  range

North Pacific Ocean

   (1995-96; 2005-06; 2011-12)
                                   July analog
                                  PDO values
                 Warm             ranged from
                                 neutral to cool

Neutral

                                 July 2018 PDO
                                   was in the
                  Cool            middle of the
                                  neutral range

September 2018 Forecast
Mean Upper-Air Pattern                  Upper-Air Anomalies

n   Weak anomalous troughing in 1996 is more than countered by weak
    ridging in 2006 and strong anomalous ridging in 2012.
n   A blend of the analogs (above) is remarkably similar to the 2006
    solution, which is arguably the best analog.

September 2018 Forecast
        Temperatures                            Precipitation

n   Drier and warmer than average weather expected. Both the 2006 and
    the 2012 analogs had their warmest weather in the first week with
    another warm period during the final week.
n   A cooler and wetter 1996 analog reduces forecast confidence a touch.

October 2018 Forecast
Mean Upper-Air Pattern                     Upper-Air Anomalies

n   Once again, a blend of the analog years (above) looks similar to the
    2006 analog, with 1996 having more troughing over the Pacific NW.
n   This overall pattern favors relatively dry and mild weather, but expect a
    mid-month transition to cooler and wetter weather, relative to average.

October 2018 Forecast
        Temperatures                               Precipitation

n   Dry and mild conditions likely early, with a transition to cooler and
    wetter weather for the second half of the month.
n   Large departures from “average” conditions are not indicated.

November 2018 Forecast
Mean Upper-Air Pattern                    Upper-Air Anomalies

n   Once again, the composite of the analogs (above) looks similar to 2006.
n   This pattern “opens the door” for stormy and very wet periods, which
    was especially the case in both 1996 and 2006.

November 2018 Forecast
        Temperatures                               Precipitation

n   Expect precipitation most days of the month. 1996 and 2006 had
    periods of record rainfall. Significant mountain snowfall is also likely.
n   Above-average temperatures, due to frequent storminess. Low snow
    levels, at times, with Arctic air possibly pushing close to the region.

September – November 2018 Forecast
Mean Upper-Air Pattern                      Upper-Air Anomalies

n   The analog years had markedly different solutions. 1996 had
    anomalous troughing over the Pac NW, while 2012 had anomalous
    ridging. 2006 reflected a blend of the other years, with a pattern closer
    to average and similar to the composite (shown above).

September – November 2018 Forecast
        Temperatures                            Precipitation

n   Temperatures likely near or slightly-above average.
n   Precipitation starting out below average, through early October, then
    ramping up... November appears as if it could be quite stormy, with a
    heightened chance of heavy rain and above-average mountain snowfall.

Forecast Resources
n   CPC Official US Three-Month Forecasts (Graphics):
http://www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal.php?lead=01

n   CPC US 30-Day & 90-Day Forecasts (Discussions):
http://www.cpc.ncep.noaa.gov/products/predictions/long_range/fxus07.html

n   CPC Weekly & Monthly ENSO Discussions:
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory

n   Australian Government Weekly Tropical Climate Note:
http://www.bom.gov.au/climate/tropnote/tropnote.shtml

n   Australian Government ENSO Wrap-Up:
http://www.bom.gov.au/climate/enso

n   IRI ENSO Quick Look:
http://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/

n   ODA Seasonal Climate Forecast Home:
http://www.oregon.gov/ODA/programs/NaturalResources/Pages/Weather.aspx

Water Supply Information
n   NDMC U.S. Drought Monitor:
http://droughtmonitor.unl.edu/

n   NIDIS North American Drought Portal:
http://www.drought.gov/nadm/content/percent-average-precipitation

n   NRCS Snow Water Equivalent Oregon Map:
http://www.wcc.nrcs.usda.gov/ftpref/data/water/wcs/gis/maps/or_swepctnormal_update.pdf

n   NRCS Snow Water Equivalent Products:
http://www.wcc.nrcs.usda.gov/snow/snotel-wereports.html

n   NRCS Weekly Water and Climate Update:
http://www.wcc.nrcs.usda.gov/cgibin/water/drought/wdr.pl

n   NRCS Western Snowpack Data & Water Supply Forecast:
http://www.wcc.nrcs.usda.gov/cgibin/westsnowsummary.pl

n   WRCC WestWideDroughtTracker:
http://www.wrcc.dri.edu/wwdt/

Updated Monthly
               (Around the 20th)

    Your Feedback is Welcome!
  Sign-up for Email Notification of updates at:
         https://oda.fyi/SubscribeSCF

    Contact: Pete Parsons, ODF Meteorologist
at 503-945-7448 or peter.gj.parsons@oregon.gov