Seasonal Climate ForecastApril – June 2018

Issued: March 16, 2018

Contact: ODF Meteorologist Pete Parsons503-945-7448 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 La Niña (cold) conditions are present, with below-average sea-surface temperatures (SSTs) in the central and eastern tropical Pacific Ocean.

n The Oceanic Niño Index (ONI) for Dec. – Feb. was -0.9°C. This index, which lags real-time SSTs, is in La Niña territory for the fourth consecutive month (The Climate Prediction Center’s definition of a La Niña Event includes an ONI value of -0.5°C or colder, for at least 5 consecutive months).

n The current Climate Prediction Center (CPC) forecast favors a transition to ENSO-neutral this spring with ENSO-neutral conditions likely through this summer. Please note that ENSO forecasts have relatively low skill level this time of year.

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 Two of the analog years (1996; 2006) remain unchanged from last month. However, 2014 has replaced 1963. These years ranged from cold ENSO-neutral to La Niña, in March, with warming ONI values.

n In general, cold ENSO-neutral and La Niña events typically transition from cooler-and-wetter-than-average conditions to warmer-and-drier-than-average conditions during the April-June period.

n Cool and damp weather, relative to average, is most likely early in the period. That may help to preserve below-average mountain snowpacks, which have recovered slightly since January (see next 2 slides).

IMPORTANT NOTE: This forecast is based on past and current weather data and is notassociated 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

February SST Anomalies (°C)2018 Composite: 1996; 2006; 2014

n The February 2018 observed Pacific Basin SST anomaly pattern is similar to the constructed February composite of the current analog years (1996; 2006; 2014).

n Both graphics show negative SST anomalies in the central and eastern tropical Pacific Ocean, resembling La Niña conditions.

February 2018 tropical Pacific SST anomalies were negative

Analog composite of

February tropical Pacific SST anomalies has a similar

pattern

Pacific OceanAnimated (PowerPoint only) SSTs (top) / Anomalies (bottom)

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

Central and eastern tropical Pacific SSTs are in weak La Niña range.

Tropical Pacific OceanCurrent SST anomalies (bottom) reflect La Niña (cold) conditions

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

Central and eastern Pacific SSTs remain

below average

ENSO-neutral

Tropical Pacific Ocean

El Niño

La Niña

(1995-96; 2005-06; 2013-14)

February 2018 SOI fell into

ENSO-neutral territory

February SOI for each of the three analog

years dropped into ENSO-

neutral range

Strong

Moderate

ENSO-neutral

El Niño

Tropical Pacific Ocean

(1995-96; 2005-06; 2013-14)

La Niña

Weak

Strong

Moderate

ONI for Dec. 2017 – Feb. 2018 was in

weak La Niña range

ONIs of the analog years ranged from cold ENSO-

neutral to weak La Niña

Weak

Neutral

North Pacific Ocean

Warm

Cool

(1995-96; 2005-06; 2013-14)

Feb. 2018 PDO remained in the “neutral” range

Feb. PDO for each of the three analog years was in the “neutral”

range

April 2018 ForecastMean Upper-Air Pattern Upper-Air Anomalies

n The analog composite favors anomalous troughing in the Gulf of Alaska and off of the US west coast.

n The predicted mean upper-air pattern favors at least average storminess across Oregon. April showers…

April 2018 ForecastTemperatures Precipitation

n Significant departures from average conditions are not expected.n Snowpacks should peak at below or well-below average levels.n Analogs alternated between warm and cool periods, so expect variety.

May 2018 ForecastMean Upper-Air Pattern Upper-Air Anomalies

n The composites of the analogs (above panels) indicate near-average upper-air patterns over Oregon.

n Significant variation among and within the analog years lowers short-duration (less than a month) forecast confidence.

May 2018 ForecastTemperatures Precipitation

n Analog years showed significant variation in temperature, with their resultant average near or slightly-above average.

n Precipitation should be near average, with the greatest chances for above-average precipitation west of the Cascades.

June 2018 ForecastMean Upper-Air Pattern Upper-Air Anomalies

n No significant departures from average indicated in the upper-air flow.n During La Niña events, a transition to warmer and drier conditions,

relative to average, typically initiates by the end of June.

June 2018 ForecastTemperatures Precipitation

n Temperatures likely near or slightly above average, and precipitation likely near or slightly-below average.

n The month may end up split, in terms of weather, with one-half being quite dry and the other half being relatively wet.

April – June 2018 ForecastMean Upper-Air Pattern Upper-Air Anomalies

n Weak anomalous ridging is expected to develop over the southwestern US…eventually pushing northward over Oregon.

n Although a general trend towards warmer and drier conditions, relative to average, is expected, week-to-week patterns may be highly variable.

April – June 2018 ForecastTemperatures Precipitation

n A general theme of keeping 3-month (seasonal) temperatures and precipitation reasonably close to average with a warming a drying trend.

n Analog years show considerable short-duration variation in weather conditions, so expect lots of variety…typical for Oregon in the spring.

Forecast Resourcesn 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 Informationn 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)

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

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