Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EST Thu Feb 20 2020 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS ENSO-neutral conditions continue across the equatorial Pacific Ocean, as represented in current oceanic and atmospheric observations. The official CPC ENSO forecast indicates that ENSO-neutral is most likely through the Northern Hemisphere spring 2020 (~60 percent chance) and summer 2020 (~50 percent chance). The March-April-May (MAM) 2020 temperature outlook favors above normal temperatures from central and southern portions of the West, across the southern tier of the CONUS, northward to Great Lakes, and to the East Coast states. Increased chances for below normal temperatures during MAM are forecast across the northern Great Plains. Equal chances (EC) of above, near, or below normal temperatures are indicated across the remainder of the CONUS. Above normal temperatures are favored throughout much of Alaska, with the highest odds from the Seward Peninsula to about Point Lay. The MAM 2020 precipitation outlook indicates enhanced probabilities of above normal seasonal total precipitation amounts from the Mississippi Valley to the East Coast. West of the Mississippi Valley, above normal seasonal total precipitation amounts are favored from the Northern Rockies to the Central Plains. Below normal seasonal precipitation amounts are favored across southwestern Oregon, California, southern Nevada, Arizona, New Mexico, and parts of West Texas. Equal chances (EC) are forecast among areas where seasonal precipitation amounts are expected to be similar to climatological probabilities. In Alaska, there are elevated probabilities of above normal seasonal total precipitation amounts from about the Alaska Range northward to the Arctic Coast. Elevated odds for below normal seasonal total precipitation amounts are confined to the southernmost portions of the Alaska Panhandle, while EC are indicated for southern coastal areas and Aleutians. BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS Note: For Graphical Displays of the Forecast Tools Discussed Below See: http://www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS ENSO-neutral conditions persist across the tropical Pacific Ocean. The Oceanic Nino Index (ONI) was at 0.6 degrees C for Nov-Dec-Jan of 2019-2020. The weekly Nino 3.4 index value peaked at +0.8 degrees C during the fall, but this was largely related to the Madden-Julian Oscillation (MJO). The current weekly values for Nino3.4 is 0.1 degrees C, which is slightly lower than most values for the past 3 months, and likely an short-term dip as intraseasonal variability has resulted in a slight increase in trade winds near 140W. Subsurface waters are warmer than normal from about 170E to 140W down to 150 meters, with the only reservoir of colder than average waters west of 170E and centered at approximately 150 meters below the surface. OLR anomalies show enhanced precipitation right along the Date Line, with suppressed convection over the Maritime Continent. From about 160W to the eastern Pacific, anomalies in OLR are very small. According to the National Snow and Ice Data center, ice extent was below average over parts of the Bering Sea, the Sea of Okhotsk, and the East Greenland Sea at the end of January. Sea surface temperatures along the southwest coast of Alaska were also below normal in the latest pentads, but those are highly variable this time of year. PROGNOSTIC DISCUSSION OF SST FORECASTS The CPC SST consolidation forecast, which includes three statistical forecasts along with the CFS model, predicts a continuation of ENSO-neutral conditions through the early spring before the CFS and statistical models slightly diverge. The North American Multi-Model Ensemble (NMME) ensemble mean forecast for the Nino-3.4 SST anomaly is near +0.5 degrees C through March, then a slow decline through the neutral region to near -0.5 degrees C by Sep 2020, though the spread of the ensemble means by Sep 2020 ranges from -1.2 to +0.3 degrees C, so uncertainties are large. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS The temperature and precipitation outlooks for MAM 2020 were based on dynamical model guidance. Statistical tools that include global SST anomaly patterns, a canonical correlation analysis that uses the evolution of SST and sea-level pressure as predictors, and trends. Additionally, statistically calibrated combinations (consolidations, and consolidations via bridging techniques) of those tools were used throughout the forecast period. Long-term climate trends were considered for all leads but were relied on more heavily from autumn 2020 through the next winter 2020-21. Implied soil moisture conditions, corresponding with predicted precipitation patterns were also considered during Summer 2020. PROGNOSTIC DISCUSSION OF OUTLOOKS - MAM 2020 TO MAM 2021 TEMPERATURE The temperature outlook for MAM 2020 relied on dynamical model guidance and the consolidation of SST-CA, CCA, NMME, and trends. The resultant outlook is slightly cooler than the consolidation of those tools as intraseasonal variability is likely to tilt much of March toward below normal temperatures. Shorter-term vartiability and trends favor below normal temperatures for the Northern Plains. Those intraseasonal variations are likely to reverse later in the first 3 months, which would also coincide with some stronger trends for above normal temperatures in the Northern Plains, so odds for below normal temperatures are modest, with more increased uncertainty south and east of where the early cold is predicted. Trends and most dynamical models favor above normal temperatures from the Mid-Atlantic, to the Gulf Coast and westward to the Four Corners and Pacific Coast states. Progressively earlier ice melt out in the spring heavily favors above normal temperatures, but this outlook has lower probabilities than recent trends would support, as the sea ice is near normal along the west coast of Alaska. Through late spring and early summer 2020, trends favor above normal temperatures across the Southwest, peaking in JJA. Equal chances are indicated across the Northern and Central Plains as trends are weakest in this area Additionally, the late spring precipitation outlooks favor above normal precipitation, which, during the warm season, is negatively correlated with temperatures in the following months, especially across the Great Plains and Midwest. For the remaining seasons, ASO 2020 through MAM 2021, the seasonal outlooks were heavily tilted toward historical climate trends, as incorporated into the statistical consolidation tool (which does not include the NMME guidance). PRECIPITATION The precipitation outlook for MAM 2020 favors above normal seasonal total precipitation from the Mississippi Valley to the East Coast, with the highest probabilities from the Tennessee Valley to the Ohio River Valley. Trends and dynamical model output with a largely progressive pattern favor wetness for the aforementioned region. The potential for a dry March limits the odds for above normal precipitation for the Great Lakes, but the March signal is likely related to the intraseasonal cold signal, and likely to reverse throughout the period. Persistent ridging along the West Coast during March favors below normal precipitation for the southwest, as April and May are largely dry months, while that signal weakens in California where April remains wet. Models again favor below normal precipitation for Oregon, but then little to no signal for Washington, so EC is indicated there. Ridging over the eastern Pacific is likely to steer storms into mainland Alaska, favoring above normal precipitation for interior Alaska and drier than normal conditions for the southern Alaska Panhandle. Through late spring, below normal precipitation is favored from the Pacific Northwest to the Four Corners region, aligning with the northward progression of the trend signal. The northern Plains and east of the Mississippi are favored to remain wetter than normal, consistent with model guidance and potential for persistent early wetness to feedback into later months. By the end of the summer, the precipitation outlooks largely resemble trends, which would be the dominant mode represented through next autumn if the ENSO neutral conditions persist as the NMME models indicate. For next winter, trends dominate the predicted patterns. FORECASTER: Matthew Rosencrans The Climatic normals are based on conditions between 1981 and 2010, following the World Meterological Organization convention of using the most recent 3 complete decades as the climatic reference period. The probability anomalies for temperature and precipitation based on these new normals better represent shorter term climatic anomalies than the forecasts based on older normals. For a description of of the standard forecast tools - their skill- and the forecast format please see our web page at http://www.cpc.ncep.noaa.gov/products/predictions/long_range/tools.html (Use Lower Case Letters) Information on the formation of skill of the CAS forecasts may be found at: http://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/US/Outlook/outlook.shtm l (use lowercase letters) Notes - These climate outlooks are intended for use prior to the start of their valid period. Within any given valid period observations and short and medium range forecasts should be consulted. This set of outlooks will be superseded by the issuance of the new set next month on Mar 19 2020 1981-2010 base period means were implemented effective with the May 19, 2011 forecast release. $$