Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EST Thu Jan 16 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 February-March-April (FMA) 2020 temperature outlook favors above normal temperatures from central and southern portions of the West, across the southern tier of the CONUS, and the East Coast states. Increased chances for below normal temperatures during FMA are forecast across the northern Great Plains, the Upper Mississippi Valley, and the western half of the Great Lakes. 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 exception of EC over the extreme southeastern mainland and the Southeast Panhandle region. The FMA 2020 precipitation outlook indicates enhanced probabilities of above normal seasonal total precipitation amounts east-southeastward from the northern Intermountain region and northern Rockies across the northern Plains, most of the Mississippi Valley, the Great Lakes region, and Ohio and Tennessee Valleys. Below normal seasonal precipitation amounts are favored across southwestern Oregon, California, much of 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, and EC for approximately the southern third of the state. 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 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). This index value has recently decreased to around +0.5 degrees C (for both the most recent week and the Oct-Dec 2019 season). Weekly sea-surface temperature (SST) index values remain the largest (near +1.0 degree C) in the westernmost Nino 4 region, and the smallest (near +0.2 degree C) off the South American coast in the Nino 1+2 region. A weakening of the low-level trade winds has resulted in westerly wind anomalies near the Date Line. These low-level westerly wind anomalies, in turn, often initiate the development of an oceanic Kelvin wave and associated downwelling. The result is an increase in both the magnitude of positive temperature departures at the sea surface, and the volume of warmer-than-normal sub-surface reservoir over the central and eastern Pacific. Equatorial subsurface temperature anomalies (averaged across 180 to 100 degrees W) re-bounded in accordance with this anticipated short-term warming. Despite this recent warmup of surface and subsurface temperatures in the Pacific, model guidance suggests this is only temporary and is not likely to result in the formation of an El Nino. OLR anomalies (used as a proxy for tropical convection) indicated enhanced convection was generally confined to an area west of the Date Line, and suppressed convection was noted over Indonesia and also east of the Date Line. 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 during mid-winter and then slowly decreases towards zero thereafter, reaching the zero anomaly line by April. Based on the latest observations and model forecasts, the CPC/IRI ENSO outlook favors ENSO-neutral conditions to persist through at least this spring. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS The temperature and precipitation outlooks for FMA 2020 were based on dynamical model guidance and statistical tools that include global SST anomaly patterns and a canonical correlation analysis that uses the evolution of SST and sea-level pressure as predictors. During the next several leads, the seasonal outlooks were based largely on the calibrated probabilistic forecasts from the NMME and a consolidation forecast of dynamical and statistical tools. Long-term climate trends were considered for all leads but were relied on more heavily from summer 2020 through the next winter 2020-21. PROGNOSTIC DISCUSSION OF OUTLOOKS - FMA 2020 TO FMA 2021 TEMPERATURE During FMA 2020 there are increased chances of above normal temperatures from central and southern portions of the West across the southern tier of the CONUS, and the East Coast states. This is based on the temperature consolidation tool (which includes the NMME), the CFS, the ENSO-OCN tool, and to some degree the CBaM. The latest outlook differs from the one issued last month (also valid for target season FMA) in that the Pacific Northwest/northern Rockies is now indicated as EC rather than favoring above normal, and trends support the highest probabilities for above normal temperatures over the Southwest to be shifted over/near New Mexico (in excess of 50%). The latest outlook also differs from the previous one for FMA over the Northeast/Upper Mid-Atlantic where indications generally show a slight westward shift of above normal temperatures. Increased chances for below normal seasonal mean temperatures during FMA are forecast across the northern Great Plains, the Upper Mississippi Valley, and the western half of the Great Lakes, which differs slightly from the previous outlook in that the eastern portion of the favored below normal temperatures (Lower Lakes region) now looks less convincing. This is borne out by the temperature consolidation tool (which includes the NMME suite of forecasts), CCA, and OCN trends. The probabilistic NMME and the PAC predict enhanced odds of near normal temperatures for this region. Above normal temperatures are favored throughout much of Alaska, with the exception of EC over the extreme southeastern mainland and the Southeast Panhandle region, with this greater uncertainty indicated by the CFS and CBaM (which predict near to below normal temperatures), and the NMME-based solutions. Maximum probabilities for above normal temperatures are depicted over northwestern Alaska, in part related to the climatologically earlier breakup of sea ice near the coast, and historical temperature trends. For remaining areas of the CONUS and Alaska, where models and tools are either contradictory or predict weak signals, EC is favored. For MAM and AMJ 2020 (leads 2 and 3) above normal temperatures are favored over all of Alaska, with the highest probabilities (in excess of 70% and 60%, respectively) focused over the northwest part of the state. This is supported by the climatological breakup of sea ice approximately a month earlier in recent decades, related historical temperature trends, the temperature consolidation tool, CCA, SST Constructed Analog (SST-CA) tool, and to some degree the CFS. Above normal temperatures are also favored for much of the CONUS, with the exception of the northern High Plains generally eastward across the northern half of the Mississippi Valley into the Great Lakes region. Most tools suggested a larger extent of above normal temperatures across the CONUS, but part of the reason for the extensive area of EC across the northern CONUS is the likelihood of an increasing contribution from soil moisture, with above normal precipitation forecast for FMA, MAM, and AMJ 2020. For the remaining seasons, MJJ 2020 through FMA 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 FMA 2020 favors above normal seasonal total precipitation amounts east-southeastward from the northern Intermountain region and northern Rockies across the northern Plains, parts of the Mississippi Valley, the Great Lakes region, and Ohio and Tennessee Valleys. Within this broad area, there are two separate areas of slightly higher probability (>40%); one in the northern High Plains, and the other in Kentucky/Tennessee. In-between these two probability maxima (in the unseasonably wet Dakotas & Upper Midwest), there are slightly lower probabilities for above normal precipitation, between 33% and 40%. The monthly precipitation outlook for February depicts below normal precipitation over portions of the Middle Mississippi Valley, which at first glance appears to conflict with the seasonal precipitation outlook. However, February is typically a drier month for this region, so this is consistent with short-term dryness and variability. The updated FMA outlook is supported by the precipitation consolidation tool (which includes the NMME), the CFS, and trends. The ENSO-OCN, which is often used as a first guess, depicts above normal precipitation over the northern High Plains and northern Rockies, and from the south-central Mississippi Valley northeast to the Great Lakes. Above normal precipitation is also favored over Alaska from about the Alaska Range poleward to the Arctic Coast, as supported by various models/tools. There are increased odds of below normal precipitation over southwestern Oregon, California, much of Nevada, Arizona, New Mexico, and parts of West Texas. This area of favored below normal precipitation has been shifted somewhat west and north from last month's outlook (valid for FMA). Equal chances (EC) is indicated for those areas where seasonal precipitation amounts are expected to be similar to climatological probabilities. For MAM and AMJ 2020 (leads 2 and 3), above normal precipitation continues to be favored for northern and central Alaska (north of the Alaska Range) based on the precipitation consolidation tool, the CBaM, NMME guidance, and the SST-CA. Over the CONUS, the large area of favored wetness in FMA gradually shifts eastward in MAM and AMJ, with the highest probabilities (>40%) depicted over the Ohio Valley, most of the Appalachians, and the Mid-Atlantic. This expected evolution generally parallels the precipitation consolidation and ENSO/OCN tool outputs during these seasons. By AMJ, the CFS and the SST-CA differ from the ENSO/OCN and consolidation by focusing the heaviest precipitation farther south and west over the Gulf Coast states. The area of favored below normal precipitation across the western CONUS gradually shifts northward by AMJ to include the Pacific Northwest, northern Intermountain region, and northern Rockies, signaling the transition from the climatological rainy season to the dry season. Coverage of favored areas for anomalous precipitation decrease during the summer as forecast confidence diminishes with a weakening signal among tools and convective precipitation becomes more dominant. The favored areas of below or above normal precipitation at later lead times are based largely on historical trends. FORECASTER: Anthony Artusa 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 Feb 20 2020 1981-2010 base period means were implemented effective with the May 19, 2011 forecast release. $$