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Prognostic Discussion for Monthly Outlook NWS Climate Prediction Center College Park MD 300 PM EDT Fri Mar 31 2023 30-DAY OUTLOOK DISCUSSION FOR APRIL 2023 The updated temperature and precipitation outlooks for April 2023 reflect recent dynamical model guidance from the GEFS and CFSv2, as well as current WPC week 1 outlooks and the CPC week 2 and week 3-4 outlooks. The Madden Julian Oscillation (MJO) was recently active with convective activity over the Maritime Continent, although the Real-time Multivariate MJO (RMM) index now indicates a reduced MJO signal, as subseasonal variability interacts with the background climate state. Dynamical models , such as the ECMWF and GEFS, forecast a possible reemergence of the MJO signal over the tropical Pacific. However, there is uncertainty in the timing and phase of a future MJO signal and potential impacts to the temperature and precipitation patterns over North America. While the recent La Niña event has ended, residual atmospheric conditions similar to La Niña continue, such as suppressed convection near the date line. The updated April temperature outlook indicates an expansion of enhanced probabilities for below normal temperatures for the western and north-central contiguous U.S. (CONUS), due to recent dynamical model guidance and outlooks for the beginning of the month. WPC temperature outlooks for the first week of April indicate a very similar temperature pattern, as do recent CPC 6-10 day period outlooks and dynamical model consolidation tools. The updated April temperature outlook shows a reduction in the probabilities favoring above normal temperatures for parts of the Southwest, while continuing to indicate likely above normal temperatures for the Southern Plains, the Central and Lower Mississippi Valley, the Ohio Valley, the Southeast, and the Mid-Atlantic region. This pattern of below and above normal temperatures across this CONUS is supported by the CFSv2 model guidance for the month, in addition to the WPC and CPC outlooks for the beginning of the month. Above normal temperatures are favored for a small coastal area of northwestern Alaska, while below normal temperatures are favored for the south coast of the Alaska Mainland, supported primarily by the most recent CFSv2 model forecasts. A considerable increase in uncertainty leads to a forecast of equal chances (EC) of above, near and below normal temperatures for much of Alaska, with conflicting signals among various tools. The updated April precipitation outlook indicates an increased probability of above normal precipitation for the Pacific Northwest, supported by recent WPC outlooks for the first week of the month, the CFSv2 April precipitation forecast, and the CPC Week 3-4 Outlook. The area of enhanced probabilities of below normal precipitation over parts of the Southwest has decreased in the updated April Outlook, with increased chances of precipitation in both the CPC 8-14 day outlook and the Week 3-4 Outlook over eastern areas of the Southwest, and over parts of Central California in the first week of April. The updated April precipitation outlook indicates increased probabilities of above normal precipitation from East Texas across the Lower Mississippi Valley into the Ohio and Tennessee Valleys, as well as for eastern areas of the Northern Plains, the Great Lakes region, and western New York state. Chances of above normal precipitation for the month of April are increased over these areas by precipitation forecasts for the first week of the month. Probabilities exceed 50 percent for parts of East Texas northeastward to the Mississippi, where predicted precipitation in the first week approaches April climatological precipitation amounts. The April precipitation outlook favors above normal precipitation for northwestern Alaska into parts of the Alaska interior and below normal precipitation for the Alaska Peninsula and the southwestern coast, supported by the most recent CFSv2 model forecasts and consistent with precipitation outlooks for the start of the month. An area of enhanced probabilities for below normal precipitation over the Alaska Panhandle has been removed in the updated outlook, considering recent outlooks for week 2 and weeks 3 and 4. ******************************************************************************* ***** The previous discussion from mid-March is below ***** ******************************************************************************* The La Niña event has ended as of March, 2023. Sea surface temperature (SST) anomalies have tended towards positive across most of the equatorial Pacific Ocean in recent weeks, and the most recent Niño 3.4 region anomaly is approaching zero degrees Celsius. The East Pacific is particularly warm with an anomaly of +1.5 C in the Niño 1+2 region. Easterly equatorial wind anomalies over the Pacific Ocean have weakened in the last month and are confined to a small area of the central Pacific. Upper-level westerly wind anomalies continued over the eastern equatorial Pacific. Positive subsurface temperature anomalies observed in the western and central equatorial Pacific Ocean have expanded eastward, while extending towards the surface in the eastern Pacific Ocean. Negative subsurface temperature anomalies near the surface of the central Pacific Ocean have weakened. Although ENSO-neutral conditions are predicted in the official ENSO outlook to continue through the Northern Hemisphere spring, a rapid warming of the Niño 3.4 region SST anomaly is forecast by most statistical and dynamical models , with an increasing chance of an El Niño from summer into autumn. Consolidated dynamical model forecasts from the North America Multi-Model Ensemble (NMME) predict positive SST anomalies in the Niño 3.4 region, bordering on El Niño conditions near the 0.5 degree C threshold, from summer through autumn. The Madden-Julian Oscillation (MJO) strengthened significantly in the beginning of March with convective activity currently over the Western Hemisphere. Dynamical model forecasts of the Real-time Multivariate MJO (RMM) index indicate a weakening MJO signal propagating eastward into the Indian Ocean towards the end of March. The ECMWF dynamical model forecasts for the beginning of April indicate likely below-normal temperatures for much of the western contiguous U.S. (CONUS) and parts of the northern Great Plains. Anomalous snowpack and snow cover over parts of the West play a role in the temperature outlook for April. In addition to surface boundary conditions, near-coastal sea surface temperature anomalies were considered. Linear regression forecasts based on the RMM index indicate a potential for below-normal temperatures across much of the CONUS at the beginning of April, followed by warming, particularly in the East. The temperature and precipitation outlooks for April are based primarily on a skill-weighted consolidation of dynamical model forecasts from the North America Multi-Model Ensemble (NMME). Statistical tools, such as the Canonical Correlation Analysis (CCA), Constructed Analog (CA), and a linear regression model based on the CPC SST Consolidation forecast of the Nino 3.4 index and decadal trends were considered, but played a lesser role given the uncertainty of ENSO-related signals given the rapid transition in the ENSO state. In addition, skill-based consolidations of statistical and dynamical tools for temperature and precipitation were consulted. The April Monthly Outlook favors below-normal temperatures for southwestern Alaska, as indicated by the NMME consolidation tool, with negative SST anomalies along the coast contributing to cooler temperatures. Above-normal temperatures are favored for northeastern Alaska, supported by the NMME consolidation tool, as well as the statistical forecast tool consolidation. The probability of below-normal temperatures is enhanced in the Pacific Northwest, Northern Rockies, and parts of the Great Basin, supported by recent CFSv2 and ECMWF dynamical model forecasts for April, and consistent with areas of anomalous snow cover and deep snowpack. Negative SST anomalies near the Pacific coast contribute to an increased likelihood of below-normal temperatures for the coasts of California, Oregon and Washington. Above-normal temperatures are favored from parts of the Southwest eastward across the Southern Plains, and from the Gulf Coast region northward across the eastern CONUS, as indicated by the NMME model forecasts. Strong positive SST anomalies along the Gulf Coast increase the likelihood of above-normal temperatures. Conflicting signals in the temperature forecast tools lead to equal chances of below, near and above-normal temperatures in the April outlook over a large area of the north-central CONUS. Above-normal precipitation is favored for parts of the west coast of Alaska, as indicated in the precipitation consolidation of dynamical and statistical tools and the CFSv2 model forecasts. Below-normal precipitation is slightly favored for parts of the south coast of Alaska, as predicted by the NMME precipitation anomaly forecast. Below-normal precipitation is favored for a large area of the western CONUS from California and southern Oregon to the Central and Southern Rockies, as predicted by most dynamical and statistical model forecasts and consistent with decadal precipitation trends for April. Above-normal precipitation is favored from the western Gulf Coast region northward into parts of Oklahoma and Arkansas, as predicted by the dynamical and statistical model forecast consolidation. Above-normal precipitation is also favored for parts of the Midwest and Great Lakes region, supported by recent dynamical model forecasts such as the CFSv2 and ECMWF, and consistent with decadal precipitation trends for April. FORECASTER: Dan Collins The climatic normals are based on conditions between 1991 and 2020, following the World Meteorological Organization convention of using the most recent 3 complete decades as the climate 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. The next monthly outlook...for May ... will be issued on Thu Apr 20 2023 These outlooks are based on departures from the 1991-2020 base period. $$
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