FXUS07 KWBC 151332 PMD30D Prognostic Discussion for Monthly Outlook NWS Climate Prediction Center College Park MD 830 AM EST Thu Feb 15 2024 30-DAY OUTLOOK DISCUSSION FOR MARCH 2024 A number of climate factors are considered in preparing the March 2024 temperature and precipitation outlooks. In addition to the ongoing, albeit weakening El Nino, an ongoing MJO event continues. To further complicate matters, there are indications of a weakening in the stratospheric polar vortex potentially leading to a Sudden Stratospheric Warming (SSW) sometime during the second half of February. Moreover, El Nino wintertime residual impacts are also considered in developing the outlook. Even though El Nino oceanic conditions have peaked - SSTs are decreasing and oceanic heat content along the equator with depth in the Pacific basin has decreased considerably, the induced atmospheric response can often linger and so common El Nino impacts are likely to continue at times through March and potentially into April. So the March 2024 temperature and precipitation outlooks continued to consider El Nino as part of the large scale base state and so potential impacts. The MJO has been quite active the last several weeks, but its current coherency is being impacted by multiple modes of both subseasonal [i.e., atmospheric Kelvin waves and Equatorial Rossby waves (KW/ERW)] and inter-annual forcing (i.e. ENSO). With this the case, some standard realtime metrics of the MJO amplitude and phase are disturbed and at times less clear when monitoring. But given recent Pacific Ocean jet strength and extensions and monitoring the circulation only portion of the signal (e.g., 200-hPa velocity potential) it appears the MJO remains active and has entered and is crossing western Hemisphere. Model predictions of the RMM index, vary highly, but most generally favor continue eastward propagation of a signal across Africa back towards the Indian Ocean over the next couple of weeks. If this becomes the case and enhanced convection redevelops in the eastern Indian Ocean and Maritime Continent, ridging and above-normal temperatures for the eastern half of the CONUS would tend to be favored. Weak signals or troughing would be most likely at modest odds across the western CONUS. Recent monitoring of the stratosphere and model predictions of the 10-hPa zonal wind indicate a potential for a SSW and potential coupling with the troposphere and a tendency to favor a negative AO for periods during the month of March. However, there remains high uncertainty in the eventual evolution after any SSW event and so follow on -AO potential. Even with a SSW event, there always remains considerable variability in how the vortex is impacted (i.e. displaced vortex vs. a split vortex) and the hemisphere (eastern vs. western) where the odds are the greatest for more frequent Arctic air outbreaks during March. In mid-February, substantial snow deficits are evident from the northern High Plains eastward to the Great Lakes and Northeast - common after El Nino winters. Increased wetness and snowpack has developed in recent weeks for portions of the western CONUS primarily in California, Nevada, and the central and southern Rockies as a result of active Pacific storminess. Weighing all these factors, the March 2024 temperature outlook favors above-normal temperatures for much of the Far West, Pacific Northwest eastward across the northern Plains, Great Lakes and for much of the eastern CONUS. El Nino and negative snow departures support the forecast for much of this highlighted area. Potential MJO influence supports the extension of favored above-normal warmth for the eastern third of the CONUS. Lower odds for above-normal temperatures in the northern Plains and western Great Lakes, large area of Equal-Chances (EC) in the interior of the CONUS and slightly favored below-normal temperatures for parts of the Southeast and Texas are in deference to potential influence from negative AO periods. Elevated odds for above-normal precipitation also contributes slightly to the below-normal temperature forecast in this region. Potential troughing associated with the MJO and elevated chances for above-normal precipitation in some areas support a slight tilt toward below-normal temperatures for parts of the Southwest. Above-normal temperatures are most likely for the entire state of Alaska. For precipitation, El Nino background conditions and potential MJO influence at times in March, favor above-normal monthly total precipitation amounts from California eastward across the central Rockies to the north-central Plains. Dynamical model guidance (NMME, C3S) and long term positive precipitation trends also support this forecast. El Nino considerations and dynamical model guidance support elevated odds for above-normal precipitation for the Gulf Coast, the Southeast and much of the eastern seaboard as well as smaller regions of favored below-normal precipitation for parts of the Pacific Northwest and central Great Lakes. The majority of dynamical model guidance favored below-normal monthly precipitation amounts for southern Texas. For Alaska, above-normal precipitation is most likely for most of the southern portion of the state. FORECASTER: Jon Gottschalck 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. An updated monthly outlook... for Mar will be issued on Thu February 29 2024 These outlooks are based on departures from the 1991-2020 base period. $$