United States: Transitional pattern, no locked-in regimes.
Climate: Madden Julian oscillation is weak but favors a cooler than normal national climate. Lingering snow cover also increases the risk of cold across the North. Dry soils across the southwest sector of the U.S. favor anomalous warmth and possibly early season extreme heat once into May.
Week 2 (April 15-21): Favoring a stormy period set-up by thermal contrast between northern chill and southern warmth. Strong front with heavy rain in the East early period followed by another cold front with heavy precipitation Texas to Midwest. Cooler (not cold) air masses follow each front. Nationally, generally cool with potential for warming Southwest to Great Plains very late in the period.
Week 3 (April 22-28): Warm Southwest to Great Plains early period. Warmth expands to the East mid-period. Significant northern U.S. snow cover melt adds to water to stream flows Ohio Valley to Mississippi River and across central/northern Continental Divide. The warmth is brief. Another cold front brings rain/possible severe weather mid-period with following cooler changes although not extreme cold.
Week 4 (April 29-May 5): Low confidence. Favor the ECMWF with significant warming generating across the Southwest U.S. drought area. The Midwest to Northeast is cool and Midwest wet.
South America: Wet pattern next 10 days. Brazil stays wet into May.
Climate: Madden Julian oscillation affects the climate pattern the next 2 weeks. As MJO shifts east from the tropical East Pacific/Atlantic to the Indian Ocean the South America climate is susceptible to a trailing upper trough. Once MJO is in the Indian Ocean an upper ridge builds over South America. A wet to dry transition occurs over the next 1-2 weeks. There is significant warming taking place off the northwest coast of South America as La Nina appears to be ending. This warming could support locally heavy rains across northwest South America.
Week 2 (April 15-21): Northwest South America looks wet likely associated with the warming of the oceans northwest of the continent. The wet weather can provide a wet source region for climate to the east therefore expect most of Brazil to be wetter than normal except far eastern areas. Northern Argentina is wet early period then turning drier. The drier pattern for Argentina follows a wet pattern through the next 10 days.
Week 3 (April 22-28): Wet weather will continue over northwest South America and act as a (wet) source region for western and central Brazil. Eastern Brazil is likely normally wet. High pressure builds in the subtropics leaving Argentina drier than normal.
Week 4 (April 29-May 5): Low confidence. Seasonal persistence is forecast. Upper trough forms east-southeast of Brazil with a showery tail extending across Brazil. South of the low pressure trough Argentina is dry.
Europe/Western Russia: Widespread wet/cool pattern change later APR
Climate: The east-shifting Madden Julian oscillation across the tropical Atlantic toward the western Indian Ocean the next 1-2 weeks affects the Europe/Western Russia climate. Strong low pressure troughs surge eastward across the north-central North Atlantic bringing above normal precipitation to Western Europe while upstream a warm dry high pressure ridge affects Eastern Europe/Western Russia. Once MJO is locked-in the Indian Ocean in 2+ weeks the North Atlantic upper trough shifts east and weakens the warm pattern.
Week 2 (April 15-21): The North Atlantic storm track is able to shift farther east and affects more of Europe. A cool and wet upper trough affects west/central Europe most of the period not eroding until late week then shifting east into Western Russia and Ukraine. The very warm pattern across Eastern Europe and Western Russia emerging the next 2 weeks fades April 18-21. Dryness could linger in the Black Sea region.
Week 3 (April 22-28): Another wet trough into Europe while a relatively limited upper ridge re-emerges over Western Russia bringing dryness and marginal warmth. There is susceptibility to late season cold air in Central Russia which could back westward. Once again there is lack of compelling evidence to bring wet weather to the Black Sea region.
Week 4 (April 29-May 5): Low confidence. Favoring a wet trough over Southwest/South Europe and dry ridge centered on the Black Sea/Ukraine region.
China: Pattern change, trough to ridge
Climate: A persistent long wave trough has affected eastern Asia climate of late in response to cooling of the Western Pacific SSTA. East-shifting Madden Julian oscillation from the tropical Atlantic to the Indian Ocean brings emergence of an upper ridge over China to northeast Asia in 2 weeks. This pattern lingers into May.
Week 2 (April 15-21): Departing chilly upper trough early period replaced by a significant warm-up mid-to-late week. The warmer pattern brings rain showers along weak cold fronts. So…warmer but on the wetter side.
Week 3 (April 22-28): More widespread warmth and less showery. Strongest anomalous warmth across northeast China.
Week 4 (April 29-May 5): Low confidence. Favoring a dominant upper ridge bringing warmth to most of China, strongest eastern sections,. Dry in eastern sections but turning showery on the back side of the upper ridge in central China.
Australia: The national hot/dry pattern breaks down
Climate: Although Tropical Cyclone Iris is flirting with the Queensland Coast most of Australia is dry. The dryness is linked to presence of the subsidence phase of the Madden Julian oscillation. The MJO shifts east to the Indian Ocean the next 2 weeks increasing the risk of wet climate in Australia. The wet pattern arrives during week 2 in northwest Australia and could affect areas farther east into early May.
Week 2 (April 15-21): Late season warmth and attendant dryness dominates south and east Australia. A late season subtropical storm to the east affects New Zealand. Potential for heavy tropical/subtropical rainfall across northwestern continent.
Week 3 (April 22-28): Most of the continent is warmer than normal due to tropical (MJO) influences. There is presence of wet weather risk centered on northern and central Australia. Dryness continues to affect the southeast Australia drought area. Dryness returns to Western Australia.
Week 4 (April 29-May 5): Low confidence. Favoring a wetter regime across areas that need the rain…eastern half of the continent. Drier climate is across Western Australia.