Watching The Great Plains, Europe and Western Russia For Possible Summer Drought

Highlight: Doubting a U.S. Corn Belt drought, Europe/Western Russia drought risk is uncertain, Australia and Northern Brazil go wetter.

Fig. 1: The NOAA/CPC soil moisture ranking percentile valid June 2020 with Climate Impact Company annotated 3-month trend.

Observation discussion: In the U.S. dryness continues to emerge across the Great Plains particularly centered on the west/southwest sections due to an emerging area of mean high pressure centered on Ontario during late spring. More recently an upper trough across the Interior Northwest has caused a wet soil moisture trend. Late spring rains caused a wet soil moisture trend in the Carolinas.

In Europe a previously feared zone for possible drought in summer 2020…Eastern Europe to the Black Sea region lost much of its end of winter dry soil moisture signature due to spring rains. U.K. to France trend drier and parts of France and Germany have dry soil moisture conditions.

Farther to the east a dominant hot high pressure has caused substantial drying of soil moisture conditions in central Asia. Dry soils worsened beneath record-strength high pressure (and attendant heat) in northeast Russia.

During late spring the Madden Julian oscillation (MJO) became near-stationary over the warmer-than-normal waters of the western tropical Indian Ocean. The result was an early wet monsoon flow causing wetter soil moisture trend in parts of India arcing northeastward across China.

A tendency for a wetter climate in Indonesia usually occurs if ENSO trends toward La Nina which helps to explain the wetter soil moisture trend in that region. La Nina has not formed yet but a La Nina Watch has been issued by the Australia Bureau of Meteorology.

The warm bias in the western tropical Indian Ocean and no La Nina (yet) leaves the Australian climate mostly dry (again). Soil moisture trend is sharply drier across Queensland and Southwest Australia.

Quasi-stationary MJO in the western Indian Ocean during June lead to stronger-than-normal tropical waves across tropical/subtropical Africa where wetter soils emerged. The west-traveling tropical waves into the tropical North Atlantic were defeated from further tropical development by stronger than normal northeast to southwest Saharan Dust trajectories into the eastern tropical North Atlantic.

In South America the southern portion of the long-standing Chilean drought eased. To the east, central Argentina drought conditions also dissipated. Drought remains in much of Brazil although the western Amazon Basin trended much wetter.

Fig. 2: The June 2020 global SSTA analysis and annotated key features.

Fig. 3: The ECMWF global SSTA forecast for September 2020.

Global SSTA discussion: The ECMWF global SSTA forecast offers some very interesting transitions from the June 2020 analysis to the September 2020 projection. First (and foremost) a weak La Nina develops. During the northern hemisphere warm season a La Nina causes a wet climate across India, Indonesia and northern South America while in the southern hemisphere a warm climate develops in eastern Australia and dryness persists in Argentina. If La Nina lasts through DEC/JAN/FEB a dry climate emerges in the southern U.S. while the Ohio Valley and Pacific Northwest are wet. Northern Brazil turns wet and the Indonesia wet pattern expands to northeast/east Australia.

The La Nina is forecast by most models. HOWEVER, the typical coinciding cool phase of the Pacific decadal oscillation is not forecast. The La Nina outlook is NOT confident.

Another “curve ball” is evolution of negative Indian Ocean Dipole (-IOD) by the ECMWF whereas Australia Bureau of Meteorology indicates neutral phase. The –IOD pattern offers a wet climate into the spring season for western and southern Australia (and they’ll need that rainfall). The IOD forecast must be monitored closely the next couple months.

Notice that ECMWF does not warm the North Atlantic. The Atlantic multi-decadal oscillation (AMO) is marginally positive and the North Atlantic warm hole (NAWH) south of Greenland is dominant. If the North Atlantic does not warm-up (compared to normal) the next 2-3 months the very buoyant tropical cyclone season forecast for the North Atlantic will under-perform and the current tendency for drier soil moisture across and in the vicinity of the U.S. Corn Belt will ease (or reverse).

While the North Atlantic does not look that warm in September according to ECMWF the north/northeast Pacific is very warm as another “warm blob” is forecast. The “warm blob” is a large area of very warm surface and subsurface water first noticed in the northeast Pacific in 2013 and occasionally redeveloping in following years including 2020 according to ECMWF. This forecast supports an upper ridge pattern over Alaska and possibly western North America with a downstream trough across the East-central U.S. for late summer. The result is a bad fire season in the West while North Atlantic tropical cyclones may approach the East Coast then veer north or northeast missing the coast.

Forecast discussion: The outlook is mostly dependent on the ECMWF global SSTA forecast. The forecast anomalies indicated are reasonably confident. If confidence is not reasonable no forecast is made (in Europe and Western Russia, for example). The North America outlook is reasonably confident that western North America will trend somewhat drier the next several months. The Caribbean and northern South America are soaked by tropical events. Across the Central and East U.S. there is a lack of compelling evidence to support evolution of drought.

As previously mentioned the Europe/Western Russia precipitation forecast is not compelling wet or dry to forecast a dramatic soil moisture change. The “gut” forecast is for evolution of an upper ridge across Europe toward Black Sea, to the east of the upper trough across the NAWH in the North Atlantic to cause an AUG/SEP hot/dry “scare” for crops.

In South America a wet climate (possible flooding) is likely for southern Argentina while the central Chile drought re-intensifies and central/southeast Brazil drought continues. The La Nina signature promises wet climate across northern South America.

The trend toward –IOD (low confidence) favors a wetter scenario for Australia, drier climate in tropical Africa and a sustained wet pattern in Indonesia spreading to Southeast Asia.

The wetter trend in northern Russia is late in the 3-month forecast period. Additionally, the drier trend in the Middle East is for late in the period.

Fig. 4: The NOAA/CPC soil moisture ranking percentile valid June 2020 with Climate Impact Company annotated 3-month forecast.