One of the most persistent climate features GLOBALLY during the past several months has been a strong cold upper trough anchored over northwest Russia. Previously, the cold upper trough stretched out across most of Russia late last year sustained by deep snow cover. As the cold season began last year a series of stratospheric warming events lead to the evolution of arctic air and attendant snows. Aloft the air grew colder (causing the persistent trough). During later winter and spring the trough shifted north to northwest Russia but has remained strong. Interestingly, the trough pattern replaces an immense upper ridge pattern that dominated most of 2016 and caused intensifying Central and Northwest Russia drought.
Russian wheat growing areas have been on the southern periphery of the weather extremes caused by the semi-permanent trough pattern much of late last year and into winter. During April and through mid-May precipitation has averaged DRIER THAN NORMAL across most of Ukraine while WETTER THAN NORMAL climate has persisted farther south across Bulgaria and Romania (Fig. 1). Georgia and areas just north of Georgia have been DRIER THAN NORMAL the past 6 weeks. (There are conflicting [precipitation] reports). Occasional cold pulses have affected Russian wheat due to the proximity of the persistent chill beneath the upper trough to the north (Fig. 2). In summary, much of the wheat growing areas have seen volatile temperature featuring cold periods after a mostly mild late winter while precipitation has favored the dry side.
Fig. 1 and 2: Precipitation rate anomalies across Southwest Russia/Black Sea region April 1-May 17, 2017 (left). Temperature anomalies for the same timeframe (right).
According to CWG calculations, the Eastern Europe/Western Russia forecast skill for the 15-day forecast during spring is best when using the ECMWF ensemble (ECM ENS) model. Therefore the 15-day forecast commentary is based on that model. Persistence wins out through the next 5 days as the upper trough anchored over northwest/north-central Russia ejects energy into the Black Sea region to cause more cold and rain showers. Heaviest rain is in Georgia. In the 6-10 day period the upper trough weakens briefly and is replaced by another less potent trough centered on Ukraine for later next week/weekend. Temperatures are near to cooler than normal in the 6-10 day period for Southwest Russia, Ukraine and the Black Sea region eastward while is near normal except heavy rains for Romania to Central Ukraine. Finally, in the 11-15 day period the ECM ENS indicates drier and slightly warmer weather as the upper trough is displaced farther north. Other models such as the GFS operational (GFS OP) bring the cold and wet trough back into the Black Sea region. In the 11-15 day period expect some improvement in the weather but with low forecast confidence. In summary, more of the same – intermittent cool and wet periods with no anomalous warmth.
In the extended-range for the middle third of June a pattern change is forecast by ECMWF. The NCEP CFS V2 is in agreement. An emerging upper ridge over South-Central Europe evolves June 5-12 and amplifies June 12-19 (Fig. 3) to cover most of Europe to Ukraine. Warm to hot and dry weather forms across southwest and south-central Europe. To the east in the Russian wheat territory the persistent upper trough pattern fades in early June allowing some warming and drying followed by the return of a weak trough during mid-June promoting more showers. In summary, week 3 and 4 ahead could turn hot and dry in Europe but Southwest Russia, Ukraine and the Black Sea region miss the heat.
A low confidence forecast projects the hot and dry ridge predicted by Climate Impact Company to evolve over Ukraine this summer season arriving in late June/early July (Fig. 4)!
Fig. 3-4: A 500 MB ridge pattern settles over Central Europe June 12-19 (left) expanding to Southwest Russia/Black Sea region in late June.
