Why Drought Risk is Above Average for the Black Sea/Southwest Russia and Vicinity Regions for the 2020 Warm Season Discussion: Due to climate change (warming polar region) the Greenland ice sheet is melting faster during springtime and the increased runoff/ice melt is spreading a large mass of fresh water into the North Atlantic to the south of Greenland changing the oceanic salinity, blocking the Gulf Stream and causing a general large cool pool of water which is present throughout the year. While this cool pool has become semi-permanent the general trend of the North Atlantic the past 2-3 decades is warming. Climate scientists have coined this persistent cool pool of water as the “North Atlantic Warm Hole.”   Large persistent regions of cool or warm ocean water is also reflected in the upper atmosphere. The persistent cool water south of Greenland has caused the upper air to also cool and a semi-permanent upper trough has formed. During winter the upper trough can break down as the upper air flow is faster. However, during the warm season when the jet stream push eases there is a reliable tendency for an upper trough to drop anchor in-between Greenland and Europe. The atmosphere compensates for that persistent trough by forcing an amplified upper ridge over Europe to Western Russia. Presence of an upper ridge increases the risk of dryness and sometimes drought during the warm season. Making the ridge most effective to produce drought (and attendant heat) is the presence of long-term rainfall/soil moisture deficit. When the upper ridge causes a period of dryness and anomalous heat once summer is underway the anomalous heat is made more effective at drying soils and causing drought or flash drought. This scenario is possible in the Black Sea region during summer 2020. Surrounding areas (Ukraine to Southwest Russia) are also at risk as these regimes have a tendency to expand fairly quickly. Once a region of dryness, anomalous heat and reduced soil moisture has developed a feedback to the atmosphere to amplify the upper ridge occurs and causes increased widening of the drought risk area occurs. Of increased importance during the regime described is both the long and short-term precipitation pattern. Drought is most effectively produced when long-term precipitation deficits are present. If long-term rainfall deficits are present a period (7-10 days) of hot and dry weather during the warm season can cause drought to emerge quickly. In fact, this condition is the signature catalyst to flash drought. The 9-3-1 method of monitoring precipitation is helpful to quickly determine a drought risk area. Of course, short-term precipitation patterns are always most notable for market and operational farming concerns. However, combining that knowledge with the long-term rainfall pattern is required to quickly determine a regional drought risk. The one-month and three-month precipitation rate anomalies across Europe and Western Russia indicate patchy dryness in the Black Sea region and more profound dryness across Italy into far Southeast Europe (especially in the 90-day analysis). The nine-month precipitation rate anomalies identify a large rainfall deficit in Southwest Russia to the Black Sea region. Despite recent precipitation the Black Sea to Southwest Russia region is at risk of returning dry-to-drought conditions if a period of dry and hot weather develops during the warm season. The reason is the long-term precipitation deficit and likely below normal deep layer soil moisture. This condition is also possible in Italy to parts of Southeast Europe although the lack of long-term dryness leaves that region in lower risk. If dryness and anomalous heat develop in the Black Sea/Southwest Russia region during summer and Climate Impact Company is firm on that projection, areas susceptible to expanding drought are westward to Poland possibly reaching Germany. Climate Impact Company operational forecasts (issued shortly) reveal the timing of events. Fig. 1: The North Atlantic Warm Hole is vividly present in the late March global SSTA analysis. Fig. 2: The NCEP CFS V2 maintains the NAWH for JUN/JUL/AUG 2020. Fig. 3-4: Optimum climate normal (OCN) is a short-term (5 or 10 year) climatology different from the conventional 30-year climatology. Due to the evolution of the NAWH an OCN is an essential component to Europe/Russia climate forecasts especially during the MAY-SEP warm season. Note the persistent NAWH-inspired trough and downstream ridge (over Eastern Europe) which on average has been the summertime climate pattern for this region during the past decade (returning in 2020). The upper ridge increases the risk of dry climate and hot weather. Fig. 5-7: Precipitation rate anomalies provided by NCDC/PSD are used to determine short, medium and long-term precipitation shortages which help to identify potential summertime drought areas.

Coastal Gulf of Mexico drought and early season heat risk Potential for excessive rainfall events in summer Potential for rapidly intensifying tropical cyclones Sea height rise Fig. 1: The daily sea surface temperature anomaly (SSTA) analysis across the Gulf of Mexico indicates possible record results for late March. Analysis: The Gulf of Mexico has attained what may be the warmest surface temperatures anomalies on record for late March (Fig. 1). The regional sea surface temperature anomalies (SSTA) is a whopping +1.79C which includes widespread +3C to +5C anomalies across the northern and eastern Gulf of Mexico. The primary contributor to the warming is a strengthening subtropical high pressure area present across the Gulf of Mexico since early winter (Fig. 2) although particularly intense the past 30 days (Fig. 3). The strengthening subtropical ridge in recent weeks has caused a generally cloud-free weather regime as the early spring sun strengthens causing the rapid warming. Climate effects include the persistent very warm bias to the Southeast and East U.S. and more recently the rapid drying of soil moisture in each Gulf of Mexico state near the coast (Fig. 4). The warm Gulf surface implies exceptional low atmospheric available moisture. In-between the warm Gulf States climate and the colder regime to the north an intense storm track has emerged this mid-to-late winter and early spring season as deep abundant moisture from the Gulf has enhanced the storm track causing frequent flooding events from the Mid-South U.S. to the Tennessee Valley and into the Interior Southeast States (Fig. 5). Warm SSTA also imply sea level rise. NOAA analysis indicates a sea level rise of 10-15 CM (4-6 in.) across the north and east Gulf of Mexico (Fig. 6). Implications: Natural is the emergence of the subtropical ridge across very warm waters of the Gulf of Mexico and western North Atlantic basin compared to the mean upper trough over the much colder wintertime continent to the north. However, as the continent warms with the arrival of summertime the subtropical ridge may have a tendency to also shift north. The warm Gulf of Mexico flips purpose as an enhancing warm climate feature to a potential heavy rainfall catalyst. However, until the pattern-flip the Gulf Coast continues to dry and risk of mid-to-late spring unusual heat continues. Once the wet influence on the coastal Gulf of Mexico emerges the character of the precipitation is convective, i.e. hit-and-miss. Gully-washer thunderstorms dropping substantial rainfall can occur while other areas stay dry. So the expected heavy rainfall once the warm season arrives is patchy and not widespread. Of course, the primary concern is significant upper ocean heat to cause tropical cyclones to intensify rapidly. The 2020 North Atlantic basin tropical cyclone season is likely very active due to the warm SSTA pattern in the North Atlantic and an ENSO pattern that is neutral or possibly a weak La Nina. The Gulf of Mexico will be susceptible to unusually strong tropical cyclones if the warm SSTA pattern holds (as forecast by most models). Finally, the unusual warm SSTA implies rising sea level as already described. Strong onshore wind will bring unexpected flooding spring into summer while flooding associated with tropical cyclone activity approaching/crossing the coast will be made more severe by the already rising Gulf surface. Regions of warm SSTA are catalysts to unusual climate regimes and high impact weather to the affected communities. Fig. 2-3: The 90-day and 30-day 500 MB anomalies identify a strong subtropical ridge across the Gulf of Mexico intensifying in March. Fig. 4: The subtropical ridge across the Gulf of Mexico is drying coastal soils. Fig. 5-6: The 90-day precipitation anomalies by NOAA/CPC identifies the dry influence of the subtropical ridge on the Gulf Coast while to the north entrainment of abundant Gulf moisture into the prevailing storm track has caused excessive rainfall. The warm SSTA in the Gulf has caused 10-15 CM sea-height rise according to NOAA/CPC.