Synoptic Discussion - June 2019

Note: This Synoptic Discussion describes recent weather events and climate anomalies in relation to the phenomena that cause the weather. These phenomena include the jet stream, fronts and low pressure systems that bring precipitation, high pressure systems that bring dry weather, and the mechanisms which control these features — such as El Niño, La Niña, and other oceanic and atmospheric drivers (PNA, NAO, AO, and others). The report may contain more technical language than other components of the State of the Climate series.


Summary

Indices and their agreement with the temperature, precipitation, and upper-level circulation anomaly patterns, by time period (month, week, or other sub-monthly period).
Time Period Key Driver Other Drivers
Month EP–NP PNA, NAO, AO
June 1–9 EP–NP PNA, NAO
June 10–16 EP–NP PNA, NAO, AO
June 17–23 EP–NP PNA NAO, AO
June 24–30 PNA

The synoptic pattern in June 2019 was dominated by a ridge in the Northeastern Pacific and a trough over the Northern Midwest. The ridge was associated with record heat and dry conditions in Alaska and the West Coast. Meanwhile the trough was associated with severeweather and flooding around the Ohio Valley and Lower Mississippi. The trough was also associated the moderately below normal temperatures across much of CONUS.

The circulation was associated with a series of atmospheric waves extending across the North Pacific, consistent with the positive phase of the East Pacific-North Pacific (EP-NP) pattern. A moderately negative Arctic Oscillation (AO) played a role in reducing the strength of the jet stream and fostering this wavy pattern. Meanwhile, the Pacific–North American (PNA) modulated the pattern, which shifted eastward around June 7 and again around June 23. The moderate El Niño conditions continued over the Pacific Ocean, but their amplitude declined under the influence of an upwelling Kelvin wave. El Niño teleconnections are weaker during the summer, so it is not surprising that they did not really manifest themselves during June 2019.

Monthly Mean

Submonthly Evolution

June 1–9

June began with a propagating pattern. A ridge moved across the northern CONUS from the Pacific Northwest towards the Great Lakes. This ridge produced anomalously hot and dry conditions along the West Coast and the Northern Plains. Meanwhile, a trough moved from the Great Lakes northeastward to the Canadian Maritimes. It brought moderately cooler temperatures to the Northeast and wetter conditions to the Southeast.

June 10–16

The ridge established itself near the coast of Washington and British Columbia around June 10. It produced extreme heat all along the West Coast, including San Francisco experiencing just its second 100°F day in its history. Meanwhile, the downstream trough brought slightly cooler than average temperatures across most of the country east of the Rockies.

June 17–23

The ridge and trough strengthened and moved westward during June 17–23. The West Coast remained warmer than normal, but the heat was tempered by the ridge moving farther off the coast. The trough brought cooler than normal temperatures to the northern and central Rockies, which led to more than a foot of snow to portions of the region. The other side of the trough brought severe weather and flash flooding to Pennsylvania, New Jersey, Ohio, and Illinois.

June 24–30

The trough continued moving westward during the final week of June. It brought relief to the West Coast in the form of cooler than normal temperatures. However, the associated moisture was confined to Washington and Oregon. The southwest remained dry, which is typical during June. A week ridge developed over the Northern Midwest during the final days of the month. It brought hotter than normal temperatures across the region and to the Northeast.

Atmospheric Drivers

Global Linkages

  • The weak El Niño and the MJO combined to delay and weaken the monsoon onset in India.
  • The U.S.-Affiliated Pacific Islands were generally drier than normal during June 2019. Warm SSTs associated with El Niño enhanced rainfall along the equatorial Pacific, while the USAPI affected by the compensating subsidence. One marginal tropical storm, Four, lasted for just two days (June 29–30) in the Philippine Sea northwest of Palau. Tropical Storm Four was notably only in that it was the first tropical storm in the Western North Pacific since Super Typhoon Wutip in late February.
  • The Atlantic had no tropical systems during June. On average, it has a named tropical storm about every other year. The last time the Atlantic had a June tropical storm was 2017, which featured two: Bret and Cindy.
  • The eastern North Pacific finally became active during late June with the development of Hurricanes Alvin and Barbara. Alvin became a tropical storm on June 26, which marked the latest start to the eastern Pacific hurricane season since 1969 (July 2).
  • Central and Eastern Europe experience warmer than normal temperatures. The associated ridge was part of the same wave train that produced the ridge over Greenland and the negative NAO. Much of central and western Europe had a cooler than normal June due to a persistent trough that was part of the negative NAO pattern. However, the European ridge is not a typical feature for the NAO.

Citing This Report

NOAA National Centers for Environmental Information, State of the Climate: Synoptic Discussion for June 2019, published online July 2019, retrieved on July 23, 2019 from https://www.ncdc.noaa.gov/sotc/synoptic/201906.

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