Synoptic Discussion - October 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.


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 PNA- WPO-, EPO-
October 1-5 PNA-
October 6-10 PNA- AO
October 11-17 WPO- EPO-
Tropical Storm Melissa
October 18-23 WPO+ Tropical Storm Nestor,
Super Typhoon Hagibis
October 24-31 WPO- EPO-
Tropical Storm Olga

The weather was particularly dynamic during October 2019. The month began with a summer-like ridge that set all-time October heat records across the eastern US. It ended with a winter-like surge of cold air along the Rockies that set all-time October records on the cold side. In between, three weak tropical storms brought rain from the Gulf Coast to the Northeast, and energy from a super typhoon in the Pacific helped spur the rapid transition from summer to winter. All the while, a ridge extending southward from the Gulf of Alaska prevented any moisture from alleviating the fire season in the Southwest.

The general pattern in October 2019 with a trough in the West and a ridge over the Southeast is consistent with a negative Pacific/North American (PNA) pattern. The PNA wave train usually traces back to the tropical Pacific, but the pattern during October 2019 was more tied to variations in the Pacific jet associated with fluctuations in the West Pacific Oscillation (WPO) and the East Pacific Oscillation (EPO). Meanwhile, the El Niño-Southern Oscillation (ENSO) remained on the warm side of neutral.

Monthly Mean

Submonthly Evolution

October 1-5

October began with a trough over the northwestern US and a strong ridge over the Southeast. The ridge brought record heat to the Southeast with many locations setting all-time October heat records. The trough was associated with cooler temperatures in the Northwest. A cold front on the east side of that trough brought a plume of moisture from the southern Rockies to the Great Lakes. The resulting rainfall was a primary contributor to the record-wet October for portions of the Great Lakes region.

October 6-10

A cold front swept across the eastern US bring needed relief from the record heat. The northwest remained cooler than average, but otherwise conditions were normal to warmer than normal for most of the CONUS.

October 11-17

The first significant cold air outbreak filtered down the Northern Plains. With it came 1-2 feet of snow over portions of the Northern Rockies. Meanwhile the Northeast experienced a significant nor'easter from the remnants of Tropical Storm Melissa.

October 18-23

Temperatures moderated to near-normal October 18-23. Tropical Storm Nestor made landfall along the Florida Panhandle bringing significant rains to the Southeast. However, the bigger impacts may have come from the remnants Super Typhoon Hagibis. The extratropical transition of this intense storm helped extend the jet stream over the North Pacific. This ultimately enhanced the trough over western Canada and set the stage for major surge of cold air along the Rockies.

October 24-31

Cold air surged southward along the Rockies October 24-31. Many parts of the West set all-time record low temperatures for October during this event. It also brought significant snow from the Rockies to the Midwest. The southern end of the cold front merged with Tropical Storm Olga and the resulting moisture surge contributed to record wet October for portions of the Lower Mississippi Valley.

Atmospheric Drivers

Citing This Report

NOAA National Centers for Environmental Information, State of the Climate: Synoptic Discussion for October 2019, published online November 2019, retrieved on December 11, 2019 from