November 2016 Synoptic Discussion

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

The atmosphere was in a La Niña state during November 2016. Like the previous three months, the weather over the contiguous United States (CONUS) this month was dominated by a complex interplay between subtropical high pressure systems and jet stream weather systems. Troughs and lows in the jet stream flow dragged cold fronts and surface lows across the CONUS. These weather systems brought precipitation to much of the country. But jet stream ridges and the continuing influence of the subtropical highs kept precipitation amounts below normal in most areas. They also gave most of the CONUS warmer to much warmer than normal temperatures. The fronts and upper-level troughs provided the dynamics that triggered severe weather, but mostly in the Southeast and Midwest and mostly near the end of the month. Drought expanded in the Plains to East Coast, and contracted across parts of the West, Southern Plains, and eastern Great Lakes, with the overall national drought footprint expanding to about 31.5 percent of the CONUS. The upper-level circulation, temperature, and precipitation anomaly patterns suggested the atmospheric drivers originating in the Pacific Ocean had the greatest influence on the month's weather. See below for details.

Synoptic Discussion

Animation of daily upper-level circulation for the month.

Animation of daily surface fronts and pressure systems for the month.

In the Northern Hemisphere, November is the last month of climatological fall (autumn) which is the time of year when solar heating decreases as the sun angle decreases, and an expanding circumpolar vortex forces the jet stream to migrate southward. Polar air masses begin to influence the weather over the contiguous U.S. (CONUS) more, and the warm, dry subtropical high pressure belts influence the weather less.

The mid-latitude circulation continued to be very active during November 2016, with numerous troughs and ridges moving in the jet stream flow. But high pressure generally dominated the CONUS, manifested by interactions between the subtropical highs and ridges in the jet stream. Deep troughs and cutoff lows occasionally plunged southward, dragging cold fronts and surface lows with them. These weather systems generated precipitation, but amounts were generally below normal except along the immediate West Coast and in parts of the Southwest, Southern Plains, and Northern Plains. As the fronts moved across the eastern CONUS, the Bermuda High weakened them and starved them of moisture. Several states in the East had the twelfth driest, or drier, November in the 1895-2016 historical record, including Florida with its driest November on record.

During the second half of the month, the air behind some of the fronts was cold enough to generate blankets of snow across parts of the Northern Plains and Northeast, with 15 percent of the CONUS snow-covered beginning on November 18^th. A strong trough dove into the central CONUS near the end of the month. The low pressure system with it increased the snow coverage to 26 percent of the CONUS by November 30^th. But in spite of the late-month snow, the monthly snow cover was still below average, ranking November 2016 as the 19^th smallest November (in terms of snow cover area) in the 51-year satellite record for the CONUS.

The trough at the end of the month also sent a strong cold front charging into the Southeast, whose strength was enough to break the influence of the Bermuda High. Tapping into Gulf of Mexico moisture, the front brought significant rain to much of the Southeast drought area (weeks 1, 2, 3, 4, 5), but it was not enough to overcome deficits which had built up during the month. The frontal lifting and upper-level dynamical support, however, was strong enough to trigger severe weather. According to preliminary reports, 69 tornadoes occurred in November 2016, which is a little more than the November average of 58. Most of the tornadoes and other severe weather occurred in the Midwest and Southeast in association with the front and low pressure system near the end of the month.

The persistence of the subtropical highs and jet stream ridges gave most of the CONUS a much warmer-than-normal month, with November 2016 ranking nationally as the second warmest November in the 1895-2016 record. Twenty-five states had their tenth warmest, or warmer, November on record, including three (Idaho, North Dakota, and Washington) which ranked warmest on record. There were 7,491 record warm daily high (4,537) and low (2,954) temperature records. This was more than 40 times the 181 record cold daily high (87) and low (94) temperature records that were associated with the air masses behind the cold fronts. The REDTI (Residential Energy Demand Temperature Index) for November 2016 ranked third lowest in the 122-year record for November, due to much-warmer-than-normal temperatures across most of the country which decreased heating demand. The REDTI for September-November 2016 ranked second lowest for the fall for the same reason.

The continued dry conditions, coupled with the abnormally high temperatures which enhanced evapotranspiration, resulted in expansion and intensification of drought and abnormal dryness across the Central Plains, Northeast, and much of the Southeast to Ohio and Mississippi Valleys. Drought contracted a bit in parts of the West, Texas, and western New York. The net effect was an increase in the national moderate-to-exceptional drought footprint from 26.8 percent at the end of October to 31.5 percent at the end of November (from 22.4 percent to 26.3 percent for all of the U.S.). The prolonged drought set the stage for a conflagration. November began with a handful of large wildfires burning in the West and about ten in the Southeast (wildfire maps for November 1, 5, 9, 15, 20, 27, 30). As dry and warmer-than-normal weather continued in the Southeast, the number of large wildfires rapidly increased to nearly five dozen by November 9^th. Some three dozen continued in the Southeast as the month wore on, decreasing to about 20 by the end of the month after beneficial rains moved across the region.

La Niña conditions existed during November and La Niña conditions are typically associated with drier-than-normal weather over the CONUS. La Niña also typically suppresses hurricane activity in the central and eastern Pacific basins, and enhances it in the Atlantic basin. One named storm, Otto, which became a hurricane, formed in the Atlantic basin in November. One named storm, Tropical Storm Tina, formed in the eastern North Pacific basin in November. Tina moved away from Mexico in the easterly trade winds before quickly dissipating. In addition, Tropical Storm Otto moved into the basin from the North Atlantic basin in November. There were no tropical cyclones in the central North Pacific during November 2016. In the western North Pacific, several tropical systems developed in or near the U.S. Affiliated Pacific Islands in Micronesia. These include Meari (which eventually became a typhoon), Ma-on and Tokage (which eventually became tropical storms), and a couple tropical disturbances which did not develop into tropical cyclones.

The Climate Extremes Index (CEI) aggregates temperature and precipitation extremes across space and time. Temperature and precipitation extremes occurred during the month in many areas; four regions had a CEI that ranked in the top ten category, with a couple others close (ranking in the top 20 category). The East North Central region had its second most extreme November CEI in the 1910-2016 record due to the most extreme warm minimum and warm maximum temperature components and sixth most extreme wet spell component. The West North Central region had its third most extreme November CEI in the 1910-2016 record due to the most extreme warm minimum and second most extreme warm maximum temperature components, and fourth most extreme 1-day precipitation component. The South region had its fifth most extreme November CEI in the 1910-2016 record due to the second most extreme warm maximum and fourth most extreme warm minimum temperature components. The Northwest region had its ninth most extreme November CEI in the 1910-2016 record due to the most extreme warm minimum and third most extreme warm maximum temperature components, and 17^th most extreme days with precipitation component. When aggregated across the nation, November 2016 had the most extreme warm minimum and second most extreme warm maximum temperature components, resulting in the seventh most extreme November CEI in the 107-year record (which includes the tropical cyclone indicator) (it was the third most extreme November CEI if the tropical cyclone component is not included).

North America monthly upper-level circulation pattern and anomalies. The upper-level circulation pattern, averaged for the month, consisted of above-normal upper-level (500-mb) height anomalies over most of the CONUS and Canada, resulting from ridges frequently moving across the continent, and below-normal height anomalies over the northeast North Pacific adjacent to the North American coast. The below-normal heights reflected frequent troughs deepening as they moved through a strong storm track in the westerly flow extending across the North Pacific. Of the circulation indices usually discussed on this page, the teleconnections aggregated for a negative EP-NP and positive WP most closely match the November 2016 500-mb circulation anomalies.

Map of monthly precipitation anomalies. November was wetter than normal across Puerto Rico, the Alaska panhandle, and the parts of the Northern Plains and Southwest and adjacent Southern Plains in the CONUS. It was drier than normal across Hawaii, most of Alaska, and much of the CONUS, especially the Southeast.

Map of monthly temperature anomalies. November was much warmer than normal across most of the CONUS, with only parts of the coast from Florida to Virginia near to below normal. Most of Alaska near to warmer than normal.

Northern Hemisphere monthly upper-level circulation pattern and anomalies. Global Linkages: The upper-level (500-mb) circulation anomaly pattern over North America was part of a complex long-wave pattern that stretched across the Northern Hemisphere. It was difficult to discern trough/ridge couplets. East-west couplets could be seen over the North Pacific-North America-North Atlantic sector (trough or below-normal heights over the North Pacific, western North Atlantic, and even southwest Europe, and ridge or above-normal heights over North America and much of the North Atlantic). One might also conjecture that the below-normal heights over central to eastern Asia are coupled to the above-normal heights over the Arctic Ocean to the north and above-normal heights to the south over southern Asia and the central North Pacific. The above-normal 500-mb heights were associated with upper-level ridging at the mid-latitudes, below-normal precipitation (in parts of Asia and North America), below-normal snow cover (over North America and the Himalayas), and above-normal surface temperatures over North America and southern Asia and the oceans. The areas of below-normal 500-mb heights were associated with upper-level troughing, near- to below-normal surface temperatures over Asia and the North Pacific, and above-normal precipitation and snow cover over Asia. With the Americas and Africa having warmer-than-normal temperatures, and large portions of the Atlantic and Pacific Oceans having warmer-than-normal sea surface temperatures, the November 2016 global temperature was above normal, but the cooler-than-normal temperatures over much of Asia and parts of the Pacific had a moderating effect.

Atmospheric Drivers

Subtropical highs, and fronts and low pressure systems moving in the mid-latitude storm track flow, are influenced by the broadscale atmospheric circulation. The circulation of the atmosphere can be analyzed and categorized into specific patterns. The Tropics, especially the equatorial Pacific Ocean, provides abundant heat energy which largely drives the world's atmospheric and oceanic circulation. The following describes several of these modes or patterns of the atmospheric circulation, their drivers, the temperature and precipitation patterns (or teleconnections) associated with them, and their index values this month:

• El Niño Southern Oscillation (ENSO)
  • Description: Oceanic and atmospheric conditions in the tropical Pacific Ocean can influence weather across the globe. ENSO is characterized by two extreme modes: El Niño (warmer-than-normal sea surface temperature [SST] anomalies in the tropical Pacific) and La Niña (cooler-than-normal SST anomalies), with the absence of either of these modes termed "ENSO-neutral" conditions.
  • Status: During November 2016, La Niña conditions were present with below average equatorial SSTs in the central and east-central equatorial Pacific.
  • Teleconnections (influence on weather): To the extent teleconnections are known, the typical temperature and precipitation patterns associated with La Niña during November include above-normal precipitation in northern California and most of the Pacific Northwest; below-normal precipitation across the Southwest and most of the CONUS east of the Rockies; above-normal temperatures across the Great Plains and parts of the West; and below-normal temperatures over Florida.
  • Comparison to Observed: The November 2016 temperature and precipitation anomaly patterns agree with those expected with La Niña, except for precipitation in the Southwest.
• Madden-Julian Oscillation (MJO)
  • Description: The MJO is a tropical disturbance or "wave" that propagates eastward around the global tropics with a cycle on the order of 30-60 days. It is characterized by regions of enhanced and suppressed tropical rainfall. One of its indices is a phase diagram which illustrates the phase (1-8) and amplitude of the MJO on a daily basis. The MJO is categorized into eight "phases" depending on the pattern of the location and intensity of the regions of enhanced and suppressed tropical rainfall. The MJO can enter periods of little or no activity, when it becomes neutral or incoherent and has little influence on the weather. Overall, the MJO tends to be most active during ENSO-neutral years, and is often absent during moderate-to-strong El Niño and La Niña episodes.
  • Status: The MJO index began the month incoherent but quickly progressed through phases 5 to 8, then phases 1 to 3. Some of these phases interfered destructively with the low-frequency background state (i.e., reduced the influence of La Niña over the CONUS). Other modes of coherent subseasonal tropical variability influenced the tropical Pacific and global climate, including a pair of Kelvin waves (MJO updates for November 7, 14, 21, and 28).
  • Teleconnections (influence on weather): The MJO's temperature and precipitation teleconnections to U.S. weather depend on time of year and MJO phase. To the extent teleconnections are known, the November (October-December) teleconnections for temperature are shown here and for precipitation are shown here.
  • Comparison to Observed: The MJO is transitory and can change phases (modes) within a month, so it is more closely related to weekly weather patterns than monthly. In the case of November 2016, the MJO index rapidly transitioned through seven phases (phases 5-8 then 1-3). The monthly temperature and precipitation anomaly patterns, and their corresponding weekly anomaly patterns, show little similarity for the teleconnections expected with the MJO phases.
• The Pacific/North American (PNA) pattern
  • Description: The PNA teleconnection pattern is associated with strong fluctuations in the strength and location of the East Asian jet stream. PNA-related blocking of the jet stream flow in the Pacific can affect weather downstream over North America, especially the West and especially in the winter half of the year.
  • Status: The daily PNA index was positive for the first half of the month, then finished the month out as neutral (near zero), but averaged positive for the month as a whole. The 3-month-averaged index was also positive.
  • Teleconnections (influence on weather): To the extent teleconnections are known, a positive PNA for this time of year (October on the quarterly teleconnection maps) is associated with above-normal temperatures in Alaska and western Canada extending down the west coast of the CONUS; below-normal temperature anomalies in the southern Plains to Southeast; above-normal upper-level circulation anomalies across western North America; and below-normal upper-level circulation anomalies across the Southern Plains to Southeast and Gulf of Mexico. There are few precipitation teleconnections, but below-normal precipitation is suggested over the Great Lakes.
  • Comparison to Observed: The November 2016 temperature and upper-level circulation anomaly patterns show little agreement to those expected with a positive PNA. The precipitation anomaly pattern has little to compare to (few correlations over the CONUS) but it agrees where there are correlations over the Great Lakes.
• The Arctic Oscillation (AO) pattern
  • Description: The AO teleconnection pattern relates upper-level circulation over the Arctic to circulation features over the Northern Hemisphere mid-latitudes and is most active during the cold season.
  • Status: The daily AO index oscillated between negative and positive during the month, averaging negative for the month. The 3-month-averaged index was slightly negative.
  • Teleconnections (influence on weather): To the extent teleconnections are known, a negative AO in November (October-December in the AO Composites table) is typically associated with areas of dryness from the Southern Plains to Southeast; scattered wet conditions in northern California and New England; below-normal temperatures from the Northern Plains to the Southeast and Northeast; and upper-level circulation anomalies which are above normal across the Arctic, Alaska, and Greenland, and below normal across the much of the North Pacific and across eastern North America into the North Atlantic.
  • Comparison to Observed: The November 2016 upper-level circulation anomaly pattern agrees with that expected with a negative AO over the Arctic Ocean and North Pacific but not over North America, Alaska, and the North Atlantic. The November 2016 monthly temperature anomaly pattern is opposite that expected with a negative AO. The precipitation anomaly pattern agrees from the Southern Plains to Southeast.
• The North Atlantic Oscillation (NAO) pattern
  • Description: The NAO teleconnection pattern relates upper-level circulation over the North Atlantic Ocean to circulation features over the Northern Hemisphere mid-latitudes.
  • Status: The daily NAO index was mostly near zero to slightly positive, averaging near zero (neutral) for the month. The 3-month-averaged index was slightly positive.
  • Teleconnections (influence on weather): There are no teleconnections for a neutral NAO.
• The West Pacific (WP) pattern
  • Description: The WP teleconnection pattern is a primary mode of low-frequency variability over the North Pacific and reflects zonal and meridional variations in the location and intensity of the (East Asian) jet stream in the western Pacific.
  • Status: The monthly WP index and three-month average WP index were both positive.
  • Teleconnections (influence on weather): To the extent teleconnections are known, a positive WP during November (October on the quarterly teleconnection maps) is typically associated with above-normal temperatures across the Central and Northern Plains to Upper Midwest; below-normal precipitation in the Pacific Northwest, Upper Midwest, and Deep South; above-normal circulation anomalies over central Canada to the north central CONUS and across the western North Pacific; and below-normal circulation anomalies over the eastern North Pacific off the U.S. coast and over eastern Siberia.
  • Comparison to Observed: The November 2016 monthly upper-level circulation anomaly pattern agrees across much of the Northern Hemisphere where teleconnections exist. The temperature anomaly pattern agrees where teleconnections exist. The precipitation anomaly pattern agrees where teleconnections exist, except over Minnesota.
• The East Pacific-North Pacific (EP-NP) pattern
  • Description: The EP-NP teleconnection pattern relates SST and upper-level circulation patterns (geopotential height anomalies) over the eastern and northern Pacific to temperature, precipitation, and circulation anomalies downstream over North America. Its influence during the winter is not as strong as during the other three seasons.
  • Status: The North Pacific SSTs continued to cool in the central North Pacific, and cooled in parts of the eastern North Pacific adjacent to the North American coast. The net result was a SST anomaly pattern consisting of cooler-than-normal SST anomalies between 40 and 50 degrees North latitude that stretched from Asia almost to the North American coast. SSTs were warmer than normal north and south of this cool area. The SST anomalies next to the North American coast were still warmer than normal, but not as warm as the previous month. Sea level pressure and upper-level height anomalies were below normal across the North Pacific from the Sea of Okhotsk to the U.S. Pacific Northwest coast, reflecting the frequent occurrence of low pressure systems which comprised the storm track. Sea level pressure anomalies were above normal over the southern CONUS, reflecting the continuing influence of the subtropical highs (North Pacific and North Atlantic Highs). The November 2016 monthly EP-NP index and 3-month running mean were both negative.
  • Teleconnections (influence on weather): To the extent teleconnections are known, a negative EP-NP index during November (October on the quarterly teleconnection maps) is typically associated with warmer-than-normal temperatures across the CONUS from the Great Plains to East Coast; colder-than-normal temperatures along the West Coast and over western Alaska; below-normal upper-level circulation anomalies (weaker upper-level ridge) over Alaska and western Canada; and above-normal upper-level circulation anomalies across eastern North America (weaker upper-level trough) and over the central North Pacific. The precipitation teleconnections are weak but show above-normal precipitation in the Pacific Northwest.
  • Comparison to Observed: The November 2016 temperature and upper-level circulation anomaly patterns match those expected with a negative EP-NP over North America very well, except they are shifted slightly to the west. In fact, the upper-level circulation anomaly pattern over the North Pacific matches the teleconnection pattern, with a slight shift in latitude. The precipitation anomaly pattern has few teleconnections to compare to, but agrees along the coast in the Pacific Northwest.

Examination of the available circulation indices and their teleconnection patterns, and comparison to observed November 2016 temperature, precipitation, and circulation anomaly patterns, suggest that the weather over the CONUS in November was traced mostly to atmospheric drivers originating over the North Pacific Ocean, with possibly some influence from the equatorial Pacific. The MJO transitioned through phases quickly during the month with little agreement to the observed anomaly patterns. The temperature and circulation anomaly patterns were not consistent with those expected with the PNA, NAO, and AO drivers. There was some agreement in the observed precipitation anomaly pattern and those expected with the PNA and AO in a few places, but that could have been a coincidence. The circulation anomaly teleconnection patterns for the EP-NP and WP, and the temperature anomaly teleconnection patterns for the EP-NP, WP, and La Niña, match the observed anomalies very well, especially when they are aggregated. The precipitation anomaly pattern matches the teleconnections for La Niña in most areas. There is some agreement with the teleconnections for the other indices (WP and EP-NP), but most have few precipitation teleconnections and the agreement may be simple coincidence.

This month illustrates how the weather and climate anomaly patterns can be strongly influenced by atmospheric drivers (or modes of atmospheric variability) originating in the Pacific Ocean, with the Bermuda and North Pacific subtropical highs continuing to play an important role.

Citing This Report

Metadata