Pattern drivers

Climate Teleconnections

Large-scale atmospheric and oceanic patterns that modulate U.S. weather on sub-seasonal to decadal timescales. Current index charts sourced directly from NOAA/CPC.

Index Interactions

Indices rarely act in isolation. When two or more patterns align in the same direction, confidence in the forecast outcome rises — reinforcing signals are the foundation of the Pattern Regime panel below.

NAO + AO

Both negative: deep high-latitude blocking, Arctic air spills into the eastern U.S. and Europe — the canonical cold-outbreak pattern.

PNA + EPO

Positive PNA with negative EPO locks in a persistent western ridge and eastern trough, amplifying cold and storminess east of the Rockies.

ENSO + PDO

Same-sign ENSO and PDO reinforce each other's temperature and precipitation impacts; opposing signs dampen them.

MJO + AO/NAO

Phase 4–6 MJO can erode polar vortex stability and reinforce negative AO/NAO, deepening cold-air intrusions 1–3 weeks later.

How to use these indices

Reading the indices

Each index is a standardized value representing the current phase of a large-scale atmospheric or oceanic pattern. Positive and negative phases have characteristic impacts on temperature, precipitation, and storm-track position across North America. Combine several indices for a fuller picture of the pattern regime.

Warm above-avg temperatureCool below-avg temperatureWet above-avg precipitationDry below-avg precipitationVariable mixed / region-dependentNormal near-normal

Pattern Regime

Quick Presets

Polar vortex phase

About the vortex

Optional. Click a phase to include it in the synthesis below; click it again to unset.

No phases set — select a preset above or use the / toggles on the index cards below.

Historical analogs

Pattern Archive

Past winters and the index phases that characterized them. Load one into the Pattern Regime panel to see how its synthesis reads.

2009–10

El Niño with record-negative NAO and AO blocking; cold, snowy mid-Atlantic.

ENSO · El Niño
NAO · Negative
AO · Negative

2010–11

Moderate-to-strong La Niña with a blocked high-latitude pattern; snowy Northeast and Great Lakes.

ENSO · La Niña
PDO · Negative
NAO · Negative
AO · Negative

2013–14

ENSO-neutral with a western ridge and eastern trough; repeated polar vortex outbreaks.

ENSO · Neutral
PDO · Positive
PNA · Positive
EPO · Negative

2015–16

Very strong El Niño with positive AO and NAO; mild across the northern tier.

ENSO · El Niño
PDO · Positive
AO · Positive
NAO · Positive

2022–23

Third-year La Niña with negative PDO; wet Pacific Northwest, drier South.

ENSO · La Niña
PDO · Negative

Phases are approximate winter-average classifications; verify against CPC and NCEI archives.

Polar view of the Northern Hemisphere showing swirling polar vortex flow over the Arctic

Stratospheric driver

The Stratospheric Polar Vortex

A large band of strong westerly winds circling the Arctic stratosphere, roughly 10 to 50 km up. It spins up each autumn, peaks in midwinter and breaks down in spring. When it weakens, the disturbance can propagate downward over the following 1 to 6 weeks and shift the tropospheric pattern, often favoring a negative AO and NAO.

Illustrative polar view of the Arctic vortex.

Vortex phases

Strong and stable

Cold, tight and circular, centered over the pole with fast westerlies.

Cold air stays locked in the Arctic. Favors a positive AO and NAO, a fast zonal flow and milder conditions across much of the northern U.S. and Europe.

Weakened or displaced

Slowed westerlies; the vortex is stretched, shifted off the pole or elongated.

Raises odds of a wavier jet and high-latitude blocking. Cold outbreaks become more likely in parts of North America or Eurasia, depending on where the vortex shifts.

Sudden stratospheric warming

Rapid stratospheric warming of 25°C or more in days; winds at 60°N reverse to easterly. The vortex may split in two or be displaced.

The most disruptive phase. Often followed within weeks by a negative AO and NAO and a higher chance of widespread Arctic outbreaks, though the result is not guaranteed.

Final warming

The seasonal spring breakdown, when stratospheric winds turn easterly for the summer.

A normal transition, not a cold-air event. An early or late final warming can still influence spring patterns.

How it is tracked

Forecasters watch the zonal-mean zonal wind at 60°N and 10 hPa. Westerlies reversing to easterlies define a major sudden stratospheric warming.

CPC Stratosphere Products

Stratospheric influence is one factor among many; combine it with the QBO, AO and NAO above.

Right now

Current Vortex Status

Current state

Weakened or displaced

Slowed westerlies; the vortex is stretched, shifted off the pole or elongated.

CPC Polar Stratosphere Charts All CPC Stratosphere Products

How to read the charts

Zonal wind

Shows the average west-to-east wind at 60°N, usually at 10 hPa. Positive values are westerlies and mean an intact vortex. The faster the wind, the stronger the vortex. A line dropping below zero means the winds have reversed to easterly, the mark of a major sudden warming.

Polar temperature

Shows the average temperature over the polar cap, often 10 hPa from 60°N to 90°N, against the long-term mean and record range. A sharp spike of 25°C or more within days signals a warming event, while a line far below average points to a cold, strong vortex.

What to look for

Compare the current line with the shaded climatology. Weakening winds and rising temperatures together raise the odds of a weak vortex. Any downward impact typically takes 1 to 6 weeks to reach the surface and is not guaranteed.

Stratospheric analogs

Past Vortex Events

Notable winters that saw a major sudden stratospheric warming, and what followed in the weeks after. Load one into the Pattern Regime panel to see how its setup reads, with the polar vortex set to sudden stratospheric warming.

2008–09

Late January 2009

Major warming, vortex split

A strong split warming was followed by a negative AO and NAO into February, with notable cold across parts of Europe and Eurasia.

2012–13

Early January 2013

Major warming, vortex split

High-latitude blocking developed later in the winter, and a persistent negative NAO brought a cold, late-lingering spring to Europe and the eastern U.S.

2017–18

Mid-February 2018

Major warming, vortex split

Blocking set up within about two weeks. Severe cold hit Europe in the "Beast from the East," and a run of nor'easters followed in the northeastern U.S. in March.

2020–21

Early January 2021

Major warming, vortex displacement

A negative AO developed in the following weeks, and a deep Arctic outbreak in mid-February brought record cold and a major winter storm to the central U.S.

Index phases are approximate winter classifications. Not every warming leads to a cold outbreak; verify against CPC and NCEI archives.

Filter

Atmospheric Oscillations

NAONov–Mar

North Atlantic Oscillation

Shifts the Atlantic storm track; negative phase drives cold outbreaks and enhanced snowfall into the eastern U.S. and Europe.

+ Phase

WarmDry

Track shifts NE; mild E. U.S. & NW Europe

− Phase

CoolWet

Blocking; enhanced NE snowfall, cold E. U.S.

Phase	Temp	Precip	Pattern
+ Phase	Warm	Dry	Track shifts NE; mild E. U.S. & NW Europe
− Phase	Cool	Wet	Blocking; enhanced NE snowfall, cold E. U.S.

NeutralNormal

Weak Atlantic steering; storm track near normal and eastern U.S. temperatures driven by other factors.

Daily NAO Index — CPC

AONov–Mar

Arctic Oscillation

Describes polar vortex strength; negative AO weakens the vortex, allowing Arctic air and cold anomalies to spill southward across the mid-latitudes.

+ Phase

WarmNormal

Zonal, fast pattern; cold confined to Arctic

− Phase

CoolWet

Amplified blocking; Arctic air into mid-latitudes

Phase	Temp	Precip	Pattern
+ Phase	Warm	Normal	Zonal, fast pattern; cold confined to Arctic
− Phase	Cool	Wet	Amplified blocking; Arctic air into mid-latitudes

NeutralNormal

Polar vortex near average; Arctic air stays mostly contained, with no strong cold-outbreak signal.

Daily AO Index — CPC

PNAOct–Mar✓

Pacific–North America Pattern

Governs jet-stream configuration across the Pacific and North America. Positive phase amplifies western ridging and eastern troughing; negative phase flattens the pattern.

+ Phase

VariableVariable

Rex block / western ridge, eastern trough

− Phase

VariableWet

Flat pattern; suppressed blocking, wet PNW

Phase	Temp	Precip	Pattern
+ Phase	Variable	Variable	Rex block / western ridge, eastern trough
− Phase	Variable	Wet	Flat pattern; suppressed blocking, wet PNW

NeutralNormal

Near-zonal jet over North America; no persistent western ridge or eastern trough.

Daily PNA Index — CPC

EPONov–Feb

East Pacific Oscillation

Modulates temperatures across western Canada and the northwestern U.S. Negative EPO often precedes cold intrusions into the northern Plains and Great Lakes.

+ Phase

WarmDry

Pacific jet suppressed northward; mild Alaska

− Phase

CoolWet

Amplified trough; cold N. Plains & Great Lakes

Phase	Temp	Precip	Pattern
+ Phase	Warm	Dry	Pacific jet suppressed northward; mild Alaska
− Phase	Cool	Wet	Amplified trough; cold N. Plains & Great Lakes

NeutralNormal

No strong modulation of western Canada or northern Plains temperatures.

EPO Index — CPC

WPONov–Mar

West Pacific Oscillation

A primary mode of low-frequency variability over the western North Pacific; interacts with the PNA and ENSO to shape mid-latitude teleconnection patterns.

+ Phase

WarmWet

Extended Pacific jet; downstream ridging

− Phase

CoolDry

Upstream trough; reinforces PNA signal

Phase	Temp	Precip	Pattern
+ Phase	Warm	Wet	Extended Pacific jet; downstream ridging
− Phase	Cool	Dry	Upstream trough; reinforces PNA signal

NeutralNormal

Little west Pacific forcing; minimal added influence on the PNA or downstream pattern.

WPO Index — CPC

Tropical & Sub-seasonal

MJONov–Apr

Madden–Julian Oscillation

An eastward-propagating tropical convection pulse with a 30–60 day cycle that modulates precipitation, temperature, and tropical cyclone activity globally.

Active

WarmWet

Ph 8–2: warm E. U.S.; active Indian Ocean convection

Suppressed

CoolDry

Ph 4–6: cold E. U.S. possible; suppressed W. Pacific

Phase	Temp	Precip	Pattern
Active	Warm	Wet	Ph 8–2: warm E. U.S.; active Indian Ocean convection
Suppressed	Cool	Dry	Ph 4–6: cold E. U.S. possible; suppressed W. Pacific

InactiveNormal

Inactive or weak: no organized tropical convection pulse, so little sub-seasonal influence on U.S. patterns.

14-Day MJO Forecast — CPC

ENSODec–Feb

El Niño–Southern Oscillation

The dominant interannual climate driver. El Niño and La Niña alter the subtropical jet and shape seasonal temperature and precipitation patterns across the U.S.

El Niño

WarmWet

El Niño: wet Gulf/SE, active subtropical jet

La Niña

CoolVariable

La Niña: wet PNW, active Atlantic TC season

Phase	Temp	Precip	Pattern
El Niño	Warm	Wet	El Niño: wet Gulf/SE, active subtropical jet
La Niña	Cool	Variable	La Niña: wet PNW, active Atlantic TC season

NeutralNormal

ENSO-neutral: subtropical jet near normal; seasonal outlooks lean on other patterns such as the AO, NAO and PDO.

ENSO Advisory — CPC

Oceanic Patterns

PDOMulti-year

Pacific Decadal Oscillation

A decadal-scale SST pattern in the North Pacific that can amplify or suppress ENSO impacts and modulate U.S. drought and precipitation regimes over multi-year periods.

+ Phase

WarmWet

Warm Gulf of Alaska; amplifies El Niño impacts

− Phase

CoolDry

Cool Gulf of Alaska; amplifies La Niña, W. drought

Phase	Temp	Precip	Pattern
+ Phase	Warm	Wet	Warm Gulf of Alaska; amplifies El Niño impacts
− Phase	Cool	Dry	Cool Gulf of Alaska; amplifies La Niña, W. drought

NeutralNormal

Near-average North Pacific SSTs; neither amplifies nor suppresses ENSO impacts.

PDO Index — NCEI

AMOMulti-year

Atlantic Multidecadal Oscillation

A decades-long oscillation in North Atlantic SSTs linked to hurricane activity, Sahel rainfall, and North American drought and precipitation patterns.

+ Phase

WarmWet

Active Atlantic hurricane era; elevated TC counts

− Phase

CoolDry

Quiet Atlantic TC era; suppressed Sahel rainfall

Phase	Temp	Precip	Pattern
+ Phase	Warm	Wet	Active Atlantic hurricane era; elevated TC counts
− Phase	Cool	Dry	Quiet Atlantic TC era; suppressed Sahel rainfall

NeutralNormal

Near-average North Atlantic SSTs; no strong tilt in hurricane activity or drought risk.

AMO Index — CPC

Stratospheric

QBOMulti-year

Quasi-Biennial Oscillation

A stratospheric equatorial wind oscillation with a ~28-month period that modulates polar vortex stability and downstream extratropical weather patterns.

+ Phase

WarmNormal

Westerly: stable polar vortex, fewer SSW events

− Phase

CoolVariable

Easterly: weakened vortex, SSW risk & blocking

Phase	Temp	Precip	Pattern
+ Phase	Warm	Normal	Westerly: stable polar vortex, fewer SSW events
− Phase	Cool	Variable	Easterly: weakened vortex, SSW risk & blocking

NeutralNormal

Transitioning winds between phases; weak, uncertain influence on polar vortex stability.

QBO Index — CPC

Quick reference

Index Glossary

Key facts for all ten climate indices on this page — category, timescale, and primary atmospheric or oceanic influence.

Atmospheric Oscillations

NAONorth Atlantic Oscillation

Atlantic storm track; eastern U.S. & European winter temperatures

Days–weeks

AOArctic Oscillation

Polar vortex strength; cold air intrusion into mid-latitudes

Days–weeks

PNAPacific–North America Pattern

Jet-stream configuration across the Pacific and North America

Weeks

EPOEast Pacific Oscillation

Western Canada & NW U.S. temperatures; northern Plains cold

Weeks

WPOWest Pacific Oscillation

Western North Pacific variability; interacts with PNA and ENSO

Weeks

Tropical & Sub-seasonal

MJOMadden–Julian Oscillation

Global precipitation and TC activity via eastward convection pulse

30–60 days

ENSOEl Niño–Southern Oscillation

Dominant interannual driver; shifts subtropical jet and seasonal patterns

Interannual

Stratospheric

QBOQuasi-Biennial Oscillation

Polar vortex stability; modulates SSW risk and extratropical blocking

~28 months

Oceanic Patterns

PDOPacific Decadal Oscillation

N. Pacific SST pattern; amplifies or suppresses ENSO impacts

Decadal

AMOAtlantic Multidecadal Oscillation

N. Atlantic SSTs; hurricane activity and Sahel / N. American drought

Multi-decadal

Reference & Data

Primary CPC and NOAA data archives used for index verification and longer historical context.

CPC Teleconnections Documentation CPC Daily Climate Indices CPC ENSO Advisory Archive CPC MJO Index & Forecasts NOAA PSL — ENSO Resources NOAA PSL — Climate Indices List

Charts sourced from NOAA/CPC and NCEI. Images refresh automatically every 5 minutes.