Climate pattern

• seasonStrong El Niño, very strong expected → slight wet lean. The El Niño link is weaker than in SoCal. The southern Sierra leans wet, but the relationship fades northward through California. low–moderate confidence
  California Geological Survey: El Niño · Climate.gov: El Niño and snowfall (L'Heureux 2023)
• CPCCPC 90-day outlook (Oct 15): “For the NDJ 2026-2027 Precipitation Outlook, there is an elevated likelihood of above-normal seasonal precipitation amounts for much of California and the Southwest, the central and southern Plains, and the Southeast and along the Eastern Seaboard.” context
  CPC 90-day outlook discussion
• pdoPDO is negative (−1.55). Southwest winters have been less consistent when El Niño coincides with a cool PDO, so hold the seasonal lean more loosely. CPC notes the "Big Three" El Niños (1982–83, 1997–98, 2015–16) all had a positive PDO. low–moderate confidence
  Brown & Comrie 2004 (GRL) · Newman et al. 2016, The PDO Revisited · CPC 90-day outlook discussion
• mjoMJO is active in phase 2 (Indian Ocean): West Coast precipitation tends to be enhanced with this phase. About 2 weeks after phase 2, atmospheric-river activity tends to shift north toward British Columbia and away from California. A 1–5 week window of opportunity, not a forecast (these links are documented for Nov–Mar). low–moderate confidence
  CPC weekly MJO update · Zhou et al. 2012 (Clim Dyn) · Mundhenk et al. 2018 (npj)

Odds, not guarantees. ENSO data through RONI JAS 2026, CPC discussion 8 October 2026.

• seasonStrong El Niño, very strong expected → near coin flip. Close to a coin flip: the ENSO relationship is weak in central and northern California. low confidence
  California Geological Survey: El Niño · Climate.gov: El Niño and snowfall (L'Heureux 2023)
• CPCCPC 90-day outlook (Oct 15): “For the NDJ 2026-2027 Precipitation Outlook, there is an elevated likelihood of above-normal seasonal precipitation amounts for much of California and the Southwest, the central and southern Plains, and the Southeast and along the Eastern Seaboard.” context
  CPC 90-day outlook discussion
• pdoPDO is negative (−1.55). Southwest winters have been less consistent when El Niño coincides with a cool PDO, so hold the seasonal lean more loosely. CPC notes the "Big Three" El Niños (1982–83, 1997–98, 2015–16) all had a positive PDO. low–moderate confidence
  Brown & Comrie 2004 (GRL) · Newman et al. 2016, The PDO Revisited · CPC 90-day outlook discussion
• mjoMJO is active in phase 2 (Indian Ocean): West Coast precipitation tends to be enhanced with this phase. About 2 weeks after phase 2, atmospheric-river activity tends to shift north toward British Columbia and away from California. A 1–5 week window of opportunity, not a forecast (these links are documented for Nov–Mar). low–moderate confidence
  CPC weekly MJO update · Zhou et al. 2012 (Clim Dyn) · Mundhenk et al. 2018 (npj)

Odds, not guarantees. ENSO data through RONI JAS 2026, CPC discussion 8 October 2026.

• seasonStrong El Niño, very strong expected → warmer, drier lean. El Niño tends to mean a warmer, drier winter with less snow, most reliably in the interior Northwest. Confidence is low for the Cascades this year: midwinter snowpack anomalies have been positive in coastal Columbia-basin areas, and CPC says the wet area may reach central Oregon or farther north given this event's strength. low confidence
  Climate.gov: El Niño and snowfall (L'Heureux 2023) · Clark, Serreze & McCabe 2001 (WRR) · CPC 90-day outlook discussion
• CPCCPC 90-day outlook (Oct 15): “An enhanced and southward and eastward shifted Pacific Jet supports elevated probabilities for above-normal precipitation for much of the West Coast including areas extending as far north as the Oregon coast.” context
  CPC 90-day outlook discussion
• mjoMJO is active in phase 2 (Indian Ocean): West Coast precipitation tends to be enhanced with this phase. About 2 weeks after phase 2, atmospheric rivers tend to favor British Columbia over California. A 1–5 week window of opportunity, not a forecast (these links are documented for Nov–Mar). low–moderate confidence
  CPC weekly MJO update · Zhou et al. 2012 (Clim Dyn) · Mundhenk et al. 2018 (npj)

Odds, not guarantees. ENSO data through RONI JAS 2026, CPC discussion 8 October 2026.

• seasonStrong El Niño, very strong expected → near-equal chances. A transition zone: El Niño winters run drier to the north and wetter to the southwest. Treat it as near-equal chances, with a slight southern-Utah wet lean. low confidence
  Clark, Serreze & McCabe 2001 (WRR) · Climate.gov: snow during El Niños 1950–2009
• pdoPDO is negative (−1.55). Southwest winters have been less consistent when El Niño coincides with a cool PDO, so hold the seasonal lean more loosely. CPC notes the "Big Three" El Niños (1982–83, 1997–98, 2015–16) all had a positive PDO. low–moderate confidence
  Brown & Comrie 2004 (GRL) · Newman et al. 2016, The PDO Revisited · CPC 90-day outlook discussion

Odds, not guarantees. ENSO data through RONI JAS 2026, CPC discussion 8 October 2026.

• seasonStrong El Niño, very strong expected → no clear snow signal. No clear El Niño precipitation signal for northern Colorado; the state's strongest El Niño signal is in temperature (cooler). low confidence
  Colorado Climate Center: ENSO · Clark, Serreze & McCabe 2001 (WRR)

Odds, not guarantees. ENSO data through RONI JAS 2026, CPC discussion 8 October 2026.

• seasonStrong El Niño, very strong expected → slight wet lean. The southern mountains (San Juans, Sangre de Cristo) lean wetter in El Niño winters. low–moderate confidence
  Climate.gov: snow during El Niños 1950–2009 · Clark, Serreze & McCabe 2001 (WRR) · Colorado Climate Center: ENSO
• pdoPDO is negative (−1.55). Southwest winters have been less consistent when El Niño coincides with a cool PDO, so hold the seasonal lean more loosely. CPC notes the "Big Three" El Niños (1982–83, 1997–98, 2015–16) all had a positive PDO. low–moderate confidence
  Brown & Comrie 2004 (GRL) · Newman et al. 2016, The PDO Revisited · CPC 90-day outlook discussion

Odds, not guarantees. ENSO data through RONI JAS 2026, CPC discussion 8 October 2026.

• seasonStrong El Niño, very strong expected → warmer, drier lean. El Niño tends to mean a warmer, drier winter with less snow in the northern Rockies. moderate confidence
  Climate.gov: El Niño and snowfall (L'Heureux 2023) · CPC 90-day outlook discussion
• CPCCPC 90-day outlook (Oct 15): “Below-normal precipitation is favored for the northern Rockies and parts of the Great Lakes as well as much of western and central interior Alaska.” context
  CPC 90-day outlook discussion

Odds, not guarantees. ENSO data through RONI JAS 2026, CPC discussion 8 October 2026.