At midday, the 12Z GFS forecasts a whopping -4 value for the East Pacific oscillation (EPO) during the 11-15-day period. Other models are averaging -2 at that timeframe, about half the strength (although still impressive). The strong (-4) index supports arctic air involvement and on day-15, 12Z GFS indicates zero for morning low temperatures from Colorado to South Dakota. Is the forecast overstated?

The monthly Climate Impact Company ENSO Outlook indicates the current weak La Nina should strengthen slightly and peak by January followed by rapid dissipation and a possible reversal in ENSO phase to El Nino during the middle third of 2026.