Climate Prediction Center - Week 3-4 Outlook

Prognostic Discussion for Week 3-4 Temperature and Precipitation Outlooks
NWS Climate Prediction Center College Park MD
300PM EDT Fri Oct 02 2026

Week 3-4 Forecast Discussion Valid Sat Oct 17 2026-Fri Oct 30 2026

El Nino is present, and the latest weekly sea surface temperature (SST) departure in the Nino3.4 region reached 2.2 degrees C above-normal. Probabilities are high for the El Nino event to strengthen, with a greater than 90% chance for a very strong event during the fall and winter months. On the other hand, the propagation of the Madden Julian Oscillation (MJO) is more uncertain. While both the Global Ensemble Forecast System version 12 (GEFSv12) and the European Centre for Medium-Range Weather Forecasts (ECMWF) model favor a weakening of the MJO over the next week, both indicate potential eastward propagation later in the forecast period. However, the GEFSv12 and ECMWF models differ on timing of this eastward propagation, and the ensemble spread is large. Overall, we expect that El Nino will remain dominant in the global tropics, and that MJO will play a much smaller role in this forecast.

Week 3-4 dynamical models are in decent agreement on troughing centered south of Alaska and extending over the western part of the state, ridging over the western and central Contiguous United States (CONUS), and neutral heights over the East. There are some differences in strength and positioning of this pattern. For example, the Climate Forecast System version 2 (CFSv2), and to an extent GEFSv12, have the strongest forecast for troughing to the south of Alaska, with troughing covering much of the state and decreasing toward the East. ECMWF and the Japan Meteorological Agency (JMA) dynamical models have weaker troughing that is located further west of Alaska. Over the CONUS, models generally agree on ridging covering the western and central U.S., though GEFSv12 depicts the ridging a bit more over the central CONUS, and CFSv2 and JMA indicate a decrease in the strength of the ridge toward the West Coast. This discrepancy is likely due to the transient nature of this pattern from Week 3 to Week 4; Week 3 has the ridging further west, while Week 4 has it further east. Interestingly, a multiple linear regression (MLR) tool that combines the influences of the El Nino Southern Oscillation (ENSO), the MJO, and trend favors ridging over much of Alaska and troughing over the CONUS, which is mainly driven by the ENSO signal. Trends lean toward above normal over the CONUS, and there is not much signal from MJO, as expected. We suspect that the shorter-term pattern of ridging may dominate this signal, at least for this Weeks 3-4 Outlook. Moreover, the agreement among dynamical models is very supportive of this broad-scale pattern.

A blend of dynamical models and MLR favors broadly above-normal temperatures over Alaska and the CONUS, with a weak title toward below-normal temperatures over parts of the eastern U.S. The Weeks 3-4 Temperature Outlook is very reminiscent of the height pattern in the dynamical models and this blend, with consideration for model uncertainty and possibility of temperature moderation in some areas. Above-normal temperature probabilities are enhanced over much of Alaska, the western and central CONUS, and parts of the Southeast. Equal chances (EC) of above-, near-, and below-normal temperatures are indicated over the western part of Alaska and parts of the eastern CONUS. Below-normal temperatures are weakly favored over parts of the Aleutians. Widespread enhanced above-normal temperature probabilities are highly supported by the forecasted ridging in dynamical models, and consistency across the models on the temperature forecast. Probabilities are highest along the Southwest coast given strong probabilities in models as well as above-average SSTs. A minor moderation of probabilities (40 to 50% chances) is indicated over the Northwest. While no precipitation shape is included due to uncertainty, some models and tools did point to a tilt toward above-normal precipitation the Northwest, which could act to moderate temperatures slightly. Troughing over western Alaska may favor below-normal temperatures; however, the uncertainty in the strength and positioning of the trough, as well as uncertainty in temperature forecasts supports EC. Similarly, some models also indicate weak chances for below-normal temperatures over the East, but there was not enough evidence or support for a tilt toward below-normal temperatures in the Outlook. On the other hand, most models did tilt toward below-normal temperatures over the Aleutians, supporting a weak tilt.

In contrast to temperatures, the Weeks 3-4 Precipitation Outlook is more El Nino-like, with above-normal precipitation favored over the southeastern mainland and Southeast Alaska, as well as much of the southern tier of the CONUS. A broad swath of elevated below-normal precipitation chances are indicated from the Northern Plains to the Northeast, dipping into the Lower Mississippi and Tennessee Valleys. Though precipitation probabilities are lower in dynamical models when compared to temperatures, there is remarkable consistency on the below-normal precipitation, as well as the above-normal precipitation over southeastern mainland and Southeast Alaska, and the Southwest. By comparison, dynamical models depict more uncertainty over the Southeast, but the MLR supports above-normal precipitation for the region driven by El Nino. As such, a weak tilt toward above-normal precipitation is indicated.

Given weakly above-average 500mb heights and ongoing El Nino conditions, above-normal temperatures are forecast over Hawaii. Precipitation forecasts were much more uncertain over Hawaii, with no clear signals in the models or tools. As such, EC is indicated for precipitation over Hawaii.

Forecaster: Johnna Infanti

The next week 3-4 outlook will be issued on Friday, Oct 09, 2026

These outlooks are based on departures from the 1991-2020 base period

These are three category outlooks consistent with what is currently used for the monthly and seasonal forecasts.

The shading on the temperature map depicts the most favored category, either above-normal (A), below-normal (B), or near-normal (N) with the solid lines giving the probability ( >33%) of this more likely category (above, below, or near).

The shading on the precipitation map depicts the most favored category, either above-median (A), below-median (B), or near-median with the solid lines giving the probability ( >33%) of this more likely category (above, below, or near).

In areas where the likelihoods of 2-week mean temperatures and accumulated precipitation amounts are similar to climatological probabilities, equal chances (EC) is indicated.