Climate Prediction Center - Week 3-4 Outlook

Prognostic Discussion for Week 3-4 Temperature and Experimental Precipitation Outlooks
NWS Climate Prediction Center College Park MD
300PM EST Fri Dec 13 2024

Week 3-4 Forecast Discussion Valid Sat Dec 28 2024-Fri Jan 10 2025

A La Niña watch remains in effect and El Niño Southern Oscillation (ENSO)-neutral conditions are present. Equatorial sea surface temperatures (SSTs) are near to below average in the central and eastern Pacific Ocean. La Niña is favored to emerge in October-December (57% chance) and is expected to persist through January-March 2025. The Madden-Julian Oscillation (MJO) propagated eastward from the Indian Ocean to the Maritime Continent starting in late November, however the propagation speed slowed in early December. Dynamical model forecasts depict continued eastward propagation of the MJO signal with a sluggish phase speed. A continued eastward MJO propagation over the Pacific would favor a period of below normal temperatures across the eastern U.S. heading into the New Year, however, dynamical model guidance indicates a different outlook.

Dynamical models generally agree on a wavetrain-like pattern across the northern latitudes. A pattern of below average heights are forecast over the North Pacific Ocean, above average heights are forecast over most of North America, and below average heights are again forecast over Greenland, in the average of the 14-day outlook period. However, the dynamical guidance also indicates a pattern change in these height fields from week 3 to week 4. The pattern shift tends to favor a breakdown of the anomalous ridging pattern over North America. The GEFS and ECMWF indicate the largest pattern shift from anomalous ridging to anomalous troughing. This shift could indicate a teleconnection response to the currently active MJO that is in phase 5.

Broadly speaking, the dynamical guidance agrees on above average temperatures for nearly all of CONUS and Alaska, during the outlook period. There are differences worth noting between the week 3 and week 4 forecasts, for instance, for most of the dynamical models, the week 3 forecast indicates larger departures from normal than in week 4. During week 3, ECMWF and CFS in particular forecast anomalies at least 4 degrees Celsius above normal for the Northern Plains and Central Alaska, with anomalies decreasing from that value toward 1 degree Celsius above normal in southern CONUS. GEFS follows a similar pattern in week 3 but restrains the largest forecast departures from normal to Alaska. In contrast, JMA forecasts more near normal temperatures across southern CONUS in week 3, and weak to moderately above average anomalies across the northern half of CONUS.

In the calibrated dynamical guidance, ECMWF forecasts the strongest probabilities of above (>80%) for the Plains, New England, and parts of the Alaska Panhandle during the 14-day outlook. JMA is the least bullish with the warm probabilities (>50%) and even tilts toward weak chances (>50%) of below average temperatures for the Gulf Coast along with near-to-normal anomalies forecast for that area. GEFS and CFS generally agree on a moderate chance (>60%) of above average temperatures. The temperature outlook for this Weeks 3-4 period reflects the consistent agreement among the dynamical model forecasts with moderate chances of widespread above average temperatures. Equal Chances of above and below normal temperatures is carved out for the Gulf Coast in deference to the forecast disagreement from JMA. Statistical tools forecast a starkly different outlook. Guidance from the operational multiple-linear regression tool (MLR), which uses ENSO, MJO, and trend as predictors, indicates below average temperatures for central to eastern CONUS. The MLR tool agrees with the dynamical models in forecasting above average anomalies for Alaska. Given the relatively strong agreement between the dynamical models, and disagreement with the statistical guidance, the statistical guidance was weighted less when making the outlook this week. However, it is worth noting again that the differences between week 3 and week 4 in the model height and temperature patterns may be an indication of a significant pattern shift to below average temperatures within the outlook period. Guidance does suggest that a changing pattern is in the forecast, however it is not certain to what extent that change will impact the average during the 14-day outlook period.

Precipitation forecasts were largely in agreement on above average rainfall for the Alaska Panhandle and Northwest Washington. The model guidance differed on the forecast for below average rainfall. CFS and ECMWF favor drier than average conditions for the Mississippi Valley and Mid-Atlantic during the outlook period, and GEFS and JMA favor a drier than average West Coast. Based on a high performing blended tool, this precipitation outlook favors enhanced probabilities of above average rainfall for the Alaska Panhandle, Southern Alaska, and the Aleutians. Slight chances for above average rainfall are also forecast for Northwest Washington and Montana. Drier than average conditions are forecast for the Southwest, West Coast, Midwest, and Southeast. Equal Chances are forecast for the Plains and Northeast because most of the model guidance indicates near normal, or weak anomalies for those areas.

For Hawaii, surrounding SST anomalies are slightly above average. The temperature outlook favors near normal temperatures for all the islands except Hilo where model guidance indicates slightly enhanced chances of above average temperatures (55%). Drier than average conditions are forecast for the islands overall, however it is worth noting that guidance indicates week 3 is forecast to be drier than week 4 for all the islands except Hilo, where drier conditions are forecast to prevail during the outlook period (60%).

Temperature Precipitation

FCST FCST

Hilo A55 B60

Kahului EC B55

Honolulu EC B55

Lihue EC B55

Forecaster: Emerson LaJoie

The next week 3-4 outlook will be issued on Friday, Dec 20, 2024

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

These are two category outlooks and differ from official current three category outlooks currently used for the monthly and seasonal forecasts.

The shading on the temperature map depicts the most favored category, either above-normal (A) or below-normal (B) with the solid lines giving the probability ( >50%) of this more likely category (above or below).

The shading on the precipitation map depicts the most favored category, either above-median (A) or below-median (B) with the solid lines giving the probability ( >50%) of this more likely category (above or below).

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

As of May 19, 2017, the temperature outlook is operational, while the precipitation outlook is still experimental

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