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 Nov 29 2024

Week 3-4 Forecast Discussion Valid Sat Dec 14 2024-Fri Dec 27 2024

Equatorial sea surface temperatures (SSTs) are mostly near average in the central and eastern Pacific Ocean, and El Niño Southern Oscillation (ENSO)-neutral conditions are currently present. A weak La Niña is favored to emerge and forecast to persist through January - March 2025. Though the La Niña is still favored to emerge, it does not play a key role in the Weeks 3-4 Outlook this week as SSTs are currently near average. The Madden Julian Oscillation (MJO) regained amplitude and propagated eastward during the past week, and dynamical models favor continued eastward progression over the next few weeks though uncertainty increases in late December. Despite the uncertainty in late December, MJO played a comparatively larger role in this Outlook compared to ENSO. In addition to large-scale teleconnections, the Weeks 3-4 Temperature and Precipitation Outlooks are based on dynamical model guidance from GEFSv12, CFSv2, JMA, ECMWF, the predicted evolution from the Week-2 forecast, statistical multiple linear regression (MLR) estimates of the influence of ENSO, MJO, and trend, and experimental blends of dynamical and statistical tools.

Week-2 forecasts have favored ridging over the western half of the Contiguous United States (CONUS) and troughing over the east, which is forecast to deamplify toward the end of the Week 2 period. In the Weeks 3-4 period, dynamical models indicate a shift toward neutral 500-hPa heights over the western CONUS, and weakly above normal 500-hPa heights over the east, which is a change from the fairly consistent Week-2 pattern. It is also a change from the pattern that was favored by the models during Week 3 last week, which tilted toward troughing and cooler temperatures over the Northeast, and agrees more with the pattern forecast in Week 4. This forecasted change in the mid-level height pattern in the Weeks 3-4 period led to some uncertainty and changes from the prior week's forecast.

Given the forecasted shift in the 500-hPa height pattern, above normal temperatures are forecast for the eastern third of the CONUS. Probabilities are enhanced over the Southeast where models agree, along with trends and any influence from MJO that additionally supports above normal temperatures. Probabilities are also enhanced over the Southwest where model agreement was strong, and due to a lack of recent precipitation and expected continuation of below median precipitation. Though model forecasts and above normal 500-hPa heights support the tilt toward above normal temperatures over the Northeast, probabilities are weakened compared to a blend of tools given uncertainty in timing of the transition from cooler to warmer temperatures. Above normal temperatures are also favored over southeastern Alaska and the Northwestern CONUS given model agreement. Though most models tilted toward above normal over the northern tier of the CONUS, the potential influence of MJO is toward below normal temperatures over the north central CONUS and parts of the Great Lakes leading to favored equal chances (EC) of above and below normal temperatures. EC is also indicated over much of the Western and Central CONUS due to the forecasted weak or neutral height pattern.

The Weeks 3-4 Precipitation Outlook is comparatively more uncertain than the Temperature Outlook, with large areas of EC where signals were weak or inconsistent among tools. In addition, any MJO impact that we might see on precipitation competes with trend as these influences often show opposite signals according to the MLR tool. Below median precipitation is indicated over parts of the Southwest and southern California where uncalibrated dynamical model guidance was in agreement, as well as due to an experimental subsampling blend of dynamical models favoring below median precipitation. In contrast, above median precipitation is favored over parts of eastern Texas and Oklahoma, and western Arkansas and Louisiana where flow may be onshore from the Gulf of Mexico. Above median precipitation is also indicated over southeastern Alaska and the Northwest CONUS where models agreed, and despite the currently neutral NINO3.4 SSTs, where we may see some early influence of La Niña.

SST and 500-hPa height anomalies are slightly above normal over Hawaii, with SST anomalies larger over the north. EC is indicated over Hilo, with a weak tilt toward above normal temperatures over the northern parts of the Hawaiian Islands. There is disagreement among tools on precipitation, and as such EC of above and below median precipitation is favored.

Temperature Precipitation

FCST FCST

Hilo EC EC

Kahului A55 EC

Honolulu A55 EC

Lihue A55 EC

Forecaster: Johnna Infanti

The next week 3-4 outlook will be issued on Friday, Dec 06, 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