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 EDT Fri Apr 16 2021

Week 3-4 Forecast Discussion Valid Sat May 01 2021-Fri May 14 2021

La Nina conditions continued but weakened across the Pacific Ocean. Equatorial sea surface temperatures (SSTs) have trended closer to average across the west-central equatorial Pacific Ocean, but enhanced upper level westerly wind anomalies persist across the eastern tropical Pacific. The RMM index depicts an eastward propagation of the MJO over the West Pacific during mid-April. Dynamical models continue to favor the eastward propagation of the MJO over the Pacific and the Western Hemisphere during the remainder of April. The Week 3-4 temperature and precipitation outlooks are based primarily on dynamical model forecasts from the NCEP CFS, ECMWF, and JMA, and the Subseasonal Experiment (SubX) multi-model ensemble (MME) of experimental and operational ensemble prediction systems with additional considerations for MJO, La Nina, and long-term trends, as well as the predicted evolution of the pattern from Week-2 forecasts.

The forecast circulations are reasonably consistent among model guidance regarding the anomalous 500-hPa height patterns over the week 3-4 period. Dynamical model 500hPa height anomaly forecasts during week 3-4 show a fairly consistent evolution from the forecast state during Week-2. Most dynamical models feature anomalous ridging with above normal 500-hPa heights over the West Coast and southwest CONUS, while anomalous trouging is forecast across the north-central CONUS. Above normal 500-hPa heights are predicted over most of Mainland Alaska. Near normal 500-hpa heights are likely over Hawaii.

Below normal temperatures are favored over parts of the Northern Rockies, the Northern Plains and the Upper Mississippi Valley due to below normal 500-hpa heights. Above normal temperatures are more likely across the remainder of the CONUS, under predicted above normal 500-hPa heights. The highest confidence for above-normal temperatures lies across Arizona and New Mexico (greater than 60%) tied to the forecast position of the anomalous 500-hPa ridge axis. Predicted ridging and above normal 500-hPa heights lead to above normal temperatures favored over Alaska.

The dynamical model guidance is in reasonably good agreement on the spatial pattern of anomalous precipitation during the Week 3-4 period. Near to below normal precipitation is favored throughout most of the western CONUS, under the near to above normal 500-hPa heights, while predicted troughing and below normal 500-hPa heights increase the chances of above normal precipitation over the Great Lakes, Ohio Valley, and Mid-Atlantic, consistent with dynamical and statistical guidance. Anomalous ridging and above normal 500-hPa heights lead to enhanced probabilities of below normal precipitation over Alaska.

Most dynamical model guidance, including the experimental SubX models, depict enhanced chances for above normal temperatures for Hawaii. Dynamical model precipitation forecasts generally favor below normal precipitation over the southeastern Hawaiian islands.

Temperature Precipitation

FCST FCST

Hilo A50 B50

Kahului A50 B50

Honolulu A50 EC

Lihue A50 EC

Forecaster: Luke He

The next week 3-4 outlook will be issued on Friday, Apr 23, 2021

These outlooks are based on departures from the 1981-2010 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