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 May 29 2020

Week 3-4 Forecast Discussion Valid Sat Jun 13 2020-Fri Jun 26 2020

ENSO-neutral conditions currently are present across the equatorial Pacific Ocean. Equatorial sea surface temperatures (SSTs) are near average across most of the Pacific Ocean. The RMM index propagated over the Indian Ocean beginning in mid-May, and quickly moved to the West Pacific, which is likely associated with robust Kelvin wave activity. Both the GEFS and ECMWF depict a fast eastward propagation of the MJO signal to the Western Hemisphere during Week-1, and a slow propagation is favored during Week-2. The Week 3-4 Outlook is based primarily on dynamical model forecasts, including the NCEP CFS, ECMWF, and JMA ensemble prediction systems, as well as the Subseasonal Experiment (SubX), a multi-model ensemble (MME) of both operational and experimental ensemble prediction systems. Statistical forecasts, including a multivariate linear regression (MLR) of lagged temperature and precipitation forecasts to currently observed MJO and ENSO indices, are also consulted. Decadal timescale temperature trends are also a source of predictability in both dynamical and statistical forecast tools.

Dynamical model 500hPa height anomaly forecasts during Week-34 show a fairly consistent evolution from the forecast state during Week-2. The CFS, ECMWF and JMA models appear consistent in predicting ridging over the mainland Alaska. The CFS model indicates positive 500-hPa heights anomalies over the West Coast of the CONUS, while the ECMWF model favors positive 500-hPa height anomalies extending over most of the CONUS. Near to above-normal 500-hPa heights are also favored over Hawaii.

The week 3-4 temperature outlook calls for elevated probabilities of above normal temperatures over all of Alaska, with greater probabilities over the northern regions of the state exceeding 60 percent, under predominantly above normal mid-level heights. Above normal temperatures are also likely for most of the western CONUS under predicted ridging in most model forecasts. Probabilities exceed 60 percent in much of the Southwest region, where positive decadal temperature trends are greatest. Below normal temperatures are favored over parts of the Northern Rockies, the Northern Plains, and the Upper Mississippi Valley, consistent with most model forecasts and moderated by likely cloudy conditions. Probabilities of above normal temperatures increase across the eastern CONUS, under near or above normal 500-hPa heights. Dynamical model forecasts predict elevated probabilities of above normal temperatures across the Hawaiian Islands during the week 3-4 period with continued positive sea surface temperature anomalies.

The week 3-4 precipitation outlook calls for elevated probabilities of above median precipitation over the Aleutians, where dynamical models indicate the potential for storminess during the period. Below median precipitation is likely for much of the Alaska mainland, under predicted positive 500-hPa height anomalies in most dynamical model forecasts. Below normal precipitation is favored for most of the northwestern CONUS and the Great Basin, under a predicted ridge during the week 3-4 period. Above median precipitation is likely for parts of the Northern and Southern Plains, as most models, such as many components of the SubX MME, indicate increased storm activity over the regions during the week 3-4 period. Below median precipitation is likely for parts of the Ohio Valley, the Tennessee Valley, and the Middle Atlantic, under predicted near to above normal 500-hPa heights. Dynamical model forecasts show a slight increase in the probabilities of below median precipitation for Hawaii during the week 3-4 period.

Temperature Precipitation

FCST FCST

Hilo A65 B55

Kahului A65 B55

Honolulu A65 B55

Lihue A65 B55

Forecaster: Luke He

The next week 3-4 outlook will be issued on Friday, Jun 05, 2020

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