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 Mar 31 2023

Week 3-4 Forecast Discussion Valid Sat Apr 15 2023-Fri Apr 28 2023

Below average sea surface temperature (SST) anomalies across the equatorial Pacific Ocean weakened during February 2023 and are near average across most of the Pacific Ocean, and El Niño Southern Oscillation (ENSO) neutral conditions are observed. Though ENSO-neutral is expected to continue through the Northern Hemisphere spring and early summer, the tropical Pacific atmosphere is still consistent with a weak La Niña signal. Following the remarkably strong Madden Julian Oscillation (MJO) event observed throughout March, forecasts of the Real Time-Multivariate MJO (RMM) index from the Global Ensemble Forecast System (GEFS) and European Centre for Medium-Range Weather Forecasts (ECMWF) models are in good agreement on short-term weakening of the MJO signal, followed by renewed strengthening in early April with ECMWF forecasting that the MJO will emerge possibly near phase 6. However, dynamical model forecasts are uncertain about the strength and propagation speed of the renewed MJO activity, potentially due to destructive interference from the lingering La Niña signal. In addition to uncertainty in the evolution of the MJO, tropical sources of predictability have a weaker impact on North American Temperature and Precipitation Outlooks as we move into the spring. The Week 3-4 Temperature and Precipitation Outlooks are based on expected evolution from Climate Prediction Center (CPC) 6-10 and 8-14 day forecasts, dynamical model forecasts from the Climate Forecast System (CFS), ECMWF, GEFS, Japan Meteorological Agency (JMA), and Subseasonal Prediction Experiment (SubX) multi-model ensemble (MME) of experimental and operational ensemble prediction systems, and a statistical Multiple Linear Regression (MLR) tool including influences of La Niña, MJO, and decadal trends.

Dynamical model guidance favors ridging over the Aleutians which is consistent among the available models. Troughing is favored over eastern Alaska and western Canada stretching into the Pacific Northwest, though models disagree on the positioning of the southern edge of the trough. Greater uncertainty exists for the predicted 500 hPa height pattern over the Contiguous United States (CONUS), where CFS, GEFS, and JMA favor ridging with some uncertainty in the location of the ridge; and ECMWF favors neutral heights over the lower 48. JMA and GEFS also forecast troughing over parts of New England, at odds with CFS and ECMWF. Though guidance is slightly more certain than the prior Week 3-4 forecast, signals are weak over the central U.S. where models disagree on the pattern.

Given differences in the forecasted height pattern and lack of extratropical forcing, the Weeks 3-4 Temperature Outlook remains somewhat uncertain. Overall, models show a general pattern of below normal temperatures over the west coast and Pacific Northwest, transitioning to above normal temperatures over the Southeast. However, the location of the transition is highly uncertain as CFS, JMA, and GEFS favor above normal temperatures stretching across the central CONUS to the Southeast, with disagreement on the spatial extent of above normal temperatures, while ECMWF tilts towards below normal temperatures across much of the CONUS. As such, a broad region of equal chances (EC) of above and below normal temperatures is depicted from parts of the Southwest through the Central Plains and Mid-Atlantic. Probabilities of below normal temperatures are elevated over the Pacific Northwest and Northern Great Basin where ECMWF, JMA, and CFS agree, supported by forecasted troughing as well as anomalous snow cover. Negative SST anomalies, along with consistent weak below normal probabilities in all models, supports a tilt toward below normal temperatures along much of the west coast. Despite some uncertainty in the extent of the forecasted below normal temperatures into the central U.S., strong probabilities of below normal temperatures in ECMWF and JMA along with decadal trends support favored probabilities of below normal temperatures across the northern U.S. A weak tilt toward below normal temperatures is also depicted over parts of the Northeast where some dynamical models favor troughing and due to potential cooling from the forecasted re-emerging MJO. Above normal temperatures are indicated over parts of the Southwest stretching to the Southeast, with highest probabilities over the Southeast where models are consistent. Ridging has been persistent over the Aleutian Islands and supports below normal temperatures over southern and central Alaska and northerly flow.

The Weeks 3-4 Precipitation Outlook is comparatively more uncertain, as models showed weak or conflicting signals across much of the CONUS. Areas of strongest model agreement support enhanced probabilities of above median precipitation over the Pacific Northwest and Northern Great Basin, western Great Lakes, and for the region stretching from the Southwest over Texas and parts of the Lower Mississippi Valley. Disagreement among models leads to large coverage of EC of above and below median precipitation elsewhere across the CONUS. Offshore flow supports a weak tilt toward below median precipitation over parts of the Alaska Peninsula and parts of South Central Alaska, though anomalous troughing over the eastern and southeastern parts of the state support a weak tilt toward above median precipitation.

Over Hawaii, anomalously warm SSTs and strong model consensus in the SubX MME continue to support elevated probabilities for above normal temperatures. The SubX MME also supports enhanced probabilities of below median precipitation, with weakest probabilities over Hilo and Kahului, increasing toward Lihue.

Temperature Precipitation

FCST FCST

Hilo A60 A55

Kahului A70 A55

Honolulu A70 A60

Lihue A70 A70

Forecaster: Johnna Infanti

The next week 3-4 outlook will be issued on Friday, Apr 07, 2023

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