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 Jun 02 2023

Week 3-4 Forecast Discussion Valid Sat Jun 17 2023-Fri Jun 30 2023

A transition from ENSO-neutral conditions to El Niño is underway with weekly sea surface temperature (SST) anomalies in the Niño 3.4 region at 0.4 degrees Celsius above normal and negative OLR anomalies (enhanced convection) observed over parts of the central equatorial Pacific since late April. The Madden-Julian Oscillation (MJO) remains active with its enhanced phase recently propagating eastward over the Western Hemisphere. According to the 200-hPa Velocity Potential anomaly field, the ECMWF and GEFS models are in good agreement that the MJO remains coherent and will continue to shift eastward through late June. This forecast evolution would result in anomalous upper-level convergence overspreading the Americas by mid-June. Following a favorable large-scale environment for tropical cyclone development across the East Pacific, western Caribbean, and Gulf of Mexico to start the month, a more hostile environment is expected by late June. Although the MJO influence on the mid-latitude circulation pattern typically diminishes by early summer, the temperature and precipitation composites for May-June-July were considered. Soil moisture conditions were a factor in the temperature outlook with increasingly dry (wet) topsoil present across the Corn Belt (High Plains). The Weeks 3-4 temperature and precipitation outlooks are based primarily on dynamical model forecasts from the CFS, GEFS, ECMWF, and SubX multi-model ensemble (MME) of experimental and operational ensemble prediction systems. A statistical Multiple Linear Regression (MLR) tool which includes input from ENSO, MJO, and decadal trends was also considered.

During early to mid-June, dynamical model forecasts depict a persistent negative Arctic Oscillation (AO) pattern with positive (negative) 500-hPa height anomalies at the high (middle) latitudes of North America. The CFS, GEFS, and ECMWF models have this pattern continuing into week-3 but diverge by week-4. The ECMWF model is most persistent with the longwave pattern over North America throughout June. The manual 500-hPa blend, most heavily weighted towards the dynamical models, depicts an amplified ridge over western Canada and a trough undercutting this ridge. This trough and associated negative 500-hPa height anomalies increase probabilities for below-normal temperatures across the Southwest, Great Basin, and central to southern California. The predicted cooler-than-normal temperatures extend east to the High Plains, based on the calibrated ECMWF and wet topsoil considerations. Anomalous ridging over western Canada favors above-normal temperatures across parts of the northern Intermountain West, although there is less model agreement. Positive 500-hPa height anomalies along with support from the dynamical models results in elevated probabilities of above-normal temperatures across the East, Midwest, and Gulf Coast states. The favored warmth across the Corn Belt is consistent with rapidly drying topsoil for this region. The largest probabilities for above-normal temperatures are forecast across the Lower Mississippi Valley and western Gulf Coast where dynamical models have the strongest signal. A predicted trough (ridge) over the Aleutians (eastern Mainland Alaska) yields enhanced probabilities for below-normal temperatures across the Aleutians and the Alaska Peninsula with above-normal temperatures more likely across Northern Mainland Alaska and southeastern Alaska.

Although dynamical models differ on the amplitude and exact placement of a 500-hPa trough near the West Coast, they agree that negative 500-hPa height anomalies extend eastward to the Rockies. This anomalous troughing over the interior West favors a broad coverage of enhanced probabilities for above-median precipitation across the northern half of the West along with parts of the Central to Southern Great Plains and Lower Mississippi Valley. Equal chances (EC) of below or above-median precipitation are forecast for the Gulf Coast region and East where signals are weak among the precipitation tools. Below-median precipitation is slightly favored for the Upper Mississippi Valley, consistent with a mean 500-hPa ridge upstream over western Canada and supported by the calibrated ECMWF model. The Desert Southwest is climatologically dry during early to mid-June, but precipitation associated with the Monsoon typically begins to increase by the end of the month. Based on the expectation of a slow start to the Monsoon, westerlies aloft with the trough over the West, and good agreement between the CFS and GEFS models, below-median precipitation is slightly favored for southeast Arizona and southwest New Mexico. An amplified trough favors above-median precipitation across the Aleutians and Alaska Peninsula, while EC is forecast for the remainder of Alaska due to weak signals among the precipitation tools.

The ECMWF and SubX MME depict increased probabilities for above-normal temperatures for Hawaii. Since SST anomalies surrounding the state are near average, above-normal temperature probabilities are limited to 70 percent. The Week 3-4 precipitation outlook is based largely on MJO precipitation composites with the expectation that its enhanced phase shifts back to the Pacific later this month. Therefore, above-normal precipitation is slightly favored for Hawaii.

Temperature Precipitation

FCST FCST

Hilo A70 A55

Kahului A70 A55

Honolulu A70 A55

Lihue A70 A55

Forecaster: Brad Pugh

The next week 3-4 outlook will be issued on Friday, Jun 09, 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