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 Sep 27 2024

Week 3-4 Forecast Discussion Valid Sat Oct 12 2024-Fri Oct 25 2024

Across the tropical Pacific, the El Niño Southern Oscillation remains neutral although sea surface temperatures (SSTs) in the Niño 3.4 region are slightly negative. The Madden Julian Oscillation (MJO) has been propagating eastward and recently entered the Western Hemisphere. Dynamical models are in good agreement in favoring continued eastward propagation of the intraseasonal signal over the Indian Ocean during week-2, but losing amplitude as it approaches the Maritime Continent by week-3. While the extratropical impacts/teleconnections are less certain, the predicted MJO evolution supports an uptick in late season Tropical Cyclone (TC) activity in the Atlantic Ocean. The current Week 3-4 Outlook takes thisMJO activity into account as well as the dynamical model guidance.

The dynamical models strongly agree on the large-scale circulation pattern characterized by a strong anomalous trough just south of Alaska and broad anomalous ridging over the central contiguous U.S. (CONUS). The largest source of uncertainty regarding the forecast large-sale circulation occurs in the east: models are mixed on the eastward extent with some solutions (particularly the JMA) favoring a weak trough for the Northeast.

The temperature outlook is dominated by above normal temperatures across much of the CONUS extending from the Southwest to New England as the result of the aforementioned ridging and strong agreement among the models. Equal Chances (EC) of above or normal temperatures are forecast for the Mid-Atlantic and Southeast where model signals disagree. Above normal temperatures for the North Slope of Alaska are indicated while the southern coast, including the Panhandle, favor below normal temperatures under the troughing. Some models extend the below normal probabilities into the Pacific Northwest, but the forecast anomalies are weak and inconsistent.

The anticipated anomalous ridging over CONUS will also increase probabilities of below median precipitation across much of the Great Plains from Texas to the Great Lakes. Dynamical guidance tends to extend this dry signal further into the Southeast, but Week 3-4 TC tools indicate possible activity during this time. As such, EC is forecast for that region. The dynamical models are more consistent with the TC tools on a wet signal for Florida. Probabilities for above normal precipitation are also enhanced for the south Alaska coast and Panhandle due the anomalous onshore flow that results from the troughing.

Sea surface temperatures around Hawaii are slightly elevated, supporting a slightly enhanced signal for above normal temperatures for the majority of the islands but the Big Island where EC is indicated. Dynamical model guidance also favors below normal precipitation for the southeastern islands.

Temperature Precipitation

FCST FCST

Hilo EC B55

Kahului A55 B55

Honolulu A55 EC

Lihue A55 EC

Forecaster: Laura Ciasto

The next week 3-4 outlook will be issued on Friday, Oct 04, 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