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 Nov 26 2021

Week 3-4 Forecast Discussion Valid Sat Dec 11 2021-Fri Dec 24 2021

The Madden-Julian Oscillation (MJO) is forecasted by some models to emerge in phase 6 by the beginning of the Week 3-4 forecast period, however the uncertainty regarding that signal is large. The current Week 3-4 outlook is based on other large scale signals such as the present La Nina conditions and the projected positive phase of the NAO, as well as blends from the dynamical model guidance including the GEFS, CFS, Canadian, ECMWF, JMA, the SubX multi-model ensemble (MME), and statistical guidance.

With an updated La Nina Advisory issued in early November, and forecast to last through the boreal winter, overall, the Week 3-4 forecast averages of temperature and precipitation resemble a combination of canonical La Nina and positive NAO patterns. As we look toward the middle two weeks of December, the dynamical models generally agree on anomalous troughing over Alaska and the Alaskan Panhandle and anomalous ridging over much of CONUS. This pattern appears to be the evolution of a similar pattern from Week-2. The positive height anomalies favor above normal temperatures for much of CONUS while the troughing near Alaska favors below normal temperatures for Alaska. Some of the dynamical model guidance and blends presented a 70% chance or higher of probabilities of above normal temperatures for localized areas such as Texas and neighboring regions. Model guidance was more mixed for the western states, however probabilities for either above or below temperatures were low in those states therefore the area is forecast with equal chances.

Given the troughing pattern, likely areas for above normal precipitation include much of the west coast and eastward to the Rocky Mountains. Model guidance also indicated some enhanced chances for above normal precipitation in the Upper Mississippi Valley and eastward to the Northeast with highest probabilities along northern Michigan and New England. Slightly drier than normal conditions are forecast across the lower tier of CONUS with mixed model guidance up through the Plains. Alaska is broadly forecast to be slightly drier than normal, with chances increasing toward the North Slope.

Above normal temperatures and below average precipitation are favored for Hawaii, based on guidance from the SubX MME. The SubX MME also indicates anomalies for these conditions are only slightly above (for temperature) and slightly below (for precipitation).

Temperature Precipitation

FCST FCST

Hilo A60 B55

Kahului A70 B55

Honolulu A80 B55

Lihue A80 B55

Forecaster: Emerson LaJoie

The next week 3-4 outlook will be issued on Friday, Dec 03, 2021

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