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 Jul 23 2021

Week 3-4 Forecast Discussion Valid Sat Aug 07 2021-Fri Aug 20 2021

ENSO-neutral conditions continue to persist with near average sea surface temperatures (SST) observed across the tropical Pacific. The Madden Julian Oscillation (MJO) signal has emerged over the last week with current RMM indices indicating active convection propagating from the Maritime Continent to the West Pacific. However, the continued propagation may be short-lived as dynamical model guidance indicates increased uncertainty as to the strength and position of the MJO by early August. The temperature and precipitation forecasts for the Week 3-4 period are based primarily on dynamical model guidance. Long-term trends were also a factor as well as the evolution of the Week-2 forecast.

Several of the dynamical models (CFS, GEFS, JMA, and the SubX multi-model ensemble) are in reasonable agreement with respect to the forecast 500-hPa circulation patterns. These models predict troughing over western Alaska and a broad region of positive height anomalies across the Northern Tier of CONUS, though the CFS favors stronger amplitudes over the northeast. The ECMWF solution indicates stronger positive height anomalies over the Pacific Northwest extending to eastern Alaska with slight troughing and near normal heights predicted across the Ohio and Mississippi Valley regions.

As a result of the aforementioned ridging as well as decadal trends, the temperature forecast tilts toward above normal probabilities for much of the western and northern portions of CONUS, extending from California through Michigan and across New England. The highest probabilities are forecast over the Northern Plains and Pacific Northwest where model agreement is strongest. Below normal temperatures are favored along the Gulf Coast by dynamical model guidance and are further supported by the high soil moisture in that region and below normal SSTs along the Gulf Coast. Equal chances are forecast across the Ohio Valley and the middle Atlantic where the ECMWF favored a colder solution that conflicted with other model guidance.

The precipitation forecast for the Week 3-4 forecast period also reflects the predicted ridging and decadal trends as well as strong agreement between statistical and dynamical model guidance. Enhanced probabilities for dry conditions dominate the Northern Plains extending down into Texas. The dry conditions are consistently favored to extend across the Gulf Coast and Florida where the strong upper level convergence is thought to suppress tropical cyclone activity through at least the beginning of the period. Enhanced monsoon precipitation is favored in the Southwest with highest probabilities across Arizona. There is also widespread agreement among dynamical and statistical guidance indicating enhanced probabilities of above normal precipitation throughout the Ohio Valley and Lower Great Lakes.

Over Alaska, equal chances for above and below normal temperatures are forecast for much of the state due to conflicting signals among the model guidance, but above normal temperature probabilities are consistently favored for the North Slope. Similar to last week, enhanced probabilities of above normal precipitation is favored for western Alaska with equal chances over the North Slope where model agreement is weak.

Near-normal sea surface temperatures have recently been observed in the region surrounding Hawaii. Dynamical model guidance from the SubX suite favors a slight tilt toward above normal temperature probabilities across the majority of the islands with equal chances for the southeast. Dynamical model guidance also indicates enhanced probabilities of below normal precipitation across the region.

Temperature Precipitation

FCST FCST

Hilo EC B55

Kahului A55 B55

Honolulu A55 B55

Lihue A55 B55

Forecaster: Laura Ciasto

The next week 3-4 outlook will be issued on Friday, Jul 30, 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