Prognostic Discussion for Week 3-4 Temperature and Experimental Precipitation Outlooks
NWS Climate Prediction Center College Park MD
300PM EDT Fri Jun 18 2021
Week 3-4 Forecast Discussion Valid Sat Jul 03 2021-Fri Jul 16 2021
ENSO-neutral conditions remain across the tropical Pacific. As indicated by RMM indices, weak convection associated with the Madden Julian Oscillation (MJO) is observed over the Indian Ocean. Dynamical model guidance suggests that the MJO will become inactive in the coming days. There is potential for weak convection to re-emerge over the Western Hemisphere during Week-2, but model uncertainty exists with regard to the amplitude of the signal. Furthermore, tropical impacts on North American sensible weather during the summer months are often weak. Today's Week 3-4 temperature and precipitation forecasts rely on dynamical model guidance with considerations from long-term trends and soil moisture conditions.
There is reasonable agreement among forecast guidance in terms of the predicted large-scale 500-hPa circulation patterns. The dynamical models (CFS, GEFS, ECWMF, JMA, and the SubX multi-model ensemble) consistently forecast ridging over the Aleutian Islands and over the Northern Rockies and Plains, although the JMA solution is weaker in amplitude relative to the ECWMF and the CFS. Larger discrepancies are also noted over the Gulf of Alaska where solutions range from weakly negative 500-hPa height anomalies (GEFS) to positive height anomalies (CFS).
The temperature forecast for the Week 3-4 period tilts toward above normal probabilities for much of the northern tier of CONUS, consistent with the predicted ridging over the region and decadal trends. The highest probabilities are forecast over the Intermountain West where model agreement is strongest. Below normal temperature probabilities along the Gulf Coast are favored by dynamical model guidance and are further supported by the high soil moisture in that region. Over Alaska, equal chances are forecast for much of the state due to conflicting signals across the model guidance, but above normal temperature probabilities are consistently favored for the Aleutian Islands and the North Slope.
The precipitation forecast also reflects the aforementioned ridging over the Northern Plains and decadal trends resulting in enhanced probabilities for dry conditions over the Pacific Northwest extending into the Plains. Elevated probabilities for above normal precipitation are forecast along the Gulf Coast from Alabama to Texas. Some models (particularly the GEFS) indicated the potential for moisture into the Southwest related to tropical cyclone activity during the Week 2-3 period, but track/intensity are highly uncertain at these time scales and thus equal chances are forecast. Equal chances are also favored for the East Coast as well as Alaska due to high model uncertainty.
Near-normal sea surface temperatures dominate the region surrounding Hawaii. Dynamical model guidance from the SubX suite indicates equal chances with a slight tilt toward above normal temperature probabilities in the northwest islands. Similarly, dynamical models favor equal chances in the southeast, increasing to slightly above normal probabilities in the northwest.
| Temperature | Precipitation |
| FCST | FCST |
| Hilo | EC | EC |
| Kahului | A55 | A55 |
| Honolulu | A55 | A55 |
| Lihue | A55 | A55 |
Forecaster: Laura Ciasto
The next week 3-4 outlook will be issued on Friday, Jun 25, 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