Prognostic Discussion for Week 3-4 Temperature and Experimental Precipitation Outlooks
NWS Climate Prediction Center College Park MD
300PM EDT Fri Jul 26 2024
Week 3-4 Forecast Discussion Valid Sat Aug 10 2024-Fri Aug 23 2024
El Niño Southern Oscillation (ENSO) neutral conditions are currently present in the Equatorial Pacific and are expected to continue for the next few months, though a La Niña Watch has been issued. Equatorial sea surface temperatures (SSTs) are above average in the western and west-central Pacific, near average in the east-central Pacific, and below average in the eastern Pacific Ocean. The Madden Julian Oscillation (MJO) has been weak since June with little propagation. Forecasts of the Realtime-Multivariate MJO (RMM) index from GEFS and ECMWF have been weak with signals more indicative of a fast-moving Convectively-Coupled Kelvin wave rather than MJO. Given the current and forecasted continuation of ENSO-neutral and weak MJO conditions, both La Niña and MJO impacts were not strongly considered in this week's Outlook. Soil moisture, particularly increased soil moisture over east Texas and Louisiana and dry soils over the northwestern Contiguous United States (CONUS) are a consideration, as are local SSTs along the west coast of Alaska that are anomalously cold, and along the Gulf and East Coasts that are anomalously warm. In addition, the Weeks 3-4 Temperature and Precipitation Outlooks are based on dynamical model forecasts from the CFS, GEFS, ECMWF, JMA, and experimental blends. A statistical Multiple Linear Regression (MLR) tool which includes input from ENSO, MJO, and decadal trends was also used, mainly for how influence of trend may impact the forecast given weak ENSO and MJO activity.
Dynamical model guidance generally agrees on troughing over Alaska and ridging over the northern tier of the CONUS. The placement and strength of the trough over Alaska varies between models, with CFS and GEFS favoring stronger troughing over and off the coast of western Alaska, and ECMWF favoring weaker troughing that is mostly off the coast with more neutral heights over land. While the ridging over the northern tier of CONUS is a common feature among the models, CFS and ECMWF have higher 500 hPa heights over the northwestern and northeastern CONUS, while GEFS favors higher heights stretching across the entire northern tier. 500 hPa heights tilt slightly above normal over Hawaii.
The Weeks 3-4 Temperature Outlook favors enhanced probabilities of above normal temperatures across the lower 48, with higher probabilities over the northern tier of the CONUS beneath favored ridging. The highest probabilities, reaching 70 to 80%, are over the interior west where soils have been anomalously dry, precipitation is expected to be below median or equal chances (EC) of above and below median, decadal temperature trends are above normal, ahead of and under higher 500 hPa heights in CFS and ECMWF, and where dynamical models had the strongest agreement. Probabilities are also higher along the eastern seaboard of the CONUS and parts of the eastern Great Lakes where model agreement was high and supported by above normal coastal SSTs. While remaining enhanced, probabilities for above-normal temperatures are lower over coastal California where model signals were weaker, and over roughly the Lower and Middle Mississippi, Tennessee, and Ohio Valley regions where soil moisture is above normal (toward the coast) and where convection has been prominent recently. Strong model agreement along with onshore flow and anomalously cold SSTs support probabilities of below normal temperatures over western Alaska. EC is indicated for the northern and eastern parts of the state where trends are stronger and models had more disagreement. Slightly above normal temperatures are forecast for Hawaii underneath weak ridging along with weak but positive SST anomalies.
The Weeks 3-4 Precipitation Outlook is comparatively more uncertain, particularly over the central CONUS where there was model disagreement. Somewhat better model agreement and low soil moisture over the northwestern CONUS support a tilt toward below median probabilities, and models generally agree that below median precipitation may stretch eastward toward the Great Lakes during the period. Above median precipitation is indicated over parts of Arizona, the Gulf States, and along the east coast into parts of New England. The above median precipitation over Arizona is common across all models, though the location and strength of probabilities is mixed, as such a low probability is indicated. Along with model agreement, higher soil moisture over eastern Texas and Louisiana supports a tilt toward above median precipitation. Probabilities are enhanced over Florida and along the Gulf and East Coasts due to the potential for tropical cyclone activity. Troughing over Alaska supports above median precipitation, though models disagreed on the location of strongest probabilities. With the exception of CFS, below median precipitation is forecast for Hawaii, with stronger probabilities over Honolulu and Lihue.
| Temperature | Precipitation |
| FCST | FCST |
| Hilo | A55 | B55 |
| Kahului | A55 | B55 |
| Honolulu | A55 | B60 |
| Lihue | A55 | B60 |
Forecaster: Johnna Infanti
The next week 3-4 outlook will be issued on Friday, Aug 02, 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