Prognostic Discussion for Week 3-4 Temperature and Experimental Precipitation Outlooks
NWS Climate Prediction Center College Park MD
300PM EDT Fri May 17 2019
Week 3-4 Forecast Discussion Valid Sat Jun 01 2019-Fri Jun 14 2019
The Week 3-4 Outlook is based primarily on dynamical model forecasts, including the NCEP CFS, ECMWF and JMA ensemble prediction systems, as well as the Subseasonal Experiment (SubX), a multi-model ensemble (MME) of both operational and experimental ensemble prediction systems. Statistical forecasts, including a multivariate linear regression (MLR) of lagged temperature and precipitation forecasts to current observed MJO and ENSO indices, were also consulted. Decadal timescale temperature trends are also a source of predictability in both dynamical and statistical forecast tools. The MJO has recently been active with subseasonal convective activity moving across the Western Pacific into the Western Hemisphere. Dynamical model forecasts indicate large uncertainty on the state of the MJO after week 2, such that MJO was not a large component of the forecasts. A weak El Nino continued into May, however the ENSO base state did not appear to be a primary source of predictability in dynamical and statistical model forecasts.
The CFS, ECMWF and JMA dynamical models exhibit considerable differences between their respective forecasts for the week 3 and 4 period, indicating significant uncertainty. The SubX also shows considerable uncertainty in the week 3 and 4 period with very weak 500-hPa height anomalies over the CONUS in the MME mean and considerable disagreement among the individual model forecasts that make up the SubX MME. The consensus of dynamical models generally indicates a transition of the circulation pattern forecast after week 2, leading to weak ridging over the central CONUS. The ECMWF ensemble and most ensemble members of the SubX predict weak troughing over the eastern CONUS. Models are in general agreement on the persistence of troughing near the Pacific coast into weeks 3 and 4. The consensus of the SubX MME predicts weak troughing over and south of the Aleutian Islands and positive 500-hPa height anomalies over mainland Alaska and the panhandle.
The Week 3-4 Outlook indicates enhanced probabilities of below normal temperatures over parts of the Great Plains, from the Rocky Mountains to the Central and Upper Mississippi Valley. Troughing over the western CONUS and ridging over the eastern CONUS in week 2 transitions to weaker troughing over parts of the west coast in weeks 3 and 4 in most dynamical model runs. Temperature forecasts from the ECMWF and several component models of the SubX predict a broader area of below normal temperatures across much of the CONUS, while the CFS and some individual models of the SubX, including the CCSM4 and Canadian models, predict likely above normal temperatures for much of the western and eastern CONUS. The area of greatest consensus among dynamical models for below normal temperatures is indicated in the Week 3-4 Outlook, with equal chances (EC) shown for significant portions to the southwest and northeast. Above normal temperatures are likely for much of the Pacific Northwest, under predicted above normal 500-hPa heights. Above normal temperatures are also likely for parts of the Southwest, where decadal temperature trends play a significant role. Continued ridging over the Southeast leads to likely above normal temperatures in the Week 3-4 Outlook. Above normal temperatures are most likely for Alaska under predicted positive 500-hPa height anomalies and where decadal temperature trends are relatively strong.
The Week 3-4 Outlook indicates likely above normal precipitation for parts of the Northern Rockies into the Northern Plains and for parts of the Southern and Central Plains, ahead of troughing in the forecast, primarily early in weeks 3 and 4. Dynamical model forecasts indicate a chance of storm systems moving up the Atlantic Coast during the period, leading to likely above normal precipitation for the Florida Peninsula and parts of New England. Below normal precipitation is likely for the remaining areas of the Gulf Coast northward into the Ohio Valley and parts of the Great Lakes region, under predominately northerly flow behind the predicted trough over the eastern CONUS in a consensus of models. Below normal precipitation is also likely for much of the Alaska Panhandle and the Pacific Northwest under above average 500-hPa heights. Above normal precipitation is likely for parts of the Aleutian Islands and Southwest Alaska, ahead of a predicted trough.
Surrounding above average sea surface temperatures and predicted positive 500-hPa height anomalies over Hawaii lead to enhanced probabilities of above normal temperatures for the Week 3-4 Outlook. A consensus of the SubX dynamical models predicts likely below normal precipitation for the northwestern Hawaiian Island and above normal precipitation for the southeastern islands.
| Temperature | Precipitation |
| FCST | FCST |
| Hilo | A70 | A55 |
| Kahului | A70 | EC |
| Honolulu | A70 | B55 |
| Lihue | A70 | B55 |
Forecaster: Dan Collins
The next week 3-4 outlook will be issued on Friday, May 24, 2019
These outlooks are based on departures from the 1981-2010 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