Prognostic Discussion for Week 3-4 Temperature and Experimental Precipitation Outlooks
NWS Climate Prediction Center College Park MD
300PM EDT Fri Apr 19 2024
Week 3-4 Forecast Discussion Valid Sat May 4 2024-Fri May 17 2024
The present Weeks 3-4 forecast is on the lower end of the confidence spectrum given a confluence of factors including: the forecast occurring during the Spring transition season as well as limitations on forecast guidance availability due to an ongoing IT outage at our data center. Furthemore, teleconnections related to the tropical Madden Julian Oscillation and extratropical North Atlantic Oscillation are modest, which is typical during this time of year. As a result of these factors, the forecasts rely primarily on GEFS and ECMWF with additional considerations for ENSO, decadal, and evolution from previous forecasts.
Similar to the previous Week 3-4 forecast, the large-scale circulation continues to exhibit anomalous ridging over the central CONUS juxtaposed by anomalous troughing over Nova Scotia and Newfoundland and off the west coast of southern California. The largest discrepancies between models are in the strength and location of these centers of action. The CFS favors stronger troughing over New England and southern California and weaker ridging over central CONUS. Alternatively, the ECMWF highlights stronger ridging and weaker troughing, particularly in Week-4. The GEFS solution represents more of a blend between the CFS and ECMWF. These discrepancies are a source of uncertainty for the temperature and precipitation forecasts.
The Week 3-4 temperature forecast continues to tilt toward above normal temperatures across the north-central CONUS, extending from the Pacific Northwest to the Great Lakes regions. Probabilities are highest for the Northern Plains where both ECMWF and GEFS favor warmer than normal conditions under the aforementioned ridging. Below normal temperatures are predicted for the Southwest, consistent with the troughing and further supported by statistical guidance that explicitly accounts for ENSO and the trend. Elsewhere across CONUS, Equal Chances (EC) of above or below normal temperatures are forecast due to the weak and conflicting signals among the limited model guidance. Models are also split on a coherent temperature signal for western Alaska but agree on above normal temperatures for southeastern Alaska and the Panhandle.
The Week 3-4 precipitation forecast favors above median precipitation across much of the Great Plains with EC for the Southeast and Southwest. This is a shift from previous forecasts in which the southern tier has been dominated by an anomalous wet signal. While dynamical model guidance indicates a drier than average signal for parts of the desert Southwest that is consistent with the recent Monthly Outlook, parts of southern California and Arizona are climatologically dry for the current outlook period. Throughout the East and Southeast, model guidance is limited and mixed. Below median precipitation is predicted for the Pacific Northwest extending to the Alaska Pandle. The remainder of Alaska is EC due to weak model signals.
Sea surface temperatures around Hawaii remain near normal, and model guidance is generally mixed leading to a lower confidence forecast. The ECMWF and GEFS solutions both favor a slight tilt toward below normal temperatures across the islands. EC is forecast for precipitation as signals remain weak and inconsistent between models.
| Temperature | Precipitation |
| FCST | FCST |
| Hilo | B55 | EC |
| Kahului | B55 | EC |
| Honolulu | B55 | EC |
| Lihue | B55 | EC |
Forecaster: Laura Ciasto
The next week 3-4 outlook will be issued on Friday, Apr 26, 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