August 14, 2022 Looking Ahead 28 Days Plus a Review of State Temperature and Precipitation Rankings

Now we address Weeks 3 and 4. This is a time frame that is very important. It is half of the 28-Day forecast period. That is why we include the discussion that accompanies the maps.

Prognostic Discussion for Week 3-4 Temperature and Experimental Precipitation Outlooks

NWS Climate Prediction Center College Park MD

300PM EDT Fri Aug 12 2022

Week 3-4 Forecast Discussion Valid Sat Aug 27 2022-Fri Sep 09 2022

Dynamical model forecasts of the Realtime Multivariate Madden Julian Oscillation (RMM) index were mixed at the beginning of the week, with forecasts from the Climate Forecast System version 2 (CFSv2) and Bureau of Meteorology (BOM) indicating weak but coherent eastward propagation in mid-August. However, more recent forecasts from the Global Ensemble Forecast System version 12 (GEFSv12) remain within the unit circle with uncertainty into the week 3-4 period. The active La Niña has more influence on the Week 3-4 temperature and precipitation Outlooks than the Madden Julian Oscillation (MJO). Antecedent soil moisture conditions, dynamical model forecasts of week 3-4 500-hPa heights, temperature, and precipitation, persistence from week 2 forecasts, as well as dynamical model trends are considered in addition to potential La Niña impacts.

Predictions of anomalous 500-hPa heights from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the 4-member CFSv2 models for the week 3-4 period depict troughing over the western coast of Alaska and parts of the Aleutians. The GEFSv12 model favors neutral 500-hPa anomalies for the mean week 3-4 period, but depicts troughing in week 3 that diminishes by week 4. Persisting from week 2 forecasts, dynamical models generally agree on ridging over the northern contiguous United States (CONUS). The ECMWF and GEFSv12 models forecast a region of stronger positive 500-hPa anomalies over the Northwest. The 4-member CFSv2 500 hPa height forecast is an outlier and depicts troughing over the Great Lakes. 500-hPa heights are forecast to be near normal over the southern CONUS.

Consistent with the forecasted ridging over the northern CONUS, particularly over the Northwest, enhanced above normal temperature probabilities are forecast for the region stretching from the western CONUS to the Great Lakes. Probabilities of above normal temperature reaching 60-70 percent are indicated for eastern Washington and Oregon to Montana beneath strong anomalous ridging. Elevated probabilities of above normal temperature are also indicated for the Northeast and the Southeast, where decadal trends support a tilt toward above normal temperatures, along with consistent dynamical model forecasts. Weakly enhanced probabilities of below normal temperatures are favored for the Desert Southwest given dynamical model forecasts of a robust monsoon. Equal-chances (EC) for above- and below-normal temperatures are indicated for parts of the Southern Plains through parts of the Tennessee Valley where dynamical models showed conflicting signals. EC is also indicated over the Great Lakes due to anomalously cool Lake Superior temperatures and a weak height pattern. Over Alaska, EC is favored for the western part of the state and the Aleutians given forecasted inconsistent dynamical model temperature forecasts, as well as uncertainty in the location and timing of the forecasted troughing. Elevated probabilities of above normal temperature are indicated over central Alaska given dynamical model certainty, but EC is favored over the eastern parts of Alaska as increased probabilities for above normal precipitation are expected to moderate temperatures for this region.

Downstream of forecasted ridging over the northern CONUS along with regions of low soil moisture supports a tilt toward below median precipitation over the region stretching from Washington to the Great Lakes, and southward into the Central Plains. The highest probabilities are depicted over parts of the Northern Plains and Upper Mississippi Valley given model consistency amongst CFSv2, ECMWF, GEFSv12, and the Japan Meteorological Agency (JMA) model which favor below median precipitation. Models remain in agreement on robust and widespread monsoon over the Desert Southwest that reaches as far northward as parts of southern Idaho. Dynamical models also indicate weakly enhanced probabilities of above median precipitation over the Gulf States under neutral 500 hPa height anomalies and elevated soil moisture anomalies. This is in contrast to what might be expected during an active La Niña, which favors a tilt toward below normal probabilities over parts of the Ozarks, thus EC is maintained northward of the Gulf States. EC is also maintained over the East Coast where dynamical model signals are weak or inconsistent. Dynamical models generally agree on a tilt toward below median precipitation over northwestern Alaska associated with forecasted 500-hPa troughing, while models agree on above median precipitation over southeastern Mainland Alaska and parts of the Alaska Panhandle.

Above-average sea surface temperatures in the vicinity of Hawaii, as well as the Subseasonal Prediction Experiment (SubX) multi-model ensemble (MME) probabilistic temperature forecast favor above average temperatures over Hawaii during Week 3-4. The highest probabilities of above normal temperatures in the SubX MME are over northern parts of Hawaii. Below median precipitation is favored for Honolulu and Lihue given a tilt toward below normal probabilities in SubX models, but EC is favored over the remaining islands given inconsistent model signals.