Climate Prediction Center - Week 3-4 Outlook

Prognostic Discussion for Week 3-4 Temperature and Experimental Precipitation Outlooks
NWS Climate Prediction Center College Park MD
300PM EDT Fri Oct 11 2019

Week 3-4 Forecast Discussion Valid Sat Oct 26 2019-Fri Nov 08 2019

Forecast uncertainty is once again high this week as we attempt to forecast the evolution of the autumnal transition season. The MJO remains weak. The RMM index is still stuck in Phase 1 as the positive Indian Ocean Dipole (IOD) event projects onto the index, creating a stationary signal. There is also low equatorial wave activity; both Kelvin and equatorial Rossby wave signals are weak. Typhoon Hagibis in the northwestern Pacific is forecast to recurve during the next week, which could have significant implications on downstream predictability over the CONUS during Week-2 (and therefore Weeks 3 and 4). This potential source of forecast error, combined with a lack of subseasonal tropical forcing and divergent model solutions makes this a difficult forecast.

The CFS, ECMWF, and JMA are in poor agreement during both forecast weeks. The JMA's solution is most similar to the Week-2 forecast, implying a relatively persistent pattern whereas the CFS and ECMWF models forecast pattern shifts, albeit in slightly different ways.

The CFS favors ridging over the central CONUS during Weeks 3 and 4 resulting in above normal temperatures over the northwestern CONUS and northern Alaska, as well as below normal temperatures over the entire eastern CONUS. The ECMWF forecasts the strongest ridging to expand from the northwestern CONUS in Week-3 to the East Coast by Week-4. The ECMWF temperature forecast has a similar warm signal in the West, but its probabilities of below normal temperatures throughout the Mississippi River Valley are muted compared to those of the CFS. Furthermore, the ECMWF predicts slightly enhanced probabilities of above normal temperatures over the Eastern Seaboard. The JMA, on the other hand, forecasts anomalous troughing over the western CONUS and anomalous ridging over the eastern CONUS during the entire period, leading to above normal temperatures over Alaska and the southeastern CONUS and below normal temperatures over the northwestern CONUS.

Model agreement about the precipitation forecast is similar to the temperature forecast. The CFS and ECMWF favor below normal precipitation over many portions of the CONUS, including the northwest. The JMA persists the above normal precipitation signal throughout the Mississippi Valley from Week-2 into Weeks 3 and 4.

Our final forecast is most similar to a blend of the CFS and ECMWF, leaning towards the ECMWF when appropriate. This forecast suggests that a major pattern transition is likely during Weeks 3-4, which is not uncommon during late October and early November. The SubX suite of models also behaves similar to this blend, on average. We forecast above normal temperatures over most of Alaska and the western two-thirds of the CONUS during the Week 3-4 period. We also forecast about a 55-60% chance of below normal temperatures over much of the Mississippi Valley. Our forecast also features a 55-60% chance of above normal rainfall over much of eastern Alaska, with the highest probabilities of 60-65% over the Panhandle. We also forecast below normal precipitation over the Pacific Northwest and throughout the central of the CONUS from the Plains to the Appalachians.

Observed sea surface temperatures remain 2 to 3 degrees C above normal surrounding Hawaii, supporting above normal temperatures during the Weeks 3-4 period. Guidance from most models suggests slightly above normal precipitation favored across the islands.

Temperature Precipitation

FCST FCST

Hilo A90 A60

Kahului A90 A60

Honolulu A90 A60

Lihue A90 A60

Forecaster: Kyle MacRitchie

The next week 3-4 outlook will be issued on Friday, Oct 18, 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