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 04 2024

Week 3-4 Forecast Discussion Valid Sat Oct 19 2024-Fri Nov 01 2024

Neutral ENSO conditions persist along the tropical Pacific, but the intraseasonal Madden Julian Oscillation (MJO) signal has been active and is expected to continue its eastward propagation through at least the middle of October. While the North Atlantic Oscillation has been in the negative phase over the last few weeks, it is forecast to transition to weakly positive by the start of the forecast period. The Pacific North America pattern, currently in the positive phase, is forecast to become neutral. Neither are expected to impact this outlook, which largely relies on the dynamical models and statistical tools incorporating MJO teleconnections.

Consistent with the previous Week 3-4 Outlook, the large-scale circulation over the CONUS continues to be dominated by anomalous ridging over the Northern Plains and troughing across Alaska. However, the dynamical model guidance suggests this pattern may shift through from Week-3 to Week-4. The positive height anomalies driving the ridge are strongest with good model consistency during Week-3. By Week-4, these height anomalies weaken and model guidance differs on placement, leading to more uncertainties in the forecast.

The temperature outlook for the Week 3-4 period tilts toward above normal temperatures for much of the central and eastern CONUS associated with the anomalous ridging. This pattern is primarily a Week-3 signal with amplitudes diminishing noticeably as the pattern shifts in Week-4. As a result, the temperature probabilities are lower due to uncertainty in the timing of this shift. Equal Chances (EC) of above or below normal temperatures are predicted for the Pacific Northwest and the Southeast where model signals are weak.

The precipitation outlook is more uncertain due to the timing of the weakening and/or shifting of the circulation pattern. During Week-3, many of the dynamical models favor below normal precipitation across the central and eastern CONUS, consistent with both the Week-2 and Monthly outlooks. By Week-4, this signal is largely diminished so confidence in the precipitation outlook is low. Elsewhere across CONUS, including Florida, model signals are mixed so EC if forecast.

For Alaska, the manual blend of dynamical and statistical tools indicates a broad but weak anomalous troughing with onshore flow. As a result, probabilities for above normal precipitation are forecast throughout the southern coast and Panhandle. Temperatures are favored to be above normal for the northern half of the state.

Temperature probabilities lean slightly below normal for the southeastern Hawaiian islands, with EC favored for the northwest. Dynamical model guidance indicates a transition from drier than normal conditions for the southeastern islands to wetter than normal conditions for Lihue.

Temperature Precipitation

FCST FCST

Hilo B60 B60

Kahului B55 B55

Honolulu EC EC

Lihue EC A55

Forecaster: Laura Ciasto

The next week 3-4 outlook will be issued on Friday, Oct 11, 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