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 Aug 05 2022

Week 3-4 Forecast Discussion Valid Sat Aug 20 2022-Fri Sep 02 2022

The upper-level presentation of the Madden-Julian Oscillation (MJO) became increasingly incoherent over the last few days, and dynamical model forecasts of the Realtime Multivariate MJO (RMM)-based index are mixed and generally weak. Therefore, the MJO is not anticipated to play a substantive role in the evolution of the tropical convective pattern over the next few weeks, with an unusually robust summer La Niña response remaining the primary driver. La Niña and long term trends are the main contributors to the multivariate linear regression (MLR) statistical tool for Weeks 3-4, though teleconnections between the tropics and Northern Hemisphere extratropics are generally weak this time of year. While East Pacific tropical cyclone activity has been above-average despite the La Niña background state, the Atlantic basin has been unusually quiet due to frequent intrusions of dry Saharan air layers. Dynamical model forecasts indicate that Atlantic tropical cyclone activity will likely pick up through the end of August as storm climatology increases precipitously. Therefore, there is a potential for tropical cyclones to impact the United States during the Weeks 3-4 period, though it is too early to predict individual formations or tracks.

Dynamical model 500-hPa height anomaly forecasts are generally consistent over the contiguous United States (CONUS), favoring above-average heights across the northern tier and weak anomalies elsewhere, while some differences exist upstream in the vicinity of Alaska and the Northeast Pacific. The ECMWF favors anomalous troughing across southern Alaska and the Northeast Pacific, while the GEFSv12 places anomalous ridging in the same location. A manual blend of CPC’s operational dynamical and statistical model guidance shows a potential for mean southerly flow across Alaska, reflecting a potential pattern change towards warmer conditions. Over the CONUS, anomalous ridging is most favored over the Northwest and Northeast, while height anomalies are more weakly positive across the central CONUS. This pattern overall favors a fairly warm solution for the US, with no areas of increased odds for below-normal temperatures indicated on the outlook.

Consistent with the manual blend height anomaly forecast, the highest probabilities for above-normal temperatures extend across the West and along the eastern seaboard. Equal-chances (EC) for above- and below-normal temperatures are maintained across the southern Four Corners region due to a potential for continued enhanced monsoonal convection. EC is also maintained across the Great Lakes, due to the potential for brief intrusions of milder and drier airmasses from Canada during the period, continued below-average lake surface temperatures across Lake Superior, and areas of enhanced soil moisture across the eastern Corn Belt. Across Alaska, above-average temperatures are favored for western and central areas.

Two regions of consistency emerged among the various precipitation forecast tools. Most of the guidance continues to favor an active monsoon regime across the Four Corners, with differences in placement and northward extent of the signal. Enhanced chances for above-normal precipitation are extended as far north as southern Wyoming as dynamical model guidance is generally wetter and more expansive than in previous weeks. Dynamical models also consistently indicated increased odds for below-normal precipitation across the north-central CONUS, with the GEFSv12 extending this signal into the Deep South, while the ECMWF showed wetness along the Gulf Coast. Due to these model differences, EC is maintained across the interior South and much of the eastern seaboard, while enhanced chances for above-normal precipitation extend from southern Texas along the immediate Gulf Coast, excluding the Florida Peninsula. Dynamical model forecasts favored below-normal precipitation for western and central Alaska, with increased odds for wetness across the Panhandle.

Slightly above-average height anomalies and above-normal SSTs favor above-normal temperatures across Hawaii. Guidance from the Subseasonal Experiment multi-model ensemble (SubX MME) favors below-average precipitation, while the operational dynamical models depict a mixed signal. Based on these conflicting signals, EC for precipitation is maintained across Hawaii.

Temperature Precipitation

FCST FCST

Hilo A55 EC

Kahului A55 EC

Honolulu A55 EC

Lihue A60 EC

Forecaster: Adam Allgood

The next week 3-4 outlook will be issued on Friday, Aug 12, 2022

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