Sig Silber

It is very useful to read the excellent discussion that NOAA issues with this Seasonal Outlook.  The overall level of confidence in the Seasonal Outlook is addressed in the NOAA discussion. It is best to read the full discussion but here are some of the highlights:

Re ENSO:

• The observed weekly SSTs, centered on July 12, feature positive anomalies throughout the equatorial Pacific with the largest anomalies of more than +1 degree C generally east of 160°W.
• The CFSv2 continues to depict a strong El Niño by ASO, while the North American Multi-Model Ensemble (NMME) mean keeps the anomalies below 1.5 degrees C. The statistical tools vary with the strength of the El Niño during the next six months. As of early July, NOAA’s CPC forecast calls for more than a 90 percent chance of El Niño persisting through JFM 2024 with a 52 percent chance of a strong El Niño (> 1.5 degrees C) during OND 2023.

For August

• The August temperature outlook favors above normal temperatures over much of Alaska, consistent with dynamical model guidance and the monthly temperature consolidation.
• Widespread above normal temperatures are favored over much of the contiguous U.S. (CONUS), supported by the consolidation of statistical and dynamical forecast tools. Probabilities for above normal temperatures exceed 60 percent over the Pacific Northwest, due to dynamical model forecasts and dry soil moisture anomalies.
• Below normal temperatures are favored for parts of the eastern Northern Plains and upper Mississippi Valley.
• El Niño impacts favor potential troughing over the eastern central CONUS with northerly flow into this region.
• Statistical forecasts based on the current state of ENSO predict a larger area of favored below normal temperatures, resulting in a reduction in probabilities of above normal temperatures for much of the east-central CONUS.
• Above average SST anomalies along the Gulf and East Coasts increase the probability of above normal temperatures in these regions.
• The August precipitation outlook favors below normal precipitation near the coast of the southwestern Alaska Mainland.
• Though above normal precipitation is slightly favored in southwestern Arizona at the start of the month by the Week 3-4 Outlook, El Niño impacts and statistical forecast tools favor a suppressed monsoon for the full month of August.
• Below normal precipitation is favored for much of the Southwest Monsoon region from West Texas to northeastern Arizona and northward across the Intermountain West into parts of eastern Oregon and southern Idaho.
• Above normal precipitation is favored from eastern areas of the Central Plains across the central Mississippi Valley to the Atlantic Coast, along a preferred potential storm track and supported by the consolidation of precipitation forecast tools.
• Above normal precipitation is favored from northeastern Florida along the Atlantic Coast into southern New England, supported by the consolidation.

For ASO 2023:

• The August-September-October (ASO) 2023 temperature outlook favors above-normal seasonal mean temperatures across a majority of the U.S.
• The highest probabilities (more than 60 percent) of above-normal temperatures are forecast across parts of the Southwest.
• The ASO precipitation outlook depicts elevated probabilities of below-normal precipitation for parts of the Southwest and Pacific Northwest,
• while above-normal precipitation is favored across much of the central and southern Great Plains, parts of the Middle to Lower Mississippi Valley, the Tennessee Valley, and the central Atlantic Coast from the Carolinas to southern Virginia.
• Equal chances (EC) are forecast in areas where the likelihood of seasonal mean temperatures or seasonal accumulated precipitation amounts are expected to be similar to climatological probabilities.

Beyond ASO 2023:

• Beginning in NDJ 2023-24 through JFM 2024, predicted El Niño conditions result in enhanced chances for above-normal temperatures across the northern tier of the CONUS with an increasing coverage of EC across California, the Southwest, Southern Great Plains, and Lower Mississippi Valley.
• During the winter 2023-24, above-normal temperatures are favored across the East based on the statistical consolidation.
• From MAM to ASO 2024, the temperature outlook is consistent with decadal trends.
• The [precipitation] outlook for SON maintains most of those signals , except for the signal in the Plains as SON are not the core monsoon months.
• During OND the area where above-normal precipitation is favored expands from the Southeast to the Southern Plains, associated with likely impacts from the predicted states of ENSO. Correspondingly odds for below-normal precipitation expand in the Northwest.
• During NDJ 2023 to JFM 2024, the outlooks largely favor above-normal precipitation across the southern tier and below-normal precipitation across the northern tier of the CONUS. That pattern is largely aligned with ENSO impacts and model guidance.
• From FMA 2024 through ASO 2024, the outlooks primarily reflect the consolidation of available tools, which largely follows trends and ENSO impacts.