SEPTEMBER-AUGUST 2017 90-DAY OUTLOOK
354 PM EDT Fri. Sep. 1, 2017
Atmospheric patterns, 700 MB and 500 MB height anomalies, statistical data, and various models such as the ECMWF monthly, NMME, IMME and the CFSv2, along with observed cases from past such months, data from 1895-2000 were used in this forecast.
During July, neutral continued were observed, as equatorial sea surface temperatures were near normal across most of the Pacific Ocean. The latest weekly Nino sea surface temperature index values were close to zero in all four Nino regions, having recently decreased from higher levels in the Nino-4 and Nino-3.4 regions. The upper-ocean heat content anomaly was near normal in July, reflecting below-normal temperatures along the thermocline across the central and eastern Pacific overlain by slightly above normal temperatures. Tropical convection was near normal over the eastern half of the Pacific and enhanced over the western Pacific and the Maritime Continent. The lower-level trade winds were slightly enhanced near the International Date Line, and upper-level winds were near normal over most of the tropical Pacific. Overall, the ocean and atmosphere system remains consistent with neutral conditions. The majority of models depict neutral conditions through the remainder of 2017.
The ECMWF Monthly depicts above normal heights in the West and near to above normal heights in the East. The North American Multi-Model Ensembles indicate above normal temperatures across much of the nation. The NMME depicts near to below normal precipitation for the nation.
The NAO starts out positive in September and then trends negative by day 10 and remains negative through day 14. The PNA is forecast to remain positive through the first 2 weeks of September. There is little skill in forecasting these indexes past the 2-week period.
Above normal temperatures are forecast for the western states and most of the area east of the Mississippi River. Anomalies of 4F are fore in the West and 4F in the East. The probability of above normal temperatures for this region is 57 percent in the West and 55 percent in the East. The remainder of the nation is not expected to exceed normal climatology.
Below normal precipitation is forecast for the northern Rockies, the northern Plains and the upper Mississippi Valley. The probability of below normal precipitation for these regions is 57 percent. Above-normal precipitation is forecast for the central Four Corners, the eastern Gulf Coast States, the Southeast, the Tennessee Valley and the lower Mid-Atlantic. The probability of above normal precipitation for this area is 54 percent for the Four Corners and 56 percent for the eastern Gulf Coast States, the Tennessee Valley, the Southeast and the Mid-Atlantic. The remainder of the nation is not expected to exceed normal climatology.
Jim Munley Jr.
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