AUGUST 2017 30-DAY OUTLOOK
358 PM EDT Sat. June 31, 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 June, neutral ENSO conditions continued, although equatorial sea surface temperatures remained above average in the central and east-central Pacific Ocean. The latest weekly Nino index values were near +0.5C in the Nnño-4 and Nino-3.4 regions, and closer to zero in the Nino-3 and Nino-1+2 regions. The upper-ocean heat content anomaly was above average during June, reflecting above-normal sub-surface temperatures across the central and eastern Pacific. In the atmosphere, tropical convection was suppressed over the west-central tropical Pacific and enhanced over the Maritime Continent. The lower-level and upper-level winds were near normal over most of the tropical Pacific, and the Southern Oscillation Index and Equatorial SOI were slightly negative to near-zero. Overall, the ocean and atmosphere system remains consistent with ENSO-neutral.
During the past week, the atmosphere became more consistent with a weak MJO, with a convectively enhanced phase over the Maritime Continent. Both the RMM-based MJO index and the CPC velocity potential index indicate enhancement of vertical motions near 120-140E. Dynamical and statistical guidance point to a continued propagation of the coherent signal through Week-1, with the ECMWF forecasting a signal turning back to the west slightly earlier. During Week-2, many of dynamical models latch on to the westward moving features, while the statistical models indicate little to no signal. Based on recent observations, statistical guidance, and dynamical model guidance, propagation of a weak, but coherent, MJO signal is favored over the upcoming week, but then in Week-2, the signal is likely to stagnate and become unrelated to MJO. The NJO will likely be in phase 5 favoring cool in the East and warm in the West.
Most of the North American Multi-Model Ensembles indicate above normal temperatures across much of the nation. The CMC1 CanCM3depict below normal temperatures in the Northeast and along the Appalachians. The NMME forecast above normal precipitation of the East Coast and the South and below normal precipitation for parts of the Mississippi Valley and the Midwest.
The NAO is forecast to be negative through day 14. The PNA will be negative and is forecast to remain negative through much of the period.
Above normal temperatures are forecast for the West Coast States, the Great Basin and the northern Rockies. Anomalies of 2-4F are forecast. The probability of above normal temperatures for this region is 57 percent. Below normal temperatures are forecast for the southern Plains, the lower Mississippi Valley, a portion of the Ohio Valley and the interior Mid-Atlantic and the Northeast. The probability of below normal temperatures for the southern Plains and the lower Mississippi Valley is 57 percenter. The remainder of the nation is not expected to exceed normal climatology.
Below normal precipitation is forecast for the West Coast states, the northern Rockies and the northern Plains. The probability of below normal precipitation for these regions is 57 percent. Above-normal precipitation is forecast for the central Four Corners, the southern Plains, the Southeast, the Tennessee Valley, the Mid-Atlantic and the Northeast. The probability of above normal precipitation for this area is 54 percent in the central Four Corners and 57 percent elsewhere. The probabilities decrease to 54 percent in the interior Northeast and the Ohio Valley. The remainder of the nation is not expected to exceed normal climatology.
Jim Munley Jr.
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