FEBRUARY 2018 30-DAY OUTLOOK
250 PM EDT Wed. Jan. 31, 2017
Atmospheric patterns, 700 MB and 500 MB height anomalies, statistical data, and various models such as the ECMWF monthly and weekly, NMME, IMME and the CFSv2, along with observed cases from past such months, data from 1895-2000 were used in this forecast.
A cold episode continued during the past month, as indicated by the pattern of below-normal sea surface temperatures across the central and eastern equatorial Pacific Ocean. The latest weekly Nino-3.4 index value was -0.8C, and the Nino-3 and Nino-1+2 indices were at or below -1.0C during much of the month. Negative sub-surface temperature anomalies in the central and east-central equatorial Pacific weakened at the end of the month as anomalously warm waters in the western Pacific at depths greater than 100 m propagated eastward to approximately 140W. The atmospheric conditions over the tropical Pacific Ocean also reflected La Nina, with suppressed convection near and east of the International Date Line and enhanced convection to the north of Indonesia. Also, the low-level trade winds continued to be stronger than normal over the western and central Pacific. Overall, the ocean and atmosphere system remained consistent with a cold episode.
The MJO remains consistent, with both the RMM-based and CPC velocity potential based MJO indices depicting good amplitude and eastward propagation. The enhanced convective phase of the MJO is over the Maritime Continent, constructively interfering with the Pacific Cold episode. A large area of enhanced trade winds persists over the western and central Pacific, with westerly anomalies extending from the Indian Ocean to Borneo. The upper-level velocity potential anomalies continue to reflect a consistent Wave-1 pattern, with the anomalous upper-level divergence in phase with negative OLR anomalies over the Maritime Continent. Dynamical and statistical model RMM-index forecasts consistently depict a continuation the MJO activity over the next several weeks, with the enhanced convective phase propagating over the West Pacific by Week-2. The ECMWF depicts a slightly faster propagation of the signal, and the 30-day ECMWF run maintains an amplified signal over the East Pacific and Western Hemisphere through Weeks 3 and 4. Based on these observations and forecasts, the MJO is anticipated to play a large role in the evolution of the global tropical convective pattern, and will likely continue to influence the mid-latitude response. This MJO event has teleconnected well with the North American longwave pattern, and has contributed to the warming trend across the central and eastern U.S. A West Pacific MJO event would potentially support a pattern change during early to mid-February, with increased ridging over western North America, and downstream troughing over eastern Canada and the U.S.
Two ridges are forecast in the pattern. One is forecast off the U.S Coast and another centered over the Bering Sea. These two ridges are forecast to merge over the next two weeks stretching from Baja to eastern Siberia. This will force the development of negative height anomalies across eastern North America. This pattern favors mostly cold temperatures in the east and warm temperatures in the in the West. A pulse of energy transfer from the troposphere to the stratosphere is expected to occur this week. The pulse will maintain a disturbed stratospheric Polar Vortex and maintain a displaced of the Polar Vortex center on the North America side of the Arctic. Simultaneous polar stratospheric warming near Alaska should support cold temperatures in eastern North America.
The AO is positive and is forecast to trend negative by day 7 and remain negative for the next two weeks. The PNA is negative and is forecast to trend positive by day 7 and remain positive through day 14. The NAO is positive and is forecast to remain positive through the same period.
The ECMWF Monthly depicts above normal heights in the West and the Plains and variable heights in eth East. The CFSv2 weeklies depicts above normal heights in the West and below normal heights in the East with height rises in the East during the last week.
Most of the North American Multi-Model Ensembles indicate above normal temperatures in the East and below normal temperatures in the West. The NCAR CCM4, depicts the opposite.
Above normal temperatures are forecast for California into the Four Corners, the southern Plains, the lower Mississippi Valley, the Gulf Coast States, and the Southeast. Anomalies near 5F or more are forecast. The probability of above normal temperatures for this region is 58 percent. Below normal temperatures are forecast for the northern Rockies, the upper Mississippi Valley and the Midwest into the northern Mid-Atlantic and the Northeast. Anomalies of 4F are forecast. The probability of below normal temperatures is 55 percent. The remainder of the nation is not expected to exceed normal climatology.
Above normal precipitation is forecast for Washington, Oregon, the Southeast, the Mid-Atlantic and the Northeast. The probability of above normal precipitation for these regions is 55 percent for Washington and Oregon and 30-55 percent for the Southeast to the Northeast. Below normal precipitation forecast for most of California, the Four Corners into the central and southern Plains. The probability of below normal precipitation is 57 percent. Below normal precipitation is forecast for Texas westward into southern California. The probability of below normal precipitation for this region is 57 percent. The remainder of the nation is not expected to exceed normal climatology.
Jim Munley Jr.
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