December 2011-February 2012 90-DAY OUTLOOK
535 PM EST Thu. Dec. 1, 2011

TEMPERATURES

PRECIPITATION

Oceanic and atmospheric observations indicate La Nina conditions across the tropical Pacific Ocean. Sea surface temperature anomalies are between -0.5 C and -1.0 C along the Equator from the Date Line eastward to about 120W. Equatorial sea surface anomalies are between -1.0 C and -2.0 C from 120W to the South American coast. Sub-surface ocean temperatures are well below average throughout the eastern equatorial Pacific. The average heat content of ocean water to a depth of 300 meters just over 1 C below normal. There has been a considerable amount of variability in the atmospheric conditions over the Pacific basin during the past month due to an active Madden-Julian Oscillation. Monthly mean atmospheric conditions over the tropical Pacific Ocean, however, continue to be consistent with a cold episode, with a tendency for suppressed convection near the Equator over the central Pacific with enhanced low-level easterly winds and upper level westerly winds observed in parts of the Pacific basin.

A majority of the models indicate that the cold episode is likely to continue through the Northern Hemisphere winter and then gradually weaken after peaking late in the year. The models are roughly split between those that predict La Nina to remain weak and those that predict a stronger episode.

Thinking is that without indications of Greenland blocking by the models and a positive PNA, there will be a trough and cold air in the East but the cold will be short-lived. Any cold air mass will pose the threat of snow in the East.

Models are in good agreement on the expected 500-hpa circulation pattern for winter. A strong ridge is forecast over the eastern Pacific Ocean, a broad trough is forecast over the central U.S. extending southwestward to the Southwest U.S. A sub-tropical ridge is forecast by most models near the Southeast coast. This ridge may push systems closer to the coast and further north along the East coast.

Below normal temperatures are forecast for the northern Rockies, and the northern Plains. The probability of below normal temperatures for this area is 58 percent. Above normal temperatures are forecast for portion of the Southwest, the gulf coast states, the Southeast and the lower mid-Atlantic. The probability of above normal temperatures for this region is 57 percent. The remainder of the nation is not expected to exceed climatological values.

Above normal precipitation is forecast for the Northwest. The probability of above normal precipitation for this area is 58 percent. Above normal precipitation is also forecast for the Northeast and the mid-Atlantic. The probability of above normal precipitation for this area is 55 percent. Below normal precipitation is forecast for the Southwest, the gulf coast states and the Southeast. The probability of below normal precipitation for this area is 57 percent. The remainder of the nation is not expected to exceed climatological values.

Jim Munley Jr.
http://www.jimmunleywx.com

Surface Fcsts 500mb Heights & Anomalies