MAY 2009 30-DAY OUTLOOK
335 PM EDT Thu. Apr. 30, 2009
Atmospheric patterns, 700 MB and 500 MB height anomalies, statistical
data, and various models, along with observed cases from past such
months and also data from 1895-2000 were used in this forecast.
Sea surface temperature anomalies along the equator in the eastern and
central Pacific Ocean have weakened considerably during the last few
weeks and are now averaging near 0C east of the International Date
Line. Most models support the transition from La Nina to neutral
conditions in May. Atmospheric conditions over the tropical Pacific
Ocean in early April still are related of La Nina, with below normal
convection and enhanced low level easterly winds in the central
equatorial Pacific Ocean. Currently, convection is enhanced across
the Indian Ocean. This area of convective activity is expected to move
eastward to the western Pacific by the start of May, and weaken
thereafter. This activity related to MJO activity is likely to
influence the atmospheric circulation of the tropical Pacific in May,
possibly disrupting any weak residual La Nina atmospheric circulation
patterns.
NAO is currently in a positive phase and is forecast to remain
positive during the first 14 days of the month. The PNA is also
positive and is forecast to trend neutral to slightly negative during
the same period. The models are in fair agreement with the 500-HPA
flow across North America. Above normal heights are expected across
the north Pacific, below normal heights are expected from the central
Pacific, Canada, into the north Atlantic. A trough is forecast across
the west-central part of the nation. Above normal heights will extend
from Hawaii into the Southwest A ridge is forecast along the East
coast into the Atlantic.

Above normal temperatures are forecast across a large portion of the
West, except the Northwest and parts of the Plains, the Southeast into
the lower mid-Atlantic. The forecast is dependent on soil moisture
content across portions of the Plains. The probability of above normal
temperatures across this region is 56 percent. Below normal
temperatures are forecast across the upper Mississippi Valley. The
probability of below normal temperatures across this region is 57
percent. The remainder of the nation is expected to average near
normal with no significant deviation from normal climatology.
Above normal precipitation is expected across the Northwest. This is
due to a Pacific flow into the region. The probability of above
normal precipitation across this region is 57 percent. Below normal
precipitation is expected across a large portion of the west and the
western and central Plains. The probability of below normal
precipitation in this region is 56 percent. The position of a trough
across the west-central part of the nation is likely to cause a moist
southwest flow across parts of the Ohio and Tennessee Valley resulting
in above normal precipitation. The probability of above normal
precipitation across this region is 57 percent. Below normal
precipitation is forecast for portion of the Southeast. The
probability of below normal precipitation across this region is 56
percent. The remainder of the nation is expected to be near normal
with no significant deviation from climatology.
Jim Munley Jr.
http://www.geocities.com/jimmunleywx