Our Spring Outlook
March 2007 - May 2007
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The official spring outlook from
the Climate Prediction Center places northwest
Louisiana, southwest Arkansas, northeast Texas,
and southeast Oklahoma, within an area considered
to have equal chances of having above or below
average seasonal temperatures for the four state
region. Likewise, equal chances of above and
below average precipitation amounts are also
anticipated during the three month period. The
phrase "equal chances of above or below normal"
is meant to convey an uncertainty in the accuracy
of an entire seasonal forecast, a practical
interpretation of this prediction is that a
near normal seasonal conditions for our particular
region is the most likely scenario. For the
spring months, average rainfall amounts are
between four and five inches per month…of course
on unusually strong storm system could produce
that much rainfall in just a day or two. Over
the long term official average temperatures
for Shreveport are as follows: average high
and low temperatures in March are 69.7 and 47.2
degrees respectively. For April, 76.6 and 53.8
degrees, and for May, 83.2 and 62.7 degrees.
A long term seasonal forecast
produced by the Climate Prediction Center(CPC)
uses much different methodology and parameters
than those used in the issuance of a one week
forecast. Seasonal forecasts depict an overall
average…as naturally…above and below normal
conditions for both temperatures and precipitation
will almost certainly occur at some point within
a three month period. For our four state area
the number one factor in seasonal predictions is
the presence or absence of El Nino conditions
which is defined as occurring when above average
sea surface temperatures In tropical eastern
Pacific waters such as waters off the coast of
Peru are above normal.
When El Nino is occurring, a
persistent east to west subtropical upper level
jet stream tends to develop bringing pacific moisture
and cloud cover across the four state region. This
results in wetter and cooler conditions over the
winter months. Conversely, the term La Nina refers
to conditions when these same ocean waters become
cooler than normal. According to ocean data collected,
a weak El Nino pattern which did result in slightly
above average precipitation four our area this winter
will likely transition to La Nina conditions during
the spring. Although the three month average calls
for near normal temperatures and precipitation for
the spring months, it is possible that the month of
March could see below average temperatures and/or
above average precipitation before this transition
fully takes place, and possibly that the month of
May could be a little warmer and drier than the norm.
Other parameters used by CPC in climate
predictions include major ocean circulations in the
northern Pacific and the northern Atlantic, in addition
to El Nino previously discussed. Preexisting soil moisture
and snow cover also influence temperatures coming into the
spring months. For example, snow cover this year has been
rather meager across the central and northern plain states,
mainly six inches or less. Less snow cover means that
southward traveling cold air masses have more chance to
moderate(less of a chilling effect at surface induced by
snow cover) by the time the air reaches the southern
United States.
Storm tracks as you may know…have
occurred mainly in the northeast U.S., producing
record snowfalls in much of that area, but in
comparison have largely missed the upper Midwest.
Finally, persistence is looked at closely for any
seasonal forecast. The odds tend to be that a
particular season will mimic those of recent seasons.
Of course, this is not always to be the case. A
persistence forecast does not verify for this spring
as the springs of both 2005 and 2006 were two of the
warmest and driest springs our area has experienced
in quite some time.
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