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FXSA20 KWBC 271855
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
154 PM EST Thu Feb 27 2025

GFS data at ftpprd.ncep.noaa.gov/data/nccf/com/gfs/prod/

South America Forecast Bulletin 27 Feb 2025 at 1900UTC:

In Mid - Latitude South America...

In north - central Argentina and Uruguay, in the upper levels,
speed divergence continues to dominate in the region ahead of the
passage of a potent upper trough, with an axis at 28S 83W and 36S
80W on Thursday afternoon. This trough will traverse the region
starting Friday morning through Friday evening. Thereafter, expect
a return in speed divergence across the region through Sunday
morning, when a jet streak is likely to form across central
Argentina. Thus, divergence will be favorable for the next three
days in this region. The accelerated upper flow will also continue
to sustain mid - level shortwave troughs and meandering surface
troughs in the low levels through the next three days.

Through Friday morning, the low level moisture transport from
Bolivia will continue to favor an increase of moisture through
Saturday morning across the Amazon Basin into north Argentina,
Uruguay, and South Brasil. Moisture convergence will be most
favorable along and ahead of a meandering surface trough in this
region through the next three days. From Thursday morning through
Friday morning, expect a total precipitation maxima of 25 - 50mm
across the Buenos Aires region of Argentina, where a marginal risk
for severe weather is possible. From Friday morning through
Saturday morning, there will be an overall increase in moisture in
the region, and thus yielding to a greater total precipitation
maxima of 30 - 60mm with a slight risk for severe weather. After
Saturday morning, an upper trough located across south - east
Brasil will retrograde west and enhance low level easterly flow
accompanied by dry air advection into north Argentina, Uruguay,
and south Brasil. Though speed divergence will be favorable during
this period, expect a decrease in precipitation accumulations from
Saturday morning through Sunday morning.

In Chile, a series of mid - to -upper level troughs will continue
to impact the region. The period of greatest precipitation impact
will be from Saturday morning through Sunday evening. A potent
upper trough will be moving across this region through this period
and will be accompanied by a long fetch moisture tongue in the
lower levels. In the lower levels, an increase in wind speeds will
favor orographic effects. These conditions will favor a total
precipitation maxima of 15 - 25mm during this period for north
austral Chile.

In Tropical South America...

In the upper levels, a system of interest is a potent upper trough
with an axis 18S 44W on Thursday afternoon. This system is
expected to broaden and retrograde westward. By Sunday morning,
its axis should be located at 19S 53W. This feature will favor the
increase of low level easterly winds across south Brasil,
Paraguay, and southeast Bolivia. Note, diurnal convection will
persist, especially along its west periphery. Overall, this upper
level feature should yield to a decrease in precipitation across
this region.

Another feature of interest is the return of upper level easterly
winds across Colombia, Ecuador, and Peru starting Saturday
morning, which will favor uuper diffluence and upper divergence
through the rest of the forecast cycle. In the low levels, north
and westerly flow will continue to impact the region, enhancing
moisture convergence and orographic effects across the coast. The
greatest precipitation impact will occur from Thursday morning
through Saturday morning when upper divergence and moisture
convergence will be most favorable, where a daily total
precipitation maxima of 30 - 60mm is likely.

Elsewhere, in the north - central Amazon Basin, speed divergence
will become favorable after Saturday afternoon. During this
period, an increase in moisture across the region is expected,
yielding to a total precipitation maxima of  25 - 50mm from
Saturday morning through Sunday morning.

In northeast Brasil, a series of low level troughs, associated
with moisture convergence, and the ITCZ will continue to favor the
development of convection. As the aforementioned Brasilian upper
trough retrogrades, an increase in upper diffluence and divergence
is possible in this region. The period of greatest precipitation
impact will be Saturday morning through Sunday morning, when an
intense moisture plume is expect to migrate across this region.
These conditions will yield a total preicpitaiton maxima of 30 -
60mm during this period.

Elsewhere in tropical South America, the ITCZ and NET will
continue to favor the diurnal convection. Low level troughs will
continue to propagate across the region and will be accompanied by
moisture convergence, helping yield to higher total precipitation
maxima.


Morales...(WPC)



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