South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
141 PM EST Thu Feb 20 2025

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

South America Forecast Bulletin 20 Feb 2025 1900UTC:
In Mid - Latitude South America...

In Chile, a series of negatively tilted upper troughs and jet
streaks will traverse the region through the forecast cycle.
Expect upper divergence to be favorable across central Chile
during this period.

At the low levels, the wind flow will become stronger, with speeds
in excess of 50 knots starting Friday evening. This will favor the
enhancement of moisture convergence and orographic effects across
central Chile for Friday. By Saturday, expect an increase in
moisture in north Austral Chile. The period of greatest impact
will begin Thursday morning through Friday morning, where expect a
total rainfall maxima of 20 - 45mm across Austral Chile. In
Argentina, on Friday, in northeast Argentina, upper-to-mid level
shortwave troughs, an increase in moisture, and cooling of the mid
levels will yield an increase in precipitation chances in the
region starting on Friday through Sunday. Precipitation chances
will be more sparse for Friday morning through Saturday morning,
where expect a rainfall maxima of 15 - 25mm in northeast Argentina
with a marginal risk for severe weather. From Saturday morning
through Sunday morning, an increase in moisture convergence will
yield to a total rainfall maxima of 20 - 40mm for the same region.

In Tropical South America...

In the upper levels, a feature of interest is the Bolivian High,
centered at 22S 74W on Thursday afternoon, which will retain,
which will begin to lose its definition through the next three
days. In north Tropical South America, enhanced upper easterly
flow will be associated with some speed divergence across
northwest Brasil, Peru, Ecuador, and south Colombia for the next
three days.

In South Brasil, at the upper levels, a shortwave upper trough,
with an axis from 26S 53W to 35S 46W on Thursday afternoon, will
favor upper divergence through the day on Thursday across south
Brasil. At the lower levels, moisture convergence along the
southeast Brasil coast will persist through Sunday morning,
yielding to daily maximum precipitation totals of 20 - 35mm/Day
from Thursday morning through Sunday morning.

In Bolivia, after Thursday morning, the Bolivian High will begin
to lose definition, and an upper jet streak will develop across
central Bolivia, sustaining upper divergence. Moisture convergence
will still be favorable in the lower levels and will yield a total
precipitation maxima of 20 - 35mm for Thursday Morning through
Friday morning. Thereafter, the low level wind flow will become
more easterly, increasing moisture convergence in the region.
However, dry air advection is anticipated to increase Saturday
morning.

Elsewhere in Tropical South America, the ITCZ, NET, and Southern
ITCZ will continue to favor diurnal convection. A series of
moisture plumes will continue to traverse across the region,
helping increase precipitation chances. Starting on Friday
evening, to the east of the Colombian - Ecuadorian - Peruvian
Andes, low level wind flow will become more easterly for the rest
of the forecast cycle and will help in increasing moisture
convergence across the Amazon Basin. Expect total precipitation
maxima of 30 - 60mm across in this region from Friday morning
through Saturday morning. To the west of the Andes, ongoing
moisture convergence associated with the ITCZ and Southern ITCZ
will continue to favor orographic enhancement, yielding to higher
total precipitation maxima across Colombia, Ecuador and Peru.
Elsewhere, in the Amazon delta and northeast Brasil, the ITCZ and
Southern ITCZ will be the main driving force for convection in
this region. Incoming low level troughs will help increase
moisture convergence and yielding to higher total precipitation
maxima for the next three days.


Morales...(WPC)
Castellanos...(WPC)