108
FXUS20 KWBC 271745
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
145 PM EDT Mon Jul 27 2026

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

Forecast Bulletin 27 July 2026 at 1745 UTC:
**CORRECTED VERSION AS OF 1745 UTC
In the mid-latitudes and subtropics...
In the upper levels, the axis of an upper level trough will be
moving into the Chilean Andes today and at the same time, a jet
streak max will be across north-central Argentina, Uruguay, and
south Brasil, where upper diffluence will dominate across the
region for Monday afternoon. The trough axis will move east of the
Andes during the morning on Tuesday while a jet streak max and
upper diffluence will continue to be present across south Brasil
and into the northern Mesopotamia region (Argentina). This trough
axis is anticipated to move into the Atlantic by Wednesday. In the
low to mid levels, across Chile, a frontal boundary will also be
moving into the continent during the day, where an occluded front
will be converging into central Chile while a cold front will be
decaying across north-central Chile. These frontal systems will be
accompanied by above average precipitable water values, though
precipitable water is expected to decrease after Monday. Moderate
precipitation accumulations are likely with these conditions.

Meanwhile across northeast Mesopotamia (Argentina), Paraguay, and
south Brasil for Monday, a warm front will be moving across the
region. At the same time, expect the presence of a broad low level
ridging pattern across Brasil, which will support the transport of
moist tropical air into the region. Thus, above normal
precipitable water values are likely for Monday and Tuesday. The
region will be unstable and the presence of mid-level shortwave
troughs will trigger the development for convection and hail
across the region. Elevated total precipitation maxima is expected
in Uruguay and south Brasil for Monday and Tuesday with these
conditions.

Another upper level shortwave trough will be arriving into
Paraguay, Pantanal (Brasil), and southeast Bolivia on Wednesday,
leading to the brief development of a surface to low level trough
across Paraguay. During this period, also anticipate the presence
of an upper ridge across northeast Brasil that is anticipated to
broaden across the Amazon by Wednesday. This ridge will support
the increasingly low level northerly winds across the Mato Grosso,
Pantanal (Brasil), and Paraguay region for Wednesday. Expect the
most intense moisture convergence to be across the Pantanal/Parana
(Brasil) and Paraguay, where upper diffluence is also anticipated
to exist. Rainfall accumulations will be on the moderate side with
these conditions.

By Wednesday, expect the arrival of another frontal boundary into
Chile that will be accompanying an amplified upper trough. The
warm front will be approaching the central Chilean coastline by
early Thursday morning. There will be an increase in precipitable
water with the arrival of this frontal boundary across
north-southern and central Chile. Precipitation coverage will be
increasing early Thursday morning with the heavier precipitation
accumulations expected for Thursday into Friday.


Meanwhile across the Patagonia region of Argentina, a series of
mid-level shortwave troughs will continue to propagate across the
region for the next three days. With the eastward propagation of
upper level troughs across the region, expect a resurgence in
northerly low level winds into the region that will support the
transport of moisture, leading to above normal precipitable water.
On Monday, a region of interest is Buenos Aires/ La Pampa
(Argentina), where a frontal boundary will be moving across the
region. By Tuesday, the region of interest will be northern
Patagonia. On Wednesday, a broad low level ridging pattern will
dominate across northeast Argentina and Uruguay and northerly low
level winds with above normal precipitable water will extend into
northern and central Patagonia.  Thus, expect an increase in
precipitation chances in these regions for Wednesday.

Across the tropics...
Calm conditions will dominate for the next three days. Diurnal
showers and thunderstorms will occur across the entire basin.
Other regions for precipitation interest for the next three days
will be in the vicinity of a westward propagating tropical wave
across the extreme north regions of South America. Moderate
rainfall accumulations are likely in the vicinity of the tropical
wave for the next three days. The aforementioned upper ridge will
lead to a drying trend across the eastern regions of the tropics.


Tinoco-Morales...(WPC)





$$