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FXUS20 KWBC 141916
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
316 PM EDT Mon Jul 14 2025

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

South American Forecast Bulletin from 14 July 2025 at 1915 UTC

Model guidance is indicating a relatively significant rainfall
event developing across parts of northeastern Argentina into
Uruguay from tonight through Thursday morning. A deepening
upper-level trough currently located over the southeastern Pacific
will shift eastward and evolve into a closed upper low over
northern Argentina by Wednesday night. As this feature moves
inland, it will place northeastern Argentina and Uruguay under the
divergent side of the upper-level flow, enhancing large-scale
ascent and supporting thunderstorm development. There is a
low-level jet moving into the area, which combined with the
moisture convergence and the frontal boundary nearby, it may
support the development of MCS.

At the same time, mid-level moisture increases steadily, with
relative humidity around 700 mb rising to 70 to 90% by Tuesday
night into Wednesday. Precipitable water values climb to 45 to 50
mm, indicating a deep moisture plume extending into northeastern
Argentina and Uruguay. The aforementioned low-level jet at 850 mb
is forecast to develop Tuesday into Wednesday, transporting warm,
moist air from the north, southeastward across northern Argentina
and into Uruguay. Winds along this jet are expected to reach 30 to
40 knots, helping to saturate the lower atmosphere and increase
instability in the region.

Near the surface, a low-pressure system and frontal boundary will
organize over northern Argentina and shift east northeastward,
helping to focus low-level convergence and reinforce upward
motion. Rainfall across northeastern Argentina into Uruguay is
expected to begin increasing tonight, with the heaviest and most
organized precipitation likely from Tuesday night into Thursday
morning. Model QPF suggests 72-hour totals of 50 to 100 mm, with
localized maxima exceeding 150 mm across northeastern Argentina
into southern Uruguay. Southeastern Brazil may also be affected by
convective spillover, but the core rainfall axis remains farther
southwest.

Therefore, from tonight through Thursday morning, northeastern
Argentina and Uruguay are expected to experience the most
significant impacts from a well-organized upper-level system
interacting with deep moisture and favorable surface conditions.
The peak of the event is expected between Tuesday night and
Thursday morning, with a high potential for heavy rainfall and
thunderstorms. Forecast confidence is moderate to high, as the
different global model guidance is in general agreement on the
synoptic scale features, even though there is some discrepancy
between the models in the location of heaviest rainfall, the
general consensus is that there will be significant rain in the
general area of northeastern Argentina into southern Uruguay over
the next 3 days.

Over central and southern Chile, the GFS model indicates the
presence of a deep upper-level trough offshore tonight into
Tuesday, supporting widespread cloudiness and rain along the coast
and inland. Enhanced mid and upper-level moisture, along with
increasing precipitable water values, suggests an atmospheric
river may affect the area,  especially from La Araucania to Biobio
and parts of Los Rios, especially from Wednesday into Thursday.
This significant increase in moisture could bring periods of
steady rainfall in the lower elevations, while snow is forecast in
the higher elevations.

Note:
The low-level analysis charts are now expected to be issued
regularly.
The forecast bulletins are still being issued intermittently.

For the latest available charts please visit:
https://www.wpc.ncep.noaa.gov/international/sam_day1-3.shtml

Alamo...(WPC)
$$