Prognostic Meteorological Discussion
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FXSA20 KWBC 241613
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1212 PM EDT MON JUL 24 2017

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM JUL 24 AT 0000 UTC): IN A HIGHLY
AMPLIFIED SINUSOIDAL WAVE PATTERN...THE GLOBAL MODEL GUIDANCE
FOLLOW A SIMILAR EVOLUTION ACROSS THE CONTINENT THROUGH DAY 06.
THIS SOLUTION IS WELL SUPPORTED BY THE GLOBAL ENSEMBLE
MEMBERS...LEADING TO HIGH CONFIDENCE IN THE FORECAST.

OVER THE SOUTH PACIFIC...A BUILDING MID/UPPER LEVEL RIDGE ALONG
130W/140W IS TO INDUCE THE NORTHWARD AMPLIFICATION OF A LONG WAVE
TROUGH TO THE EAST. THE POSITIVELY TILTED TROUGH REACHES MAXIMUM
AMPLITUDE ON WEDNESDAY MORNING...WHEN IT IS TO EXTEND TO THE
NORTHWEST FROM THE ANTARCTIC PENINSULA/DRAKE PASSAGE...ALONG 45S
90W...30S 120W...TO 20S 130W. THE LONG WAVE TROUGH IS TO THEN
FOCUS SHORT WAVE ENERGY ACROSS THE SOUTHERN REGIONS OF
CHILE-PATAGONIA IN ARGENTINA ON TUESDAY-THURSDAY. LATER ON FRIDAY
THE BOTTOM HALF OF THE TROUGH IS TO ACCELERATE ACROSS THE WEDDELL
SEA...WHILE MAIN BODY REMAINS OVER THE SOUTHERN CONE-EASTERN
PACIFIC. AT LOW LEVELS THIS IS TO SUSTAIN A BROAD TROUGH OVER THE
SOUTHEAST PACIFIC...WITH AXIS TO SLOWLY PULL ACROSS THE ANTARCTIC
PENINSULA TO THE SOUTHERN CONE EARLY ON THURSDAY. AS IT MEANDERS
OVER THE SOUTHERN CONE...POLAR FRONTS WILL REVOLVE AROUND THIS
TROUGH. THESE ARE TO THEN STREAM ACROSS SOUTHERN CHILE-PATAGONIA
IN ARGENTINA. THESE ARE TO SUSTAIN SCATTERED CONVECTION ACROSS
SOUTHERN REGIONS OF CHILE...WHERE WE EXPECT RAINFALL MAXIMA OF
15-20MM/DAY DURING THE NEXT FEW DAYS.

OVER THE ATLANTIC...MEANWHILE...A LOW AMPLITUDE SHORT WAVE TROUGH
IS TO PULL ACROSS 35W AND SOUTH OF 30S LATER TODAY. AT LOW LEVELS
THE ASSOCIATED FRONT TRAILS TO THE NORTHWEST ACROSS NORTHERN
URUGUAY/RIO GRANDE DO SUL IN BRASIL TO MENDOZA IN ARGENTINA. THE
BOUNDARY IS TO REMAIN NEARLY STATIONARY DURING THE NEXT 72-84
HRS...TO THEN FRONTOLIZE. MEANWHILE...IN A MOIST NORTHERLY FLOW
ACROSS PARAGUAY...EXPECTING SCATTERED CONVECTION TO AFFECT
URUGUAY-ENTRE RIOS IN ARGENTINA. INITIALLY THIS IS TO TRIGGER
RAINFALL MAXIMA OF 00-05MM/DAY. ON TUESDAY IT INCREASES TO
15-20MM/DAY. ON WEDNESDAY...AS THE FRONT WEAKENS...IT WILL
DECREASE TO 00-05MM/DAY.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE IS
TO REMAIN ILL ORGANIZED DURING THE NEXT 72-96 HRS. AS A
RESULT...UPPER LEVEL WESTERLIES ARE TO DOMINATE THE FLOW ACROSS
NORTHERN SOUTH AMERICA. IN THIS PATTERN DIURNAL CONVECTION WILL
LIMIT TO EQUATORIAL SOUTH AMERICA...WITH MOST ACTIVE OVER NORTHERN
AMAZONAS IN BRASIL-SOUTHERN COLOMBIA/NORTHERN JUNGLE OF PERU TO
RESULT IN MAXIMA OF 15-30MM. THROUGH WEDNESDAY THIS DECREASES TO
10-15MM/DAY. OVER AMAPA IN BRASIL THIS IS TO FAVOR RAINFALL MAXIMA
OF 15-20MM/DAY. OTHER CONVECTION IS EXPECTED BETWEEN RECIFE AND
SALVADOR DE BAHIA IN NORTHEAST BRASIL...WHERE TRADE WIND
CONVERGENCE IS TO RESULT IN RAINFALL AMOUNTS OF 15-20MM/DAY OVER
THE NEXT TWO DAYS...AND 10-15MM/DAY ON WEDNESDAY AND ONWARD.

ESPINOLA...DNM (PARAGUAY)
GONZALEZ...DMC (CHILE)
DAVISON...WPC (USA)
$$





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