Prognostic Meteorological Discussion
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FXSA20 KWBC 011619
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1218 PM EDT WED APR 01 2015

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

MODEL DISCUSSION (VALID FROM APRIL 01 AT 0000 UTC): CONFIDENCE IN
THE FORECAST IS HIGH THROUGH THE SHORT RANGE PERIOD...WITH MODELS
THEN DIVERGING ON PATTERN EVOLUTION LATER ON DAYS 05-06. DURING
THAT PERIOD THE MODELS START TO DIVERGE ON THE SPEED AND AMPLITUDE
OF SHORT WAVE PERTURBATIONS STREAMING ACROSS THE CONTINENT.

SOUTH OVER THE CONTINENT...A BROAD MID LEVEL TROUGH DOMINATES THE
FLOW ACROSS THE BELLINGSHAUSEN SEA/ANTARCTIC PENINSULA TO THE
SOUTHERN CONE OF SOUTH AMERICA OVER THE NEXT FEW DAYS. SHORT WAVE
TROUGHS CONTINUE TO ROTATE AROUND THE LONG WAVE AXIS...WITH A
STRONG MID LEVEL PERTURBATION FORECAST TO PULL ACROSS
CHILE/PATAGONIA IN ARGENTINA EARLY IN THE CYCLE. ANOTHER IS TO
FOLLOW...AND IT IS FORECAST TO ENTER THE SOUTHERN CONE BY 30-36
HRS. THESE ARE TO SUSTAIN A COLD ADVECTIVE PATTERN AND GRADUAL
DROP IN TEMPERATURES THROUGH DAY 02. AT LOW LEVELS...BROAD TROUGH
IS TO DOMINATE THE DRAKE PASSAGE/SOUTHERN CONE THROUGH 72-84
HRS...WITH SUCCESSIVE POLAR FRONTS EXPECTED TO RACE ACROSS
SOUTHERN PORTIONS OF CHILE-PATAGONIA IN ARGENTINA. A TIGHT
PRESSURE GRADIENT IS TO RESULT IN STRONG LOW LEVEL WINDS ACROSS
SOUTHERN CHILE/PATAGONIA IN ARGENTINA OVER THE NEXT FEW
DAYS...WITH WINDS TO PEAK AT 35-50KT OVER THE NEXT FEW DAYS. THE
INFLOW OF SHORT WAVE ENERGY AND STRONG BOUNDARY LAYER WINDS WILL
SUSTAIN SCATTERED SHOWERS...WITH RAINFALL AMOUNTS OF 15-20MM/DAY
EXPECTED OVER SOUTHERN PORTIONS OF CHILE THROUGH 36 HRS...AND
10-15MM/DAY AT 36-60 HRS. IN A COLD ADVECTIVE PATTERN...THERE IS
RISK OF SNOW/MIXED PRECIPITATION ON DAY 02.

ON THE NORTHERN STREAM...A SHORT WAVE TROUGH OFF THE SOUTH COAST
OF BRASIL IS TO PULL ACROSS 35W EARLY IN THE CYCLE...AND ALONG 25W
BY 48 HRS. A SUBTROPICAL JET MAXIMA IS TO ACCOMPANY THIS TROUGH AS
IT MIGRATES ACROSS MID SECTIONS OF SOUTH AMERICA...TO FAVOR A
DIVERGENT PATTERN ALOFT AS IT PULLS ACROSS SOUTHEAST BRASIL EARLY
IN THE CYCLE. AT LOW LEVELS...THE TROUGH ALOFT IS TO SUSTAIN A
BAROCLINIC BOUNDARY ACROSS RIO DE JANEIRO-SOUTHEAST BRASIL. THIS
IS TO SUSTAIN SCATTERED DEEP CONVECTION ACROSS RIO DE
JANEIRO-SOUTHERN MINAS GERAIS AND ESPIRITO SANTO...WITH RAINFALL
AMOUNTS OF 25-50MM EXPECTED THROUGH 36 HRS...AND 20-30MM AT 36-72
HRS.

THE NEXT MID LEVEL TROUGH PULLS ACROSS CENTRAL/NORTHERN CHILE BY
48 HRS...INTO NORTHERN PROVINCES IN ARGENTINA TO THE SOUTHERN
STATES OF BRASIL BY 72-96 HRS. MODELS DIVERGE ON INTENSITY OF THIS
FEATURE...WITH BOTH EUROPEAN MODELS FAVORING A DEEPER TROUGH THAN
WHAT THE GFS SUGGESTS. BUT VARIABILITY AMONG THE ENSEMBLE MEMBERS
IS TOO HIGH TO ESTABLISH CONFIDENCE IN EITHER FORECAST. SO
EXPECTING FURTHER CORRECTIONS IN THE NEXT COUPLE OF RUNS.
MEANWHILE...INFLOW OF SHORT WAVE ENERGY ALOFT WILL COMBINE WITH A
WARM/MOIST LOW LEVEL PATTERN ACROSS PARAGUAY TO NORTHERN ARGENTINA
TO SUSTAIN A SURGE IN CONVECTION ON DAYS 03-04. IN THIS AREA WE
FORESEE A LOW TO MODERATE RISK OF SEVERE CONVECTION...WITH HIGHER
RISK POSSIBLE ON DAY 04 WHEN THE OTHER MODELS SHOW INTENSIFICATION
OF UPPER TROUGH PATTERN. ACROSS CHACO ARGENTINO-CORRIENTES TO
PARAGUAY THIS IS TO SUSTAIN ORGANIZED CONVECTION WITH MAXIMA TO
PEAK AT 30-60MM ON DAY 04.

UPSTREAM OVER THE EASTERN PACIFIC...A SPLIT FLOW PATTERN IS TO
DEVELOP BY 72 HRS...WITH FLOW TO DIVIDE BETWEEN A RIDGE ON THE
SOUTHERN STREAM AND A TROUGH TO THE NORTH. THE NORTHERN STREAM
PERTURBATION IS TO MOVE TOWARDS CENTRAL CHILE BY 120 HRS. ALTHOUGH
GLOBAL MODELS AGREE ON THE TIMING OF THIS PERTURBATION THEY
CONTINUE TO DISAGREE ON ITS INTENSITY...WITH THE GFS NOW FAVORING
A WEAKER TROUGH THAN WHAT THE EUROPEAN MODELS FORECAST. AT LOW
LEVELS THIS IS TO SUSTAIN A BROAD TROUGH OVER THE FAR EASTERN
PACIFIC LATER ON DAY 04...TO MOVE INTO CENTRAL CHILE ON DAY 05.
THIS TROUGH IS TO SUSTAIN A SUBTROPICAL CONNECTION AS IT ENTERS
THE CONTINENT. THIS IS TO THEN SUSTAIN SCATTERED CONVECTION ACROSS
CENTRAL-SOUTHERN PORTIONS OF CHILE LATER IN THE CYCLE...WITH
RAINFALL MAXIMA OF 20-30MM.

AT UPPER LEVELS...THE SUBTROPICAL RIDGE EXTENDS WEST-TO-EAST FROM
SOUTHERN PERU/BOLIVIA TO SOUTHEAST BRASIL. EARLY IN THE CYCLE IT
IS TO CENTER ON A CLOSED HIGH OVER MINAS GERAIS. BUT THROUGH 48-72
HRS THE HIGH RELOCATES TO BOLIVIA/SOUTHERN JUNGLE OF PERU...WHERE
IT IS TO REMAIN THROUGH THE END OF THE CYCLE. AS THE HIGH
RELOCATES...IT WILL ALLOW FOR A TROUGH TO ESTABLISH ALONG THE
NORTH COAST OF BRASIL. THE TROUGH ALOFT IS TO ENHANCE CONVECTIVE
INSTABILITY ALONG THE NEAR EQUATORIAL TROUGH OVER NORTHERN
BRASIL...TO FAVOR SCATTERED DEEP CONVECTION. RAINFALL MAXIMA OF
25-50MM IS FORECAST TO AFFECT THE NORTHERN STATES OF BRASIL OVER
THE NEXT FEW DAYS. THE RIDGE ALOFT...MEANWHILE...IS TO VENT DEEP
CONVECTION ACROSS BOLIVIA-SOUTHERN PERU/ACRE-RONDONIA IN
BRASIL...WITH RAINFALL AMOUNTS OF 15-20MM. HIGHER AMOUNTS ARE
EXPECTED ACROSS NORTHERN PERU TO EASTERN ECUADOR/SOUTHERN
COLOMBIA...WITH MAXIMA OF 25-50MM OVER THE NEXT TWO DAYS...AND
15-20MM/DAY THEREAFTER.

CALLE...UNALM (PERU)
SCHNEIDER...INMET (BRASIL)
DAVISON...WPC (USA)
$$




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