Prognostic Meteorological Discussion
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FXSA20 KWBC 301524
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1123 AM EDT THU JUL 30 2015

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

MODEL DISCUSSION (VALID FROM JUL 30 AT 0000 UTC): GLOBAL MODELS
MAINTAIN CONTINUITY ONLY THROUGH 72-84 HRS...THEN MAKE PATTERN
CORRECTIONS TO EVOLVING MID LEVEL PATTERN ACROSS THE EASTERN
PACIFIC. IN CONTRAST WITH PREVIOUS RUNS...THEY NOW FAVOR A SLOWER
EVOLUTION. ALTHOUGH THE GLOBAL MODELS HAVE STARTED TO REACH A
CONSENSUS ON THIS EVOLUTION...VARIABILITY AMONG THE MEMBERS
REMAINS TOO HIGH TO ESTABLISH CONFIDENCE IN THE MEDIUM RANGE
FORECAST.

MEANWHILE...A MID/UPPER LEVEL TROUGH OVER THE EASTERN PACIFIC IS
TO MOVE ACROSS CHILE INTO ARGENTINA THROUGH 36 HRS...ACCELERATING
ACROSS THE SOUTHERN CONE TO THE WESTERN ATLANTIC BY 48 HRS. THIS
IS TO THEN PULL ACROSS 30W BY 72 HRS. AT LOW LEVELS THIS IS TO
SUSTAIN A POLAR FRONT ACROSS PATAGONIA IN ARGENTINA-CUYO-CENTRAL
CHILE EARLY IN THE CYCLE. IN A NORTHERLY LOW LEVEL FLOW...DEEP
MOISTURE IS TO ADVECT ACROSS PARAGUAY TO ARGENTINA...WITH
PRECIPITABLE WATER TO PEAK AT 40-50MM OVER ENTRE RIOS/BUENOS AIRES
PROVINCE BY 30-36 HRS. THIS IS TO FEED CONVECTION AHEAD OF THE
FRONT DURING THE EARLY MORNING HOURS ON FRIDAY. THE FRONT IS TO
THEN SURGE ACROSS URUGUAY TO NORTHERN ARGENTINA BY 42-48
HRS...WHERE IT IS TO MEANDER THROUGH AT LEAST 96-108 HRS. THE
FRONT IS TO TRIGGER MODERATE TO HEAVY CONVECTION ACROSS THE BUENOS
AIRES PROVINCE-ENTRE RIOS IN ARGENTINA/ SOUTHERN URUGUAY...WITH
BULK OF THE CONVECTION EXPECTED OVER ARGENTINA WITH MAXIMA OF
30-60MM IN POTENTIALLY SEVERE CONVECTION. ACROSS SOUTHERN URUGUAY
THE MAXIMA IS LIKELY TO PEAK AT 20-40MM. THROUGH 60 HRS THIS
DECREASES TO 05-10MM WHILE FOCUSING OVER URUGUAY-RIO GRANDE DO
SUL. AN INCREASE IN CONVECTION IS EXPECTED BY 72-84 HRS...WHEN MID
LEVEL TROUGH IN INTERACTION WITH THE SURFACE FRONT OVER
URUGUAY/ENTRE RIOS IN ARGENTINA IS TO TRIGGER SCATTERED
CONVECTION. DURING THAT PERIOD THE MAXIMA IS TO PEAK AT 20-30MM.

A DEEPENING MID LEVEL TROUGH IS TO THEN LIFT ACROSS THE SOUTHEAST
PACIFIC THROUGH 24 HRS...WITH PERTURBATION TO THEN RAPIDLY DEEPEN
AS IT APPROACHES SOUTHERN CHILE BY 48-60 HRS. CONSISTENT WITH
PREVIOUS FORECASTS...THE TROUGH IS TO THEN RAPIDLY WEAKEN THROUGH
84-96 HRS AS SHORT WAVE ENERGY SHEARS TO THE EAST-SOUTHEAST ACROSS
THE SOUTHERN CONE. MEANWHILE...THE SLOW TO EVOLVE SYSTEM IS TO
FOCUS MOISTURE AND ENERGY ACROSS SOUTHERN-CENTRAL CHILE. FOCUS OF
MOST INTENSE IS EXPECTED BETWEEN CONCEPCION AND ISLA DE
CHILOE...WITH MAXIMA OF 15-30MM ON DAY 02...AND 20-40MM ON DAY 03.
OVER CENTRAL CHILE COASTAL CONVECTION IS TO SUSTAIN RAINFALL
AMOUNTS OF 05-10MM...WHILE OVER THE CENTRAL ANDES THE MAXIMA IS TO
PEAK AT 20-30CM IN SCATTERED SNOW SHOWERS.

NORTH OVER THE CONTINENT...AT 200 HPA...MODELS CONTINUE TO
FORECAST A SEASONAL NEAR ZONAL WESTERLY NEAR ZONAL FLOW TO ENVELOP
AREA TO THE NORTH OF 10S. THIS PATTERN IS TO PERSIST OVER THE NEXT
FIVE DAYS. THIS WILL CONTINUE VENTING DIURNAL CONVECTION ACROSS
EQUATORIAL SOUTH AMERICA...WITH MOST INTENSE OVER NORTHERN
AMAZONAS IN BRASIL-SOUTHERN AMAZONIA IN COLOMBIA-NORTHERN JUNGLE
OF PERU TO EASTERN ECUADOR. RAINFALL MAXIMA IS TO PEAK AT
10-15MM/DAY OVER THE NEXT COUPLE OF DAYS...AND AROUND 05-10MM/DAY
THEREAFTER. ON THE  NORTHEAST STATES OF BRASIL...TRADE WIND
EASTERLY CONVERGENCE IS TO ENHANCE COASTAL CONVECTION BETWEEN
ESPIRITO SANTO AND PERNAMBUCO. IN THIS AREA EXPECTING RAINFALL
AMOUNTS OF 05-10MM/DAY.

CHARPENTIER...DMC (CHILE)
ROMERO...DMC (CHILE)
DAVISON...WPC (USA)
$$





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