Prognostic Meteorological Discussion
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000
FXSA20 KWBC 081721
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1220 PM EST THU DEC 08 2016

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

MODEL DISCUSSION (VALID FROM DECEMBER 08 AT 0000 UTC): THE GLOBAL
MODELS REACHED A CONSENSUS AND NOW FOLLOW SIMILAR EVOLUTION OVER
THE CONTINENT THROUGH DAY 06. THIS IS WELL SUPPORTED BY THE MEAN
OF THE GLOBAL ENSEMBLES. OUR CONFIDENCE IN THE FORECAST IS HIGH.

A SHORT WAVE TROUGH ON THE NORTHERN STREAM MEANDERS OFF THE COAST
OF CHILE...WHILE ANCHORING ON A CLOSED LOW THAT REPOSITIONS TO THE
WEST-NORTHWEST OF LA SERENA CHILE LATER THIS EVENING. THE SHORT
WAVE TROUGH IS TO SLOWLY SHEAR SHORT WAVE ACROSS THE ANDES INTO
NORTHERN PROVINCES IN ARGENTINA-PARAGUAY/SOUTHERN STATES OF
BRASIL. THE TROUGH IS FORECAST TO DISSIPATE LATER ON SUNDAY/EARLY
MONDAY MORNING. ALSO...THE MEANDERING TROUGH IS TO FOCUS A JET
MAXIMA ACROSS MID SECTIONS OF SOUTH AMERICA...WHERE IT IS TO FAVOR
AN UPPER DIVERGENT PATTERN. FAVORABLE JET DYNAMICS AND INFLOW OF
SHORT WAVE ENERGY WILL FAVOR SCATTERED CONVECTION ACROSS CENTRAL
CHILE...WITH ORGANIZED SNOWFALL LIKELY TODAY TO RESULT IN
ACCUMULATION OF 15-20CM. ON THE LEE OF THE ANDES OVER ARGENTINA
EXPECTING MODERATE CONVECTION WITH ACCUMULATION OF 10-15MM/DAY
OVER THE NEXT COUPLE OF DAYS.

AT LOW LEVELS...AN ELONGATED FRONT MENDERS WEST ACROSS THE SOUTH
ATLANTIC INTO THE SOUTHERN STATES OF BRASIL-NORTHERN PROVINCES IN
ARGENTINA. A NORTHERLY LOW LEVEL JET IS ADVECTING MOISTURE ACROSS
EASTERN BOLIVIA/PARAGUAY...CONVERGING ALONG AND NORTH OF THE
MEANDERING FRONT. IN THIS PATTERN...ENVIRONMENTAL CONDITIONS
APPEAR FAVORABLE AND CONDUCIVE FOR ORGANIZED DEEP CONVECTION TO
DEVELOP OVER THE NEXT COUPLE OF DAYS. MOST INTENSE IS EXPECTED
BETWEEN TODAY AND FRIDAY MORNING...WITH MAXIMA OVER
CHACO/CORRIENTES IN ARGENTINAPARAGUAY AND PORTIONS OF MATO GROSSO
DO SUL FORECAST TO PEAK AT 75-125MM. ON FRIDAY THE MAXIMA IS TO
PEAK AT 40-80MM WHILE SPREADING EAST INTO THE SOUTHERN STATES OF
BRASIL. ON SATURDAY TO SUNDAY...AS THE MID LEVEL TROUGH
WEAKENS...FOCUS OF THE CONVECTION WILL GRADUALLY SHIFT TO THE
SOUTHERN-SOUTHEAST STATES OF BRASIL...WITH MAXIMA IN THIS AREA TO
PEAK AT 20-45MM. THE MDI LEVEL TROUGH IS TO ALSO ENHANCE
CONVECTION ALONG THE ALTIPLANO OF BOLIVIA/SOUTHERN SIERRA OF
PERU...WITH MAXIMA OF 15-20MM EXPECTED OVER THE NEXT COUPLE OF
DAYS. THROUGH SATURDAY MAXIMA OVER NORTHERN-CENTRAL BOLIVIA WILL
INCREASE TO 20-35MM.

UPSTREAM OVER THE EASTERN PACIFIC...PROGRESSIVE SHORT WAVE TROUGH
STREAMS ACROSS THE SOUTHERN CONE EARLY ON FRIDAY. THIS WILL BE
FOLLOWED BY ANOTHER PERTURBATION THAT MAKES LANDFALL OVER SOUTHERN
CHILE EARLY ON SUNDAY MORNING. AT LOW LEVELS THESE ARE TO FAVOR A
DEEP OCCLUDED LOW THAT MEANDERS OVER THE BELLINGSHAUSEN SEA OVER
THE NEXT TWO DAYS. AS A BROAD TROUGH MEANDERS TO THE SOUTH...THIS
IS TO THEN SUSTAIN AN ELONGATED FRONT ACROSS SOUTHERN PORTIONS OF
CHILE-PATAGONIA IN ARGENTINA DURING THE NEXT COUPLE OF DAYS. AS IT
MEANDERS ACROSS THE SOUTHERN CONE MODELS AGREE ON A DEEP FRONTAL
WAVE TO PROPAGATE ACROSS SOUTHERN CHILE EARLY ON SUNDAY
MORNING...AND ACROSS PATAGONIA IN ARGENTINA LATER IN THE DAY.
ACROSS SOUTHERN CHILE THE MEANDERING FRONT WILL FAVOR RAINFALL
AMOUNTS OF 10-15MM/DAY...WHILE OVER TIERRA DEL FUEGO ONLY
EXPECTING LIGHT CONVECTION WITH ACCUMULATION OF 00-05MM/DAY.

CONSISTENT WITH PREVIOUS FORECASTS...AT 200 HPA...BROAD CELL OF
THE SUBTROPICAL RIDGE WILL BECOME THE DOMINANT FEATURE ACROSS
NORTHERN SOUTH AMERICA LATER ON FRIDAY...WHILE ANCHORING ON A
CLOSED HIGH THAT IS TO MEANDER BETWEEN NORTHERN SAO PAULO AND
SOUTHERN MINAS GERAIS. THIS PATTERN WILL THEN HOLD THROUGHOUT THE
WEEKEND/EARLY NEXT WEEK. RIDGE ALOFT IS TO VENT DIURNAL CONVECTION
OVER NORTHERN SOUTH AMERICA. MOST INTENSE IS TO CLUSTER ACROSS
BAHIA-MINAS GERAIS-TOCANTINS/GOIAS AND PARA. IN THIS AREA DAILY
MAXIMA PEAKS AT 20-35MM THROUGH SATURDAY MORNING. THROUGH SUNDAY
THIS INCREASES TO 20-45MM WHILE BUILDING SOUTH ACROSS PORTIONS OF
SAO PAULO. OTHER CONVECTION IS EXPECTED TO CLUSTER ACROSS
AMAZONAS-ACRE-RONDONIA IN WESTERN BRASIL...WITH MAXIMA IN THIS
AREA TO PEAK AT 15-20MM/DAY. ACROSS ECUADOR DIURNAL CONVECTION IS
TO GENERALLY FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY.

ALVA...SENAMHI (PERU)
DURAN...SMN (ARGENTINA)
DAVISON/GALVEZ...WPC (USA)
$$




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