Prognostic Meteorological Discussion
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000
FXSA20 KWBC 131813
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
112 PM EST WED DEC 13 2017

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

MODEL DISCUSSION (VALID FROM DEC 13 AT 0000 UTC): MINOR
CORRECTIONS TO PREVIOUS FORECAST...WITH GLOBAL MODEL GUIDANCE
FOLLOWING A SIMILAR EVOLUTION THROUGH DAY 06. THIS IS WELL
SUPPORTED BY THE GLOBAL ENSEMBLE MEMBERS...LEADING TO A HIGH
CONFIDENCE IN THE FORECAST.

AS PREVIOUSLY FORECASTED...A PROGRESSIVE MID LEVEL TROUGH PULLS
ACROSS THE SOUTHERN CONE TO THE WESTERN ATLANTIC EARLY IN THE
CYCLE...CROSSING 50W LATER ON THURSDAY WHILE CONFINING TO THE
SOUTH OF 40S. AT LOW LEVELS THE TROUGH ALOFT SUSTAINS A DEEP
OCCLUDED LOW OVER THE BELLINGSHAUSEN SEA/SOUTHEAST PACIFIC. THIS
IS TO GRADUALLY WEAKEN AS IT SLOWLY PULLS ACROSS THE DRAKE PASSAGE
EARLY ON THURSDAY MORNING. MEANWHILE...THE ASSOCIATED FRONT IS TO
MEANDER ACROSS CENTRAL PATAGONIA IN ARGENTINA-SOUTHERN REGIONS OF
CHILE THROUGH THURSDAY EVENING...MEANDERING NORTH ACROSS LA PAMPA
IN ARGENTINA ON FRIDAY. OVER SOUTHERN CHILE THIS IS TO FAVOR
MODERATE RAINFALL AMOUNTS WITH MAXIMA OF 20-30MM THROUGH THURSDAY
MORNING...AND 10-15MM ON THURSDAY TO FRIDAY. AS IT MEANDERS ACROSS
LA PAMPA TO CENTRAL ARGENTINA ON FRIDAY THIS IS TO FAVOR SCATTERED
CONVECTION WITH MAXIMA OF 05-10MM.

A MID LEVEL TROUGH ON THE NORTHERN STREAM ENTERED THE CENTRAL
REGIONS OF CHILE EARLY THIS MORNING. THIS IS TO THEN TRACK ACROSS
CENTRAL ARGENTINA TO THE WESTERN ATLANTIC EARLY ON THURSDAY
MORNING. AS IT SPILLS ACROSS THE CENTRAL ANDES...THE MID LEVEL
TROUGH TRIGGERED CYCLOGENESIS OVER CENTRAL ARGENTINA. THROUGH THIS
EVENING THE FRONT MOVES NORTH ACROSS THE BUENOS AIRES
PROVINCE-CORDOBA IN ARGENTINA...AND ON THURSDAY IT CROSSES URUGUAY
TO SOUTHERN BRASIL-NORTHERN PROVINCES IN ARGENTINA. OVER CENTRAL
ARGENTINA THIS IS TO TRIGGER RAINFALL AMOUNTS OF 15-25MM THROUGH
THURSDAY MORNING...WHILE OVER SOUTHERN BRASIL IT WILL SUSTAIN
RAINFALL AMOUNTS OF 05-10MM.

CONSISTENT WITH THE PREVIOUS FORECAST...THE NEXT MID LEVEL
PERTURBATION ENTERS SOUTHERN CHILE EARLY ON FRIDAY MORNING. THIS
IS TO QUICKLY PULL ACROSS THE SOUTHERN CONE TO THE WESTERN
ATLANTIC EARLY ON SATURDAY... NEARING 40W LATER ON SUNDAY. AT LOW
LEVELS THIS IS TO SUSTAIN A DEEP FRONTAL LOW THAT MOVES ACROSS
SOUTHERN CHILE/PATAGONIA IN ARGENTINA ON FRIDAY. ON
SATURDAY...UNDER INFLUENCE OF A PAMPERO LOW LEVEL JET AND BUILDING
POLAR RIDGE OVER ARGENTINA...THE FRONT SURGES ACROSS LA
PAMPA/CENTRAL ARGENTINA ON SATURDAY. ON SUNDAY IT CONTINUES NORTH
ACROSS SOUTHERN BRASIL-PARAGUAY TO SOUTHERN BOLIVIA. AS IT MAKES
LANDFALL OVER SOUTHERN CHILE ON FRIDAY THIS WILL SUSTAIN MODERATE
CONVECTION WITH ACCUMULATION OF 15-20MM. MOST INTENSE IS EXPECTED
OVER ENTRE RIOS IN ARGENTINA-URUGUAY ON SATURDAY...WHEN THE FRONT
SURGES ACROSS CENTRAL ARGENTINA WHILE TRIGGERING MODERATE TO HEAVY
CONVECTION WITH MAXIMA OF 25-50MM. DURING THIS PERIOD...THE MODELS
CONTINUE TO FORESEE AN ELEVATED POTENTIAL OF SEVERE THUNDERSTORMS.
ON SUNDAY...AS THE FRONT MEANDERS OVER SOUTHERN
BRASIL-PARAGUAY...MOST ACTIVE CONVECTION IS EXPECTED ACROSS
SOUTHERN BOLIVIA-NORTHWEST ARGENTINA AND THE CHACO
PARAGUAYO...WITH MAXIMA OF 30-60MM.

NORTH OVER THE CONTINENT...AT 200 HPA...AN ILL ORGANIZED CELL OF
THE SUBTROPICAL RIDGE IS INITIALIZED OVER NORTHERN BRASIL. THIS...
HOWEVER...IS FORECAST TO GRADUALLY BUILD ACROSS WESTERN
BRASIL-PERU DURING THE NEXT THREE DAYS. AXIS IS TO THEN CENTER ON
A CLOSED HIGH OVER NORTHERN BOLIVIA. AS THE RIDGE BUILDS TO THE
WEST...IT IS TO INDUCE THE NORTHWARD AMPLIFICATION OF A TROUGH
ACROSS SOUTHEAST BRASIL. IN THIS PATTERN...THE MOST INTENSE
CONVECTION IS EXPECTED OVER THE CONTINENT TO THE NORTH OF 20S. ON
THE NORTHEAST STATES OF BRASIL INITIALLY EXPECTING RAINFALL MAXIMA
OF 35-70MM...WITH LOCALLY HIGHER AMOUNTS HIGHLY PROBABLE. THIS
DECREASES TO 20-30MM ON FRIDAY. ON SATURDAY-SUNDAY THIS SURGES
ACROSS TOCANTINS-GOIAS TO PARA IN BRASIL...WHERE IT IS TO TRIGGER
RAINFALL MAXIMA OF 40-80MM. ACROSS PARA-AMAZONAS IN BRASIL
INITIALLY EXPECTING RAINFALL MAXIMA OF 20-35MM. ON THURSDAY THIS
INCREASES TO MAXIMA OF 20-45MM...WHILE ON FRIDAY IT WILL PEAK AT
30-60MM. ON THE NORTHERN JUNGLE OF PERU-EASTERN ECUADOR EXPECTING
RAINFALL MAXIMA OF 15-20MM IN SCATTERED DEEP CONVECTION...WHILE ON
THE SOUTHERN SIERRA/ALTIPLANO THE CONVECTIVE ACTIVITY IS TO
GRADUALLY BECOME MORE ACTIVE/BETTER ORGANIZED...WITH MAXIMA OF
00-05MM/DAY EARLY IN THE CYCLE INCREASING TO 10-15MM ON
FRIDAY-SATURDAY.

OVIEDO...SHN (ARGENTINA)
POMIER...SENAMHI (BOLIVIA)
RIVAS...SENAMHI (PERU)
DAVISON/GALVEZ...WPC (USA)
$$




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