Prognostic Meteorological Discussion
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000
FXSA20 KWBC 011548
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1147 AM EDT WED JUL 01 2015

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

MODEL DISCUSSION (VALID FROM JUL 01 AT 0000 UTC): SYSTEM OF
CONCERN IS A DEEPENING MID LEVEL TROUGH THAT ENTERS THE SOUTHERN
CONE EARLY IN THE CYCLE. UNDER INFLUENCE OF A BUILDING RIDGE TO
THE WEST THE TROUGH IS FORECAST TO DEEPEN AS IT MOVES ACROSS
ARGENTINA TO THE WESTERN ATLANTIC THROUGH 48-60 HRS. DEEP MID
LEVEL TROUGH IS TO THEN MEANDER OFF THE COAST OF ARGENTINA/URUGUAY
THROUGH 72-84 HRS...WITH AXIS TO PULL ACROSS 25W LATER IN THE
CYCLE. AS IT PULLS ACROSS THE CONTINENT A SUBTROPICAL JET MAXIMA
IS TO ACCOMPANY THIS TROUGH...TO FAVOR AN UPPER DIVERGENT PATTERN
ACROSS PARAGUAY/SOUTHERN BRASIL BY 48-60 HRS...AND ACROSS
BOLIVIA-SOUTHERN PERU BY 72-108 HRS. AT LOW LEVELS AN ELONGATED
FRONT MEANDERS WEST ACROSS THE SOUTH ATLANTIC TO SOUTHEAST
BRASIL-PARAGUAY/BOLIVIA...WHERE IT IS TO REMAIN NEARLY STATIONARY
OVER THE NEXT 48-60 HRS. THE DEEPENING POLAR TROUGH TO THE
SOUGH...AND BUILDING POLAR RIDGE TO THE WEST...WILL THEN DRIVE A
SURFACE FRONT NORTH ACROSS PATAGONIA TO LA PAMPA IN ARGENTINA BY
42/48 HRS. THROUGH 72 HRS...UNDER INFLUENCE OF A PAMPERO JET...THE
FRONT WILL THEN SURGE ACROSS SOUTHERN BRASIL-PARAGUAY. THIS IS TO
THEN REINFORCE/MERGE WITH THE OLD BOUNDARY TO THE NORTH THROUGH
78-84 HRS. AS IT SURGES ACROSS MID SECTIONS OF SOUTH AMERICA THIS
IS LIKELY TO TRIGGER SQUALLY WEATHER. ACROSS SOUTHERN CHILE THE
FRONTAL LOW IS TO SUSTAIN SCATTERED CONVECTION WITH ACCUMULATION
OF 05-10MM EARLY IN THE CYCLE...WITH SIMILAR AMOUNTS TO AFFECT THE
BUENOS AIRES PROVINCE BY 48 HRS. MOST INTENSE CONVECTION IS
INITIALLY EXPECTED TO THE NORTH ALONG THE OLD FRONT...WITH RISK OF
AN MCS FORMING ACROSS SOUTHERN BRASIL-PARAGUAY BY 48-66 HRS...TO
SUSTAIN RAINFALL AMOUNTS OF 40-80MM. ACROSS BOLIVIA-RONDONIA/ACRE
IN BRASIL THERE IS A MODERATE TO HIGH RISK OF AN MCS TO DEVELOP BY
72-84 HRS. IN POTENTIALLY SEVERE CONVECTION EXPECTING RAINFALL
MAXIMA OF 75-125MM. CONVECTIVE ACTIVITY IS TO THEN SURGE ACROSS
CENTRAL PERU WITH DAILY MAXIMA OF 25-50MM.

BROAD MID LEVEL TROUGH IS TO SLOWLY FOLLOW...WITH AXIS ALONG 80W
TO 20S BY 96 HRS. AS IT NEARS THE CONTINENT THIS IS TO PRESS
AGAINST A RIDGE TO THE EAST. THIS WILL TEND TO SLOW DOWN THE
EASTWARD PROGRESSION OF THIS TROUGH WHILE FORCING THE SHORT WAVE
ENERGY TO SHEAR ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA.
AS A RESULT...THE TROUGH IS TO GRADUALLY WEAKEN AS IT PUSHES EAST
ACROSS SOUTHERN CHILE TO PATAGONIA. ALTHOUGH THE GLOBAL MODELS
AGREE ON THIS EVOLUTION THROUGH 84-96 HRS...THEY THEN DIVERGE ON
HOW QUICK THE TROUGH IS TO WEAKEN AS IT MOVES INLAND ACROSS CHILE
TO ARGENTINA. SO EXPECTING CHANGES TO THIS PATTERN OVER THE NEXT
FEW RUNS. AS IT PROPAGATES ACROSS THE SOUTH PACIFIC TO THE
SOUTHERN CONE THIS TROUGH WILL SUSTAIN A SUBTROPICAL
CONNECTION...TO FAVOR SCATTERED CONVECTION ACROSS SOUTHERN CHILE
LATER IN THE CYCLE...WITH RAINFALL AMOUNTS OF 10-15MM.

AT 200 HPA...A SHORT WAVE RIDGE IS INITIALIZED OVER PERU WHILE A
TROUGH EXTENDS NORTH ACROSS CENTRAL BRASIL. THROUGH 72-84 HRS THE
RIDGE MOVES FARTHER EAST ACROSS BRASIL...DISPLACING THE TROUGH TO
THE EAST INTO THE TROPICAL ATLANTIC BY 96-108 HRS. A NEAR ZONAL
WESTERLY FLOW IS TO THEN ESTABLISH ACROSS NORTHERN SOUTH AMERICA
BY THE END OF THE CYCLE. AS IT MEANDERS OVER THE CONTINENT THE
TROUGH ALOFT IS TO ENHANCE DIURNAL CONVECTION ACROSS EQUATORIAL
SOUTH AMERICA...WITH CONVECTION OVER NORTHERN AMAZONAS IN
BRASIL-SOUTHERN COLOMBIA/NORTHERN JUNGLE OF PERU FORECAST TO PEAK
AT 10-15MM/DAY. ON THE AMAZON DELTA AND NORTH COAST OF BRASIL THE
DAILY MAXIMA IS TO PEAK AT 05-10MM. OVER NORTHEAST
BRASIL...MEANWHILE...TRADE WIND CONVERGENCE IS TO FAVOR SCATTERED
COASTAL CONVECTION...WITH PERIODS OF MODERATE TO HEAVY RAINS TO
RESULT IN RAINFALL AMOUNTS OF 15-30MM.

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




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