Prognostic Meteorological Discussion
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000
FXSA20 KWBC 061559
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1159 AM EDT MON JUL 06 2015

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

LAST NO AMENDS...NEXT ON MONDAY JULY 06.

MODEL DISCUSSION (VALID FROM JUL 02 AT 0000 UTC): UNDER INFLUENCE
OF A MID LEVEL RIDGE OVER THE EASTERN PACIFIC...A SHORT WAVE
TROUGH OVER THE SOUTHERN CONE IS TO LIFT TO THE NORTH-NORTHEAST
ACROSS CENTRAL PROVINCES/RIO DE LA PLATA BASIN THROUGH 30-36
HRS...AND OFF THE COAST INTO THE WESTERN ATLANTIC BY 48-54 HRS.
THE MID LEVEL PERTURBATION IS TO THEN DEEPEN AS IT MEANDERS EAST
THROUGH 84-96 HRS. AT 250 HPA A SUBTROPICAL JET MAXIMA ACCOMPANIES
THIS PERTURBATION. THIS JET IS TO SUSTAIN AN UPPER DIVERGENT
PATTERN ACROSS PARAGUAY/SOUTHERN BRASIL THROUGH 36 HRS...AND
ACROSS BOLIVIA-SOUTHERN PERU BY 48-60 HRS. AT LOW LEVELS AN
ELONGATED FRONT MEANDERS WEST ACROSS THE SOUTH ATLANTIC TO
SOUTHEAST BRASIL-PARAGUAY/BOLIVIA. ANOTHER FRONT IS TO APPROACH
FROM THE SOUTH...WHICH UNDER THE INFLUENCE OF A BUILDING POLAR
RIDGE OVER PATAGONIA/LA PAMPA IS TO MOVE TO THE BUENOS AIRES
PROVINCE-CENTRAL CUYO BY 24 HRS. THROUGH 48 HRS...UNDER INFLUENCE
OF A PAMPERO JET...THE FRONT MOVES NORTH TO SOUTHERN
BRASIL-PARAGUAY. THIS IS TO THEN REINFORCE/MERGE WITH THE OLD
BOUNDARY TO THE NORTH THROUGH 54-60 HRS. AS IT ACCELERATES ACROSS
CENTRAL ARGENTINA THIS IS TO SUSTAIN ISOLATED TO SCATTERED
CONVECTION...WITH ACCUMULATION OF 05-10MM ACROSS THE BUENOS AIRES
PROVINCE. MOST INTENSE CONVECTION IS EXPECTED TO THE NORTH ALONG
THE OLD FRONTAL BOUNDARY OVER BRASIL-PARAGUAY. IN THIS AREA
CONDITIONS APPEAR FAVORABLE FOR AN MCS TO DEVELOP EARLY IN THE
CYCLE...TO RESULT IN RAINFALL AMOUNTS OF 40-80MM. THROUGH 48 HRS
THE FOCUS OF THE CONVECTION SHIFTS TO CENTRAL-NORTHERN
BOLIVIA-RONDONIA IN BRASIL...WITH RAINFALL MAXIMA OF 75-150MM IN
ORGANIZED DEEP CONVECTION. DURING THAT PERIOD CONDITIONS ARE
FAVORABLE FOR SEVERE CONVECTION TO DEVELOP OVER BOLIVIA. BY 60-96
HRS MODERATE TO HEAVY CONVECTION IS TO THEN BUILD ACROSS CENTRAL
PERU/ACRE IN BRASIL...WITH MAXIMA TO PEAK AT 25-50MM/DAY.

CONSISTENT WITH PREVIOUS FORECASTS A BROAD MID LEVEL TROUGH IS TO
SLOWLY FOLLOW. THIS IS TO MOVE ACROSS 80W TO 20S BY 72 HRS. AS IT
NEARS THE CONTINENT THE TROUGH IS TO PRESS AGAINST A RIDGE TO THE
EAST. AS THEY COLLIDE THE TROUGH WILL SLOW DOWN WHILE SLOWLY
SHEARING SHORT WAVE ENERGY EAST AND SOUTH ACROSS CHILE/PATAGONIA
IN ARGENTINA. THROUGH 84-96 HRS THE RIDGE WEAKENS ENOUGH TO ALLOW
THE TROUGH TO PUSH ACROSS SOUTHERN CHILE TO PATAGONIA IN
ARGENTINA... WITH AXIS TO MEANDER EAST ACROSS 50W/55W THROUGH 120
HRS. A SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO THEN PHASE
WITH THIS PERTURBATION AS IT MOVES TO NORTHERN ARGENTINA/SOUTHERN
BOLIVIA-PARAGUAY BY 108-120 HRS. FURTHERMORE...THE LONG WAVE
TROUGH...AS IT MIGRATES ACROSS THE EASTERN PACIFIC TO THE SOUTHERN
CONE...IS FORECAST TO SUSTAIN A SUBTROPICAL CONNECTION.
THIS...IN-TURN...WILL FAVOR SCATTERED CONVECTION ACROSS SOUTHERN
CHILE BY 72-96 HRS...WITH MOST INTENSE BETWEEN PUERTO MONTT AND
CONCEPCION...WHERE THE DAILY MAXIMA IS TO PEAK AT 15-20MM.

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 72-84 HRS. A NEAR ZONAL
WESTERLY FLOW IS TO THEN ESTABLISH ACROSS NORTHERN SOUTH AMERICA.
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 RAINFALL AMOUNTS TO RESULT IN RAINFALL
ACCUMULATION OF 15-30MM.

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




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