Prognostic Meteorological Discussion
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FXSA20 KWBC 301613
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1213 PM EDT TUE JUN 30 2015

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

MODEL DISCUSSION (VALID FROM JUN 30 AT 0000 UTC): CONSISTENT WITH
PREVIOUS FORECAST...THE MODELS FORECAST A SHORT WAVE TROUGH ON THE
NORTHERN STREAM TO MOVE ACROSS SOUTHERN STATES OF BRASIL TO THE
WESTERN ATLANTIC EARLY IN THE CYCLE. THIS IS TO CONTINUE ACROSS
40W BY 48 HRS...AND IT IS TO NEAR 10W BY 72 HRS. A SUBTROPICAL JET
MAXIMA ACCOMPANIES THIS PERTURBATION AS IT MOVES ACROSS
PARAGUAY/SOUTHERN BRASIL...FAVORING AN UPPER DIVERGENT PATTERN
THAT IS VENTING DEEP CONVECTION. THE TROUGH SUSTAINS A SURFACE
FRONT THAT MOVES ACROSS SOUTHERN BRASIL TO SAO PAULO-PARAGUAY
EARLY IN THE CYCLE. BOUNDARY IS TO THEN STALL THROUGH 48-60
HRS...AND BY 72-84 HRS IT RETROGRESSES TO SOUTHERN BRASIL. AS THE
FRONT MOVES ACROSS SOUTHERN BRASIL TO MATO GROSSO DO SUL IT IS TO
SUSTAIN SCATTERED CONVECTION WITH ACCUMULATION OF 20-30MM/DAY. BY
72-96 HRS...UNDER FAVORABLE JET DYNAMICS...THIS INCREASES TO
40-80MM IN RISK OF AN MCS FORMING ALONG THE MEANDERING FRONT.

BROAD MID/UPPER LEVEL TROUGH TO THE SOUTH EXTENDS ACROSS THE
WEDDELL SEA TO THE SOUTHERN CONE OF SOUTH AMERICA. THE TROUGH IS
TO SLOWLY MIGRATE FARTHER EAST INTO THE SOUTH ATLANTIC AS THE
CYCLE PROGRESSES. MEANWHILE...AS IT MEANDERS OVER THE SOUTHERN
CONE...POLAR FRONTS ARE TO REVOLVE AROUND THIS AXIS...SUSTAINING
SCATTERED CONVECTION AND LIGHT SNOWFALL AMOUNTS OVER EXTREME
SOUTHERN PORTIONS OF CHILE...WITH ACCUMULATION OF 00-05CM.

BUILDING MID LEVEL RIDGE TO THE WEST IS TO THEN STEER A SHORT WAVE
TROUGH ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA BY 48-54
HRS. AS IT MIGRATES ACROSS THE SOUTHERN CONE...THE SHORT WAVE
TROUGH IS TO THEN PHASE WITH A CLIPPER LOW ENTERING THE DRAKE
PASSAGE. THROUGH 72-96 HRS THESE COMBINE INTO A HIGH AMPLITUDE
LONG WAVE TROUGH OVER THE WESTERN ATLANTIC-MID SECTIONS OF SOUTH
AMERICA. THROUGH 120 HRS THIS IS TO THEN PULL ACROSS 30W/35W TO
20S. THE ASSOCIATED FRONTAL TROUGH ENTERS SOUTHERN CHILE BY 36-42
HRS...INTO PATAGONIA IN ARGENTINA BY 48 HRS...AN DOFF THE COAST TO
THE WESTERN ATLANTIC BY 60-66 HRS. THIS IS TO THEN DEEPEN OVER THE
WESTERN ATLANTIC THROUGH 84-96 HRS...WHILE SIMULTANEOUSLY A POLAR
RIDGE BUILDS OVER THE CONTINENT. THE RIDGE IS TO ANCHOR ON A
1027-1031 HPA HIGH NEAR CORDOBA IN ARGENTINA BY 96 HRS. AS THE LOW
DEEPENS AND RIDGE BUILDS ACROSS THE SOUTHERN CONE...THE SURFACE
FRONT IS TO ACCELERATE ACROSS ARGENTINA. BY 48 HRS IT MOVES TO
PATAGONIA...AND BY 72 HRS IT SURGES ACROSS LA PAMPA TO THE BUENOS
AIRES PROVINCE-CENTRAL CUYO IN ARGENTINA. BY 72-96 HRS...AS THE
RIDGE INTENSIFIES ACROSS THE SOUTHERN CONE AND A SOUTHERLY LOW
LEVEL JET ESTABLISHES ACROSS ARGENTINA...THE FRONT WILL RACE
ACROSS SOUTHERN BRASIL-PARAGUAY...WHERE IT IS TO MERGE
WITH/REINFORCE THE AFOREMENTIONED BOUNDARY. AS THE FRONT ENTERS
SOUTHERN CHILE THIS IS TO TRIGGER SCATTERED CONVECTION WITH
ACCUMULATION OF 05-10MM. ACROSS ARGENTINA-RIO DE LA PLATA BASIN
THIS IS TO ONLY FAVOR LIGHT CONVECTION...WITH MOST INTENSE TO
CLUSTER ON THE SOUTHERN STATES OF BRASIL AND PORTIONS OF PARAGUAY
LATER ON DAY 03...WHEN THE MAXIMA IS TO PEAK AT 40-80MM. UNDER
INFLUENCE OF THE LOW LEVEL JET OVER NORTHERN ARGENTINA/PARAGUAY
THE FOCUS OF THE ORGANIZED DEEP CONVECTION WILL SHIFT TO THE WEST
AND NORTH ACROSS BOLIVIA TO SOUTHERN PERU BY 96-108 HRS. MOST
INTENSE IS TO AFFECT CENTRAL-NORTHERN BOLIVIA-RONDONIA IN BRASIL
WITH MAXIMA IN THIS AREA TO PEAK AT 75-125MM...WHILE OVER CENTRAL
JUNGLE OF PERU THE MAXIMA IS TO PEAK AT 25-50MM.

AT 200 HPA...A SHORT WAVE RIDGE EXTENDS OVER THE EASTERN
PACIFIC...WHILE A SHORT WAVE TROUGH LIES OVER BRASIL. THROUGH
48-72 HRS THE HIGH/RIDGE MOVES INLAND ACROSS PERU TO WESTERN
BRASIL. THE  TROUGH TO THE EAST...MEANWHILE...IS TO INITIALLY
EXTEND ACROSS MATO GROSSO TO AMAZONAS IN BRASIL. AS THE RIDGE
MOVES INLAND...IT IS TO DISPLACE THE TROUGH ACROSS BRASIL...WITH
TROUGH TO PULL ACROSS NORTHEAST BRASIL BY 60-72 HRS...TO THEN
MEANDER OFF THE COAST. MEANWHILE...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. HIGHER AMOUNTS...HOWEVER...ARE EXPECTED
BETWEEN RECIFE-SALVADOR DE BAHIA IN BRASIL...WHERE TRADE WIND
CONVERGENCE IS TO SUSTAIN RAINFALL MAXIMA OF 15-30MM OVER THE NEXT
COUPLE OF DAYS. THROUGH 72 HRS...HOWEVER...THIS DECREASES TO
10-15MM.

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




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