Prognostic Meteorological Discussion
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000
FXSA20 KWBC 011718
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1217 PM EST WED MAR 01 2017

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

MODEL DISCUSSION (VALID FROM MARCH 01 AT 0000 UTC): GLOBAL MODELS
CONTINUE TO AGREE ON PATTERN EVOLUTION DURING THE SHORT RANGE
PERIOD. SIGNIFICANT DIFFERENCES LIMIT TO MEDIUM RANGE PATTERN
FORECAST...AS THE MODELS DIVERGE ON THE INTENSITY/AMPLITUDE OF A
SOUTHERN STREAM TROUGH NEARING THE SOUTHERN CONE LATER IN THE
FORECAST CYCLE. ALTHOUGH THE MEAN OF THE GLOBAL ENSEMBLES TENDS TO
SUPPORT THE DEEPER/SLOWER GFS SOLUTION...THE VARIABILITY AMONG THE
INDIVIDUAL MEMBERS IS TOO HIGH TO ESTABLISH CONFIDENCE IN THE
FORECAST DURING THE LATTER PART OF OUR FORECAST.

A DEEP MID LEVEL TROUGH PULLS ACROSS THE SOUTHERN CONE TO THE
WESTERN ATLANTIC LATER THIS EVENING. THROUGH THURSDAY EVENING THE
TROUGH IS TO SLOWLY PULL ACROSS 40W/45W WHILE REMAINING TO THE
SOUTH OF 35S. AT LOW LEVELS IT SUSTAINS A DEEP TROUGH OVER THE
WESTERN ATLANTIC...WITH ASSOCIATED FRONT TRAILING ACROSS RIO DE LA
PLATA TO CENTRAL CHILE LATER THIS AFTERNOON. EARLY ON THURSDAY A
MID LEVEL SHORT WAVE TROUGH IS TO INTERACT WITH THIS
SYSTEM...SUSTAINING A FRONTAL WAVE OVER CENTRAL ARGENTINA. THIS
WILL COMBINE WITH A BUILDING POLAR RIDGE OVER PATAGONIA TO
DISPLACE THE FRONT NORTH ACROSS URUGUAY TO SOUTHERN
BRASIL-NORTHERN ARGENTINA LATER ON FRIDAY. FRONTAL BOUNDARY IS TO
THEN REMAIN NEARLY STATIONARY OVER MID SECTIONS OF SOUTH AMERICA
THROUGH SATURDAY EVENING/SUNDAY MORNING. EARLY IN THE CYCLE THIS
WILL FAVOR SCATTERED CONVECTION ACROSS CENTRAL ARGENTINA/RIO DE LA
PLATA BASIN...WITH MAXIMA OF 15-25MM. UNDER FAVORABLE JET
DYNAMICS...AND AS A MOIST NORTHERLY FLOW ESTABLISHES ACROSS
PARAGUAY TO ARGENTINA...THE ATMOSPHERE WILL GRADUALLY GROW
UNSETTLED LATER ON THURSDAY/EARLY FRIDAY MORNING. THE
ENVIRONMENTAL CONDITIONS ARE TO BECOME FAVORABLE FOR THE
GENERATION OF MESO SCALE CONVECTIVE SYSTEMS AND SEVERE
CONVECTION...TO SUSTAIN RAINFALL MAXIMA OF 35-70MM IN POTENTIALLY
SEVERE CONVECTION. ON FRIDAY TO SATURDAY THE MAXIMA INCREASES TO
50-100MM WHILE BUILDING NORTH ACROSS CORRIENTES IN ARGENTINA TO
PARAGUAY-SOUTHERN BRASIL. ON SATURDAY TO SUNDAY HEAVY RAINS ARE TO
PERSIST...WITH MAXIMA OF 40-80MM. ON MONDAY...IT IS TO DECREASE TO
20-45MM...WITH MOST ACTIVE OVER SOUTHERN BRASIL.

A DEEP PERTURBATION IN THE SOUTHERN STREAM IS TO FOLLOW...WITH
AXIS TO PULL ACROSS 130W LATER ON FRIDAY. ON SATURDAY-SUNDAY THIS
WILL THEN EVOLVE INTO A BROAD/DEEP TROUGH OVER THE SOUTHEAST
PACIFIC...THAT IS TO ENVELOP AREA BETWEEN 110-W80W AND TO THE
SOUTH OF 28S. AS PREVIOUSLY INDICATED THE MODELS DISAGREE ON THE
INTENSITY AND SPEED OF THIS FEATURE...SO FURTHER CORRECTIONS ARE
EXPECTED. MEANWHILE...AT LOW LEVELS THIS WILL SUSTAIN A BROAD/DEEP
TROUGH OFF THE SOUTH COAST OF CHILE LATER ON SUNDAY.

NORTH OVER THE CONTINENT...AT 200 HPA...THE BOLIVIAN HIGH IS TO
INITIALLY CENTER OVER SOUTHERN BOLIVIA...WHILE ANCHORING A RIDGE
OVER THE CONTINENT TO THE NORTH OF 30S AND WEST OF 60W. THROUGH
SATURDAY EVENING THE RIDGE WILL RELOCATE TO MATO GROSSO IN CENTRAL
BRASIL. UNDER INFLUENCE OF THIS RIDGE...A TUTT OVER THE WESTERN
TROPICAL ATLANTIC IS FORECAST TO RETROGRESS ACROSS NORTHEAST
BRASIL LATER ON SUNDAY. THE RETROGRESSING TROUGH WILL THEN SUSTAIN
AN UPPER CONVERGENT PATTERN THAT IS TO FAVOR A SUBSIDENT PATTERN
ALOFT. THIS...IN-TURN...WILL FAVOR A DRYING TREND ACROSS THE
NORTHEAST STATES OF BRASIL. MEANWHILE...THE RIDGE ALOFT IS TO VENT
DEEP CONVECTION ACROSS AMAZONAS-PARA-AMAPA IN BRASIL...WITH MAXIMA
OF 30-60MM/DAY EXPECTED THROUGH THURSDAY MORNING...AND 20-35MM ON
THURSDAY TO FRIDAY. THE RIDGE ALOFT IS TO ALSO VENT DEEP
CONVECTION ON THE CENTRAL-SOUTHERN JUNGLE OF PERU TO RESULT IN
DAILY MAXIMA OF 30-60MM. THROUGH SUNDAY...HOWEVER...THIS WILL
DECREASE TO 20-35MM/DAY. OTHER CONVECTION TO THE NORTH IS TO BUILD
ACROSS WESTERN ECUADOR/ ANDEAN REGION...WHERE A LONG FETCH
WESTERLY FLOW EARLY ON THURSDAY IS TO FAVOR A MOIST ADVECTIVE
PATTERN. THE MOISTURE ADVECTION...AS ENHANCED BY TOPOGRAPHICAL
EFFECTS...WILL FAVOR MODERATE TO HEAVY CONVECTION WITH
ACCUMULATION OF 30-60MM/DAY.

ABDEMUR...FAA (ARGENTINA)
TEPES...DMC (CHILE)
GALVEZ...WPC (USA)
$$




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