Prognostic Meteorological Discussion
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694
FXSA20 KWBC 061619
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1119 AM EST TUE DEC 06 2016

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

MODEL DISCUSSION (VALID FROM DECEMBER 06 AT 0000 UTC): THE GLOBAL
MODELS MADE PATTERN CORRECTIONS DURING THE MEDIUM RANGE
PERIOD...WITH THE GFS AND UKMET NOW FORECASTING A DEEPER LOW TO
MEANDER OFF THE NORTHERN COAST OF CHILE THROUGH DAY 05. THIS IS
WELL SUPPORTED BY THE MEAN OF THE GLOBAL ENSEMBLE MEMBERS.
CONFIDENCE IN THE FORECAST IS HIGH THROUGH DAY 05.

CONSISTENT WITH PREVIOUS FORECAST...A MID LEVEL SHORT WAVE TROUGH
ON THE NORTHERN STREAM FLOW MOVES ACROSS ARGENTINA TO THE WESTERN
ATLANTIC EARLY IN THE CYCLE. ON WEDNESDAY...AS IT MEANDERS OVER
THE SOUTH ATLANTIC...THE TROUGH IS FORECAST TO MERGE WITH A DEEPER
TROUGH TO THE SOUTH. THROUGH THURSDAY THEY ARE TO GRADUALLY EVOLVE
INTO A BROAD/LOW AMPLITUDE TROUGH BETWEEN 50W-20W AND TO THE SOUTH
OF 30S. THIS IS TO THEN DOMINATE THE FLOW THROUGH THE END OF THE
WORKWEEK. SIMULTANEOUSLY...A SHORT WAVE TROUGH ON THE NORTHERN
STREAM IS TO LIFT ALONG THE COAST OF CHILE LATER TODAY...REACHING
CENTRAL CHILE LATER ON WEDNESDAY...WHERE IT IS TO EVOLVE INTO A
CLOSED LOW. ON THURSDAY-FRIDAY THIS IS TO THEN MEANDER JUST
WEST-NORTHWEST OF LA SERENA CHILE. THE MEANDERING LOW IS TO THEN
FOCUS OF SUBTROPICAL JET MAXIMA ACROSS NORTHERN CHILE-NORTHERN
ARGENTINA-SOUTHERN BRASIL. THIS WILL FAVOR GENERATION OF LEESIDE
PERTURBATIONS ACROSS MID SECTIONS OF SOUTH AMERICA WHILE ALSO
FAVORING AN UPPER DIVERGENT PATTERN THAT IS TO VENT DEEP
CONVECTION.

AT LOW LEVELS...THE TROUGH ALOFT SUSTAINS A DEEP OCCLUDED TROUGH
OFF THE COAST OF ARGENTINA...WITH ASSOCIATED FRONT TO MEANDER
NORTH ACROSS SOUTHERN BRASIL-MENDOZA IN ARGENTINA LATER TODAY. A
SECONDARY BOUNDARY WILL FOLLOW...ENTERING PATAGONIA IN
ARGENTINA/SOUTHERN CHILE LATER TODAY. THIS FRONT IS TO THEN LIFT
ALONG THE WESTERN FRINGES OF THE LOW LEVEL TROUGH...REACHING
BUENOS AIRES PROVINCE/ CENTRAL CUYO IN ARGENTINA LATER ON
WEDNESDAY. ON THURSDAY THIS IS TO THEN MERGE WITH/REPLACE THE OLD
BOUNDARY MEANDERING OVER SOUTHERN BRASIL-NORTHERN ARGENTINA. A
NORTHERLY LOW LEVEL JET ACROSS BOLIVIA-PARAGUAY WILL ADVECT
MOISTURE SOUTH. THIS WILL CONVERGE ALONG AND NORTH OF THE
MEANDERING FRONT TO THE SOUTH. THIS PATTERN IS TO PERSIST OVER THE
NEXT FOUR DAYS...WITH ENVIRONMENTAL CONDITIONS TO QUICKLY BECOME
FAVORABLE AND HIGHLY CONDUCIVE TO THE GENERATION OF MESO SCALE
CONVECTIVE SYSTEMS. PEAK IN CONVECTION IS EXPECTED ON
WEDNESDAY-THURSDAY...WHEN MAXIMA ACROSS CHACO/CORRIENTES-MISIONES
IN ARGENTINA AND PARAGUAY IS TO RANGE BETWEEN 50-100MM...WITH
LOCALIZED MAXIMA OF 150-200MM HIGHLY LIKELY DUE TO STRONG
MESO-SYNOPTIC FORCING. ON THURSDAY-FRIDAY HEAVY CONVECTION WILL
PERSIST WHILE FOCUSING OVER SOUTHERN BRASIL-PARAGUAY-MESOPOTAMIA
VALLEY IN ARGENTINA...WITH MAXIMA IN THIS AREA TO PEAK AT
40-80MM/DAY. THE MEANDERING UPPER LEVEL LOW IS TO ALSO FAVOR
CONVECTION ALONG THE LEE OF THE ANDES OVER NORTHWEST
ARGENTINA...WITH RAINFALL AMOUNTS OF 15-20MM EXPECTED ON WEDNESDAY
AND 10-15MM/DAY ON THURSDAY AND FRIDAY. FURTHERMORE...OVER
NORTHERN CHILE...THIS IS LIKELY TO TRIGGER LIGHT SNOW SHOWERS...TO
RESULT IN ACCUMULATION OF LESS THAN 02CM DURING THE DAY ON FRIDAY.

A MID/UPPER LEVEL RIDGE IS TO THEN ESTABLISH TO THE WEST BETWEEN
110W-90W TO 40S. A BROAD TROUGH TO THE WEST WILL PRESS AGAINST
THIS AXIS...WITH SHORT WAVE ENERGY TO SHEAR TO THE EAST-SOUTHEAST
UNDER THIS AXIS. ON WEDNESDAY-THURSDAY THIS IS TO THEN FOCUS
ENERGY AND SUBTROPICAL MOISTURE ACROSS SOUTHERN PORTIONS OF
CHILE/PATAGONIA IN ARGENTINA. AT LOW LEVELS THIS WILL THEN FAVOR A
DEEP OCCLUDED LOW OVER THE BELLINGSHAUSEN SEA LATER ON
THURSDAY...WHILE THE ASSOCIATED FRONT STREAMS ACROSS SOUTHERN
CHILE TO PATAGONIA ARGENTINA. FRONTAL BOUNDARY IS TO THEN MEANDER
OVER THE SOUTHERN CONE OF SOUTH AMERICA THROUGH THE END OF THE
WEEK. ON THURSDAY THIS IS TO SUSTAIN RAINFALL AMOUNTS OF 00-05MM
ACROSS EXTREME SOUTHERN PORTIONS OF CHILE. ON FRIDAY THIS
INCREASES TO 15-25MM WHILE SHIFTING NORTH BETWEEN ISLA DE
CHILOE-TEMUCO...AND ON SATURDAY IT DECREASES TO 10-15MM AS MOST OF
THE ENERGY SPILLS ACROSS THE SOUTHERN CONE TO THE SOUTH ATLANTIC.

NORTH OVER THE CONTINENT...AT 200 HPA...THE BOLIVIAN HIGH
DOMINATES THE FLOW ACROSS NORTHWEST SOUTH AMERICA...WHILE A CLOSED
LOW DOMINATES THE FLOW OVER NORTHEASTERN BRASIL. THROUGH THURSDAY
THE RIDGE WILL BUILD EAST AND NORTH TO ENVELOP MOST OF BRASIL. AS
IT BUILDS...IT WILL DISPLACE THE TROUGH NORTH AND EAST INTO
EQUATORIAL SOUTH AMERICA/TROPICAL ATLANTIC. THE RIDGE ALOFT WILL
VENT SCATTERED CONVECTION ACROSS PARA-AMAZONAS TO THE SOUTHEAST
STATES OF BRASIL... WITH RAINFALL AMOUNTS OF 15-20MM IN SCATTERED
DEEP CONVECTION. THROUGH THURSDAY MORNING...AS THE RIDGE
BUILDS...ACTIVITY ACROSS BAHIA-MINAS GERAIS WILL INTENSIFY...WITH
DAILY MAXIMA TO PEAK AT 20-35MM. ACROSS ECUADOR EXPECTING MAXIMA
OF 05-10MM/DAY...INCREASING TO 101-15MM ON FRIDAY. OVER SOUTHERN
PERU-CENTRAL BOLIVIA THE DAILY MAXIMA IS TO PEAK AT 20-30MM
THROUGH WEDNESDAY MORNING...AND 15-20MM/DAY THEREAFTER.

ALVA...SENAMHI (PERU)
DURAN...SMN (ARGENTINA)
DAVISON/GALVEZ...WPC (USA)
$$





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