Prognostic Meteorological Discussion
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FXSA20 KWBC 261759
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EDT THU APR 26 2018

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

COR DTG

MODEL DISCUSSION (VALID FROM APR 26 AT 0000 UTC): THE GFS AND
EUROPEAN MODELS FOLLOW A SIMILAR EVOLUTION OVER THE
CONTINENT/WESTERN ATLANTIC THROUGH 96-108 HRS. THEY THEN DISAGREE
ON THE AMPLITUDE AND SPEED OF PROPAGATION OF UPSTREAM
PERTURBATIONS ENTERING THE SOUTH AMERICAN DOMAIN.

SOUTH OVER THE CONTINENT...A DEEP TROPOSPHERIC TROUGH IS
INITIALIZED ACROSS THE EASTERN PACIFIC/SOUTHERN CONE OF SOUTH
AMERICA...WITH AXIS ANCHORING ON A CLOSED LOW OFF THE SOUTH COAST
OF CHILE. THE DEEP TROUGH IS TO MEANDER EAST ACROSS PATAGONIA IN
ARGENTINA TO THE WESTERN ATLANTIC EARLY ON FRIDAY MORNING.
MEANWHILE...THIS IS TO SUSTAIN HEIGHT FALLS OF 75-125GPM ACROSS
SOUTHERN PORTIONS OF ARGENTINA AND LA PAMPA. ON FRIDAY EVENING THE
TROUGH IS TO SLOWLY MIGRATE ACROSS 50W...AND ON SATURDAY IT
CONTINUES ACROSS 30W. AT LOW LEVELS...THIS WILL SUSTAIN A DEEP
OCCLUDED TROUGH ACROSS THE SOUTHERN CONE...WITH POLAR FRONT MOVING
NORTH ACROSS NORTHERN PATAGONIA-CENTRAL REGIONS OF CHILE. ON
FRIDAY IT MOVES NORTH ACROSS RIO DE LA PLATA BASIN-MENDOZA IN
ARGENTINA...WHERE IT IS FORECAST TO STALL. AS IT MEANDERS ACROSS
CENTRAL CHILE EARLY IN THE CYCLE THIS IS TO TRIGGER MODERATE
RAINFALL AMOUNTS WITH MAXIMA OF 15-25MM...WHILE OVER SOUTHERN
CHILE/TIERRA DEL FUEGO IT IS TO SUSTAIN MAXIMA OF 10-15MM. OTHER
CONVECTION IS EXPECTED ACROSS THE BUENOS AIRES PROVINCE-CENTRAL
ARGENTINA...WHERE THIS IS TO TRIGGER MAXIMA OF 20-45MM IN
POTENTIALLY SEVERE CONVECTION. ON FRIDAY-SATURDAY...AS THE FRONT
SURGES ACROSS RIO DE LA PLATA...MAXIMA ACROSS URUGUAY AND ENTRE
RIOS IN ARGENTINA IS TO PEAK AT 20-35MM.

A SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO FOLLOW...TO PULL
ACROSS 90W AND SOUTH OF 20S LATER ON SATURDAY. THE SHORT WAVE
TROUGH REACHES CENTRAL REGIONS OF CHILE ON SUNDAY EVENING. SHORT
WAVE ENERGY IS TO THEN SPILL ACROSS THE CENTRAL ANDES INTO CENTRAL
ARGENTINA. THIS IS TO THEN INTERACT WITH THE AFOREMENTIONED FRONT
OVER URUGUAY/CENTRAL ARGENTINA. THE INFLOW OF CYCLONIC VORTICITY
WILL INDUCE A FRONTAL LOW ALONG THIS BOUNDARY...WHILE TRIGGERING
MODERATE TO HEAVY RAINFALL AMOUNTS. ACROSS URUGUAY-ENTRE
RIOS-CENTRAL ARGENTINA THIS IS TO THEN SUSTAIN MAXIMA OF
30-60MM/DAY ON SUNDAY AND MONDAY. NOTE THAT IN THIS AREA SOME OF
THE ENSEMBLE MEMBERS SHOW LOCALIZED MAXIMA IN EXCESS OF 75MM.

NORTH OVER THE CONTINENT...AT 200 HPA...A RIDGE EXTENDS SOUTH FROM
AMAZONAS IN WESTERN BRASIL TO CENTRAL ARGENTINA. THE RIDGE IS TO
BECOME BETTER ORGANIZED LATER DURING THE WEEKEND...WHEN IT IS TO
ANCHOR ON A CLOSED HIGH OVER NORTHERN BOLIVIA/ACRE IN BRASIL. AS
THE RIDGE HOLDS...IT IS TO INDUCE THE NORTHWARD AMPLIFICATION OF A
TROUGH ACROSS NORTHEAST BRASIL EARLY IN THE PERIOD. THIS TROUGH IS
TO ENHANCE CONVECTIVE DEVELOPMENT ALONG THE NORTH COAST OF
BRASIL...WITH MAXIMA OF 20-35MM/DAY EXPECTED DURING THE NEXT FEW
DAYS. HIGHER AMOUNTS ARE EXPECTED TO THE WEST ACROSS NORTHERN
PARA-AMAZONAS-RONDONIA IN BRASIL...WITH MAXIMA OF 25-50MM/DAY.
ACTIVITY IS TO GRADUALLY BUILD WEST ACROSS SOUTHERN COLOMBIA TO
NORTHERN PERU/EASTERN ECUADOR...WHERE THE MAXIMA IS TO PEAK
BETWEEN 20-45MM/DAY...WITH LOCALLY HIGHER AMOUNTS HIGHLY PROBABLE.
THE RIDGE ALOFT IS TO ALSO VENT CONVECTION ACROSS THE
JUNGLE/SIERRA OF PERU AND CENTRAL BOLIVIA. ON THE JUNGLE THE DAILY
MAXIMA PEAKS AT 15-20MM...WHILE OVER THE ALTIPLANO/SOUTHERN SIERRA
OF PERU EXPECTING MAXIMA OF 10-15MM OVER THE NEXT COUPLE OF DAYS.

BALBINO...INMET (BRASIL)
DIAZ...INUMET (URUGUAY)
DAVISON...WPC (USA)
$$





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