Prognostic Meteorological Discussion
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FXSA20 KWBC 251557
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1156 AM EDT WED APR 25 2018

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

MODEL DISCUSSION (VALID FROM APR 25 AT 0000 UTC): GLOBAL MODELS
CONTINUE TO AGREE ON METEOROLOGICAL BOMB TO AFFECT SOUTHERN
REGIONS OF CHILE DURING THE NEXT COUPLE OF DAYS. THIS WILL BE
ACCOMPANIED BY TROPICAL STORM INTENSITY WINDS AND MODERATE TO
HEAVY RAINFALL AMOUNTS.

CONSISTENT WITH PREVIOUS FORECASTS...A MID LEVEL LOW CLOSES OFF
THE SOUTH COAST OF CHILE EARLY IN THE CYCLE. THE DEEPENING
LOW/TROUGH IS TO THEN INDUCED HEIGHT FALLS OF 75-150GPM ACROSS
SOUTHERN CHILE TO PATAGONIA IN ARGENTINA. LATER ON THURSDAY/EARLY
FRIDAY MORNING THE MID LEVEL TROUGH IS TO SLOWLY MIGRATE ACROSS
SOUTHERN CHILE TO PATAGONIA IN ARGENTINA. THIS IS TO THEN MOVE OFF
THE COAST OF ARGENTINA INTO THE WESTERN ATLANTIC ON FRIDAY. AT LOW
LEVELS THIS SUSTAINS EXPLOSIVE CYCLOGENESIS OFF THE SOUTH COAST OF
CHILE...WITH SURFACE LOW FORECAST TO PEAK AROUND 976 HPA LATER
TODAY. THIS WILL BE ACCOMPANIED BY STRONG BOUNDARY LAYER
WINDS...EXPECTED TO PEAK AT 30-50KT. THE DEEP LOW WILL THEN DRIVE
A FRONT ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA LATER
TODAY. LATER ON THURSDAY/EARLY FRIDAY MORNING THE FRONT ADVANCES
ACROSS LA PAMPA IN ARGENTINA/CENTRAL REGIONS OF CHILE...REACHING
URUGUAY/CENTRAL ARGENTINA LATER ON FRIDAY. OVER SOUTHERN CHILE
THIS IS TO FAVOR MODERATE TO HEAVY RAINFALL AMOUNTS...WITH MAXIMA
OF 30-60MM IN DEEP CONVECTION. OVER TIERRA DEL FUEGO/EXTREME
SOUTHERN CHILE THE OCCLUDING SURFACE LOW WILL RESULT IN MODERATE
RAINFALL AMOUNTS...TRIGGERING MAXIMA OF 15-20MM. AS IT SURGES
ACROSS CENTRAL ARGENTINA ON THURSDAY THIS IS TO ALSO TRIGGER
MODERATE RAINFALL AMOUNTS...WITH MAXIMA OF 20-35MM IN POTENTIALLY
SEVERE CONVECTION. NOTE THAT IN THIS AREA SOME OF THE MODELS SHOW
LOCALIZED MAXIMA IN EXCESS OF 50MM. ON FRIDAY...AS THE FRONT
MEANDERS NORTH ACROSS URUGUAY/ENTRE RIOS IN ARGENTINA...IT IS TO
ALSO TRIGGER MAXIMA OF 20-35MM. THIS DECREASES TO 10-15MM/DAY ON
SATURDAY.

NEXT MID LEVEL TROUGH IS TO AMPLIFY ACROSS THE SOUTHEAST PACIFIC
LATER ON FRIDAY...INTO THE DRAKE PASSAGE/SOUTHERN CONE OF SOUTH
AMERICA LATER ON SATURDAY. AS IT NEARS THE SOUTHERN CONE THIS IS
TO THEN INTERACT WITH A SHORT WAVE TROUGH TO THE NORTH. THIS WILL
DRIVE THE SHORT WAVE PERTURBATION EAST TOWARDS CENTRAL REGIONS OF
CHILE LATER DURING THE WEEKEND...WITH AXIS TO THEN SPILL ACROSS
THE CENTRAL ANDES INTO ARGENTINA EARLY NEXT WEEK. AS IT SPILLS
ACROSS THE ANDES THIS VORTEX IS TO THEN INTERACT WITH SURFACE
FRONT MEANDERING ACROSS URUGUAY-CENTRAL ARGENTINA. EARLY ON MONDAY
MORNING ENVIRONMENTAL CONDITIONS ARE LIKELY TO BECOME FAVORABLE
FOR GENERATION OF A MESO SCALE CONVECTIVE SYSTEM ALONG THIS
BOUNDARY. THIS IS TO FAVOR ORGANIZED DEEP CONVECTION WITH MAXIMA
OF 30-60MM. AT LOW LEVELS...THE SOUTHERN STREAM TROUGH WILL
SUSTAIN A BROAD/LOW AMPLITUDE TROUGH ACROSS THE ANTARCTIC
PENINSULA-DRAKE PASSAGE TO TIERRA DEL FUEGO LATER ON
SATURDAY...WHILE THE ASSOCIATED FRONT SURGES ACROSS TIERRA DEL
FUEGO TO PATAGONIA LATER DURING THE WEEKEND. AS IT ENTERS SOUTHERN
CHILE THIS IS TO FAVOR LIGHT RAINFALL AMOUNTS...WITH MAXIMA OF
05-10MM.

AT 200 HPA...OVER NORTHERN SOUTH AMERICA...A RIDGE OVER
BOLIVIA/PARAGUAY IS TO INDUCE THE NORTHWARD AMPLIFICATION OF A
SHORT WAVE TROUGH ACROSS THE NORTHEAST STATES OF BRASIL EARLY IN
THE CYCLE. BROAD TROUGH IS TO DOMINATE THE FLOW DURING THE NEXT
FEW DAYS. AS IT HOLDS...THIS IS TO ENHANCE CONVECTIVE DEVELOPMENT
OVER NORTHERN BRASIL...WITH MAXIMA OF 20-30MM/DAY EXPECTED OVER
THE NEXT FEW DAYS. HIGHER AMOUNTS ARE EXPECTED OVER EQUATORIAL
SOUTH AMERICA-NORTHERN PARA/AMAZONAS IN BRASIL...WITH MAXIMA IN
THIS AREA FORECAST TO PEAK AT 25-50MM/DAY. LOCALLY HIGHER AMOUNTS
ARE HIGHLY PROBABLE ALONG THE NEAR EQUATORIAL TROUGH TO THE NORTH.
OVER NORTHERN PERU-EASTERN ECUADOR INITIALLY EXPECTING RAINFALL
AMOUNTS OF 15-20MM/DAY. AN UPPER LEVEL HIGH CLOSED OVER WESTERN
ECUADOR/EASTERN TROPICAL PACIFIC LATER ON FRIDAY. THIS TO THEN
FAVOR AN UPPER DIVERGENT PATTERN THAT IS TO VENT DEEP CONVECTION.
AS A RESULT...MAXIMA IN THIS AREA INCREASES TO 25-50MM ON FRIDAY.
LESSER AMOUNTS ARE EXPECTED ON THE SOUTHERN SIERRA OF PERU AND THE
ALTIPLANO OF BOLIVIA...WITH DAILY MAXIMA OF 05-10MM EXPECTED EARLY
IN THE PERIOD. THROUGH FRIDAY THIS INCREASES TO 10-15MM/DAY...WITH
POTENTIAL FOR HIGHER AMOUNTS.

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




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