Prognostic Meteorological Discussion
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FXSA20 KWBC 241629
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1229 PM EDT TUE APR 24 2018

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

MODEL DISCUSSION (VALID FROM APR 24 AT 0000 UTC): THE SYSTEM OF
CONCERN IS A DEEPENING MID LATITUDE TROUGH THAT IS TO ENTER
SOUTHERN CHILE EARLY ON WEDNESDAY MORNING. THIS IS TO FOLLOW A
RAPID RATE OF INTENSIFICATION WITH GLOBAL MODEL GUIDANCE
FORESEEING A HIGH RISK OF EXPLOSIVE CYCLOGENESIS. THIS WILL BE
ACCOMPANIED BY NEAR HURRICANE INTENSITY WINDS AND HEAVY RAINFALL
AMOUNTS.

UNDER INFLUENCE OF A RIDGE TO THE WEST...A MID LEVEL TROUGH IS TO
AMPLIFY ACROSS THE SOUTHEAST PACIFIC EARLY IN THE CYCLE...TO
EVOLVE INTO A DEEP CLOSED LOW OFF THE SOUTH COAST OF CHILE ON
WEDNESDAY. AS IT DEEPENS THIS IS TO SUSTAIN HEIGHT FALLS OF
75-150GPM ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA. LATER
ON THURSDAY THE MID LEVEL TROUGH IS TO THEN PULL ACROSS SOUTHERN
CHILE TO PATAGONIA IN ARGENTINA...INTO THE SOUTHWEST ATLANTIC ON
FRIDAY. AT LOW LEVELS THE DEEPENING MID LEVEL TROUGH WILL SUSTAIN
EXPLOSIVE CYCLOGENESIS OFF THE SOUTH COAST OF CHILE EARLY ON
WEDNESDAY MORNING...WITH ASSOCIATED SURFACE LOW DEEPENING FROM A
1004 HPA LOW EARLY IN THE CYCLE TO A 974/978 HPA LOW AS IT NEARS
SOUTHERN CHILE ON WEDNESDAY MORNING. NOTE THAT THIS RAPID RATE OF
INTENSIFICATION IS CONSISTENT WITH A METEOROLOGICAL BOMB. THE
ASSOCIATED FRONT IS TO ENTER SOUTHERN CHILE EARLY ON WEDNESDAY
MORNING. THIS WILL BE ACCOMPANIED BY STRONG BOUNDARY LAYER
WINDS...EXPECTED TO PEAK AT 30-50KT. THE SURFACE FRONT WILL
CONTINUE ACROSS PATAGONIA TO LA PAMPA IN ARGENTINA ON
THURSDAY...AND ON FRIDAY IT WILL RACE ACROSS RIO DE LA PLATA
BASIN-CENTRAL PROVINCES IN ARGENTINA. OVER SOUTHERN CHILE THIS IS
TO FAVOR MODERATE TO HEAVY RAINFALL AMOUNTS...WITH MAXIMA OF
30-60MM ON WEDNESDAY-THURSDAY. OVER TIERRA DEL FUEGO/EXTREME
SOUTHERN CHILE THIS IS TO ALSO TRIGGER LIGHT TO MODERATE RAINFALL
AMOUNTS...WITH MAXIMA OF 15-20MM. AS IT SURGES ACROSS CENTRAL
ARGENTINA ON THURSDAY THIS IS TO SUSTAIN MODERATE RAINFALL AMOUNTS
WITH MAXIMA OF 20-35MM IN POTENTIALLY SEVERE CONVECTION. ON FRIDAY
THIS IS TO ALSO FAVOR SIMILAR RAINFALL AMOUNTS ACROSS ENTRE
RIOS-CORRIENTES IN ARGENTINA AND PORTIONS OF URUGUAY.

A MEANDERING FRONT TO THE NORTH...MEANWHILE...EXTENDS ACROSS THE
SOUTH ATLANTIC TO RIO DE LA PLATA BASIN/CENTRAL PROVINCES IN
ARGENTINA. MID LEVEL VORTICES SHEARING ACROSS THE CENTRAL ANDES OF
CHILE TO ARGENTINA ARE TO INTERACT WITH THIS BOUNDARY...TO TRIGGER
SCATTERED DEEP CONVECTION. MOST ACTIVE IS EXPECTED ACROSS ENTRE
RIOS/CENTRAL ARGENTINA EARLY IN THE CYCLE...WITH MAXIMA OF
30-60MM. ON WEDNESDAY THIS DECREASES TO 10-15MM/DAY...WHILE ON
THURSDAY THE FRONT IS FORECAST TO FRONTOLIZE.

NORTH OVER THE CONTINENT...AT 200 HPA...A SHORT WAVE TROUGH
EXTENDS OVER THE SOUTHEAST STATES OF BRASIL. A BUILDING RIDGE OVER
CENTRAL BRASIL IS TO SUSTAIN THE GRADUAL AMPLIFICATION OF THIS
TROUGH ACROSS NORTHEAST BRASIL ON WEDNESDAY-THURSDAY. THE TROUGH
IS TO THEN PERSIST THROUGH THE END OF THE WEEK. THE DEEPENING
TROUGH WILL INTERACT WITH SEA BREEZE RELATED CONVERGENCE ALONG THE
NORTH/NORTHEAST COAST OF BRASIL. IN THIS AREA INITIALLY EXPECTING
SCATTERED DEEP CONVECTION TO TRIGGER MAXIMA OF 20-35MM/DAY. ACROSS
NORTHERN PARA/AMAZONAS-RORAIMA IN BRASIL...NEAR EQUATORIAL TROUGH
RELATED CONVERGENCE IS TO TRIGGER RAINFALL AMOUNTS OF 20-45MM/DAY.
THIS IS TO ALSO PERSIST DURING THE NEXT FEW DAYS. UNDER INFLUENCE
OF THE DEEPENING UPPER LEVEL TROUGH THIS INCREASES TO 25-50MM/DAY
LATER ON FRIDAY. LESSER AMOUNTS ARE EXPECTED ON THE PERUVIAN
JUNGLE/EASTERN ECUADOR...WITH DIURNAL CONVECTION TRIGGERING DAILY
MAXIMA OF 10-15MM.

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





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