Prognostic Meteorological Discussion
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FXSA20 KWBC 241649
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1249 PM EDT FRI MAY 24 2019

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

MODEL DISCUSSION FROM MAY 24/00UTC: GLOBAL MODELS AND ENSEMBLE
MEMBERS ARE IN GOOD AGREEMENT THROUGH 96 HRS. CONFIDENCE THEN
DECREASES VERY GRADUALLY THROUGH 120-132 HRS.

INITIALLY...A ROBUST TROUGH IN THE NORTHERN STREAM EXITING INTO
THE SOUTH ATLANTIC ON MONDAY WILL CONTINUE SUSTAINING CYCLOGENESIS
IN SOUTHERN BRASIL. AS THE OCCLUDED LOW SLOWLY MEANDERS OFFSHORE
FROM MISIONES/WESTERN RIO GRANDE DO SUL TO AREAS OFF THE COAST OF
SANTA CATARINA ON FRIDAY THROUGH EARLY SATURDAY...HEAVY RAINFALL
WILL CONTINUE. UNDER THE INFLUENCE OF ECHO TRAINING FROM THE
EAST...UPPER TROUGH DYNAMICS...THE DIVERGENT EXIT OF AN UPPER JET
AND OROGRAPHIC ENHANCEMENT BY THE SERRA DO MAR...EXPECTING
ACCUMULATIONS PEAKING AT 75-150MM/DAY IN NORTHEASTERN RIO GRANDE
DO SUL/EASTERN SANTA CATARINA ON FRIDAY. WEST ACROSS
MISIONES/WESTERN SOUTHERN BRASIL EXPECTING MAXIMA OF 25-50MM/DAY.
ASSOCIATED WITH THIS SYSTEM...FRONTAL CONVECTION IN SOUTHEASTERN
BRASIL WILL PRODUCE MUCH LIGHTER ACCUMULATIONS. ON FRIDAY
EXPECTING ISOLATED MAXIMA OF 10-15MM/DAY IN MINAS GERAIS/RIO DE
JANEIRO. THIS DECREASES TO MAXIMA OF 05-10MM/DAY IN ESPIRITO SANTO
ON SATURDAY. BY SUNDAY...TRADE WINDS BECOME SOUTH EASTERLIES ALONG
THE FRONT. THIS WILL ENHANCE MOISTURE CONVERGENCE TO SUSTAIN AN
INCREASE TO MAXIMA OF 20-30MM/DAY.

MODELS ARE CONFIDENT ON RIDGE BUILDING OFF THE COAST OF SOUTHERN
CHILE INTO ANTARCTICA ALONG 90W-100W THROUGH SATURDAY/SUNDAY. THIS
WILL INDUCE LONG-FETCH SOUTHERLY FLOW INTO THE DRAKE
PASSAGE/TIERRA DEL FUEGO. AN ANTARCTIC FRONT IS FORECAST TO ARRIVE
LATE ON SUNDAY. THIS WILL SWITCH PRECIPITATION TO SNOWFALL FOR
MONDAY. EXPECTING ACCUMULATIONS OF 10-15CM IN SOUTHERN SLOPES OF
THE DARWIN CORDILLERA. THE COLD ANTARCTIC WILL THEN MEANDER INTO
THE ATLANTIC WITHOUT AFFECTING THE CONTINENT DIRECTLY.

ANOTHER UPPER TROUGH CROSSES THE ANDES OF CENTRAL CHILE INTO
ARGENTINA ON SUNDAY/EARLY MONDAY. THE MOST SIGNIFICANT IMPACT WITH
THIS TROUGH WILL BE THE INTERACTION WITH A MOIST LOW-LEVEL JET
FROM THE NORTH IN CENTRAL PORTIONS OF THE CONTINENT. PRECIPITABLE
WATER VALUES WILL REACH 35-40MM IN EASTERN/SOUTHEASTERN PARAGUAY.
THE ENVIRONMENT WILL BE SUFFICIENTLY UNSTABLE TO SUSTAIN A RISK
FOR SEVERE CONVECTION IN EASTERN PARAGUAY/WESTERN PARANA AND RIO
GRANDE DO SUL AND MISIONES...WHERE EXPECTING ACCUMULATIONS OF
30-60MM/DAY BY MONDAY THROUGH EARLY TUESDAY.

A SITUATION OF INTEREST IS THE SPLIT FLOW DEVELOPING OFF THE COAST
OF SOUTHERN CHILE IN ASSOCIATION WITH THE AFOREMENTIONED RIDGE.
THIS WILL ALLOW UPPER TROUGHS TO PROPAGATE WESTWARD ACROSS CENTRAL
CHILE. ALTHOUGH CONFIDENCE IS STILL LOW...MODELS ARE BECOMING MORE
IN PHASE WITH RESOLVING AN UPPER TROUGH ENTERING CENTRAL CHILE ON
THURSDAY/FRIDAY NEXT WEEK. ALTHOUGH IT IS EARLY...A SUBTROPICAL
MOISTURE CONNECTION WILL LIKELY ACCOMPANY THIS SYSTEM...WHICH
OPENS THE WINDOW FOR PRECIPITATION IN CENTRAL CHILE. GIVEN THE
CURRENT EVOLUTION...AN EXTREME EVENT DOES NOT APPEAR LIKELY...BUT
MODERATE PRECIPITATION MIGHT AREAS AS FAR NORTH AS SOUTHERN
COQUIMBO ON THURSDAY. THERE IS STILL UNCERTAINTY IN RAINFALL
ACCUMULATIONS...BUT GIVEN THE POSITIONING OF THE SUBTROPICAL
MOISTURE PLUME AND MODEL SUGGESTED RAINFALL TOTALS...EXPECTING
MAXIMA IN THE ORDER OF 10-25MM IN COASTAL LOCATIONS BETWEEN LOS
VILOS AND VALPARAISO ON THURSDAY...AND MUCH LIGHTER ACCUMULATIONS
IN INTERIOR PORTIONS OF THE COAST AND NORTHERN PARTS OF THE
COQUIMBO REGION. THE MOST SIGNIFICANT IMPACT IS EXPECTED IN TERMS
OF SNOWFALL IN THE ANDES...AS THE SYSTEM ARRIVES WITH 1 110-140KT
UPPER JET. OROGRAPHIC ENHANCEMENT BY THE JET AND DYNAMICS IN THE
RIGHT EXIT REGION OF THE JET MAXIMA ON THURSDAY HAVE THE POTENTIAL
FOR SUSTAINING SNOWFALL ACCUMULATIONS NEAR/SLIGHTLY OVER 1
METER/DAY IN THURSDAY THROUGH EARLY FRIDAY IN THE CORDILLERA
BETWEEN SANTIAGO AND MAULE.

DIAZ... DMC (CHILE)
MATHIAS...CHM (BRASIL)
GALVEZ...WPC (USA)
$$




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