Prognostic Meteorological Discussion
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FXSA20 KWBC 171643
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1242 PM EDT TUE OCT 17 2017

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

NOTE: THERE IS A RISK FOR SEVERE CONVECTION IN NORTH-CENTRAL AND
NORTHEASTERN ARGENTINA ON TUESDAY AND ESPECIALLY WEDNESDAY. NOTE
THAT THE RISK FOR HAIL IS HIGH...PARTICULARLY DURING THE DAY ON
WEDNESDAY...WHEN A RISK FOR LARGE HAIL EXISTS FROM LA PAMPA-BUENOS
AIRES PROVINCE NORTH ACROSS CORDOBA/SANTA FE.

MODEL DISCUSSION (VALID FROM OCT 17 AT 0000 UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS CONTINUE AGREEING ON THE FORECAST EVOLUTION
THROUGH 96-108 HRS. AFTER THIS PERIOD...THE CONFIDENCE DECREASES
VERY RAPIDLY TO THE SOUTH OF 45S...ESPECIALLY IN THE EASTERN
PACIFIC.

ACTIVE WEATHER PATTERN IS UNRAVELING FOR NORTHEASTERN
ARGENTINA-URUGUAY-SOUTHERN BRASIL AND PARAGUAY. SEVERAL SHORT WAVE
TROUGHS ARE TO CROSS THE ANDES AND INTERACT WITH A MOIST AND
UNSTABLE AIR MASS BREWING IN THE REGION. AT LOW-LEVELS...AN
UNSEASONABLY WARM AIR MASS IS LEADING TO EXTREME TEMPERATURES IN
THE REGIONS. NOTE THAT FORECAST MINIMUM TEMPERATURES CLOSE TO 30C
ARE EXPECTED FOR THE PARAGUAYAN CHACO AND EXTREME NORTHERN
ARGENTINA. THE WARM AIR MASS WILL FAVOR THE DEVELOPMENT OF STRONG
INSTABILITY ON WEDNESDAY...WITH LIFTED INDEX VALUES APPROACHING
-10C. DURING TUESDAY...SEVERE CONVECTION WILL CONTINUE DEVELOPING
IN ENTRE RIOS-CORRIENTES/NORTHERN BUENOS AIRES PROVINCE INTO
URUGUAY...TO PRODUCE MAXIMUM ACCUMULATIONS OF 40-80MM/DAY.
ALSO...STRONG CONVECTION IS TO DEVELOP IN LA PAMPA/SOUTHERN BUENOS
AIRES PROVINCE...TO PRODUCE ISOLATED MAXIMA OF 15-25MM. BY
WEDNESDAY-THURSDAY...THE RISK FOR SEVERE CONVECTION WILL PEAK
DURING THE DAY...ESPECIALLY BETWEEN CORRIENTES-ENTRE RIOS-SANTA FE
AND URUGUAY/SOUTHERN RIO GRANDE DO SUL. EXPECTING ACCUMULATIONS OF
50-100MM/DAY...YET ISOLATED LARGER AMOUNTS ARE POSSIBLE IN AREAS
UNDER THE INFLUENCE OF STRONGEST THUNDERSTORMS. BY
THURSDAY...LARGEST ACCUMULATIONS WILL CLUSTER BETWEEN SOUTHERN
BOLIVIA AND MOST OF PARAGUAY...WHERE SCATTERED CONVECTION WILL
LEAD TO MAXIMA OF 35-70MM. ENHANCED CONVECTION ALONG THE BOLIVIAN
YUNGAS AND SOUTHERN PERU WILL LEAD TO MAXIMA OF 25-50MM. IN
SOUTHERN BRASIL/MISIONES...EXPECTING MAXIMA OF 20-30MM/DAY. DURING
FRIDAY...A SHORT WAVE TROUGH WILL INTERACT WITH MOISTURE POOL
SITTING IN PARAGUAY TO LEAD ONCE AGAIN TO STRONG CONVECTION.
EXPECTING ACCUMULATIONS OF 75-125MM/DAY AND THE RISK FOR MCS
FORMATION IN SOUTHEASTERN PARAGUAY/MISIONES/PARANA AND WESTERN
SANTA CATARINA IN BRASIL. BY SATURDAY-SUNDAY...CONVECTION WILL
REMAIN ACTIVE ALONG THE SURFACE FRONT THAT IS FORECAST TO MEANDER
NORTHWARD INTO SOUTHERN BOLIVIA-NORTHERN PARAGUAY-SOUTHERN MATO
GROSSO DO SUL...WHERE EXPECTING MAXIMA OF 30-60MM.

ELSEWHERE IN SOUTH AMERICA...FRONTAL CONVECTION IN ESPIRITO SANTO
WILL LEAD TO ISOLATED MAXIMA OF 15-20MM/DAY ON MONDAY-TUESDAY.
MAXIMA WILL SHIFT TO SALVADOR DE BAHIA ON TUESDAY-WEDNESDAY WHERE
EXPECTING AMOUNTS OF 15-25MM/DAY IN A REGION OF ENHANCED TRADE
WIND CONVERGENCE. AMOUNTS WILL DECREASE AFTER.

ALSO IN TROPICAL SOUTH AMERICA...UNSEASONABLY ACTIVE CONVECTION IS
EXPECTED IN THE PERUVIAN/BOLIVIAN ANDES EARLY IN THE CYCLE AS
UPPER TROUGH TO THE SOUTH WEST INTERACTS WITH MOIST AIR MASS IN
PLACE. THIS WILL LEAD TO MAXIMA OF 10-15MM/DAY ON
TUESDAY-WEDNESDAY...DECREASING AFTER.

VANNUCCI...SMN (ARGENTINA)
RIVAS...SENAMHI (PERU)
GALVEZ...WPC (USA)
$$





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