Prognostic Meteorological Discussion
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FXSA20 KWBC 111810
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
110 PM EST MON DEC 11 2017

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

MODEL DISCUSSION (VALID FROM DEC 11 AT 0000 UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS AGREE QUITE WELL ON FORECAST EVOLUTION AS
THEY SHOW THE REINFORCEMENT OF A LONG-WAVE PATTERN IN SOUTHERN
SOUTH AMERICA. FORECAST CONFIDENCE IS HIGH THROUGH 108-120 HRS AND
STARTS DECREASING GRADUALLY AFTER.

A TROUGH IN THE EASTERN PACIFIC OFF THE COAST OF CENTRAL CHILE IS
FORECAST TO SHEAR A SHORT WAVE AXIS THAT WILL CROSS THE ANDES OF
CENTRAL CHILE ON TUESDAY/EARLY WEDNESDAY. AS THE SHORT WAVE
CROSSES THE ANDES...IT WILL INTERACT WITH AN UNSTABLE AIR MASS
BREWING IN INTERIOR PORTIONS OF NORTHERN PATAGONIA. DUE TO THE
PRESENCE OF THE SOUTH ATLANTIC CONVERGENCE ZONE (SACZ) IN TROPICAL
PORTIONS OF THE CONTINENT...MOISTURE IN ARGENTINA WILL BE LIMITED.
THIS WILL LIMIT THE POTENTIAL FOR ACCUMULATIONS...YET WILL ALLOW
FOR SCATTERED THUNDERSTORM DEVELOPMENT. ON TUESDAY-EARLY
WEDNESDAY...EXPECTING A PEAK IN ACTIVITY LATE ON TUESDAY INTO
EARLY HOURS OF WEDNESDAY...WHERE MAXIMA WILL REACH 15-20MM/DAY. BY
WEDNESDAY INTO EARLY THURSDAY...REMAINING CONVECTION WILL LEAD TO
MAXIMA OF 10-15MM/DAY IN THE SOUTHERN BUENOS AIRES PROVINCE...AND
MAXIMA OF 05-10MM OTHERWISE. THE NEW ROUND OF CONVECTION IN
ARGENTINA IS EXPECTED DURING THE WEEKEND...WHEN MOISTURE IS
FORECAST TO START RECOVERING AS THE SACZ COLLAPSES.

ALSO IN SOUTHERN SOUTH AMERICA...A SUBTROPICAL MOISTURE
CONNECTION/PLUME OR ATMOSPHERIC RIVER WILL ARRIVE INTO SOUTHERN
CHILE ON WEDNESDAY. THE CONNECTION WILL BE ZONAL ACCOMPANIED BY
850 WINDS EXCEEDING 35KT. THIS WILL LEAD TO ACCUMULATIONS OF
20-30MM/DAY BETWEEN LOS LAGOS AND AYSEN ON WEDNESDAY-EARLY
THURSDAY. A NEW SUBTROPICAL MOISTURE CONNECTION ARRIVES DURING
FRIDAY...ACCOMPANIED BY A BETTER STRUCTURED UPPER TROUGH.
EXPECTING A NEW INCREASE IN ACCUMULATIONS TO PRODUCE MAXIMA OF
15-20MM BY FRIDAY-EARLY SATURDAY.

A SYSTEM OF INTEREST IN TROPICAL SOUTH AMERICA IS THE PRESENCE OF
THE SACZ. THIS SYSTEM IS FORECAST TO REMAIN ORGANIZED THROUGH
WEDNESDAY...TO THEN START LOSING DEFINITION. WHILE THE SACZ
REMAINS IN PLACE...IT WILL STIMULATE CONVECTION TO PRODUCE
ACCUMULATIONS OF 40-80MM/DAY AND THE RISK OF MCS FORMATION IN
EASTERN BRASIL ON MONDAY THROUGH WEDNESDAY. AMOUNTS WILL START TO
DECREASE GRADUALLY AFTER WEDNESDAY. SIMILAR AMOUNTS ARE EXPECTED
IN CENTRAL PERU ON MONDAY. BY TUESDAY...THE FOCUS FOR STRONG
CONVECTION IN THE WESTERN AMAZON WILL CONCENTRATE BETWEEN NORTHERN
PERU AND ECUADOR WHERE EXPECTING MAXIMA OF 25-50MM. AMOUNTS WILL
DECREASE AFTER.

OVIEDO...SHN (ARGENTINA)
POMIER...SENAMHI (BOLIVIA)
RIVAS...SENAMHI (PERU)
DAVISON/GALVEZ...WPC (USA)
$$





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