SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1248 PM EDT FRI JUN 22 2018

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

MODEL DISCUSSION (VALID FROM JUN 22 AT 0000 UTC): MODELS CONTINUE
IN GOOD AGREEMENT THROUGH THE CYCLE. THERE ARE SOME DISCREPANCIES
ON THE EVOLUTION FROM DAY 4 THROUGH 6 IN THE SOUTHERN CONE...AS A
LONG-WAVE UPPER LOW APPROACHES FROM THE WEST. THE GFS HAS
OVERCORRECTED THIS SYSTEM AND NOW PLACES IT FURTHER WEST THAN THE
ECMWF AND UKMET MODELS ON DAYS 5 AND 6. YET...EXPECTING AN
INCREASE IN WIND SPEEDS AND PRECIPITATION IN THE SOUTHERN CONE ON
DAYS 6 THROUGH 7 AS THE LOW CROSSES INTO THE ATLANTIC ACCOMPANIED
BY SHORT WAVE PERTURBATIONS PROPAGATING ALONG ITS PERIPHERY.

LONG WAVE UPPER TROUGH IS CROSSING INTO THE ATLANTIC EARLY IN THE
CYCLE...AND SHORT WAVE PERTURBATIONS ARE REVOLVING AROUND ITS
PERIPHERY. ONE OF THESE PERTURBATIONS IS FORECAST TO CROSS
PATAGONIA ON FRIDAY-SATURDAY. THE AIR MASS IS COLD ENOUGH TO
PRODUCE SNOWFALL IN TIERRA DEL FUEGO...WHERE EXPECTING
ACCUMULATIONS OF 03-05CM OF SNOW THROUGH EARLY SATURDAY. BY
SATURDAY-SUNDAY...EXPECTING A TRANSITION TO RAIN/SNOW IN SOUTHERN
CHILE WITH LIQUID ACCUMULATIONS OF 10-15MM/DAY. ISOLATED SNOW
SHOWERS IN THE SIERRA DE LA VENTANA REGION IN THE SOUTHERN BUENOS
AIRES PROVINCE WILL LEAD TO 02-03CM OF SNOW IN HIGHER ELEVATIONS.
OTHERWISE EXPECTING A RAIN-SNOW MIX. ALSO IN ARGENTINA INTO
SOUTHERN PARAGUAY AND SOUTHERN BRASIL...FRONTAL CONVECTION WILL
INCREASE IN ASSOCIATION WITH INCREASING CONVERGENCE IN THE MOUTH
OF A STRENGTHENING LOW-LEVEL JET. THIS WILL LEAD TO MAXIMA OF
20-30MM/DAY STRETCHING FROM EASTERN FORMOSA/SOUTHERN PARAGUAY INTO
RIO GRANDE DO SUL. BY SUNDAY-MONDAY EXPECTING AMOUNTS OF
15-25MM/DAY FROM MISIONES INTO THE SIERRA GAUCHA
REGION...DECREASING TO 10-15MM/DAY BY MONDAY-TUESDAY.

A SUBTROPICAL MOISTURE CONNECTION IS FORECAST TO ARRIVE INTO
SOUTHERN CHILE ON MONDAY ACCOMPANIED BY A SHORT WAVE TROUGH.
ALTHOUGH MODELS ARE DIVERGING ON THE EXACT
EVOLUTION...INTERACTIONS BETWEEN THE TROUGH...TERRAIN AN UPPER JET
WILL FAVOR ACCUMULATIONS OF 20-30MM/DAY BETWEEN SOUTHERN BIO-BIO
AND LOS LAGOS FROM MONDAY INTO EARLY TUESDAY. AMOUNTS WILL
DECREASE AFTER.

IN TROPICAL SOUTH AMERICA...MODELS ARE RESOLVING THE STRENGTHENING
OF THE UPPER RIDGE AS THE CYCLE PROGRESSES. THIS WILL FORM AN AXIS
FROM A RIDGE IN ESPIRITO SANTO-BRASIL INTO NORTHERN PERU ON
SATURDAY EVENING...TO A CLOSED UPPER HIGH CENTERING OVER ACRE ON
MONDAY EVENING. AS THE HIGH STRENGTHENS...THIS WILL LEAD TO AN
INCREASE IN ACCUMULATIONS IN THE NORTHWESTERN AMAZON TOWARDS LATE
CYCLE. EXPECTING MAXIMA INCREASING TO 20-45MM/DAY BY
SUNDAY-MONDAY...TO THEN PERSIST IN THE 15-30MM/DAY RANGE
AFTERWARDS.

ALSO IN TROPICAL SOUTH AMERICA...TRADE WIND SHOWERS WILL PERSIST
THROUGH THE CYCLE ALONG THE EASTERN COAST OF BRASIL. THIS WILL
PEAK ON SUNDAO-MONDAY TO PRODUCE ISOLATED MAXIMA OF 10-15MM/DAY IN
PARTS OF BAHIA AND THE NORDESTE.

DIAZ...INUMET (URUGUAY)
SANCHEZ...SMN (ARGENTINA)
DAVISON/GALVEZ...WPC (USA)