Prognostic Meteorological Discussion
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FXSA20 KWBC 021739
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1239 PM EST FRI DEC 02 2016

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

MODEL DISCUSSION (VALID FROM DECEMBER 02 AT 0000 UTC): GLOBAL
MODELS ARE STILL DIVERGING ON THE EVOLUTION OF SHORT WAVE TROUGHS
ACROSS THE CENTRAL AND SOUTHERN PORTIONS OF SOUTH AMERICA.
CONFIDENCE ON THE EVOLUTION OF THE LONG WAVE PATTERN IS...HOWEVER
HIGHER AS THEY ALL END UP WITH A LONG WAVE TROUGH PATTERN ACROSS
THE SOUTHERN CONE AND THE SOUTHERN ATLANTIC BY TUESDAY.

INITIALLY...ACTIVE CONVECTION IS EXPECTED IN CENTRAL SOUTH
AMERICA. A NORTHERN STREAM TROUGH IS CROSSING THE ANDES AND IS
FORECAST TO EXTENDS ACROSS CORDOBA-SALTA-TARIJA BY 24 HRS. THIS
TROUGH WILL INTERACT WITH A VERY UNSTABLE AIR MASS BREWING OVER
PARAGUAY AND NORTHEASTERN ARGENTINA. AS THE TROUGH MOVES
IN...EXPECTING HEIGHT FALLS IN THE ORDER OF 50 GPM IN SOUTHEASTERN
PARAGUAY-SOUTHERN BRASIL. THIS WILL LEAD TO SEVERE CONVECTION
INCLUDING THE RISK FOR SCATTERED SMALL HAIL. EXPECTING RAINFALL
ACCUMULATIONS OF 30-60MM/DAY. ALSO ON FRIDAY...PRE-FRONTAL
CONVECTION IN CENTRAL ARGENTINA WILL LEAD TO MAXIMUM ACCUMULATIONS
OF 15-30MM/DAY. AS THE UPPER TROUGH AMPLIFI9ES OVER SOUTHERN
BRASIL ON SATURDAY...EXPECTING FOCUS FOR STRONGEST CONVECTION TO
CONCENTRATE ACROSS PARANA/SOUTHERN MATO GROSSO DO SUL AND EASTERN
PARAGUAY. HERE...EXPECTING ONCE AGAIN 30-60MM/DAY WITH THE RISK
FOR SEVERE CONVECTION. BY SUNDAY...THE STRONG UPPER TROUGH WILL
PRODUCE CYCLOGENESIS OFF THE COAST OF SOUTHEASTERN BRASIL. THIS
SYSTEM WILL INITIALLY BEHAVE AS A SUBTROPICAL CYCLONE...BUT IS
EXPECTED TO TRANSITION INTO AN EXTRATROPICAL SYSTEM RAPIDLY AS IT
MOVES TO THE SOUTHEAST ON MONDAY. LARGEST ACCUMULATIONS WITH THE
COLD FRONT ARE EXPECTED ON SUNDAY...WHERE SCATTERED CONVECTION
WILL PRODUCE MAXIMA OF 20-40MM/DAY ACROSS RIO DE JANEIRO/MINAS
GERAIS/SOUTHERN ESPIRITO SANTO AND SOUTHERN GOIAS IN BRASIL.

A POTENT UPPER TROUGH WILL ARRIVE INTO SOUTHERN CHILE ON SATURDAY
AND CROSS THE SOUTHERN ANDES ON SUNDAY. INITIALLY...THIS WILL
ENHANCE PRECIPITATION IN THE WESTERN AYSEN AND MAGALLANES REGIONS
IN CHILE. EXPECTING MAXIMA OF 10-15MM/DAY ON A DAILY BASIS ON BOTH
FRIDAY AND SATURDAY. DURING SUNDAY...MAXIMA OF 10-15MM/DAY WILL
CONCENTRATE BETWEEN THE ARAUCANIA AND ISLA CHILOE. ALSO DURING
SUNDAY...THE UPPER TROUGH WILL GENERATE CYCLOGENESIS ACROSS
PATAGONIA. THIS WILL UNDULATE A SURFACE COLD FRONT AND A
PRE-FRONTAL SQUALL LINE. THE LATTER WILL EXTEND ACROSS VIEDMA-LA
PAMPA-SOUTHERN MENDOZA BY SUNDAY EVENING...AND PROGRESS NORTH TO
WEAKEN DURING MONDAY EVENING ACROSS INTERIOR PORTIONS OF CENTRAL
ARGENTINA. ONCE AGAIN...EXPECTING THE DEVELOPMENT OF SEVERE
CONVECTION IN NORTHERN PATAGONIA/AND INTERIOR PORTIONS OF CENTRAL
ARGENTINA ON SUNDAY. RAINFALL ACCUMULATIONS ARE TO REACH
30-60MM/DAY. THIS INCLUDES THE POTENTIAL FOR SMALL AND LARGE HAIL.
BY MONDAY CONVECTION WILL CLUSTER IN SANTIAGO DEL
ESTERO/TUCUMAN/SALTA WHERE EXPECTING MAXIMA OF 25-50MM/DAY AND
SEVERE CONVECTION. SIMILAR ACCUMULATIONS ARE EXPECTED ON TUESDAY
ACROSS EXTREME NORTHERN ARGENTINA/PARAGUAY AND SOUTHERN BOLIVIA.

NORTH ACROSS THE CONTINENT...THE SUBTROPICAL RIDGE WILL MEANDER
FROM RONDONIA/MATO GROSSO ON FRIDAY NORTHWESTWARD TO CENTER OVER
BOLIVIA/SOUTHERN PERU BY SUNDAY THROUGH MID-NEXT WEEK. DEEP-LAYER
MOISTURE AND ENHANCED INSTABILITY WILL GENERALLY CLUSTER OVER THE
WESTERN AMAZON...WHERE EXPECTING DAILY ACCUMULATIONS IN THE ORDER
OF 15-20MM/DAY IN AREAS AFFECTED BY DIURNAL THUNDERSTORMS. ANOTHER
REGION WITH ACTIVE DIURNAL CONVECTION WILL BE TOCANTINS/SOUTHERN
PARA INTO MATO GROSSO...WHERE EXPECTING ALSO MAXIMA OF 15-20MM/DAY
IN A GENERAL BASIS.

ALVA...SENAMHI (PERU)
DURAN...SMN (ARGENTINA)
DAVISON/GALVEZ...WPC (USA)
$$




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