Prognostic Meteorological Discussion
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FXSA20 KWBC 211543
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1043 AM EST FRI NOV 21 2014

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

MODEL DISCUSSION (VALID FROM NOVEMBER 21 AT 00UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS ARE HAVING TROUBLE WITH THE EVOLUTION OF THE
FORECAST AS A SHORT WAVE PATTERN IS ESTABLISHING. THE GFS IS
HAVING THE MOST TROUBLE. IT HAS CORRECTED YESTERDAYS SOLUTION AND
NOW IS CLOSER TO THE ECMWF...WHICH SHOW A LESS AMPLE TROUGH
ENTERING REGIONS SOUTH OF 40S BY 96-120 HRS. HOWEVER...IT IS
HAVING TROUBLE RESOLVING THE SHORT WAVES. WITH SOLUTIONS STARTING
TO DIVERGE AS EARLY AS 72 HRS. CONFIDENCE IS HIGH THROUGH 72
HRS...DECREASING AFTERWARDS...ESPECIALLY AFTER 108 HRS AND TO THE
SOUTH.

SHORT WAVE UPPER TROUGH IS CROSSING THE ANDES INTO CENTRAL
ARGENTINA. AS THE TROUGH CROSSES...IT IS ENHANCING AN UPPER JET TO
THE NORTH WITH AREAS OF UPPER DIVERGENCE DEVELOPING ACROSS
SOUTHERN BOLIVIA INTO SOUTHERN BRASIL. A SURFACE COLD FRONT IS
ALSO PRESENT AND WILL BE A FOCUS FOR LOW-LEVEL MOISTURE
CONVERGENCE. BY FRIDAY EVENING...THE FRONT WILL EXTEND FROM RIO
GRANDE DO SUL INTO SOUTHERN PARAGUAY AND EXTREME SOUTHERN BOLIVIA.
BY SATURDAY EVENING IT WILL EXTEND INTO SANTA CATARINA IN
BRASIL...LOSING DEFINITION IN CONTINENTAL AREAS. BY THIS
TIME...BEST VENTILATION ASSOCIATED WITH UPPER TROUGH WILL EXTEND
FROM SAO PAULO/WESTERN MINAS GERAIS IN BRASIL INTO EASTERN PARANA.
BY SUNDAY EVENING...THE FRONT WILL EXTEND INTO WESTERN RIO DO
JANEIRO IN BRASIL. HIGHEST INSTABILITY AND VENTILATION IN THIS
PERIOD WILL CONCENTRATE ACROSS RIO DO JANEIRO/ESPIRITO SANTO AND
MINAS GERAIS. BY MONDAY EVENING...WESTERN TAIL FRONT IS TO STALL
AND START WEAKENING NEAR EASTERN RIO DO JANEIRO. AT THIS
TIME...HIGH CONVECTIVE INSTABILITY AND GOOD VENTILATION WILL
CONCENTRATE ACROSS MINAS GERAIS AND NORTHERN SAO PAULO...IN
SOUTHEASTERN PERIPHERY OF UPPER HIGH. THIS REGION IS EXPECTED TO
CONTINUE ACTIVE UNDER FAVORABLE VENTILATION AND HIGH INSTABILITY
INTO TUESDAY. IN TERMS OF ACCUMULATIONS...THROUGH EARLY SATURDAY
EXPECTING MAXIMA OF 40-80MM/DAY WITH THE RISK OF MCS FORMATION
ACROSS THE BOLIVIAN AND PARAGUAYAN CHACO REGIONS/PANTANAL. ACROSS
SOUTHEASTERN PARAGUAY INTO SOUTHERN BRASIL EXPECTING MAXIMA OF
30-60MM/DAY STILL WITH THE RISK OF MCS FORMATION. FURTHER
SOUTH...STRONG THUNDERSTORMS ACROSS NORTHEASTERN ARGENTINA/URUGUAY
WILL LEAD TO MAXIMA OF 20-40MM/DAY. BY SATURDAY INTO EARLY
SUNDAY...LARGEST AMOUNTS ARE EXPECTED ACROSS SOUTHEASTERN
PERU/CENTRAL/NORTHERN BOLIVIA WITH MAXIMA OF 35-70MM/DAY AND THE
RISK FOR MCS FORMATION. BY SUNDAY INTO EARLY MONDAY EXPECTING
LARGEST AMOUNTS ACROSS EASTERN MINAS GERAIS/ESPIRITO SANTO WITH
SCATTERED MAXIMA OF 25-50MM/DAY. INLAND ACROSS THE REST OF MINAS
GERAIS INTO THE MATO GROSSOS EXPECTING MAXIMA OF 20-40MM/DAY.

NORTH OVER THE CONTINENT AND AT UPPER LEVELS...THE SUBTROPICAL
HIGH IS STARTING TO REORGANIZE ONCE AGAIN. THE HIGH IS NOT
FORECAST TO MOVE MUCH DURING THE NEXT FIVE-SIX DAYS...CENTERING
NEAR NORTHWESTERN MATO GROSSO AND ELONGATING FROM ACRE TO MINAS
GERAIS IN BRASIL. THIS WILL PROVIDE GOOD VENTILATION FOR SCATTERED
DIURNAL CONVECTION IN MOST OF THE CENTRAL AND SOUTHWESTERN AMAZON
REGION THROUGH THE CYCLE. AN ACTIVE REGION WILL BE THE CENTRAL
AMAZON FROM WESTERN PARA/MATO GROSSO INTO MOST OF AMAZONAS IN
BRASIL WHERE EXPECTING SCATTERED MAXIMA OF 20-35MM/DAY. ISOLATED
HIGHER AMOUNTS ARE ALSO POSSIBLE IN THUNDERSTORMS. EXPECTING AREA
GRADUALLY EXPANDING TO THE NORTHWEST AS THE CYCLE PROGRESSES. AS
THE RIDGE BUILDS INTO SOUTHEASTERN BRASIL THROUGH THE
CYCLE...VENTILATION IS TO IMPROVE AND INTERACT WITH INCREASING
CONVECTIVE INSTABILITY. THIS WILL LEAD TO SCATTERED MAXIMA OF
30-60MM/DAY ACROSS MONAS GERAIS/RIO DO JANEIRO/ESPIRITO SANTO INTO
PARTS OF GOIAS/MATO GROSSO DO SUL.

SHORT WAVE UPPER TROUGH WILL APPROACH SOUTHERN CHILE DURING
SATURDAY. THIS SYSTEM WILL PRODUCE HEIGHT FALLS EXCEEDING 100
GPM/DAY AND ENHANCE ACTIVITY. SINCE MOISTURE WILL BE
LIMITED...EXPECTING LARGEST AMOUNTS TO REACH THE 10-15MM/DAY RANGE
IN AREAS FROM TEMUCO SOUTH INTO THE NORTHERN PARTS OF THE AYSEN
REGION...WITH LIGHTER AMOUNTS FURTHER SOUTH. ACCUMULATIONS ARE TO
DECREASE INTO SUNDAY. THIS TROUGH WILL RAPIDLY CROSS INTO
ARGENTINA. YET...MOISTURE WILL BE LIMITED THUS EXPECTING
ACCUMULATIONS IN THE 10-15MM/DAY RANGE. ANOTHER UPPER TROUGH...A
LARGER ONE...IS TO PUSH FROM THE SOUTHWEST DURING SUNDAY UNTO
MONDAY. THIS SYSTEM WILL START ENHANCING UPPER DIVERGENCE LATE ON
SUNDAY IN PARTS OF NORTHERN PATAGONIA...AND RAPIDLY UNDULATE A
FAST MOVING SURFACE COLD-FRONT. BY MONDAY MORNING THE FRONT WILL
EXTEND ACROSS THE CENTRAL BUENOS AIRES PROVINCE INTO NORTHERN
MENDOZA...AND BY MONDAY EVENING THE FRONT WILL EXTEND INTO
NORTHERN URUGUAY/SOUTHERN RIO GRANDE DO SUL WITH TAIL RAPIDLY
LOSING DEFINITION ACROSS THE INTERIOR OD THE CONTINENT.
NEVERTHELESS. MOISTURE WILL HAVE RETURNED FROM THE NORTH. IN
COMBINATION WITH UPPER DIVERGENT PATTERN...EXPECTING STRONG
THUNDERSTORMS TO PRODUCE SCATTERED MAXIMA OF 25-50MM/DAY ACROSS
NORTHERN ARGENTINA AND PARTS OF SOUTHERN PARAGUAY. CONFIDENCE
STARTS DECREASING AFTERWARDS...IT THUS LOOKS THAT MOST ACTIVE WILL
MOVE INTO PORTIONS OF SOUTHERN BRASIL DURING TUESDAY.

CAROCA...DMC (CHILE)
DURAN...SENAHMI (PERU)
DAVISON...WPC (USA)
GALVEZ...WPC (USA)
$$





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