Prognostic Meteorological Discussion
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FXSA20 KWBC 271841
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
241 PM EDT THU AUG 27 2015

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

MODEL DISCUSSION (VALID FROM AUG 26 AT 0000 UTC): MODELS CONTINUE
TO AGREE ON PATTERN EVOLUTION ON THE NORTHERN STREAM FLOW THROUGH
AT LEAST 120-132 HRS. ON THE SOUTHERN STREAM...CONFIDENCE STARTS
DECREASING RAPIDLY AFTER 96-108 HRS. THE GFS IS THE STRONGEST
MODEL WITH A PERTURBATION THAT STREAMS ACROSS THE DRAKE PASSAGE
WHILE OTHER MODELS AND ENSEMBLES TEND TOWARDS A MORE CONSERVATIVE
SOLUTION.

ACTIVE CONVECTION ACROSS MID-SECTIONS OF THE CONTINENT TO CONTINUE
THROUGH EARLY FRIDAY TO THEN WEAKEN. COLD FRONT HAS MADE IT INTO
SOUTHEASTERN BRASIL AND BY THURSDAY EVENING IT TILL EXTEND ACROSS
RIO DE JANEIRO-SW MINAS GERAIS-CENTRAL MATO GROSSO DO SUL INTO
NORTHERN PARAGUAY. THIS IS SUSTAINING A PREFRONTAL TROUGH TO
EXTEND ACROSS NORTHERN MATO GROSSO DO SUL/SW MATO GROSSO ON
THURSDAY EVENING AS WELL. CONVECTIVE INSTABILITY IS MODERATE
WHICH...IN INTERACTION WITH SURFACE SYSTEMS WILL LEAD TO SCATTERED
CONVECTION. FURTHERMORE MID-LEVEL SHORT WAVE TROUGH WILL MOVE INTO
THE REGION LATER TODAY. THE GFS MODEL IS NOT CAPTURING THE
POTENTIAL FOR THUNDERSTORMS BETWEEN EASTERN BOLIVIA INTO SE MATO
GROSSO/MATO GROSSO DO SUL. EXPECTING MAXIMA OF 15-25MM/DAY IN THIS
REGIONS THROUGH EARLY FRIDAY. ACROSS SE PERU INTO THE BOLIVIAN
FOOTHILLS EXPECTING MAXIMA OF 20-35MM/DAY. ELSEWHERE INTO SAO
PAULO RIO DE JANEIRO/SW MINAS GERAIS EXPECTING MAXIMA OF 15MM/DAY.
AMOUNTS ARE TO RAPIDLY DECREASE AFTERWARDS WITH LINGERING MAXIMA
OF 10-15MM/DAY ACROSS RIO DE JANEIRO/CENTRAL MINAS GERAIS BY
FRIDAY INTO EARLY SATURDAY.

SOUTHERN CHILE TO EXPERIENCE HEAVY RAINFALL THROUGH EARLY FRIDAY.
POTENT UPPER TROUGH IS PRODUCING HEIGHT FALLS EXCEEDING 100 GPM.
THIS IS COMBINED WITH A ROBUST SUBTROPICAL MOISTURE CONNECTION
WITH PWAT VALUES OF 30-35MM/DAY. NOTE THAT THIS IS ALMOST TWICE
THE PWAT EXPECTED IN SUBTROPICAL MOISTURE CONNECTIONS FOR THE
REGION. IN COMBINATION WITH OVER 40KT WINDS...THIS WILL LEAD TO
HEAVY RAINFALL WITH THE CHANCE OF ISOLATED EMBEDDED THUNDERSTORMS
FROM CHILLAN SOUTH INTO PUERTO AYSEN THROUGH EARLY FRIDAY...WITH
RAINFALL TOTALS PEAKING AT MAXIMA OF 35-70MM/DAY. FURTHER SOUTH
INTO THE WESTERN MAGALLANES REGION EXPECTING MAXIMA OF
15-30MM/DAY. RAINFALL AMOUNTS ARE TO PEAK BY FRIDAY INTO EARLY
SATURDAY WHEN EXPECTING MAXIMA OF 40-80MM/DAY BETWEEN INTERIOR
PORTIONS OF THE MAULE REGION...BETWEEN CHILLAN/CONCEPCION INTO
TEMUCO...AND INTO INTERIOR REGIONS OF THE LOS LAGOS AND LOS RIOS
REGIONS. ELSEWHERE INTO THE TAITAO PENINSULA EXPECTING MAXIMA OF
15-20MM/DAY. BY SATURDAY INTO EARLY SUNDAY EXPECTING MAXIMA OF
20-30MM/DAY PEAKING BETWEEN CHILLAN AND TEMUCO. AMOUNTS WILL
DECREASE AFTERWARDS. IN SOUTHERN CHILE...A COLD ADVECTIVE PATTERN
WILL ESTABLISH LATE FRIDAY INTO SATURDAY WHICH WILL RESULT IN A
MIX OF RAIN AND SNOW. EXPECTING LIGHT ACCUMULATIONS INTO
MONDAY...WHEN EXPECTING THE CHANGE TO SOLELY RAIN ONCE AGAIN.

NORTH OVER THE CONTINENT EXPECTING UNSEASONABLY ACTIVE CONVECTION
ACROSS NORTHERN PERU/ECUADOR/SOUTHEASTERN COLOMBIA. THIS IS A
RESULT OF THE COMBINATION OF A TROUGH IN THE TRADES...ENHANCED
CONVECTIVE INSTABILITY...VENTILATION IN THE PERIPHERY OF
SUBTROPICAL RIDGE IN NORTHERN BRASIL...AND ENHANCED LOW-LEVEL
CONVERGENCE OF SOUTHEASTERLY TRADES. THIS WILL LEAD TO SCATTERED
MAXIMA OF 15-30MM/DAY THROUGH EARLY FRIDAY...INCREASING TO
20-40MM/DAY DURING FRIDAY INTO EARLY SATURDAY. AMOUNTS ARE TO
DECREASE AFTERWARDS...YET EXPECTING UNSEASONABLE ACTIVE CONVECTION
TO CONTINUE OVER AND IN AREAS TO THE WEST OF AMAZONAS IN BRASIL
THROUGH THE CYCLE...WITH MAXIMA INCREASING TO 15-30MM/DAY AS THE
WEEKEND PROGRESSES. ELSEWHERE IN NORTHERN SOUTH AMERICA TRADE WIND
CONVERGENCE WILL LEAD TO LIGHT RAINFALL AMOUNTS IN THE
NORTHEASTERN COAST OF BRASIL.

ROMERO...DMC (CHILE)
FARINA...DMH (PARAGUAY)
DAVISON...WPC (USA)
GALVEZ...WPC (USA)

$$




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