Prognostic Meteorological Discussion
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FXSA20 KWBC 281647
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1246 PM EDT FRI AUG 28 2015

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

MODEL DISCUSSION (VALID FROM AUG 28 AT 0000 UTC): MODELS ARE IN
GOOD AGREEMENT ON FORECAST EVOLUTION THROUGH THE PERIOD. SOME
MINOR DIFFERENCES ARISE ON THE STRENGTH OF COLD FRONT AFFECTING
SOUTHEASTERN BRASIL BY LATE CYCLE...WITH THE GFS MODEL BEING THE
MOST CONSERVATIVE. ALSO...THE GFS IS HAVING TROUBLE WITH THE
EVOLUTION OF SHORT WAVES IN THE SOUTHERN STREAM AFTER 96 HRS...BUT
THESE WILL BE LIMITED TO LATITUDES TO THE SOUTH OF 50S.

SOUTHERN CHILE EXPERIENCING ANOTHER ROUND OF HEAVY RAINS TO
CONTINUE THROUGH SUNDAY. LOCALLY HEAVY RAINFALL IS TO CONTINUE
THROUGH EARLY SATURDAY ESPECIALLY IN INLAND LOCATIONS OF THE BIO
BIO AND ARAUCANIA REGIONS WHERE EXPECTING MAXIMA OF 40-80MM/DAY
AND THE RISK OF ISOLATED EMBEDDED THUNDERSTORMS. PRECIPITATION IS
TO DECREASE RAPIDLY DURING SATURDAY TO MAXIMA OF 20-30MM/DAY
STRETCHING BETWEEN CURICO AND TEMUCO. BY SUNDAY INTO MONDAY
EXPECTING A NEW TRANSIENT INCREASE IN PRECIPITABLE WATER
ACCOMPANIED BY THE DIVERGENT ENTRANCE OF AN UPPER JET. THIS WILL
LEAD TO MAXIMA OF 15-30MM/DAY BETWEEN CHILLAN AND TEMUCO. TO THE
SOUTH EXPECTING MAXIMA OF 15-20MM/DAY INTO THE CENTRAL LOS LAGOS
REGION. 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. A NEW SURGE IN
ACTIVITY IS EXPECTED BY LATE CYCLE AS A TIGHT BELT OF
WEST-SOUTHWESTERLIES ENHANCES OROGRAPHIC LIFT ALONG THE
SOUTHWESTERN TIER OF THE MAGALLANES REGION. THIS WILL LEAD TO
MAXIMA OF 10-15MM/DAY. THE AIRMASS WILL BE TOO WARM FOR
SNOWFALL...AS A LARGE SCALE BROAD RIDGE ESTABLISHES OVER THE
SOUTHERN CONE.

OTHER AREA OF INTEREST IS THE NORTHWESTERN AMAZON. UNSEASONABLY
ACTIVE CONVECTION ACROSS NORTHERN PERU/ECUADOR/SOUTHEASTERN
COLOMBIA IS EXPECTED TO PEAK ON FRIDAY AFTERNOON/SATURDAY MORNING
AS 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 25-50MM/DAY ACROSS NORTHERN PERU/EASTERN
ECUADOR THROUGH EARLY SATURDAY...AND 20-40MM/DAY ACROSS SAN
MARTIN/NORTHERN UCAYALI IN PERO EAST INTO MOST OF AMAZONAS IN
BRASIL. A NEW BURST IN ACTIVITY IS EXPECTED TOWARDS LATE CYCLE DUE
TO A COMBINATION OF ENHANCED CONVECTIVE INSTABILITY...A NEW
TROPICAL WAVE IN THE CARIBBEAN REGION AND INCREASING VENTILATION
AS A TUTT DEVELOPS OVER THE WESTERN AMAZON. THIS WILL LEAD TO AN
INCREASE IN MAXIMA FO 20-35MM/DAY ACROSS THE EXTREME WESTERN
AMAZON BY MONDAY/TUESDAY.

A COLD FRONT WILL MOVE INTO SOUTHERN BRASIL ON MONDAY AND APPROACH
THE COASTS OF SAO PAULO AND RIO DE JANEIRO ON TUESDAY. THE GFS IS
THE MOST CONSERVATIVE WITH THE NORTHWARD ADVANCE OF THIS
SYSTEM...YET WE ARE FAVORING THE MORE AGGRESSIVE ECMWF AND UKMET
SOLUTIONS. THIS WILL LIKELY STIMULATE OROGRAPHIC UPLIFT ALONG THE
SERRA DO MAR TO PRODUCE ISOLATED MAXIMA OF 10-15MM/DAY DURING
TUESDAY INTO EARLY WEDNESDAY. ELSEWHERE IN SOUTH AMERICA...TRADE
WIND CONVERGENCE WILL PRODUCE ISOLATED LIGHT PRECIPITATION AMOUNTS
ALONG THE EASTERN COAST OF BRASIL.

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

$$





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