Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6
000
FXSA20 KWBC 271539
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1139 AM EDT WED MAY 27 2015

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

NOTE: THERE IS A RISK FOR STRONG WINDS AND HEAVY RAINS IN EASTERN
RIO GRANDE DO SUL AND SANTA CATARINA THROUGH THURSDAY
AFTERNOON/EVENING. LARGEST AMOUNTS ARE EXPECTED IN THE EASTERN
FOOTHILLS OF THE SERRA DO MAR WHERE STRONG OROGRAPHIC UPLIFT WILL
LEAD TO LOCALIZED EVENT ACCUMULATIONS APPROACHING 200MM IN 36
HOURS.

MODEL DISCUSSION (VALID FROM MAY 27 AT 0000 UTC): CONFIDENCE IN
THE FORECAST CONTINUES HIGH THROUGH 96/108 HRS...WITH
DETERMINISTIC GLOBAL MODELS AND ENSEMBLE MEMBERS CONVERGING ON A
SIMILAR SOLUTION INTO THE MEDIUM RANGE PERIOD.

LARGE AND POTENT MID-UPPER TROUGH HAS CROSSED THE ANDES FROM THE
WEST AND WILL CONTINUE ENHANCING ACTIVITY ACROSS MID-SECTIONS OF
THE CONTINENT. THIS TROUGH IS SUSTAINING A SURFACE COLD FRONT THAT
WILL EXTEND ACROSS CENTRAL PARANA IN BRASIL-MATO GROSSO DO
SUL-CENTRAL BOLIVIA BY WEDNESDAY EVENING...TO ADVANCE INTO SAO
PAULO-SOUTHWESTERN MATO GROSSO-NORTHERN BOLIVIA-SOUTHERN PERU BY
THURSDAY EVENING...WHILE TAIL RAPIDLY WEAKENS. THIS WILL ALSO LEAD
TO THE DEVELOPMENT OF A SHEAR LINE DURING THURSDAY. THE SHEAR LINE
WILL EXTEND FROM SOUTHWESTERN MATO GROSSO INTO SOUTHWESTERN
AMAZONAS-NORTHERN PERU BY THURSDAY EVENING...TO THEN RAPIDLY
WEAKEN. UPPER TROUGH IS FORECAST TO CONTINUE AMPLIFYING AS IT
MOVES INTO SOUTHEASTERN BRASIL WITH HEIGHT FALLS EXCEEDING 100 GPM
OVER AND JUST TO THE EAST OF RIO GRANDE DO SUL AND SANTA CATARINA
DURING WEDNESDAY AND THURSDAY. THIS IS LEADING TO STRONG
CYCLOGENESIS...AND IS POSING A RISK FOR HEAVY PRECIPITATION AND
STRONG EASTERLY WINDS OVER THE REGION DURING THROUGH EARLY FRIDAY.
THROUGH EARLY FRIDAY EXPECTING LOCALIZED MAXIMA OF 100-150MM/DAY
IN EASTERN RIO GRANDE DO SUL/SANTA CATARINA. TO THE NORTHWEST
ALONG PARANA/NORTHERN SANTA CATARINA INTO EASTERN PARAGUAY EXTREME
SOUTHEASTERN BOLIVIA EXPECTING MAXIMA OF 20-35MM/DAY. FURTHER
WEST...EXPECTING ISOLATED MAXIMA OF 20-45MM/DAY AS SOUTHERLY JET
INTERACTS WITH THE BOLIVIAN/SOUTHERN PERUVIAN ANDES AND ENHANCES
LOW-LEVEL MOISTURE CONVERGENCE. BY THURSDAY INTO EARLY FRIDAY
EXPECTING LARGEST AMOUNTS ACROSS EASTERN RIO GRANDE DO SUL AND
SANTA CATARINA WITH MAXIMA OF 30-60MM/DAY. FURTHER NORTH EXPECTING
ACCUMULATIONS OF 20-35MM/DAY STRETCHING FROM SAO PAULO/RIO DO
JANEIRO NORTHWEST INTO MATO GROSSO DO SUL. SHEAR LINE CONVECTION
IN INTERACTION WITH TROPICAL AIR MASSES IN EQUATORIAL SOUTH
AMERICA WILL LEAD TO MAXIMA OF 25-50MM/DAY STRETCHING FROM EASTERN
ECUADOR/NORTHERN PERU INTO NORTHWESTERN BRASIL/SOUTHERN COLOMBIA.
BY FRIDAY INTO EARLY SATURDAY EXPECTING A RAPID DECREASE IN
ACCUMULATIONS IN SOUTHEASTERN BRASIL. EXPECTING MAXIMA OF
05-10MM/DAY IN RESIDUAL CONVECTION IN RIO GRANDE DO SUL AND SANTA
CATARINA...AND MAXIMA OF 15-25MM/DAY ACROSS EASTERN RIO DE
JANEIRO/ESPIRITO SANTO AND SOUTHEASTERN MINAS GERAIS.

STRONG UPPER TROUGH IS APPROACHING THE SOUTHERN CONE. THIS TROUGH
IS ARRIVING WITH A TRAIN OF SURFACE FRONTS AND A SUBTROPICAL
MOISTURE CONNECTION. EXPECTING ENHANCED MOISTURE CONVERGENCE TO
DEVELOP SOUTH OF TEMUCO/VALDIVIA INTO THE NORTHERN MAGALLANES
REGIONS LATE ON WEDNESDAY. THIS WILL LEAD TO ACCUMULATIONS OF
20-40MM/DAY BETWEEN VALDIVIA/OSORNO AND PUERTO AYSEN. LIGHTER
AMOUTNS ARE EXPECTED IN THE WESTERN MAGALLANES REGION. BY THURSDAY
INTO EARLY FRIDAY COL FRONT WILL ADVANCE INTO THE CHILLAN/TALCA
REGION. THIS WILL RESULT IN PRECIPITATIONS SPREADING NORTHWARD
WITH ACCUMULATIONS IN THE ORDER OF 20-30MM/DAY BETWEEN
TALCA/CONCEPCION AND ISLA CHILOE. BY FRIDAY INTO
SATURDAY...RESIDUAL PRECIPITATION WILL LEAD TO SCATTERED MAXIMA OF
10-15MM/DAY MOSTLY IN INLAND LOCATIONS BETWEEN TEMUCO AND THE
SOUTHERN AYSEN PROVINCE. TRACE RAINFALL AMOUNTS ARE EXPECTED TO
THE NORTH BETWEEN TEMUCO AND TALCA. UPPER TROUGH AND SURFACE
FRONTS WILL THEN ENHANCE ACTIVITY ACROSS CENTRAL ARGENTINA.
MOISTURE WILL BE LIMITED THOUGH...WHICH WILL LIMIT MAXIMA TO
10-15MM/DAY DURING SATURDAY INTO EARLY SUNDAY. NEXT SYSTEM OF
INTEREST IN CHILE ARRIVES DURING SATURDAY INTO EARLY SUNDAY. THIS
TROUGH WILL ARRIVE ONCE AGAIN WITH A SUBTROPICAL CONNECTION. THIS
WILL LEAD TO ACCUMULATIONS IN THE ORDER OF 15-20MM/DAY STRETCHING
FROM LOS ANGELES SOUTH INTO THE CENTRAL/NORTHERN AYSEN REGION.
ACCUMULATIONS ARE CONCENTRATE FURTHER NORTH ONCE AGAIN BETWEEN
TALCA AND PUERTO MONTT DURING SUNDAY INTO MONDAY WITH MAXIMA OF
15-20MM/DAY. NOTE THAT AMOUNTS MAY INCREASE AS FUTURE MODEL RUNS
BECOME AVAILABLE.

NORTH OVER THE CONTINENT...MOST ACTIVE CONVECTION WILL CONSTRAIN
TO LATITUDES TO THE NORTH OF 05S. AT UPPER LEVELS...THE
SUBTROPICAL HIGH IS WELL ESTABLISHED TO THE WEST OF WESTERN
PERU...OVER THE EASTERN PACIFIC FOLLOWING THE CURRENT WARMING OF
THE SEA SURFACE TEMPERATURES. THE HIGH IS FORECAST TO SLOWLY
MEANDER EASTWARD TO EXTEND ALONG 10S-15S BY MID/LATE CYCLE AND
FROM 90W INTO 50W. THIS WILL CONTINUE FAVORING VENTILATION ACROSS
MOST OF THE NORTHWESTERN AMAZON FAVORING MOST ACTIVE CONVECTION IN
THIS REGION. INITIALLY...EXPECTING MAXIMA OF 20-45MM/DAY
STRETCHING FROM NORTHERN MARANHAO/PARA IN BRASIL WEST INTO
NORTHERN AMAZONAS. MAXIMA WILL THEN RELOCATE TO THE WEST. ACTIVE
CONVECTION WILL ALSO DOT THE WESTERN SLOPES OF ECUADOR FAVORED BY
UNUSUALLY WARM SEA SURFACE TEMPERATURES. THIS WILL LEAD TO MAXIMA
IN THE ORDER OF 15-25MM/DAY WHERE STORMS DEVELOP.

CHARPENTIER...DMC (CHILE)
SCHNEIDER...INMET (BRASIL)
UNSIHUAY...UNALM (PERU)
GALVEZ...WPC (USA)
$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.