Prognostic Meteorological Discussion
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000
FXSA20 KWBC 281713
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
112 PM EDT THU MAY 28 2015

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

MODEL DISCUSSION (VALID FROM MAY 28 AT 0000 UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS AND IN VERY GOOD AGREEMENT ON FORECAST
EVOLUTION THROUGH 108-120 HRS. DIFFERENCES ARISE SOUTH OF 45S
ESPECIALLY OVER SOUTHERN CHILE/EASTERN PACIFIC AFTER
84-96HRS...BUT MOSTLY CONFINED TO THE EVOLUTION OF SHORT SCALE
PERTURBATIONS.

LARGE AND POTENT MID-UPPER TROUGH IS FORECAST TO EXTEND ITS AXIS
OVER SOUTHERN BRASIL DURING THURSDAY...AND THEN OFF THE COASTS OF
RIO GRANDE DO SUL/SANTA CATARINA ALONG 54W DURING FRIDAY TO THEN
START TO EXIT INTO THE SOUTHWESTERN ATLANTIC WHILE WEAKENING. THIS
TROUGH IS SUSTAINING A SURFACE COLD FRONT THAT WILL EXTEND ACROSS
SAO PAULO-SOUTHWESTERN MATO GROSSO-NORTHERN BOLIVIA-SOUTHERN PERU
BY THURSDAY EVENING WHILE TAIL RAPIDLY WEAKENS. A SHORT-LIVED
SHEAR LINE IS ALSO ESTABLISHING. BY THURSDAY EVENING...THE SHEAR
LINE WILL EXTEND FROM SOUTHWESTERN MATO GROSSO INTO SOUTHWESTERN
AMAZONAS-NORTHERN PERU...TO THEN RAPIDLY WEAKEN. ALTHOUGH STRONG
CYCLOGENESIS IS OCCURRING OFF THE COASTS OF RIO GRANDE DO
SUL/SANTA CATARINA...THE SYSTEM IS MOVING OFFSHORE MORE RAPIDLY
THAN EXPECTED. THIS WILL STILL PRODUCE PRECIPITATION OVER COASTAL
AREAS IN EXTREME SOUTHERN BRASIL WITH MAXIMA OF 20-35MM/DAY
THROUGH EARLY FRIDAY. AMOUNTS WILL RAPIDLY DECREASE AFTER. THROUGH
EARLY FRIDAY AS WELL...EXPECTING MAXIMA OF 20-35MM/DAY STRETCHING
FROM SOUTHERN MATO GROSSO/NORTHERN MATO GROSSO DO SUL INTO SAO
PAULO/WESTERN RIO DO JANEIRO AND SOUTHWESTERN MINAS GERAIS.
AMOUNTS ARE TO RAPIDLY DECREASE AFTERWARDS WITH SHOWERY CONDITIONS
REMAINING OVER EXTREME SOUTHEASTERN BRASIL. FURTHER WEST...SHEAR
LINE CONVECTION WILL LEAD TO MAXIMA OF 25-50MM/DAY STRETCHING FROM
EASTERN ECUADOR/NORTHERN PERU INTO NORTHWESTERN BRASIL/SOUTHERN
COLOMBIA THROUGH EARLY FRIDAY. ALTHOUGH SHEAR LINE RAPIDLY
WEAKENS...REMNANT MOISTURE CONVERGENCE WILL LEAD TO MAXIMA OF
20-40MM/DAY DURING FRIDAY INTO EARLY SATURDAY.

STRONG UPPER TROUGH IS APPROACHING THE SOUTHERN CONE 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. ACTIVITY
IS NEAR PEAK AND FORECAST TO WANE. STILL...EXPECTING MAXIMA 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 BUT WEAKER THAN THE CURRENT ONE. 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
15-30MM/DAY.

NORTHERN TIER OF AFOREMENTIONED SHORT WAVE TROUGH WILL CROSS THE
ANDES OF CENTRAL CHILE LATE ON SATURDAY AND AMPLIFY AS IT MOVES
INTO SOUTHERN BRASIL DURING SUNDAY. THIS WILL STRENGTHEN THE
MEANDERING FRONT IN MID-SECTIONS OF THE CONTINENT LEADING TO A NEW
PERIOD WITH PRECIPITATION. EXPECTING ACTIVITY TO REACTIVATE OVER
MATO GROSSO/MATO GROSSO DO SUL AND EXTREME NORTHERN PARAGUAY LATE
ON SATURDAY TO PRODUCE MAXIMA OF 15-30MM/DAY. ACTIVITY WILL THEN
REACTIVATE TO THE SOUTHEAST WITH SIMILAR AMOUNTS STRETCHING FROM
MATO GROSSO DO SUL INTO SAO PAULO AND SOUTHWESTERN MINAS
GERAIS/RIO DE JANEIRO ON SUNDAY INTO MONDAY. AMOUNTS ARE TO
DECREASE AFTERWARDS.

NORTH OVER THE CONTINENT...MOST ACTIVE CONVECTION WILL CONSTRAIN
TO LATITUDES TO THE NORTH OF 05S. CONVECTION IN THE WESTERN AMAZON
WILL BE AIDED BY AFOREMENTIONED SHEAR LINE. AS THE CYCLE
PROGRESSES...EXPECTING AN ACTIVATION OF CONVECTION IN THE AMAZON
DELTA TOWARDS LATE CYCLE.

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




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