Prognostic Meteorological Discussion
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000
FXSA20 KWBC 051531
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1130 AM EDT THU MAY 05 2016

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

MODEL DISCUSSION (VALID FROM MAY 05 AT 0000 UTC): ALTHOUGH THE
GLOBAL MODELS AGREE THAT A FAIRLY STRONG BLOCKING RIDGE PATTERN IS
TO DEVELOP IN THE SOUTHERN STREAM FLOW...THEY DISAGREE ON THE
SPEED/INTENSITY OF PERTURBATIONS LIFTING ALONG ITS EASTERN
FRINGES. THE ECMWF FAVORS A CONSIDERABLY STRONGER/DEEPER TROUGH TO
AMPLIFY INTO PATAGONIA BY 96-120 HRS THAN WHAT THE OTHER MODELS
SUGGEST...WITH HIGH VARIABILITY ALSO NOTED AMONG THE ENSEMBLE
MEMBERS. AS A RESULT...FORECAST CONFIDENCE ACROSS THE SOUTHERN
CONE IS LOW DURING THE SECOND HALF OF THE FORECAST.

STRONG TROPOSPHERIC RIDGE IS TO BECOME WELL ENTRENCHED OVER THE
SOUTHEAST PACIFIC/BELLINGSHAUSEN SEA. THE FAIRLY STRONG RIDGE IS
TO THEN PERSIST DURING THE NEXT SEVEN TO TEN DAYS. AT LOW LEVELS
THIS WILL SUSTAIN A RIDGE ACROSS THE BELLINGSHAUSEN SEA TO
PATAGONIA IN ARGENTINA. THE LOW LEVEL RIDGE IS TO ALSO HOLD DURING
THE NEXT SEVERAL DAYS...RESULTING IN ABOVE NORMAL TEMPERATURES
ACROSS MOST OF PATAGONIA-SOUTHERN CHILE AND TIERRA DEL FUEGO.

POLAR PERTURBATIONS...AS THEY PROPAGATE ACROSS THE SOUTH
PACIFIC...ARE TO CLASH WITH THE MID/UPPER LEVEL RIDGE. AS THEY
COLLIDE...SHORT WAVE ENERGY IS EXPECTED TO SHEAR SOUTH AROUND THE
RIDGE...THEN LIFT ACROSS THE ANTARCTIC PENINSULA/WEDDELL SEA INTO
THE SOUTH ATLANTIC. EARLY IN THE CYCLE THE INFLOW OF SHORT WAVE
ENERGY WILL SUSTAIN A HIGHLY AMPLIFIED LONG WAVE TROUGH THAT IS TO
EXTEND BETWEEN 60W-15W AND TO THE SOUTH OF 30S. THIS PATTERN
REMAINS NEARLY UNCHANGED OVER THE NEXT THREE DAYS...WITH AXIS TO
THEN SLOWLY PULL TO THE EAST-SOUTHEAST LATER IN THE CYCLE. AT LOW
LEVELS THIS SUSTAINS A BROAD TROUGH ACROSS THE CENTRAL/WESTERN
ATLANTIC...WITH POLAR FRONT THAT REVOLVE AROUND THIS AXIS. ONE
MOVES TO URUGUAY-LA PAMPA IN ARGENTINA EARLY IN THE CYCLE...WHERE
IT REMAINS WHILE GRADUALLY WEAKENING THROUGH 84 HRS. THROUGH 30-36
HRS THIS IS TO SUSTAIN MODERATE CONVECTION ACROSS NORTHERN
PATAGONIA/LA PAMPA WITH ACCUMULATION OF 15-20MM...WHILE OVER THE
BUENOS AIRES PROVINCE/URUGUAY THE MAXIMA PEAKS AT 10-15MM. BY
36-84 HRS THIS WILL DECREASE TO RAINFALL AMOUNTS OF LESS THAN
05MM/DAY AS THE SURFACE FRONT WEAKENS.

IN A SPLIT FLOW PATTERN...OTHER SHORT WAVE PERTURBATIONS ARE TO
STREAM TO THE NORTH OF THE MID/UPPER LEVEL RIDGE. THESE ARE TO
TRACK ACROSS CENTRAL CHILE INTO ARGENTINA/MID SECTIONS OF SOUTH
AMERICA. AS THEY SPILL ACROSS THE ANDES INTO ARGENTINA THEY WILL
FOCUS THEIR SHORT WAVE ENERGY ACROSS MID SECTIONS OF SOUTH
AMERICA. AT 250 HPA A 70-90KT SUBTROPICAL JET MAXIMA IS TO
ACCOMPANY THESE PERTURBATIONS ARE THEY STREAM ACROSS
ARGENTINA-URUGUAY/SOUTHERN BRASIL...TO FAVOR AN UPPER DIVERGENT
PATTERN ACROSS MID SECTIONS OF SOUTH AMERICA. AT LOW LEVELS...AN
ELONGATED FRONT WILL STRETCH ACROSS THE SOUTH ATLANTIC INTO
SOUTHEAST BRASIL-PARAGUAY. IN A NORTHERLY FLOW OVER BOLIVIA/MATO
GROSSO IN BRASIL...MOISTURE IS TO ADVECT SOUTH INTO MID SECTIONS
OF SOUTH AMERICA...TO THEN CONVERGE ALONG THE MEANDERING FRONT TO
THE SOUTH. THE INFLOW OF MID LEVEL ENERGY AND TROPICAL MOISTURE
WILL THEN SUSTAIN CONVECTIVE DEVELOPMENT ACROSS PARAGUAY-MATO
GROSSO DO SUL AND THE SOUTHERN STATES OF BRASIL. ACROSS PARAGUAY
EXPECTING RAINFALL AMOUNTS OF 10-15MM THROUGH 36 HRS...INCREASING
TO 25-50MM IN DEEP CONVECTION BY 36-60 HRS. BY 96-120 HRS...AS
DEEPER MOISTURE CONVERGES ALONG THE MEANDERING FLOW THE MAXIMA
WILL INCREASE TO 35-70MM...WITH POTENTIAL FOR LOCALLY HIGHER
AMOUNTS AS AN MCS DEVELOPS OVER THE CONTINENT. ON THE SOUTHERN
STATES OF BRASIL THE MOST ACTIVE IS EXPECTED BY 36-60 HRS...WHEN
THE MAXIMA IS TO PEAK AT 15-30MM.

NORTH OVER THE CONTINENT...AT 200 HPA...AN OPEN CELL OF THE
SUBEQUATORIAL RIDGE WILL CONFINE TO AREA TO THE NORTH OF 10S.
SOUTH OF THIS AXIS...A NEAR ZONAL WESTERLY FLOW IS TO ENVELOP
TROPICAL/SUBTROPICAL SOUTH AMERICA. THE RIDGE ALOFT IS TO VENT
DIURNAL CONVECTION ACROSS NORTHERN BRASIL-THE
GUIANAS-VENEZUELA-COLOMBIA-NORTHERN PERU AND ECUADOR. ACROSS
PARA-AMAPA EXPECTING RAINFALL MAXIMA OF 15-30MM OVER THE NEXT DAY
OR SO...DECREASING TO 10-15MM. OVER NORTHERN AMAZONAS/RORAIMA
EXPECTING MAXIMA OF 20-30MM OVER THE NEXT FEW DAYS...DECREASING
LATER IN THE CYCLE. ON THE CENTRAL/SOUTHERN JUNGLE OF PERU TO
NORTHERN BOLIVIA...IN A MOIST NORTH-NORTHEAST FLOW...EXPECTING
RAINFALL AMOUNTS OF 05-10MM/DAY THROUGH 48-60 HRS...AND 20-40MM AT
60-84 HRS. OVER ECUADOR...MOST ACTIVE IS EXPECTED ON THE
ANDES...WHERE A MOIST WESTERLY LOW TO MID LEVEL FLOW IS TO FEED
DIURNAL DEVELOPMENT. IN THIS AREA THE DAILY MAXIMA IS TO PEAK AT
15-20MM.

ENRIQUEZ...DGAC (ECUADOR)
AYALA...DINAC (PARAGUAY)
GALVEZ/DAVISON...WPC (USA)

$$




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