Prognostic Meteorological Discussion
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FXSA20 KWBC 021614
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1214 PM EDT MON MAY 02 2016

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

MODEL DISCUSSION (VALID FROM MAY 02 AT 0000 UTC): CONFIDENCE IN
THE FORECAST IS HIGH THROUGH 72-84 HRS...WITH MODELS THEN
DIVERGING ON PATTERN EVOLUTION OVER THE EASTERN PACIFIC DURING THE
SECOND HALF OF THE FORECAST. IN THIS AREA THE GLOBAL ENSEMBLES
FAIL TO REACH A GENERAL CONSENSUS ON WHEN BLOCKING RIDGE PATTERN
IS GOING TO WEAKEN. IN THIS AREA THE NCEP ENSEMBLE MEMBERS ARE
TRENDING TOWARDS A WEAKER RIDGE THAN WHAT THE CANADIAN AND
EUROPEAN MEMBERS SUGGEST. BUT THUS FAR THIS RIDGE HAVE BEEN QUITE
RESILIENT...AND THERE ARE NO CLEAR INDICATIONS THAT IT SHOULD
COLLAPSE AS SOME OF THE MODELS SUGGEST. AS A RESULT...WE ARE
LEANING TOWARDS THE SOLUTION PRESENTED BY THE EUROPEAN AND
CANADIAN ENSEMBLE MEMBERS.

MID/UPPER LEVEL RIDGE IS TO THEN HOLD ON THE SOUTHERN STREAM
FLOW...DOMINATING THE FLOW BETWEEN SOUTHERN COAST OF CHILE AND THE
BELLINGSHAUSEN SEA. POLAR PERTURBATIONS ARE TO THEN PRESS AGAINST
THIS AXIS. THE SHORT WAVE ENERGY IS TO THEN SPLIT AROUND OF THIS
AXIS...WITH SOME OF THE ENERGY TO STREAM SOUTH AROUND THE RIDGE
WHILE THE OTHER PROGRESSES INTO CENTRAL PORTIONS OF CHILE. IN THIS
PATTERN EXPECTING A WANING MID LEVEL VORTEX TO ENTER CENTRAL CHILE
BY 96-108 HRS...TO SLOWLY SPILL ACROSS THE ANDES INTO
ARGENTINA/MID SECTIONS OF SOUTH AMERICA LATER IN THE CYCLE. AS IT
NEARS CENTRAL CHILE THIS IS TO SUSTAIN A FRONTOLIZING BOUNDARY
THAT IS TO TRIGGER LIGHT RAINS BY 96-120 HRS WITH ACCUMULATION OF
00-05MM/DAY. SIMILAR AMOUNTS ARE EXPECTED OVER CENTRAL ARGENTINA.
OVER NORTHERN ARGENTINA/PARAGUAY THIS IS TO THEN FAVOR
CYCLOGENESIS/FRONTOGENESIS LATER IN THE CYCLE...TO TRIGGER
MODERATE CONVECTION ACROSS PARAGUAY-SOUTHERN BRASIL WITH
ACCUMULATION OF 15-30MM.

EAST OF THE RIDGE...OVER THE SOUTH ATLANTIC...BROAD MID/UPPER
LEVEL TROUGH WILL DOMINATE THE FLOW DURING THE NEXT FIVE DAYS. AS
IT HOLDS...SHORT WAVE TROUGHS ARE TO REVOLVE AROUND THE LONG WAVE
AXIS. SIMILAR PATTERN IS EXPECTED AT LOW LEVELS OF THE
ATMOSPHERE...WITH BROAD LOW LEVEL TROUGH DOMINATING THE
WESTERN-CENTRAL SOUTH ATLANTIC. POLAR FRONTS ARE TO REVOLVE AROUND
THIS TROUGH...LIFTING ALONG THE COAST OF PATAGONIA INTO THE
CENTRAL PROVINCES IN ARGENTINA/RIO DE LA PLATA BASIN-URUGUAY. BUT
LACKING UPPER LEVEL SUPPORT THESE ARE TO ONLY FAVOR LIGHT RAINFALL
AMOUNTS.

A SOMEWHAT STRONGER BOUNDARY LIES TO THE NORTH...TRAILING ACROSS
THE CENTRAL SOUTH ATLANTIC TO ESPIRITO SANTO/MINAS GERAIS IN
BRASIL. THE BOUNDARY IS FORECAST TO GRADUALLY WEAKEN THROUGH 66-72
HRS. MEANWHILE...THIS IS TO FAVOR A PREFRONTAL SHEAR LINE INTO
EASTERN BAHIA IN BRASIL. IN THIS AREA A BRISK SOUTHEASTERLY FLOW
IS TO CONVERGE ALONG THE COAST...TO RESULT IN MODERATE RAINFALL
AMOUNTS THROUGH 36 HRS WITH ACCUMULATION OF 20-45MM. THROUGH 36-60
HRS THIS WILL DECREASE TO 20-35MM...WITH LIGHT CONVECTION LATER IN
ON DAY 03 AS THE FRONT FRONTOLIZES.

AT 200 HPA...A NEAR ZONAL WESTERLY FLOW IS TO ENVELOP CONTINENTAL
AREA TO THE NORTH OF 20S. THIS PATTERN IS TO GENERALLY HOLD OVER
THE NEXT FEW DAYS. THE PATTERN ALOFT IS TO ALLOW FOR DIURNAL
CONVECTION TO DEVELOP ACROSS EQUATORIAL SOUTH AMERICA...WITH
RAINFALL MAXIMA OF 20-45MM TO AFFECT RONDONIA/NORTHERN
PARA-AMAZONAS IN BRASIL-THE SOUTHERN GUIANAS AND VENEZUELA TO
COLOMBIA OVER THE NEXT TWO DAYS. THROUGH 72-96 HRS THIS WILL
DECREASE TO 15-30MM/DAY. OTHER CONVECTION IS EXPECTED ALONG THE
NORTH COAST OF BRASIL...WITH MAXIMA OF 20-35MM EXPECTED OVER THE
NEXT TWO DAYS. BUT THIS IS TO ALSO BECOME SOMEWHAT MORE SPARSE AND
LESS INTENSE THROUGH 96 HRS. ACROSS ECUADOR...SCATTERED DIURNAL
CONVECTION WILL RESULT IN RAINFALL AMOUNTS OF 10-15MM/DAY...WITH
MOST INTENSE TO CLUSTER ALONG THE CORDILLERA.

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

$$





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