SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1000 AM EDT FRI MAY 24 2013

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

MODEL COMPARISON (VALID FROM 00 UTC MAY 24): THE GLOBAL MODELS ARE
IN EXCELLENT AGREEMENT THROUGH 96-108 HRS...AS THEY FAVOR A
SIMILAR EVOLUTION OF A DEEP MID/UPPER LEVEL TROUGH ENTERING THE
CONTINENT. THIS SYSTEM IS FORECAST TO SUSTAIN MODERATE TO HEAVY
CONVECTION ACROSS CENTRAL PORTIONS OF CHILE...WITH HEAVY SNOWFALL
AMOUNTS ACROSS THE CENTRAL ANDES.

BROAD MID/UPPER LEVEL TROUGH IS TO PULL ACROSS THE EASTERN PACIFIC
THROUGH 30-36 HRS...TO ENTER THE SOUTHERN CONE AT 48-60 HRS. AS IT
ENTERS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA THIS IS TO SUSTAIN
HEIGHT FALLS OF 75-125GPM. BY 72-84 HRS...AS A RIDGE BUILDS TO THE
WEST...THE TROUGH IS THEN FORECAST TO DEEPEN/AMPLIFY ALONG THE
COAST OF CHILE...WITH AXIS TO EVOLVE INTO A HIGH AMPLITUDE LONG
WAVE TROUGH BY 84-96 HRS. THE AMPLIFYING TROUGH IS TO FOCUS ITS
SHORT WAVE ENERGY AS FAR NORTH AS CENTRAL CHILE...WITH HEIGHT
FALLS IN THIS AREA TO PEAK AT 50-75GPM. A POLAR JET MAXIMA IS TO
ACCOMPANY THIS TROUGH AS IT ENTERS CENTRAL CHILE...WITH ITS RIGHT
EXIT REGION TO ENHANCE VENTILATION ALOFT. BY 96-108 HRS THE TROUGH
WILL START TO PULL ACROSS THE SOUTHERN CONE TO ARGENTINA...TO
SLOWLY MOVE TO THE WESTERN ATLANTIC BY 120-132 HRS WHERE IT
CONTINUES TO INTENSIFY.

AT LOW LEVELS EXPECTING BROAD TROUGH TO MOVE TO THE EASTERN
PACIFIC THROUGH 36-48 HRS...TO CONTINUE EAST ACROSS CHILE TO
ARGENTINA BY 96 HRS. THROUGH 120 HRS THE TROUGH PULLS ACROSS
PATAGONIA TO THE WESTERN ATLANTIC. A DEEP OCCLUDED 968 HPA LOW OFF
THE SOUTHERN COAST OF CHILE IS TO ANCHOR THIS TROUGH AS IT ENTERS
THE SOUTHERN CONE. THROUGH 108-120 HRS THIS WILL WEAKEN TO A 984
HPA LOW OVER SOUTHERN PATAGONIA. THE DEEP POLAR TROUGH IS TO
SUSTAIN STRONG LOW LEVEL WINDS OF 35-50KT ACROSS SOUTHERN CHILE TO
PATAGONIA IN ARGENTINA. ASSOCIATED SURFACE FRONT ENTERS SOUTHERN
CHILE BY 30-36 HRS...INTO PATAGONIA ARGENTINA BY 48 HRS. THROUGH
72-96 HRS THE FRONT MOVES ACROSS LA PAMPA-CUYO IN ARGENTINA TO
NEAR LA SERENA CHILE. AT 120 HRS IT WILL REACH RIO DE LA
PLATA/URUGUAY WHILE TRAILING WEST ALONG 30S. ACROSS SOUTHERN CHILE
THIS IS TO FAVOR MODERATE CONVECTION...WITH MOST INTENSE AT 36-84
HRS...WITH DAILY MAXIMA IN THIS AREA TO PEAK AT 15-20MM. OVER
CENTRAL CHILE...UNDER FAVORABLE JET DYNAMICS...THE MAXIMA WILL
INCREASE TO 20-45MM...WITH MOST INTENSE EXPECTED OVER THE ANDES.
NOTE THAT THIS IS LESS THAN WHAT THE GLOBAL MODELS SUGGEST. THE
PROGRESSIVE NATURE OF THIS SYSTEM DURING THE LATTER HALF AND LOW
MOISTURE CONTENT VALUES SUGGEST LESSER AMOUNTS THAN WHAT GLOBAL
MODELS FORECAST. ACROSS PATAGONIA...AS THE OCCLUDED LOW PULLS
ACROSS THE SOUTHERN CONE...AND AN EASTERLY JET ESTABLISHES...IT
WILL ENHANCE MOISTURE TRANSPORT/CONVERGENCE IN THIS AREA. THIS
WILL START AS RAIN/RAIN SHOWERS AND GRADUALLY TURN TO HEAVY SNOW
OVER THE SOUTHERN ANDES...WITH RAINFALL AMOUNTS TO PEAK AT 15-20MM.

AN OLD SURFACE FRONT EXTENDS WEST ACROSS THE SOUTH ATLANTIC TO RIO
DE JANEIRO/NORTHERN SAO PAULO TO CENTRAL BOLIVIA. UNDER INFLUENCE
OF A MEANDERING SUBTROPICAL JET MAXIMA OVER MID SECTIONS OF SOUTH
AMERICA THIS BOUNDARY IS EXPECTED TO PERSIST OVER THE NEXT FEW
DAYS. SHORT WAVE PERTURBATIONS ON THE NORTHERN STREAM FLOW WILL
INTERACT WITH THIS FRONT...TO ENHANCE CONVECTIVE DEVELOPMENT ALONG
THIS BOUNDARY. ACROSS CENTRAL PARAGUAY TO SAO PAULO IN BRASIL THIS
IS TO FAVOR RAINFALL AMOUNTS OF 15-30MM BY 24-48 HRS. BY 96-120
HRS...AS ENHANCED BY SUBTROPICAL JET...THIS WILL INCREASE TO
20-45MM.

FARTHER NORTH...AT 200 HPA...AN ILL ORGANIZED CELL OF THE
SUBTROPICAL RIDGE IS TO DOMINATE AREA TO THE NORTH OF 10S. EARLY
IN THE CYCLE THIS IS TO CENTER ON A CLOSED HIGH OVER AMAZONAS IN
BRASIL. THROUGH 96 HRS THE HIGH WILL RELOCATE TOWARDS NORTHEAST
BRASIL. AS THE RIDGE ALOFT PERSISTS...THIS WILL VENT DEEP
CONVECTION ACROSS NORTHERN SOUTH AMERICA...WITH ACTIVITY ACROSS
PARA-AMAZONAS TO SOUTHERN COLOMBIA/NORTHERN JUNGLE OF PERU
EXPECTED TO PEAK AT 15-20MM. LOCALLY HEAVY AMOUNTS ARE POSSIBLE AS
PERTURBATIONS IN THE EASTERLY TRADES PROPAGATE ACROSS THE
GUIANAS-VENEZUELA TO COLOMBIA.

MAQUEDA...DINAC (PARAGUAY)
SILVA DE SOUZA...INMET (BRASIL)
DAVISON...WPC (USA)
GALVEZ...WPC (USA)