308 
FXSA20 KWBC 131517
PMDSA 

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1117 AM EDT MON JUL 13 2020

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

FORECAST DISCUSSION FROM JULY 13/15UTC: OVER THE EASTERN
PACIFIC...GLOBAL MODELS INITIALIZE A MID LEVEL TROUGH ON THE
NORTHERN STREAM...WITH AXIS WEAKENING AS IT PRESSES AGAINST A
RIDGE TO THE EAST. THROUGH WEDNESDAY THIS IS TO DISSIPATE AS A
STRONGER/MORE ROBUST PERTURBATION ON THE NORTHERN STREAM
APPROACHES FROM THE WEST. BUT AS IT PRESSES AGAINST THE RIDGE OVER
CHILE/ARGENTINA...THE LOW/TROUGH IS FORECAST TO SLOWDOWN...WITH
AXIS STALLING OFF THE SOUTH/CENTRAL COAST OF CHILE LATER ON
THURSDAY/EARLY ON FRIDAY. AS IT STALLS OFF THE COAST...THE TROUGH
WILL START TO SHEAR SHORT WAVE ENERGY ACROSS THE CENTRAL ANDES
INTO ARGENTINA. THE INFLOW OF SHORT WAVE ENERGY WILL THEN LEAD TO
THE GRADUAL EROSION OF THE MID/UPPER LEVEL RIDGE AS IT RELOCATES
ACROSS ARGENTINA TO THE WESTERN ATLANTIC. AT LOW LEVELS...A BROAD
TROUGH IS INITIALIZED OVER THE EASTERN PACIFIC OFF THE SOUTH COAST
OF CHILE...WHILE A RIDGE ENVELOPS THE SOUTHERN CONE. FOLLOWING A
SIMILAR EVOLUTION TO UPPER LEVELS...THIS LOW/TROUGH IS TO FILL AS
IT MEANDERS EAST ACROSS THE SOUTHERN CONE ON TUESDAY. ALTHOUGH
DISSIPATING...THIS SETS THE STAGE FOR A DEEPER TROUGH TO MOVE
INLAND ACROSS SOUTHERN CHILE TO ARGENTINA EARLY ON FRIDAY
MORNING...WITH AXIS CROSSING PATAGONIA IN ARGENTINA TO THE WESTERN
ATLANTIC LATER IN THE DAY. AS THE POLAR PERTURBATIONS STREAM
ACROSS THE SOUTHERN CONE...EXPECTING LIGHT/LOCALLY MODERATE
RAINFALL TO CLUSTER OVER SOUTHERN CHILE BETWEEN TEMUCO-ISLA DE
CHILOE ON TUESDAY...WITH MAXIMA OF 15-20MM. ON WEDNESDAY-THURSDAY
THIS WILL INCREASE FROM 15-30MM TO 25-50MM AS THE DEEPER LOW MAKES
LANDFALL OVER SOUTHERN CHILE...WITH ACTIVITY SPREADING NORTH ALONG
THE COAST TO THE CENTRAL REGIONS OF CHILE...WHERE IT IS TO SUSTAIN
MAXIMA OF 20-40MM IN POTENTIALLY DEEP CONVECTION.
FURTHERMORE...THIS IS TO THEN FAVOR HEAVY SNOWFALL AMOUNTS OVER
THE CENTRAL ANDES OF CHILE...WITH MAXIMA OF 25-50CM. OTHER
CONVECTION IS EXPECTED TO AFFECT SOUTHERN PATAGONIA ON
THURSDAY-FRIDAY...WITH ACTIVITY INCREASING FROM 10-15MM ON
THURSDAY TO 15-30MM ON FRIDAY. NOTE THAT IN THIS AREA ALSO
EXPECTING MIXED PRECIPITATION...WITH HEAVY SNOWFALL POSSIBLE ON
THE EASTERN SLOPES OF THE SOUTHERN ANDES.

DOWNSTREAM FROM THE CONTINENTAL RIDGE...OVER THE WESTERN
ATLANTIC...A BROAD MID/UPPER LEVEL TROUGH DOMINATES THE FLOW EAST
OF 60W AND SOUTH OF 20S. THIS IS TO MEANDER EAST INTO THE SOUTH
ATLANTIC LATER IN THE WEEK. MEANWHILE...IT IS TO SUSTAIN A BROAD
TROUGH OVER THE SOUTHWEST ATLANTIC...WITH AXIS TO SLOWLY WEAKEN
WHILE MEANDERING EAST. THE ASSOCIATED SURFACE FRONT TRAILS ACROSS
THE SOUTH ATLANTIC-SAO PAULO IN BRASIL TO CENTRAL BOLIVIA...WHERE
IT IS TO REMAIN THROUGH TUESDAY EVENING. ON WEDNESDAY...AS THE
MID/UPPER LEVEL TROUGH PULLS AWAY...THE FRONT WILL START TO
RETROGRESS ACROSS PARAGUAY-SOUTHERN BRASIL. IT IS TO THEN
FRONTOLIZE AS IT LOSES ITS UPPER LEVEL SUPPORT ON THURSDAY-FRIDAY.
MEANWHILE...OVER SAO PAULO-SANTA CATARINA THIS WILL RESULT IN
MODERATE RAINFALL AMOUNTS WITH MAXIMA OF 15-30MM THROUGH TUESDAY
MORNING...WHILE ON TUESDAY-WEDNESDAY EXPECTING ADDITIONAL RAINFALL
AMOUNTS OF ACCUMULATION OF 15-20MM. ALONG THE TRAILING END OF THE
FRONT OVER CENTRAL BOLIVIA...CONDITIONS APPEAR FAVORABLE FOR HEAVY
CONVECTION EARLY IN THE CYCLE...WITH MAXIMA OF 35-70MM IN DEEP
CONVECTION. THIS IS UNUSUAL FOR THIS TIME OF THE YEAR...REFLECTIVE
OF THE DEEPER/HIGHER THAN NORMAL PWAT CONTENT OVER NORTHERN SOUTH
AMERICA. THE FOCUS OF THE ACTIVITY THEN SHIFTS SOUTH AS THE FRONT
RETROGRESSES TO PARAGUAY-MESOPOTAMIA VALLEY IN ARGENTINA TO
SOUTHERN BRASIL...INCREASING FROM 15-20MM ON WEDNESDAY TO 35-70MM
ON THURSDAY. OTHER CONVECTION TO THE NORTH IS TO CLUSTER ALONG THE
COAST OF BRASIL BETWEEN ESPIRITO SANTO AND EASTERN BAHIA...WHERE
UNDER INFLUENCE OF A PREFRONTAL SHEAR LINE THERE IS A AN ENHANCED
RISK OF HEAVY CONVECTION ON THURSDAY-FRIDAY.

NORTH OVER THE CONTINENT...AT 200 HPA...AN ANOMALOUSLY STRONG/WELL
ORGANIZED CELL OF THE SUBTROPICAL RIDGE DOMINATES THE FLOW TO THE
NORTH OF 20S...WITH CLOSED HIGH TO ROLL FROM THE EAST ACROSS BAHIA
ON WEDNESDAY TO MATO GROSSO IN CENTRAL BRASIL ON FRIDAY. THE RIDGE
ALOFT IS VENTING CONVECTION ACROSS EQUATORIAL SOUTH AMERICA...WITH
ACTIVITY TO CLUSTER BETWEEN PARA-AMAZONAS IN BRASIL-NORTHERN
PERU/EASTERN ECUADOR TO SOUTHERN COLOMBIA. IN THIS AREA INITIALLY
EXPECTING MAXIMA OF 15-30MM IN SCATTERED CONVECTION...WITH FOCUS
OF THE HEAVIEST CONVECTION SHIFTING WEST TO NORTHERN PERU-EASTERN
ECUADOR BY MIDWEEK. IT IS TO THEN WEAKEN ON THURSDAY...WITH A
GRADUAL SURGE POSSIBLE LATER IN THE WEEK.

DAVISON...WPC (USA)
GALVEZ...WPC (USA)
$$
