140
FXSA20 KWBC 311723
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1223 PM EST FRI JAN 31 2025
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
SOUTH AMERICAN FORECAST BULLETIN FOR 31 JAN 2025 AT 17 UTC:
AN UPPER TROUGH HAS PASSED THROUGH AUSTRAL SOUTH AMERICA
TODAY...AND ITS AXIS IS NOW OVER THE ATLANTIC. BUT RELATIVELY
STRONG WINDS ALOFT...AS IN AROUND 100 KNOTS...THIS WEEKEND. THE
ATMOSPHERIC RIVER THAT AFFECTED SOUTHERN CHILE HAS MOVED NORTH AND
IS NOW SKIRTING THE CENTRAL PORTIONS OF CHILE..AS IT CONTINUES TO
MOVE NORTH. THAT SAID...PERSISTENT ONSHORE LOW LEVEL FLOW WILL
CONTINUE FOR THE SOUTHERN PART OF SOUTH AMERICA FOR THE NEXT FEW
DAYS...CAUSING SHOWER ACTIVITY AND SOME MOUNTAIN SNOW OVER CHILE.
THERE MAY ACTUALLY BE SOME CONVECTION OVER THE AREA AS WELL. THE
FORECAST RAINFALL IS EXPECTED TO HAVE MAXIMA GENERALLY BETWEEN 15
AND 30MM EACH DAY...WITH ISOLATED HIGHER AMOUNTS. THE HIGHEST
AMOUNTS OF PRECIPITATION ARE EXPECTED TO BE ON SATURDAY INTO
SUNDAY...AS IT HAS THE UPPER LEVEL SUPPORT FROM THE STRONG WINDS
AHEAD OF AN UPPER TROUGH THAT WILL BE MOVING IN BY SUNDAY.
THE MID LEVELS WILL HAVE A SIMILAR PROGRESSION AS THE UPPER LEVELS
ACROSS SOUTHERN SOUTH AMERICA. A MID LEVEL TROUGH PASSED THROUGH
THE AREA TODAY AND NORTH WESTERLY FLOW WOULD BE EXPECTED FOR
SATURDAY AS A MID LEVEL TROUGH DEVELOPS ACROSS THE SOUTHERN
PACIFIC. THIS STRONG MID LEVEL TROUGH WILL BE MOVING INTO CHILE BY
SUNDAY MORNING AND ITS AXIS WILL EXIT INTO THE ATLANTIC BY SUNDAY
EVENING. THIS MID LEVEL TROUGH WILL PROVIDE SOME INSTABILITY FOR
THUNDERSTORM DEVELOPMENT...NOT ONLY OVER SOUTHERN CHILE BUT ALSO
IN AND AROUND BUENOS AIRES...WHERE THERE IS AN AREA THAT THE MODEL
GUIDANCE IS SUGGESTING THAT COULD OBSERVE MAX DAILY PRECIPITATION
TOTALS OF AROUND 50MM ON SATURDAY WITH THE CHANCE OF STRONG
THUNDERSTORMS. SOME INSTABILITY MAY PERSIST INTO SUNDAY...BUT THE
MOISTURE WOULD BE LESS BY THEN...SO THE MAX PRECIPITATION EXPECTED
NEAR BUENOS AIRES WILL BE ABOUT 15-25MM BUT WITH A CHANCE OF
STRONG THUNDERSTORMS.
TROPICAL SOUTH AMERICA WILL BE ACTIVE THROUGH THE WEEKEND...WITH
SOME AREAS RECEIVING DAILY RAINFALL MAXIMA NEAR 20-45MM...AND
OTHERS AS MUCH AS 50-70MM...ESPECIALLY OVER PORTIONS OF CENTRAL TO
EASTERN BRASIL ALONG A LOW LEVEL TROUGH. THIS LOW LEVEL TROUGH
WILL COMBINE WITH THE DIURNAL HEATING...AVAILABLE MOISTURE...AND A
WEAK MID LEVEL TROUGH...WHICH WILL ENHANCE THE CHANCE OF
SIGNIFICANT RAINFALL OVER THE AREA THROUGH THE WEEKEND. OTHER
AREAS OVER BRASIL...AND ESSENTIALLY EAST OF THE ANDES WILL BE
HEAVILY INFLUENCED BY THE COMBINATION OF THE DIURNAL HEATING AND
AVAILABLE MOISTURE...TO CAUSE DAILY SHOWERS AND THUNDERSTORMS OVER
THE AREA. THE LATEST GUIDANCE DOES SUGGEST MOST OF BRASIL HAVING
ISOLATED 3-DAY RAINFALL AMOUNTS THAT COULD MAX OUT AT AROUND
75-100MM...WITH THE ECMWF MODEL HAVING A STRONG PREFERENCE FOR THE
AREA FROM SAO PAULO MARANHAO...WITH ISOLATED MAX 3-DAY TOTALS NEAR
125MM.
THE REGION OF THE ALTIPLANO AND THE ANDES OF SOUTHERN PERU IS
EXPECTED TO OBSERVE AN ENHANCED MOIST EASTERLY FLOW WHICH WILL
PROVIDE PLENTY OF MOISTURE FOR THUNDERSTORM DEVELOPMENT ESPECIALLY
TODAY AND SATURDAY. HOWEVER... DRIER AIR WILL MOVE IN LATE THIS
WEEKEND...WHICH WILL CAUSE A DECREASE IN SHOWER ACTIVITY FOR
SUNDAY. THAT SAID...THERE IS A CHANCE OF MCS DEVELOPMENT ACROSS
PORTIONS OF PERU ON SATURDAY...THOUGH THE LATEST MODEL GUIDANCE
SEEMS A BIT SHY WITH THE AMOUNTS...WITH MAX TOTALS GENERALLY
BETWEEN 30-45MM.
GALVEZ...(WPC)
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