367
FXSA20 KWBC 261741
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1241 PM EST THU DEC 26 2024
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
SOUTH AMERICAN FORECAST BULLETIN FOR 26 DEC 2024 AT 1730 UTC:
MADDEN-JULIAN CONDITIONS CONTINUE TO BECOME INCREASINGLY FAVORABLE
FOR VENTILATION AND DEEP CONVECTION IN SOUTH AMERICA. THIS WILL
LIKELY FAVOR A CONTINUED INCREASE IN THE COVERAGE OF DEEP
CONVECTION AND ASSOCIATED RAINFALL AMOUNTS TOWARDS THE END OF THE
FORECAST CYCLE...PARTICULARLY IN NORTHERN AND CENTRAL PORTIONS OF
THE AMAZON BASIN AND NORTHERN SOUTH AMERICA.
IN EXTRATROPICAL SOUTH AMERICA...A SYSTEM OF INTEREST IS A CLOSED
MID-UPPER LOW THAT CENTERS OFF THE COAST OF URUGUAY AND EXTENDS A
BROAD TROUGH INTO SOUTHERN BOLIVIA. THIS TROUGH IS FORECAST TO
MOVE SLOWLY THROUGH SATURDAY...WHEN IT IS EXPECTED TO BE ABSORBED
BY ANOTHER TROUGH ARRIVING IN THE WESTERLIES NEAR 38S 38W. IN THE
LOW LEVELS...THE TROUGH IS SUSTAINING AN EXTRATROPICAL CYCLONE
THAT CENTERS ON AN OCCLUDED LOW NEAR 34S 50W ON THURSDAY MORNING.
THIS LOW IS FORECAST TO MEANDER AWAY FROM THE COAST OF URUGUAY
EXERTING LIMITED DIRECT IMPACTS ON CONTINENTAL AREAS...WITH THE
EXCEPTION OF INTERMITTENT LIGHT RAIN SHOWERS IN URUGUAY AND
SOUTHERN RIO GRANDE DO SUL THROUGH FRIDAY DUE TO MOIST ONSHORE
FLOW.
ELSEWHERE IN EXTRATROPICAL SOUTH AMERICA...EXPECT GENERALLY FAIR
WEATHER CONDITIONS GIVEN LIMITED AMOUNTS OF AVAILABLE MOISTURE AND
PREVAILING MID-UPPER RIDGE CONDITIONS IN THE SOUTHERN CONE. TWO
SHORT WAVE TROUGHS ARE FORECAST TO CROSS PATAGONIA ON
SATURDAY...TO FAVOR DE DEVELOPMENT OF SCATTERED THUNDERSTORMS
CAPABLE OF PRODUCING 05-10MM/DAY AND VERY ISOLATED MAXIMA OF 15MM.
OTHERWISE...EXPECT ISOLATED DIURNAL THUNDERSTORMS IN ELEVATED
PORTIONS OF THE ANDEAN CORDILLERA FROM SOUTHERN CHILE INTO
BOLIVIA...FORECAST TO PRODUCE DISCRETE RAINFALL ACCUMULATION.
IN TROPICAL SOUTH AMERICA AND IN THE UPPER LEVELS...THE BOLIVIAN
HIGH HAS WEAKENED WITH RESPECT TO ITS CONFIGURATION EARLY IN THE
WEEK AND EXTENDS AN ELONGATED RIDGE AXIS ACROSS NORTHERN
PERU...SOUTHERN AMAZONAS-BRASIL INTO SOUTHERN PARA...MINAS GERAIS
IN SOUTHEAST BRASIL. THIS ASSOCIATES MID-UPPER LEVEL WESTERLIES
EXTENDING FROM SOUTHERN PERU/NORTHERN BOLIVIA INTO PARAGUAY AND
MATO GROSSO DO SUL...WHICH ARE LIMITING MOISTURE AVAILABILITY IN
THE MID-UPPER TROPOSPHERE. IN THE LOW-LEVELS...A SOUTH ATLANTIC
CONVERGENCE ZONE (SACZ) HAS REORGANIZED ONCE AGAIN...AND EXTENDS
FROM A COLD FRONT IN SAO PAULO ACROSS MATO
GROSSO...CENTRAO-WESTERN AMAZONAS AND SAN MARTIN IN NORTH-CENTRAL
PERU. THE SACZ IS FORECAST TO PERSIST INTO THE WEEKEND WHILE
REMAINING ALMOST STATIONARY...TO BECOME THE DOMINANT FEATURE
MODULATING THE DISTRIBUTION OF PRECIPITATION IN TROPICAL SOUTH
AMERICA. THROUGH EARLY FRIDAU EXPECT THE LARGEST ACCUMULATIONS IN
NORTHERN PERU WHERE LOW-LEVEL MOISTURE CONVERGENCE AND TERRAIN
ENHANCEMENT WILL INTERACT WITH ENHANCED UPPER DIFFLUENCE AND
DIVERGENCE. THIS WILL FAVOR 15-20MM/DAY AND MAXIMA OF 30-60MM. IN
SOUTHEAST BRASIL EXPECT SIMILAR AMOUNTS IN ASSOCIATION WITH THE
BASE OF THE UPPER TROUGH CENTERING ON A LOW OFF THE COAST OF
URUGUAY. ON FRIDAY THROUGH EARLY SATURDAY...EXPECT THE HEAVIEST
PRECIPITATION TO CLUSTER IN AMAZONAS BRASIL/SOUTHEAST COLOMBIA
WHERE DEEP-LAYER MOISTURE IS FORECAST CO CLUSTER ALONG THE NET AND
INTERACT WITH INCREASING VENTILATION. THIS WILL FAVOR 15-20MM/DAY
AND MAXIMA OF 30-60MM. EASTERLY FLOW ALONG THE ORIENTE ECUATORIANO
AND NORTHERN PERU...IN THE WESTERN END OF THE NET AND SACZ WILL
FAVOR 10-15MM/DAY AND MAXIMA OF 20-45MM...WHILE ELSEWHERE ALONG
THE SACZ EXPECT GENERALLY MAXINA OF 20-35MM. ON SATURDAY THROUGH
EARLY SUNDAY...EXPECT THE LARGEST AMOUNTS TO CLUSTER IN NORTHWEST
BRASIL WHERE EXPECT 15-20MM/DAY AND MAXIMA OF 30-60MM...WHILE IN
NORTH PERU/ECUADOR AND SOUTHWEST COLOMBIA EXPECT MAXIMA OF
20-40MM. ALONG THE REST OF THE SACZ EXPECT GENERALLY MAXIMA OF
15-30MM EXCEPT IN FAR SOUTHEAST BRASIL WHERE EXPECT 15-20MM/DAY
AND MAXIMA OF 25-50MM.
GALVEZ...(WPC)
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