THE FIRST COLD SCARE OF THE SEASON is here for the Brazilian coffee belt. We recommend that investors bear in mind that in the past, May cold snaps do not tend to result in damaging frost.
The 1979 frost occurred on the morning of June 1, although there was cold air in the region the day prior. For DAMAGING frost to occur, key elements include:
• Central air pressure of at least 1,030 millibars, as it moves into north-central Argentina and continues without falling lower.• Air temperature of 33-34 Fahrenheit or 1-2 degrees Centigrade AND winds >12 MPH OR Air temperature of below 32F or 0 degrees Centigrade and winds <5 MPH.• A dewpoint below 32F or 0 Centigrade.
Equally important is upper-level wind patterns, as they determine the movement of surface weather systems. To have the cold system center over the Brazilian coffee belt and not be too far south or pushed out to sea, a combination of the following must occur:
• Upper-level winds blowing southwest to northeast over central and southern South America is key as they steer the cold weather.PLUS• Disruption or displacement of the south Atlantic high-pressure cell to the north or east (winds blowing counter-clockwise transport warm maritime air onshore into east Brazil)
This condition is satisfied only with calm winds or southwesterly rather than northerly or easterly. Without the cold air feed north to north Argentina and then feeding the west central Argentina high pressure system, the system will moderate as it moves east and pose less of a threat to the Brazilian coffee belt.
CONCLUSION: For damaging cold to occur, several conditions must be met including the actual temperature, the dewpoint, upper-level winds to cause the cold air to trek over the coffee belt and then the surface weather systems just prior to and during the potentially damaging cold situations and then also the high surface air pressure.