Milling & Baking News - June 4, 2019 - 38

Weather Outlook

North America weather
extremes may have peaked

ridge is expected to result from these
changes, especially as they perpetuate
into the first half of June.
A high-pressure ridge in the middle
Great Plains. The dynamics in the cen- of North America is quite normal durBY DREW LERNER
Anomalous weather in North Ameri- tral United States were so extreme that ing the late spring and summer, and
ca may have peaked in the last days rain failed to develop in both Canada if weather in North America is ever
of May, and change is probable dur- and Mexico. Both countries reported going to trend more normal, there has
ing June. That is a simple statement to well-below average precipitation to be some ridge building in the Great
make because these are unprecedent- during May. Some areas experienced Plains. Normally, the high-pressure
ed or nearly unprecedented times. To drought development. Mexico has ex- ridge begins forming in mid- to lateperpetuate rainfall in the United States perienced its driest spring since 2011, May, and it is at that time of year that
as it has been in recent weeks would and Canada's Prairies already were the typical wetter biased spring weather begins to abate.
be an epic event, and
The northward shift
quite frankly it would
14-day normal rainfall in inches ending May 28
in the jet stream that
be shocking to see.
usually results beThe United States has
cause of ridge buildhad similar bouts of
ing in the Plains norexcessive rain in the
mally brings seasonal
past, but the most
rainfall and warmer
recent two weeks of
temperatures to Cantorrential rainfall has
ada's Prairies. Typical
followed a full year
early spring weather
of wetter-than-usual
in Canada tends to
conditions. Some arinclude limited preeas in the nation's
cipitation events and
cropland have had
cooler biased temrain far too frequently
peratures. This year's
to get crops planted.
delay in developing a
Rain during the
ridge of high pressure
last two weeks of
has played a big role
May alone produced
in delaying the wet
moisture totals from
southern Iowa and parts of western Il- enduring a third year of drought when weather biased pattern.
High-pressure ridges in the middle
linois to Oklahoma that ranged from the U.S. rainfall got carried away,
6 to nearly 15 inches, which is two to which likely had a further diminish- of North America during the late
five times the normal amount of rain ing trend in rainfall potentials for the spring and early summer also control
Mexico's weather. The ridge helps to
that falls in a similar two-week period Prairies.
The U.S. wet weather and flooding develop the monsoon flow that ocat this time of year. A little farther west
in central and western Kansas, rainfall rain has affected farm land from the curs in Mexico during May through
varied from 3 to 8 inches in the same middle two-thirds of the Great Plains September. Without the ridge, the
two-week period, which compares to through the entire Midwest, a part of monsoon flow would be less likely
normal precipitation varying from 1.5 the U.S. Delta region and into south- to evolve, and weather in Mexico
eastern Ontario and Quebec in Can- would be left drier biased for a longer
to nearly 3 inches.
Atmospheric dynamics in May ada. Flooding has affected all of this period of time. Mexico does not usuwere very impressive. Cool air was land at one time or another, and plant- ally get much rainfall except when
anchored in the northern Plains and ing is just as far behind in southeastern the monsoon evolves. Delaying this
Canada's Prairies while warm and Canada as it is in the U.S. Midwest. year's ridge of high pressure in North
steamy conditions were evolving in Both regions need to dry out consider- America has played a key role in delaying the onset of monsoonal moisthe southern U.S. Plains, lower Mis- ably, but when might that happen?
As of May 28, the jet stream was ture in Mexico.
sissippi River Basin and southeastern
Today's slower jet steam, warmer
states. An extremely strong jet stream beginning to weaken and the persisthen moved between these two air tent pool of colder-than-usual air in atmosphere and developing highmasses sending one storm after anoth- the northwestern Plains and Canada's pressure ridge already have brought
er through the middle of the nation, Prairies was abating. Reducing the greater rainfall to Central America.
mixing a moisture influx from the Gulf cool air will have an immediate impact This week's outlook for southern
of Mexico with the warm and cold air on rain intensity, and there likely will and some central Mexico crop areas
to induce frequent precipitation of sig- be less prolonged, heavy rainfall in is inclusive of developing rainfall.
nificance. A similar situation occurred early June because of this factor alone. World Weather, Inc. believes this
in the summer of 1993, which also re- The slowing of the jet stream will not evolutionary change in North Ameronly reduce the number and intensity ica weather will continue for the next
sulted in significant flooding.
This year's active weather in the of storm systems rolling through the few weeks, and that should finally
central United States acted a bit like Plains and the Midwest, but seasonal diminish much of the rain in the U.S.
a large vacuum cleaner sucking the warming will begin to evolve more Midwest greatly, allow warmer days
moisture out of surrounding areas and significantly throughout the Great between rain events and support
depositing it into the Midwest and Plains. A developing high-pressure greater rainfall periodically in both
38 / June 4, 2019

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Milling & Baking News - June 4, 2019

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