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Mangled
Jet Stream Delivers Four Months Worth of Rain in One Week to
Missouri; Central, Eastern US to Remain Under Severe Flood Threat
8
August, 2013
The
Jet Stream over North America is a complete basket case. It is far
less a river of air flowing between colder northern regions and
warmer southern regions than it is a disassociated hodgepodge of cut
off air flows. In the far north over a region of coastal Alaska and
the Northwest Territory, an Arctic heat dome has formed and grown
more prominent setting off temperatures ranging from the high 70s to
high 80s as far north as the shores of the Arctic Ocean. This system,
which has already lasted for nearly a week over this region is
expected to persist until at least mid August as it ever so slowly
drifts south and east. Over the west coast of the US, another cut off
low sits almost motionless. Over a region between the Great Lakes and
Hudson Bay a second upper level low meanders, drifting slowly west,
if it moves at all. To the south, a large high pressure system also
sits over the Gulf of Mexico. And from the east, a final low moves
from east to west riding the tropical flow in toward Florida.
Between
them all sits a stationary storm system that simply cannot move. And
so it dumps rain day after day after day.
The
Jet Stream is so weak over North America that these systems are
essentially locked in place. And that means more persistent weather.
In the case of Missouri and Tennessee, where these upper level
systems are combining moisture flows from the southwest monsoons, the
Pacific Ocean, from the Atlantic and from coastal and western Canada
over a stalled frontal boundary, it means a great, daily dumping of
rain.
The
net effect of these colliding and stagnate flows is a kind of storm
sandwich that is focusing in on Missouri and Tennessee even as it
spreads broader impacts over a twelve state region. You can clearly
see these convergent and stationary systems in the water vapor image
above provided by NOAA. Note the low pressure swirls off the US West
Coast, in Canada, and off the US East Coast. You can also see
numerous streams of moisture flowing from the Gulf of Mexico, from
the monsoonal systems over Mexico and Texas, from the west coast low,
and being pulled down through a still moderately active Jet Stream
flow over western Canada. The swirl of whites and blues over the
Central US represents an ocean of atmospheric moisture readying to
dump yet more rain over Missouri, Tennessee and the central and
eastern US.
Over
the past week, satellite shots show persistent storms popping up
again and again over the same region:
What
this series of satellite shots represents is a constant, six day
heavy storm pattern. Adding in the NOAA water vapor image above, it
appears that today makes for day seven. And looking at the forecast,
it appears this system is now set to expand eastward even as it
continues to dump rain over already hard-hit ares.
The
results of this continuous dumping of moisture over the Central US
has been nothing less than staggering. In eastern Missouri, in a
region near Fort Leonard Wood, over 14 inches of rain has fallen
during the past week. Richland in central Missouri has received a
whopping 17 inches. This massive dumping of rain represents the
delivery of four months worth of precipitation in just six days.
Brandon, another Missouri town, received a total of 8 inches of rain
within the 24 hour period from Wednesday to Thursday. A broader
region stretching from Kansas to Missouri and Arkansas and on through
Tennessee received between 3 and 17 inches of rain over the same one
week period. And a still larger area encompassing Georgia, the
Carolinas, Alabama and Kentucky also experienced abnormally heavy
rainfall, washed out roads, and destroyed houses.
In
the west, rivers which, in some cases were near record low levels,
surged to new record highs. The east, which has endured far above
average precipitation since mid spring, saw already swollen rivers
leap their banks.
The
Gasconde River at Jerome, Mo., set a record high level of 31.81 feet,
breaking the old record of 31.34 feet set on Dec. 5, 1982. A
near-record crest is forecast by National Weather Service
hydrologists farther downstream on the river at Rich Fountain, Mo.
[Meanwhile,]
the Maries River in Missouri crested just below record levels.
These
very intense periods of rain set off flash flooding that inundated
roads and destroyed at least 50 homes. Hundreds of homes were also
inundated over a broader area with residents forced to flee to roof
tops as water levels rapidly rose. The scenes of highways flooded,
homes inundated, rivers reaching record or near record levels, and
people being forced to flee from raging flood waters repeated again
and again in a large swath from Kansas stretching eastward to the
Carolinas. In total, more than 12 states have been seriously
impacted.
ABC
News last night, in the below video, aptly described the hardest-hit
areas as turning into ‘a water world.’ The coverage shows storm
shocked residents staring in awe at lakes forming in roadways, being
rescued from the roofs of their homes, or being forced to rescue
heavy equipment from flash floods. One beleaguered Georgia resident,
after watching flood waters sweep his dog away, states: “I can’t
live here no more, I’m through…”
However
in depth and accurate, the above video misses the broader overall
storm context of stalling Jet Stream flows, cut off upper level lows,
and converging upper level moisture streams. ‘Stationary front’
is, therefore, a shallow and inadequate explanation of the patterns
involved. The reporters would have done well to interview Stu Ostro
and Dr. Jennifer Francis as individuals who could give this very
extreme event a proper context as it relates to ongoing changes in
the world’s climate to include meandering Jet Streams triggered by
loss of northern hemisphere snow cover and sea ice, an amping up of
the hydrological cycle due to increased rates of evaporation and
rainfall under a regime of rising temperatures, and powerful, dense
high pressure systems arising from a thickening atmosphere that just
want to sit in place for longer and longer periods. All these
emerging factors combine to increase the likelihood of extreme,
persistent weather patterns like the ongoing series of storms now
driving major US floods.
Unfortunately,
the forecast calls for this weather pattern to continue to dump rain
over an expanding area. For today and tomorrow, a stretch from the US
Midwest to the east coast is under the gun for additional heavy
rainfall and powerful, sudden storms through at least the next four
days. These weather systems aren’t moving and the powerful flows of
moisture converging over the central and eastern US are predicted to
remain in place. So it is likely that flooding will continue to
intensify over the coming days.
Links:
(Hat
tip to Commenter Steve)
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