They call them rain bombs. A new breed of severe storm fueled by a record hot atmosphere. One capable of dumping 2-4 inches of rainfall an hour and generating voracious flash floods that can devour homes and cars in just minutes. And in southeast Texas, the rain bombs have been going off like gangbusters.
In this week’s most recent iteration of flaring, climate change induced, storms, a region north of Houston and south of Dallas saw flood after flood after flood. Now, hundreds of people have been forced to abandon inundated homes, thousands of cars have been submerged, and seven people are dead. Rainfall totals for the region over the past seven days have averaged between 7 and 10 inches. But local amounts in the most intense bombification zones have come in at 16, 19, and even as high as 30 inches in Washington County. All time record rainfall totals that might be associated with a powerful hurricane. Floods that would typically happen only once every 500 years. But in the new moisture-laden atmosphere of a record warm world, a garden variety thunderstorm now has enough atmospheric oomph to frequently set off what were once multi-century floods.
(Rain bombs again explode over Texas in a huge complex of storms on Tuesday afternoon in this GOES enhanced satellite shot. It’s all part of the same stormy weather pattern — associated with a trough and an upper level low — that over the past five days produced another round of record flooding over Texas. And it’s expected to remain in place through the end of this week. With more severe storms firing and 4-8 inches of additional rainfall on the way for some sections of soggy Texas, it appears that still more extreme flooding is likely. Image source: NOAA.)
It’s under these new, freakish, conditions that the Brazos River is today expected to crest at 53.5 feet — its highest level ever recorded. And this crest is predicted to push a flood of 8-9 feet into neighboring communities. Extreme flooding that local officials say Texans are not at all prepared for. In total, more than 40,000 people have been urged to evacuate. But with the worst flooding still on the way, the situation is still very fluid.
In isolation, the current Texas floods would be an extreme record disaster worthy of the weather history books. But it is just one of three such severe rainfall events to strike southeastern Texas since April. And, unfortunately, more storms are on the way as a strong ridge of high pressure out west is expected to generate another deep Central US trough and related rain bomb inducing storm pattern over the next five days.
West Coast Turns up the Heat
As parts of Texas face never-before-seen flooding, the US West Coast is staring down the gullet of an extraordinary surge of heat. A gigantic blob of hot ocean water off that region of the world is feeding the growth of a powerful atmospheric wave. And once the ridge of this wave really starts to swell northward on Friday, Saturday, and Sunday, record hot temperatures are bound to explode all over the US West Coast and on up into Canada.
(Sea surface temperature anomalies on May 31, 2016. Extremely hot sea surface temperatures over a vast area stretching from the Equator to Alaska and all along the US West Coast enhance the development of strong ridges in the Jet Stream that have tended to spur extreme heatwaves over the past few years. Ocean temperatures over this zone now range between 1 and 6 C above normal late 20th Century values. Image source: Earth Nullschool.)
In Fresno, the mercury is expected to rocket to 108 degrees Fahrenheit by Saturday — or about 18 degrees above normal for early June. Sacramento is expected to see 106 F readings at the same time — which is around 20 degrees above average for that Central California location. Further north, temperatures are also expected to skyrocket with Portland predicted to strike near 98 F on Sunday and Spokane calling for 96 F. In fire-ravaged Fort McMurray, the mercury is expected to top out at 85 F on the same day.
This expansive bulge of heat is expected to cover pretty much all of Western North American. Rising from the Desert Southwest, it is predicted to run through Oregon and Washington, rise up through Canada, and touch even the shores of the rapidly thawing Arctic Ocean.
Conditions in the Context of Human Caused Climate Change
The broader conditions fueling both record rain and potential record high temperatures over the North American West are the same. A record hot global atmosphere is one that is burdened with more heat and moisture than ever before. One that will inevitably produce more extreme rainfall and heatwaves than we are used to.
Locally, additional features related to a fossil fuel based warming of the world further contribute to the problem. Over the Northwestern Pacific, sea surface temperatures ranging from 1-6 degrees Celsius above average (2 to 10 F) generate a tendency for heatwaves and strong high pressure formation. These systems have often taken in all of the US West even as they’ve extended on up into Canada and Alaska. Adding to the problem is sea ice loss over the Arctic Ocean — which as of today is seeing the lowest ice extent ever recorded for this time of year. This sea ice loss tends to aid in Arctic warming which weakens the Jet Stream, which in turn tends to meander — creating these exaggerated trough and ridge patterns that have been associated with so much extreme weather recently.
(Earth Nullschool map of Jet Stream wind pattern predicted for early June 5, 2016. A powerful ridge expected to form over the US West Coast is predicted to drive record heatwave conditions there by this weekend even as a facing trough will again spike the risk for extreme rainfall events over Southeastern Texas. This Jet Stream feature and related severe weather conditions — ranging from severe heat to floods — is now influenced by numerous effects currently emerging as human-forced climate change worsens. Image source: Earth Nullschool.)
Large, hot ridges forming in one region tend to generate deep, stormy troughs in another. And the ridge over the US West has resulted in the formation of a related trough and unsettled weather pattern over the South-Central US centering on Southeast Texas. This trough has pulled cold, unstable air into the upper levels of the atmosphere over Texas even as it fed upon an uncanny volume of moisture streaming in off the abnormally hot waters of the Gulf of Mexico and Pacific Ocean.
The results? Well, we’ve already experienced them in the form of record floods for Texas, periods of record heat for the Western US, and a never-before-seen May wildfire outbreak in Alberta, Canada. This week, the overall pattern is again expected to ramp into high gear — which is likely to produce possibly never-before seen June heat out west and more extreme flooding for Texas.