As the Arctic continues to warm abruptly because of anthropogenic climate change, the jet stream is exhibiting increasingly high amplitude waves later into the Spring growing season. This has been an apparent pattern through recent decades, but has become more pronounced in recent years. You can learn more about the research of Arctic amplification and the jet stream HERE (Dr. Jennifer Francis) and a more real-time analysis at the time HERE (January 2018; Paul Beckwith). Climate change is becoming abrupt enough, its changes on weather, long-term climate patterns and biology can be seen on yearly to seasonal timescales, where before, changes were over decades. So fast, scientific research can barely keep up and every story has “[faster, bigger, worse, more, etc] than expected”. Been the dizzying mantra of late-2017 into 2018 actually. It’s been rough on early agricultural activities in North America and Europe and it’s also been hard on trees trying to get started on first leaf growth.
Here in Lincoln, NE, the trees the week of April 24th have been struggling to get started with leaf growth. Lilacs are running 16-20 days behind first leaves because it has simply been too cold. We’ve had a few more warm days, recently, but yesterday and today…more chill.
Here’s a photo of my son from this time a year ago. Notice the trees.
Here’s from a walk I took on Monday.
Seeing so many leaf-less trees with only some trying to bud has left me with a weird spooky feeling going for walks. And on Monday, walking down the street for thirty blocks (longest walk I’ve done in awhile) was actually hot because of the lack of shade from any leaves. And if you want to know just what stresses these trees have been through, it’s not just about persistent chill over the course of weeks. Very extreme temperature variability as well.
-April 13th. High temperature 82 F after the passage of a strong warm front associated with the powerful mid–latitude cyclone which produced blizzard conditions across the Northern Plains and severe weather in the Deep South that week/weekend.
April 14th. Twenty-four hours later. Non-diurnal temperature drop from April 13th’s high to 32 F following the passage of a powerful cold front. This was the most extreme temperature change I’ve ever experienced at the same location (and this photo is from the same parking lot as above, looking in the opposite direction). I’ve lived in Seattle, WA, Lincoln, NE and Brookings, SD. A 50 degree F temperature drop. From early-June to early-February weather conditions.
Other locations, such as in Oklahoma experienced temperature changes last week of 50-60+ degrees in 10 hours (near freezing to around 100 degrees)!!
More persistent warming and less temperature variability is expected this weekend into next week. It may finally start to feel like Spring where I am. Severe weather looks possible to impact the Southern Plains next Tuesday and Wednesday. One oddity of note are no tornadoes reported so far in Nebraska, Kansas, or Oklahoma in 2018. Nebraska typically averages (1991-2010) six tornadoes during the January-April period, with Kansas and Oklahoma averaging 17 tornadoes. But so far…zero for all three states. Nebraska has been too cold and Kansas and Oklahoma have either been too cold and dry with occasional extreme heat (by April standards…again, 90s to near 100 in the arid drought areas). Extreme to exceptional drought conditions with little rain (and obviously few thunderstorms) have been plaguing the Southern Plains for months. Some storms in May may decrease in intensity of the drought mildly, but very destructive drought conditions for agriculture and hydrology will continue across the Southern Plains and Southwest US. Hoping it will not spread north into Nebraska, but abnormally warm conditions are expected across the southern half of the Plains this summer. Harsh on the plants and crops going from long cold to a long, hot summer. Not to mention more monster wildfires and dust storms. Oklahoma suffered unbelievable wildfires last week.
Check out this extensive (of what at the time was live) video on April 17th of the wildfires in Western OK as they were being chased by KFOR (Oklahoma City) reporters Val and Amy Castor. It’s 3 hrs worth of video, but it’s a Facebook video, easy to fast-forward through and you can see how bad the fires were as they happened.
As mentioned, severe weather may escalate on the Southern Plains (at least Oklahoma and North Texas) next week. Nebraska has been fairly quiet on the severe storm front, but with the clmatological peak months coming (May/June), there will likely be an escalation of activity. Still remains how much more activity there will actually be. While one needs wave action in the polar jet stream to stimulate the movement of warm-moist air from the Gulf of Mexico and vertical wind shear needed for rotating thunderstorms, very pronounced troughs right over the Plains with large ridging extending into Western Canada can mean cool air intrusions to the east and much of the severe weather and heavier rainfall restricted to the southeastern Plains and Southeast as has been the case much of the winter. The now weakening La Nina pattern of the El-Nino Southern Oscillation has been partly to blame for this (as well as other randomly oscillating “teleconnection” patterns”). However, in addition, the intense climate change-induced Arctic heatwaves in this winter’s polar night (climatologically extreme heat, record low ice extents, ‘atmospheric rivers’ of heat and moisture and ocean storms in the Arctic Ocean) caused the wintertime stratospheric polar vortex maintaining the circulation around the Arctic to split. This has become increasingly consistent and more intense in its effect on the Arctic and mid-latitudes the past few winters. This produced very wavy jet stream patterns and areas of abnormally very cold conditions over Europe and the Central US as well as the repeated nor’easter pattern offshore the East Coast in March.
-Splitting and migration of the winter polar vortex in the stratosphere (10 millibar pressure surface, so lines are lines of equal height…above 33,000 ft in the mid-latitudes generally).
There are signs in the long-range ensemble models that a highly amplified high pressure ridge build over Western North America late next week into early the following week, providing persistent abnormal heat and of course dry conditions. This would consistent with a pronounced positive phase of the Pacific-North American Pattern (PNA) which features abnormally high mid-atmospheric pressures and surface temperatures over western North America. Such a pattern would also decrease severe storm and rainfall potential on much of the Plains during the second week of May. While severe storms are never a positive for safety, the rainfall from convection is always a plus for keeping drought conditions at bay and the northern Plains are in need of regular rainfall as many places not in drought are still suffering precipitation deficits on the month and/or year. If Arctic sea ice retreats rapidly this melt season (and we’re within years of sea ice disappearing in the warm season), this may promote very amplified upper-level high pressure systems this summer as the low albedo (reflectivity) of exposed dark ocean warms the lower atmospheric column, causing thermal expansion and causing any upper-level high pressure systems overhead to respond with greater poleward amplification and strengthening. This could mean very anomalous heat and dry conditions in the summer which persist. This possibility seems focused on the West, although unusually high heat and continued extensive drought may impact the Southern Plains, depending on how the pattern regime sets up. Very important for agriculture this season which I’ll be watching. California, in particular, seems to be progressing into the climate change-induced “weather whiplash” pattern of extreme drought-rainfall, which will only worsen in the coming years. Intensifying drought this summer and the possible return of El Nino later this fall (still up in the air on that) could cause more of this. Lots to keep track of this year.
—Meteorologist Nick Humphrey