–Meteorologist Nick Humphrey
–Meteorologist Nick Humphrey
After a start to a 2018 tornado season which has featured numerous tornadoes across the Deep South and even scattered tornadoes out West, but not a single tornado in Nebraska, Kansas or Oklahoma, it appears near certain the tornado drought for the Great Plains will come to an end early next week. Something which as been missing thus far…pattern favorable to severe for widespread severe thunderstorms across the Central and Southern Plains…will ramp up beginning Monday across the High Plains, shift eastward Tuesday with a peak higher-end risk for more widespread severe storms Wednesday. The jet stream, the river of air separating the cold Arctic from the warmer mid-latitudes will send a major trough of low pressure over the Western US, temporarily cooling that region down, warming up the Plains, bringing in greater moisture from the Gulf of Mexico and setting up the ingredients for multiple days of severe storms.
A brief review since it’s been forever since the Plains have had severe weather and there might finally be something in my neck of the woods. Severe weather is defined by the phenomena. In the US, the criteria, which weather warnings revolve around are 1) large hail of 1 inch or larger, 2) damaging wind gusts of 50 knots/58 mph or higher or 3) a tornado. Severe convection (thunderstorms) needs three major ingredients to maximize their potential. 1) Instability, 2) Moisture, 3) Wind Shear. Instability is positive buoyancy (tendency to rise). This is aided not only by heat, but also by moisture as moist air is less dense than dry air at the same temperature. Wind shear is the change in speed and direction of the wind with height. Winds which turn and increase in speed rapidly with height can promote storm rotation, allow them to form isolated cellular structures called supercells. These can be long-lived, self-maintained and produce the most intense severe weather.
Of the three days I’m most concerned about for severe weather this week, Wednesday appears to be the most serious for the Central/Southern Plains for significant severe weather. But let’s take a quick look at all three days.
Monday, April 30th-
The National Weather Service Storm Prediction Center has a Slight Risk of severe weather (2/5 on the scale) for much of the high plains from Texas through Kansas and then, extending farther eastward into Central/NE Nebraska into SE South Dakota. This covers a 15% chance of severe thunderstorms within 25 miles of a point. A more “Marginal Risk” exists surrounding it. This would be for the afternoon and evening hours as a weak disturbance moves out of the Rockies, increasing wind shear and temperature-based instability (upper-atmosphere cooling relative to warming near the surface…warm air rises into colder air) modestly for isolated severe weather. Large hail and damaging winds are the primary hazards, but moisture will be limited, keeping the event from being widespread.
Tuesday, May 1st-
Beyond Day 3, there are now categorical outlooks, only probabilities. A 15% chance of severe thunderstorms within 25 miles of a point exists over Eastern Nebraska, Western Iowa, much of northern and Central Kansas into Western Oklahoma. This will likely be a bit more vigorous event from Monday, with the Tuesday disturbance being stronger with better shear profiles, more low level moisture available, and the combination of abnormally warm temperatures and higher moisture will mean higher atmospheric instability for tall, intense thunderstorms with strong updrafts. The storms will likely begin as supercells across Nebraska and Kansas before merging in the evening into an organized structure known as a “mesoscale convective system”. Basically a larger scale complex which can bring locally heavy rain and extensive damaging wind gusts. The initial storms will form along a cold front and threaten damaging winds, large hail and an isolated tornado.
Wednesday, May 2nd-
Wednesday is currently the most serious day for severe weather, but some uncertainty still exists. A 30% chance of severe thunderstorms within 25 miles of a point exists from extreme SE Nebraska, across much of Kansas, into western and central Oklahoma. A greater 15% area extends beyond that, including my area of Lincoln, NE. Wednesday, the main upper-level trough of low pressure over the West (seen in the above map) begins to shift eastward and a surface mid-latitude cyclone sets up over the central and southern Plains. A dryline (boundary separating warm, moist air from the Gulf of Mexico to the east from dry desert air from the Southwest US) will be located north-south somewhere over central KS/OK with a warm front either over Southeast Nebraska or Northeast KS (this is in question). The ingredients overall suggest robust thunderstorms forming along the dryline and near the area of low pressure (at the the intersection of the dryline and warm front) either in the afternoon or early evening Wednesday which vigorous supercells capable of producing large hail, some significant, damaging winds and multiple tornadoes. A possibility exists for a few of the tornadoes to be strong (EF2+; see more about the Enhanced Fujita Scale) and because of the persistent upper-level dynamics and buoyancy, storms could last after dark, posing nocturnal hazards. Later, storms will eventually merge producing greater high wind and heavy rain threats. Isolated flash flooding could be an issue Wednesday night from any heavy rain events.
For me personally, the the greatest threat for severe weather Wednesday seems to be to my south, but given the lead time, I’m watching to see how the position of the warm front ends up. If it migrates northward in the forecast and my areas is more solidly in the “warm sector”, then we will be just under as much of a hazard as the current 30% area is now. However, I note from forecast experience that warm fronts in severe storm events are notoriously challenging to forecast for as even the day of the event as they can have difficulty moving as far northward as expected because of the cold air they must erode out ahead of them. Much can also depend on the storms the previous day and how they effect the overall regional environment (temperature profiles, areas of instability, position of fronts, etc). But Monday-Wednesday all have potential to be hazardous days with Wednesday being a more potentially significant tornado day after months of silence.
So stay tuned early next week. The weather will definitely be news yet again this Spring! Stay safe and be ready this week in these regions!
–Meteorologist Nick Humphrey
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
Today/tomorrow’s mid-latitude cyclone on the Great Plains and Midwest will be a powerful one and one which will provide something for everyone. Blizzards, wind, severe storms, flash flooding, fire…pick your poison, Nature will provide.
In places like Minneapolis and much of Nebraska, this storm threatens to be a historic late-season April heavy snow or blizzard event. In the southern Midwest and South, it threatens heavy rain, flooding and a tornado outbreak. On the southern Plains, strong winds and arid conditions, could further yesterday’s extreme fire behavior. Stay safe out there folks!
A reminder, I will be interviewed on the internet-based program Environmental Coffeehouse at 9 pm EDT/6 pm PDT tonight! A livestream will be available on their public FB page (so you should be able to see it regardless of whether you have a FB page or not). I will discuss abrupt climate change and increasing extreme weather events and how current events (ocean heatwaves, changing jet stream, etc) connect to our rapidly changing climate.
If you’re wondering why all this is happening…VERY amplified…or in other words…very wavy jet stream pattern bringing extremely cold air (by April standards) down from from Canada to meet with up with extreme warm air (again by April standards) up from the south. Temps in 20s and 30s to the north with a high of 101 in Western Oklahoma yesterday to the south. Right now Lincoln, NE (where I am) is hitting 80 degrees for the first time this year. Tomorrow, Lincoln will peak in the mid-30s with falling temperatures!
The front end of this trough caused the development of the surface cyclone over Nebraska, intensifying deep moisture movement from the Gulf of Mexico (which, by the way, as a moisture source region, is running well above normal to start the year) and as and providing the deep vertical wind shear (rapidly increasing wind speeds with height) need to generate sustained severe thunderstorms. A recipe for a multi-threat mid-latitude frontal system. And it will not stop anytime soon. Saturday night, the threat will spread eastward, where a significant ice storm event may be possible for portions of upstate New York. In fact, Saturday afternoon, there may be much of Pennsylvania in the 70s while much of Upstate New York may be in the 20s! Incredible temperature contrasts for such a relatively higher latitude location.
—Meteorologist Nick Humphrey
Friday Night, I’ll be interviewed on the internet live show Environmental Coffee House by host Sandy Schoelles. The show (started by a concerned non-scientist interested in the environment, science and technology) discusses a variety of environmental and climate issues. I’ll be brought on to talk about increasing extreme weather events, climate change and abrupt tipping points, and environmental destruction, including the 6th mass extinction. The show will be live streamed on Facebook and has thousands of followers. Give it a watch, it’ll be a serious discussion (maybe 30-40 mins), but should be fun.
Below are some articles which may relate to what we discuss in the interview. Almost all are VERY recent articles! (First three articles are technical peer-review papers, remainder are recent news articles for non-scientist consumption).
More science-y but still understandable for non-scientists. Presentation by Dr. Peter Carter on major threat to food production in the United States bread basket by extreme heat: YouTube Video (2017)