Update on Severe Weather Threats for Tuesday-Wednesday

So Tuesday and Wednesday are still looking like potentially very active days for severe thunderstorms on the Central and Southern Plains. Tuesday’s event will be focused in my neck of the woods…the most intense activity expected over Southeast Nebraska, Southwest Iowa, into far Northwest Missouri and much of Northern Kansas. Wednesday event will be much more extensive. Most intense activity currently likely over far Southeast Nebraska into western Missouri, the eastern half of Kansas and much of western and central Oklahoma.
While Wednesday has garnered a lot of attention, looking at computer model trends, it appears Tuesday has the potential to be an intense day for significant severe weather. The combination of favorable vertical wind profiles (wind shear), instability (for rising motions) and increasing low level moisture (needed for enhancing the instability) is increasing the risk for scattered rotating supercell thunderstorms to develop during the afternoon ahead of a southwestward moving cold front and northeast of a surface low over northern Kansas.
The shear profiles being shown in the lowest levels of the atmosphere and the moisture content for lower thunderstorm bases means these supercell storms may be longer lived than expected in earlier forecasts and therefore capable for producing multiple tornadoes and perhaps an isolated strong tornado (EF-2 or stronger).
The Storm Prediction Center has indicated that there is a 10%+ risk of a strong tornado over the hatched region. There is also an elevated risk for very large hail in the supercells as strong updrafts will be allowed to build very thick hailstones (2 inches+). Damaging winds are of course likely over the region under some storms (60 mph gusts+). 
Meanwhile, Wednesday remains likely to be a significant event day for a large area, although it will be complicated. Areas from Central Oklahoma through Central Kansas to extreme Southeast NE could see an enhanced threat for very large hail and multiple tornadoes, including a higher strong tornado potential possible if the set up lives up to its full potential, but that is still up in the air. There are still questions about coverage and when storms will begin (too many starting earlier in the afternoon will mean a “messy” event with lots of storms and not as many isolated storms to produce stronger tornadoes). There is also some variability about how far north the warm sector will be into Southeast Neb/Southwest IA in the wake of the Tuesday storms, which could mean a greater risk for my area yet again.
Much to be determined! Stay tuned for updates if you live in these areas.
–Meteorologist Nick Humphrey

Severe Weather Threats for Central Plains Monday-Wednesday

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.


European Model forecast depiction of trough of low pressure in the upper-atmosphere over the Western US (forecast for 7 am CDT Tuesday May 1st). This system will contribute to severe weather for the Great Plains Monday-Wednesday.

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.

Schematic of a classic supercell thunderstorm.

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-

day4prob (1)

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-

day5prob (1)

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.

9-km ECMWF USA Surface undefined undefined 108
European Model forecast depiction of Precipitable Water at 7 pm CDT Wednesday (how much atmospheric moisture is available for precipitation in an instantaneous moment). This does not say how much will fall, but just how moisture laden the atmospheric column is. The plume of abnormally high PW will mean the potential for storms with locally heavy rainfall.
9-km ECMWF USA Surface Nebraska 2-m Dew Point 114
European Model forecast depiction of dew point temperature at 1 am CDT Thursday May 3rd. Dew point is a measure of atmospheric moisture. The air behind the warm front and ahead of the dry line is warm and moist (with dew points above 60 F at this time), while the air ahead of the warm front is cool, with less moisture. The air behind the dry line is extremely dry and warm (dew point temperatures in the teens and 20s F).
9-km ECMWF Global Wave United States Simulated WV Satellite 108
European Model forecast simulated upper-atmospheric water vapor imagery for 7 pm CDT Wednesday. The computer model simulates what the weather satellite water vapor channel may see Wednesday night as far as cloud structures. Water vapor imagery is a special type of infrared imagery where water vapor concentration in the upper atmosphere can be detected based on its “brightness temperature” (upper atmosphere is moist, it appears bright, upper atmosphere is dry, it appears dark, meaning water vapor is warm, located at lower level of the atmosphere). Here, the water vapor imagery is enhanced with colors to better interpret the temperature of the condensed water (clouds). We can see intense thunderstorm formation over Kansas at this time (likely supercells) with some further development into Oklahoma as well. This is NOT LIKELY how it will look exactly Wednesday evening, only a general idea of the storm structures based on the larger-scale flow pattern and expected ingredients for storm formation.

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

Interview on Friday Night

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).

Warm Arctic Episodes Linked to Increased Frequency of Extreme Winter Weather in the United States (Nature Communications; 2013)

The roles of aerosol direct and indirect effects in past and future climate change (Journal of Geo. Res. Atmos.; 2013)

Earth’s Energy Imbalance and Implications (Atmos. Chem. & Phys; 2011)

Gulf Stream current at its weakest in 1,600 years, studies show

Land suitable for certain California crops expected to shrink

Paris Agreement alone won’t stop Arctic ice from melting, studies contend

Land degradation pushing planet towards sixth mass extinction

Why ozone poses a challenge to food security

Researchers connect the data to show an accelerating trend for marine heatwaves in our oceans

Dahr Jamail | Thanks to Climate Disruption, Earth Is Already Losing Critical Biosphere Components

Broken records, remarkable stats made 2017 hurricane season one for the history books

Two degrees no longer seen as global warming guardrail

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)


Is CO2 Still Accelerating?

Open Mind

Not only is the amount of CO2 in the atmosphere on the rise, the rise itself has been getting faster — so CO2 concentration has been accelerating. A reader recently asked whether or not there’s any sign of its increase flattening out, or even stopping its acceleration.

Here’s the CO2 data from Mauna Loa:

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Major fires breaking out in Southern California

Explosive fires breaking out in Southern California right now. It’s usually the wet season by December but no rain in sight this week. Santa Ana winds instead are spreading violent wildfires which have destroyed dozens of structures and threatening thousands more. One person has died thus far. No relief expected this week as strong high pressure builds over the Western US (coinciding with the deep trough over the East).

Speaking of which, the weather has finally turned colder after very abnormally warm temps on the Plains. Traveling with my fiancé and son today to Minnesota from Nebraska to look for a new place to live. We are moving to St. Cloud January 1st so we can be closer to my family in nearby Minneapolis and I will start a second masters at St. Cloud State. Highs in Eastern Nebraska will be largely near normal today (near 40) before turning colder the rest of the work week. Central MN will see similar departures below normal…after much of the region had huge departures above normal (over 20 degrees in many cases) for days. A general pattern seen for much of the country in the month of November.

—Meteorologist Nick Humphrey

First Game of World Series Tonight…Weather Headline: HOT

The World Series begins tonight in Los Angeles between the LA Dodgers and the Houston Astros. And it begins with record heat in Southern California. Today, in fact, downtown LA is setting a record high for the day and it is the warmest temperature on record for so late in the year. This was after a record high of 102 was set for downtown LA yesterday. So far it has reached 103 downtown and the official high may be higher before the day is done.

First pitch for the World Series is at 5 pm PDT this evening. While temperatures will decrease somewhat by that time, game time temperatures will be in record territory for a World Series Game (95-100 degrees F). The hottest World Series first pitch on record was from a game (cannot remember which) in 2001 in Phoenix when the NY Yankees played on the road against the Arizona Diamondbacks in a starting game temperature of 94 degrees.

In addition to heat, fire danger remains VERY high across Southern California as Santa Ana winds intensified today and will continue into tomorrow. RED FLAG WARNINGS are in effect for parts of SoCal. Gusts of 50-60 mph have caused problems for firefighters as they dealt with brush fires in Granada Hills this morning and Rancho Cucamonga this afternoon (LA Times). 

(Map of Rancho CucamongaMap of Granada Hills)

Game 2 of the World Series (First Pitch at 5 pm PDT Wed) should be slightly “cooler”, but still quite hot…expecting temperatures to start the game in the mid-90s (92-97 degrees F). If you’re going to these games or doing any outdoor activity at all in Southern California…lots of water and be careful with anything that sparks or burns!

US Global Forecast System forecast temperatures at 5 pm PDT Tuesday.

Enjoy the game! Go American League and go Astros!

–Meteorologist Nick Humphrey