Wednesday, July 28, 2010

Intense Updrafts needed for Hail Production

Ever wonder how strong the updraft winds must be to keep large hailstones up in a cloud? The following table from the National Weather Service shows the estimated updraft windspeeds necessary to keep various hail sizes suspended in the air within a thunderstorm. Tennis ball size hail needs 77 mph updraft winds and softball size hail needs updraft winds exceeding 100 mph. No wonder jet aircraft must avoid these intense thunderstorms.
And speaking of jet aircraft, the typical transcontinental flight is around 32,000 feet above sea level . However, these intense hail producing thunderstorms can reach more than twice that height reaching levels exceeding 65,000 feet above sea level.
See the earlier post about a potential new record size hail stone in South Dakota in July 2010.

Tuesday, July 27, 2010


Ever wonder why people of the "Greatest Generation" generally were and are still pretty tough? Not only was there a Depression in the 1930's but people in this area had another reason to be tough: the weather extremes. I don't need to mention the Dust Bowl to residents of the Plains but what might be less common knowledge is how extreme the weather was in 1936.

Winter of 1936:
From January 21 to February 20, a stretch of bitter and unmatched cold engulfed the north central U.S. In Lincoln, the average temperature during that period was -1.7F and of the 31 days in that period, six had a high temperature below 0. Throughout most of this period, over a foot of snow was on the ground (reaching a maximum depth of 16 inches) and the warmest minimum temperature was 2 above zero. The low fell to 20 below or colder four times and to 10 below or colder 24 times. I don't have wind speed data for this period but given that the Winter of 1936 is known as the "Telephone Wire Winter" in Iowa, we can assume it was windy with whiteout conditions occurring on a regular basis. Of course, if you think it was bad in Lincoln, the winter of 1936 in Grand Forks, ND was close to Siberia standards. In that same 31 day period, the warmest temperature in Grand Forks was 1. Yes, 1. The high in Grand Forks on January 22, 1936 was 30 below zero and minimum temperatures of 40 below or colder were not uncommon.

The bitter cold snap ended in late February and a mild, relatively dry Spring prevailed. There were some decent rains in Lincoln in late April and the first part of May, so farmers probably were optimistic that 1936 would be a good growing season.

Summer of 1936:
Through the middle of June, their hopes were not entirely dashed. Rainfall in the previous month had been sparse, but there hadn't been much heat, so timely rains for the rest of the season could have meant success. Unfortunately, the 0.55 that fell on June 16 would be the last rainfall over 0.50 in Lincoln until August 27. With the drought and what must have been the mother of all death ridges, Lincoln and almost every place in the north central United States had a summer for the record books. The temperature reached the century mark in Lincoln on 11 consecutive days in July 1936 but hopefully nothing will ever top the fateful day of July 25, 1936. On what has to be one of the hottest days ever recorded outside a true desert, a nighttime minimum temperature of 91 was followed by a scorching high of 115. The height of the 1936 heat wave for the north central states occurred on July 13 and here are high temperatures for selected Midwestern cities:

Cedar Rapids, IA: 108
Springfield, IL: 108
Davenport, IA: 107 (it was 111 the following day)
Des Moines, IA: 107 (it would reach 110 later in the month)
Grand Forks, ND: 106
Duluth, MN: 106
Madison, WI: 106
Green Bay, WI: 104
Lincoln, NE: 104
Fort Wayne, IN: 104
Sioux Falls, SD: 103
Indianapolis, IN: 103
Chicago, IL: 102
Detroit, MI: 102
Columbus, OH: 101

New record for hailstone size?

There may be a new world record for hail size. On July 23, 2010, large hail (see the two atached photos) was observed in Vivian, South Dakota. One of the hailstones unofficially measured 8 inches in diameter with an 18.5-inch circumference. The current record-holding hailstone was one that fell in Aurora, Neb., on June 22, 2003. The Aurora hailstone was 7 inches in diameter with a circumference of 18.75 inches.
Members of the National Climate Extremes Committee will meet this week to evaluate the South Dakota stone and determine whether it is a record (as noted by Jim Scarlett, weather service meteorologist in Aberdeen, SD). The committee that reports to the National Oceanic and Atmospheric Administration assesses the scientific merit of extreme weather and validates meteorological measurements.
According to the Associated Press "Leslie Scott, who found the possible record hailstone, said it lost about 3 inches because he was without electricity for several hours after the storm. Weather service staffers told him to put it in a sealed plastic bag and to stop opening the freezer door to show it to people, he said".
Hail from the storm led to at least five reports of people being injured on Interstate 90 when hailstones crashed through vehicle windshields.

Thursday, July 22, 2010

Summer 2010 Heat Wave Update for Lincoln, NE

As of July 22, 2010 Lincoln has only had 14 days with high temperatures reaching 90 F or higher (June 7 days, and July 7 days). There have not been any days with the temperature reaching 100 F or higher in Lincoln this summer. The normal number of days with high temperatures reaching at least 90 F is 42 days. It is unlikely that Lincoln will see as many hot days this year.

The photo to the left is from July 25, 1936. With an overnight low of only 91 F after a daytime high of 115 F, residents of Lincoln spent the night on the capitol lawn to escape the heat inside their non-air conditioned dwellings. (Photo courtesy: Nebraska Historical Society). The Summer of 1936 had 82 days with high temperatures reaching 90 F or higher in Lincoln and an astounding 41 days with the high temperature reaching 100 F or higher!

See more about Lincoln's Heatwaves at:

Wednesday, July 21, 2010

Global Warming Continues

January 1- June 30, 1880-2010
Global Temperature Time Series

Global Warming is evident on this graph showing a strong warming of both the ocean and the land since the late 1970's.

January 1- June 30, 2010
Global Temperature Anomalies Map

From NCDC:
It was the warmest January–June on record for the global land and ocean temperature. The worldwide land on average had its second warmest January–June, behind 2007. The worldwide averaged ocean temperature was the second warmest January–June, behind 1998.

Two different kinds of heat

The sauna or the oven? That is the question. Ok, so maybe Hamlet didn't mutter that during his pondering of whether he should continue his existence on Earth, but the question is a valid one when describing the types of heat in the western Corn Belt. We know that at some point it will be hot in the summer, but will it be a drier heat that is akin to an oven or will it be a humid heat that is akin to a sauna? To help answer this question, I give you a case study of similar air masses yielding two different results.

The upper air charts (compliments of the Storm Prediction Center) from July 19, 2006 and July 14, 2010 show that both days featured very warm temperatures in the lower and mid levels of the atmosphere, with 850 mb temps at Omaha of 29 degrees C and 30 degrees C on 7/19/06 and 7/14/10 respectively.

* Side note
Meteorologists often use the 850 mb temp as a guide for predicting how hot it could possibly be, assuming winds are strong enough to allow for optimal mixing.
*End Side note

Both days featured a cold front moving southeast across the northern plains and both days had strong southerly winds at the surface advecting warmer air from the south. Given all of the similarities, one would expect both days to have equally high maximum temperatures. But the maximum temperatures on 7/19/06 and 7/14/10 were quite a bit different (see maps).

* 2nd side note
Comparisons in this study are only valid in eastern and southern Nebraska. Both cases featured an approaching cold front but the cold front had advanced much further southeast on 7/14/10 than the cold front on 7/19/06, thus the maximum temperatures in the 80's on 7/14/10 in northern and western Nebraska.
* End 2nd side note

So what caused the difference in maximum temperature to be 10-15 degrees F different over the study area? I'll give you a hint. Look at the SMI maps from 7/20/06 and 7/12/10. The summer of 2006 featured moderate to severe drought conditions (see U.S. Drought Monitor maps) across much of the U.S. heartland and every single AWDN station in Nebraska had an SMI well below 0.0 (indicative of water stress) by late July 2006. That stands in stark contrast to this summer, which has been the wettest in many years over much of the western Corn Belt. So, long story short, the copious amounts of soil moisture available on 7/14/10 allowed for high, unimpeded vegetation (especially corn) transpiration rates, while the drought conditions damaged vegetation health and suppressed transpiration rates. It is this difference that is primarily responsible for the difference in temperature.

The last figure featured in this case study shows the hourly dewpoint and air temperatures from the Mead Agrofarm AWDN site on 7/14/10 and 7/19/06. Both days began with equally warm temperatures but notice how the dewpoint keeps slowly increasing to 80+ F on 7/14/10, while the dewpoint on 7/19/06 slowly drops to the mid 60's. Conversely, the slope of the morning air temperature increase on 7/14/10 is much less than on 7/19/06 when temperatures quickly climbed to the upper 90's. The air temperature continued to slowly rise throughout the day on 7/19/06, topping out in the low 100's, while air temperatures remained relatively invariant during the afternoon on 7/14/10.

As alluded to earlier, the differences in moisture led to the difference in maximum temperature. All else being equal, days with high humidity are going to have lower air temperatures than days with lower humidity, because dry air is much easier to heat up (or cool down) than humid air.

* Lesson of the Day
The specific heat of air is around 1 J/g*K while the specific heat of water is around 4.18 J/g*K, so it takes far more energy to warm water 1 K (or 1 deg C) than it does to heat totally dry air 1 K.

So to sum up, the air was far more humid on 7/14/10 than on 7/19/06 because of vast differences in soil moisture and plant health. A full profile of soil water means that plants don't have to "work hard" to obtain moisture and can undergo unimpeded photosynthesis. When plants are undergoing photosynthesis, the stomata are open, and the plant will transpire. When there is little soil water to work with, as was the case on 7/19/06, then plants close their stomata to prevent water loss, and thus are not transpiring. If you recall nothing else from this post, just remember this:

Moist soils -> high transpiration and latent heat flux -> increased dewpoints -> decreased air temperature

Dry soils -> low transpiration and latent heat flux -> reduced dewpoints -> increased air temperature (lower latent heat, higher sensible heat)

Monday, July 19, 2010

June 2010 Global Temperatures Warmest on Record

From NCDC:
Global Highlights
· The combined global land and ocean average surface temperature for June 2010 was the warmest on record at 16.2°C (61.1°F), which is 0.68°C (1.22°F) above the 20th century average of 15.5°C (59.9°F). The previous record for June was set in 2005.
· June 2010 was the fourth consecutive warmest month on record (March, April, and May 2010 were also the warmest on record). This was the 304th consecutive month with a global temperature above the 20th century average. The last month with below-average temperature was February 1985.
· The June worldwide averaged land surface temperature was 1.07°C (1.93°F) above the 20th century average of 13.3°C (55.9°F)—the warmest on record.
Warmer-than-average conditions dominated the globe during June 2010, with the most prominent warmth in Mexico, northern Africa, and most of Europe, Asia, South America, and the contiguous U.S. Cooler-than-average conditions were present across Scandinavia, southeastern China, and the northwestern contiguous U.S. The world land surface temperature June 2010 anomaly of 1.07°C (1.93°F) was the warmest on record, surpassing the previous June record set in 2005 by 0.12°C (0.22°F). The anomalous warm conditions that affected large portions of each inhabited continent also contributed to the warmest June worldwide land and ocean surface temperature since records began in 1880. The previous June record was set in 2005. Separately, the worldwide ocean surface temperatures during June 2010 were 0.54°C (0.97°F) above the 20th century average—the fourth warmest June on record. Warmer-than-average conditions were present across most of the Atlantic, Indian, and the western Pacific oceans.

Thursday, July 15, 2010

A recipe for dangerous heat

On a scale of 1-10, with 1 being very comfortable and 10 being unbearable, I think most midwesterners would have given yesterday a 27. So what made it so darn hot and miserable? Well, yesterday was a textbook example of how moist ground, fully transpiring corn, and a warm air mass can combine to create deadly heat and simultaneously provide fuel for intense thunderstorms.

The left graph comes from Kanawha in northern Iowa and the right graph comes from Mead in eastern Nebraska. Both AWDN stations are located in large corn producing areas and both sites have received copious amounts of rain this summer. So here's how corn + moist ground + warm air mass = miserable...

At this time of year corn is starting to enter the reproductive phase (when the grain is produced) and it wants to maximize the time during a day when it can undergo photosynthesis. During the process of photosynthesis, stomata on the leaves of healthy corn are open and ready for business. When corn is healthy, there is usually ample soil moisture and essentially the corn will transpire (release) water vapor into the atmosphere until the vapor pressure deficit (VPD) is high enough to force the corn to close its stomata for the day.

Quick lesson:

Vapor pressure deficit (VPD) is essentially the difference between the vapor pressure of the air at a particular temperature and what the vapor pressure would be at saturation at that particular temperature. In other words, if the VPD is low, the air is quite moist and if the VPD is high, the air is quite dry. When the VPD gets high, plants close the stomata to preserve soil water and their turgor.

Back to the main show...

During drier times, the closing of stomata on the corn happens earlier in the day, and we are deprived of its water vapor making the air mass even steamier. However, the opposite is true now. The soils are very moist in almost all of eastern Nebraska and Iowa right now and the combination of soil evaporation and a warm, moist air mass being advected from the south led to very humid conditions before the corn had a chance to get to work yesterday. And yesterday the corn was getting overtime benefits once it got started..

The red dots on the graph represent the temperature and the blue dots represent the dew point temperature (i.e., temperature that air would have to cool to before dew would form). At both locations it was already miserable by 8 AM and things would only get worse. As alluded to earlier, the stomata on the corn were open for business and the corn began to release water vapor into an already very humid air mass. At both locations the temperature and dew point increased throughout the day, although the dew point increased more noticeably at Kanawha in northern Iowa.

By late afternoon residents of the Midwest were no doubt uttering expletives and wondering if they had been transplanted to the Persian Gulf as temps in the 90's and dewpoints in the 80's pushed the heat index close to 120F. Relief was on the way though...

Cold Front to the Rescue!

By late afternoon, a cold front was situated from Minnesota down into eastern Nebraska and Kansas. All of the heat and moisture that made it feel so miserable helped to form powerful thunderstorms over many parts of the north central U.S. once it interacted with the cold front. (See Storm reports from the SPC: In addition to high winds, many places received yet another soaking. Mead picked up almost 3 inches of rain and Kanawha came in with close to an inch.

Don't let guard down...

The cold front has brought relief to the region in the form of cooler and much drier air but the reprieve looks to be short lived. Heat and humidity will return by the weekend in eastern Nebraska, to most of the Midwest by early next week, and unfortunately it looks like it could be hot and miserable for a while afterward. But just think, in 5 months we can look forward to blowing snow and subzero temperatures!

Friday, July 9, 2010

January -June, 2010 U.S. Statewide Temperature Rankings

From NCDC:
Midway through 2010, four New England states (Maine, New Hampshire, Vermont and Rhode Island) have experienced their warmest January-June period on record. Eight other states in the Northeast and Great Lakes areas had a top-ten warm such period. In contrast, Florida observed its seventh-coolest year-to-date on record.

Thursday, July 8, 2010

June 2010 Statewide Temperature Ranks

June 2010 Temperatures Comapred to Normal.

From NCDC:
The nationally-averaged temperature for June was much warmer than normal. A deep layer of high pressure dominated much of the eastern United States during the month. The southerly influx of warm air contributed to record high temperatures in many cities.
The Southeast, South and Central regions experienced their second, fifth and seventh warmest June on record, respectively. Only the Northwest had an average temperature below normal for the month.
Record-warm June temperatures were observed in Delaware, New Jersey and North Carolina (tied), where each had average temperatures 5 to 6 degrees F above the long-term mean. Many other states ranked in their top ten based on 116 years of data. Only Oregon and Washington had below normal monthly average temperatures for the month.

Tuesday, July 6, 2010

A Very Wet July 3-5 in Southeast Nebraska

It was very wet 48 hour period (7 AM July 3 - 7AM July 5, 2010) in southeastern Nebraska.

As seen on the attached NWS map, rainfall amounts exceeded 2 inches in southeast Nebraska with some totals pushing past 3 inches
(Tecumseh with 3.42 inches for example).

Sunday, July 4, 2010

July 4, 2010 Rainfall in Lincoln, Nebraska

Its the 4th of July and it rained most of the day in eastern Nebraska. How often has it rained on July 4th in Lincoln, NE?

It has rained on July 4th only 32 times out of the last 124 years (1887-2010) or 26% of the time.

Prior to today, there has been an inch or more of rain on July 4th only 3 times since 1887.
The most rainfall on July 4th was 2.44 inches on July 4, 1909,
the 2nd most was 1.25 inches on July 4, 1939, and,
the 3rd most was 1.23 inches on July 4 1891.

Lincoln received 1.71 inches of rain this year, making this year the 2nd wettest July 4th on record going back to 1887.

The photo shows a flooded bike trail near Capitol Parkway in Lincoln. For more photos check out:

Friday, July 2, 2010

4th of July Extremes Climatology

4th of July is almost here! Have you ever wondered what the warmest 4th of July was? How about the coldest? Here is a list of the 4th of July extremes for many locations in the High Plains Region:


Warmest High Temp (F)/Year

Coldest High Temp (F)/Year

Warmest Low Temp (F)/Year

Coldest Low Temp (F)/Year

Wettest (in)/Year

Period of Record

Aberdeen, SD







Alamosa, CO







Bismarck, ND







Casper, WY







Cheyenne, WY







Colorado Springs, CO







Concordia, KS







Denver, CO







Dodge City, KS







Fargo, ND







Goodland, KS







Grand Forks, ND







Grand Island, NE







Grand Junction, CO







Huron, SD







Lander, WY







Lincoln, NE







Norfolk, NE







North Platte, NE







Omaha, NE







Pueblo, CO







Rapid City, SD







Salina, KS







Scottsbluff, NE







Sioux Falls, SD







Topeka, KS







Valentine, NE







Wichita, KS







Williston, ND







* indicates multiple years, latest year listed

High Plains Precipitation June 2010

"When it rains, it pours" was the story for June 2010 in Nebraska. Central Nebraska back through southern Wyoming was inundated with well above normal precipitation causing many creeks and rivers to overflow their banks and flooding many farm fields. North Central Nebraska saw over 300% of normal precipitation. Ironically not too far away in Western Kansas, there was well below normal precipitation.

See more maps, and create your own at:

June 2010 High Plains Region Temperatures

June 2010 saw warmer than normal temperatures across the southern portion of the High Plains region and cooler than normal temperatures across the northern half of the High Plains region. Nebraska, in the middle had near normal temperatures with most areas averaging above normal and some below normal temperatures.

See more maps, and create your own at: