2017 Drier, But Still Warm in Sioux Falls

Conditions at the end of 2017, while fresh for the memory, would give a very poor impression of mean

conditions for the year. A weak La Nina at the start of 2017 quickly gave way to neutral ENSO indices

through most of the year, before a weak La Nina returned late. Hazardous events were again a rare

commodity, only sporadically highlighting what was another warm but drier year for the Sioux Falls area.

The annual average temperature for 2017 was 48.4 degrees (2.7 degrees above normal), making for the

warmest year on record. This was 0.8 degree cooler than 2016, and a shade warmer than 2015.

Minimum temperatures averaged 9

warmest on record (37.8 degrees – 3.0 degrees above normal –

warmest since 1987), once again the larger part of the warmer annual mean compared to the 22

warmest average annual maximum temperature (59.0 degrees – 2.5 degrees above normal). Greatest

monthly departures were concentrated largely during the cooler season. The big story for temperatures

for the year was the ending of the consecutive above normal months at 20 (Sept. 2015 – April 2017),

when May 2017 came up a bit shy of normal with chilly low temperatures to close out the month.

Despite only three months within the top 25 warmest for the particular month [January (25

), February

) and September (25

)], the consistency to the warmth during the year helped bring the annual

ranking to the 13

warmest. The highest ranking departure occurred in February (+10.2), which also

acquired status as the warmest ranking month (5

warmest). The coolest month compared to average

occurred in August (-2.5), and May (-0.4) was the only other month that ranked in the lower half of

monthly means. During 2017, 192 days were considered “above normal” (more than 2 degrees warmer

than average), 117 “below normal” (more than 2 degrees colder than average) and 56 “normal”.

The warmest temperature of the year was 96 degrees on the 17

and 25

of July, the 23

coolest of

warmest maximum temperatures recorded during a year. 14 days with high temperatures of 90 degrees

or above matched the average number (33

fewest on record – equal to 2016), all but one occurring

during the traditional summer months of June, July and August. 2017 contained the 7

earliest

70 degree or warmer reading (March 6). Even more random, considering 67 degree or warmer readings,

the combination of second earliest (Feb. 21) and latest (Nov. 27) resulted in the longest consecutive

stretch (278 days) by more than a week.

It literally waited until the last minute of 2017 to reach the coldest reading of the year of 20 degrees

below zero. This was the 42

warmest for the coldest reading during a calendar year. There were only

13 days with below zero readings (7 of which occurred in December) which tied for the 10

fewest

below zero readings in a calendar year.

2017 annual precipitation measured up to the least since 2012, ending just a little over an inch shy of

normal with 25.20 inches (-1.18 inches), which ranked as the 55

driest year on record. Only two

months (August and October) were appreciably above normal, and primarily a result of two major

rainfall events. While not excessively dry, the combination of warm and dry conditions produced

moderate drought conditions by mid-summer, alleviated by the August and early October rainfall.

Annual snowfall totaled 36.6 inches (7.9 inches below normal), least since 2012, and more than a foot

less than 2016. Snowfall bookended the year, above normal for January and December, although no

departure was significant other than that of a very dry November. What was unlikely was the other

above normal month – May!

Above: 2017 Monthly Temperature Data for Sioux Falls, SD

Below: 2017 Daily Temperature Departures for Sioux Falls,

After the exceptionally mild finish to 2016 which wiped out the snow cover by Christmas Day, the new

year was greeted with lingering mild temperatures with a touch of light snowfall. Only a couple days

into the month, the first arctic blast of the year would change this abruptly on the 3

. While snowfall

with the system was minimal, winds increased to around 40 mph in the rush of arctic air, creating brief

periods of blowing snow and dangerous wind chills. The next week and a half would be the coolest

stretch of the month averaging over 8 degrees below normal, and containing the coldest temperatures

of the month. The 13

would be final below normal day of the month as the “January Thaw” became

reality with 13 of the final 16 days of the month more than 10 degrees above normal! This includes the

warmest high temperature of the month (45 on the 18

) as well as a pair of record high minimum

temperatures on the 19

(35) and 20

(37), the 6

and 4

warmest readings on record for January

minimums. The warmer and moist pattern would break down into a winter storm on the 24

into early

on the 25

that brought record precipitation (0.31”) and snowfall (4.2”) on the 24

to Sioux Falls. The

greatest snow depth of the year occurred on the 26

and 27

with 7 inches.

Above: 2017 Daily Precipitation Accumulation for Sioux Falls, SD

Below: 2017 Monthly Precipitation Data for Sioux Falls, SD

The most memorable feature of February 2017

was certainly the excessive warmth - the 5

warmest February on record. Much of the

area had temperatures in excess of 8 degrees

above normal for the month, and for Sioux

Falls it was the greatest departure from

normal for the year (+10.2 degrees). Record

highs were set on the 10

(59 degrees) and

the 21

(68 degrees). The 68 degree reading

tied for the 4

warmest high temperature for

the month of February. A record high

minimum temperatures (34 degrees) was also

set on the 11

Above: Daily January Temperature Departures Below: Accumulated Snowfall from Jan. 24-25

February 2017 Temperature Departures

(courtesy High Plains Climate Center)

This was not to say that February did not

have its wintry period. The Sioux Falls

metro area was on the north edge of a

significant winter storm which struck

during the afternoon on the 23

and

continued into the 24

. Blizzard

conditions with nearly impossible travel

occurred as winds topped 40 mph and 5

to 8 inches of snow accumulated around

the Tri-State area. This would be the only

measurable snowfall for the month. After

a couple of days, the above normal temps

wiped out the snow cover and bare

ground returned at the end of the month.

The winter season of Dec. 2016-Feb. 2017 with a mean temperature of 24.2 degrees (+5.1 degrees)

would go down as the 11

warmest on record. There were 14 days with temperatures below zero, well

below the 30-year normal of 24 days. Of those below zero days, only 2 had low temperatures of -10 or

colder, tied for the 10

fewest for a winter period on record. Overall, winter precipitation (3.03 inches)

was well above normal (23

wettest), with snowfall (25.4 inches) a little above normal for the period.

Snowfall generally came in pulses throughout the winter, with the greatest 24 hour accumulation on

January 24-25 (7.3 inches). However, it should be noted that without a RECORD RAINFALL event (1.23

inches) on Christmas Day 2016, complete with thunder and lightning, precipitation for the season would

surely been well below normal.

March again started on the cold side with light snowfall,

but the chill faded quickly as temperatures warmed to

well above normal by the latter half of the opening

week. A 72 degree reading on the 6

was the 7

earliest occurrence of a 70 degree reading, more than 3

weeks before the average date. Amazingly enough, the

passage of a strong cold front that afternoon would

bring not only strong winds, but enough of a

temperature drop for accumulating snow to fall a mere

9 hours after the 72 degree reading! A wintry system

on the 12

and 13

dropped 4 to 6 inches of snowfall,

and ushered in the coldest temperatures of the month. This would also be the final measurable snowfall

until – spoilers - the very end of April! As for most of the cold spells over the winter, this was a brief trek

as only two days in the final half of the month would be below normal and the month ended up the 40

warmest with a departure of +2.4 degrees. For the most part, precipitation was sparse and the Sioux

Falls area varied between one-fifth and one-third of normal precipitation. The first thunderstorm of the

year occurred on the 23

The character of April was one of mild temperatures with occasional precipitation, mostly light.

Nineteen days during the month would record at least a trace of precipitation. The fairly moist times led

to a couple days of dense fog on the 3

and 15

. Strong winds and dry conditions on the 7

led to

several fires in Minnehaha County. The warmest reading of the month occurred on the 8

(81 degrees),

which also featured a record high minimum temperature (50 degrees). Several thunderstorms rumbled

from the 15

to the 19

, including one in the predawn hours of the 15

that awoke many Sioux Falls

residents with prolific lightning and thunder. The fairly mild temperatures of the month gave a quick

start to vegetation, which then battled several freezes the last third of the month, including a record

low of 24 degrees on the 28

. The most noteworthy feature of the month was a very late season

snowfall which began on the evening of the 30

after heavy rainfall earlier in the day. This was the first

recorded snowfall on April 30 (1.3 inches), and the first measurable snow since March 13. Despite the

third greatest daily precipitation for 2017 occurring on the final day of the month (1.38 inches) - almost

half the monthly precipitation - April

2017 still ended up a shade below

normal.

The unusual late season snowfall

continued into May Day with an

additional 2.2 inches snowfall – a

record for the date. Combined with

the snowfall on April 30, this

represented the greatest snowfall

on record in Sioux Falls so late in the

March Percent of Normal Precipitation (courtesy

High Plains Regional Climate Center)

season (3.5 inches), and there was much more just north and west of the metro area, up to 6.7 inches.

A few cool days after the snowfall would yield to another very mild period through the first 17 days of

the month. No better example was Mother’s Day, which ended up a top 10 warmest at 85 degrees, as

well as the warmest May reading. Several thunderstorms occurred from the 15

to 17

, producing

rainfall from 2 to 3 inches around Sioux Falls over the three day period. A severe storm crept from near

Harrisburg into far southern portions of Sioux Falls during the afternoon of the 17

, producing damage

to trees. A sharply colder period initiated on the 18

, with a record low maximum temperature

occurred on the 20

(46 degrees). After the 21

, no day would be warmer than normal through the rest

of the month, neither more than 7 degrees below normal, but it would be enough to make the monthly

mean temperature end up below normal (-0.4 degrees) for the first time in 20 months!

The spring months of March through May accumulated 6.64 inches of precipitation (1.53 inches below

normal) and ended 52

driest on record. Temperatures averaged a shade to the warm side of normal

with a mean temperature or 47.3 degrees (departure of +1.5 degrees) to finish 40

warmest on record.

Low temperatures continued to carry a bulk of the warming weight, ranking 28

warmest on record

compared to maximum temperatures (58

warmest).

June started on a very warm and dry note. No precipitation fell through the first 11 days, with

temperatures averaging a whopping 10.3 degrees above normal, the 4

warmest start to the month on

record. Increased humidity toward the end of the period propped up low temperatures, with a record

high minimum of 72 degrees on the 11

. Rainfall finally arrived on the 12

, with an eruption of severe

storms around Sioux Falls on the evening of the 13

. Between 9 and 930 pm, winds from 60 to 75 mph

blew into the Sioux Falls metro area as well as scattered hail of nickel to quarter size. Cooler and

occasionally wetter conditions filled the balance of the month - neither cool enough to keep June 2017

from being the 28

warmest (mean 70.5 degrees/+2.7 degrees departure), nor wet enough to avoid the

driest (0.63 inches below normal). A record low temperature of 44 degrees was set on June 24.

Storm Reports for early

morning June 13 2017

(courtesy Storm Prediction

Center archives)

July 2017 saw the dry conditions across the region take a rapid turn for the worse, with moderate to

severe drought developing across southeast SD and adjacent areas. As in June, the month started with a

prolonged dry stretch. There was no measurable rainfall through the first 16 days at the Sioux Falls

Airport, and only spotty very light amounts in and around the city. The following week would feature

frequent thunderstorms, but again producing only modest rainfall at best. Storms late in the evening on

the 17

produced 52 mph winds at Joe Foss Field, the strongest winds of the month, along with blowing

dust. While July finished as the 19

driest with only 1.13 inches of rainfall, for the sake of the

developing drought there were fortunately only two days 10 degrees or more above normal. The

consistent and relatively modest warmth resulted in only a 34

warmest monthly ranking. 96 degrees

on the 9

, 15

, 17

and 25

tied for the warmest readings of the year.

In most regards, August will be

known for its astronomical, not

meteorological, phenomenon.

Of course, the solar eclipse of

the 21

was what the world

was watching, but for Sioux

Falls and some surrounding

locations, the weather would

not only throw a monkey

wrench into viewing aspects,

but would create some havoc

around the city during the

peak of the eclipse. A complex

of storms would develop

during the morning, dropping

large hail from quarter to egg

size and damaging winds from

Drought Conditions

Worsen During July 2017

Flash Flooding at 69

and Minnesota Ave.

in Sioux Falls (courtesy ArgusLeader911)

south central South Dakota to as close

as Parker. While storms weakened

from a severe perspective, they become

prolific rain producers and continued to

train across Sioux Falls into early

afternoon. Four to seven inches of rain

would drench the southeast side of

Sioux Falls in just a couple of hours,

producing significant flash flooding.

Even the lesser amount of 2.15 inches

at the airport was the greatest daily

precipitation of the year.

This was not to say there wasn’t any other

interesting weather in August. The month actually

kicked off on the 1

with severe storms on the

south side of Sioux Falls producing hail up to half

dollar size. Periodic moderate to heavy rains

during the month would accumulate to produce

the 14

wettest August (2.37 inches above

normal), easing drought conditions. Nine days

with thunder would tie June for the most of any

month of 2017.

Rainfall rates in

southeastern

Sioux Falls

Left: Radar Image at approximate time

of Flash Flooding and maximum eclipse

Below: 4pm Radar Image and Storm

Reports on August 1 (Courtesy IEM)

Flash Flooding at 69

St. and

Minnesota Ave. (courtesy of

ArgusLeader911)

For the first time in the previous 22 months, the monthly mean temperature (68.1 degrees) would

coolest August. In fact, the 89 degree maximum on the first

was the warmest reading of the month, and was the 5

coldest on record for warmest temperature of

the month of August. The high temperature of 71 degrees on the 5

would set a record low maximum

for the date.

Looking at the big picture, summer 2017 ranked close to the median for temperature (58

warmest) and

precipitation (58

driest). Despite the wet finale of the summer season, total precipitation amassing

9.84 inches would end up a shade less than a quarter inch below normal. Mean maximum and

minimum temperatures provided a fairly balanced share of the 0.9 degree above normal departure.

September arrived peacefully – mainly dry with near normal temperatures through the first nine days.

Over the following two weeks, nine days would register 10 degrees or more above normal, with only

sporadic modest precipitation. Gusty thunderstorms blasted into the Sioux Falls metro area during the

evening of the 19

with winds to 60 to 70 mph and some tree damage across northern Sioux Falls.

Shortly after these summer-like storms, the first day of autumn reached a toasty and summery 91

degrees, the second warmest start of autumn on record. The only concentrated period of rainfall

would occur from the 23

-26

, with a maximum 24 hour rainfall of 0.65 inches on the 25

-26

, the only

two days below normal toward the end of the month. With few days below normal, the month ranked

as the 25

warmest September on record. The coolest reading of the month (41 degrees) was reached

twice (17

and 27

), marking the second warmest value for warmest low during the month of

September. Monthly rainfall of 1.62 inches was back below normal, ranking 38

driest.

Three days of heavy rainfall marked the start of October. Record rainfall doused Sioux Falls residents on

the 2

(1.91 inches) and 3

(1.10 inches). Combined with over an inch of rainfall on the 1

, the first

three days were far and above the wettest start on record for October. After nearly another inch of rain

Smoke from western

U.S. fires returned in

September

on the 6

, precipitation became very scarce with only another 0.16 inches through the remainder of the

month. Even with the prolonged dry spell, it was the 7

wettest October on record. The rainfall on the

was the 10

wettest October day on record, and half the top 10 wettest October days have now

occurred in the last decade. Other than one brief period from the 9

to the 11

, temperatures through

the first 3 ½ weeks of October were above normal. This window did contain the first sub-freezing

temperature, ending the growing season with a hard freeze of 28 degrees on the 10

. The growing

season was an impressive 166 days, 20 more than the average length of 146 days, and 20

longest on

record. Four out of the last five days of the month were more than 10 degrees below normal, and the

low of 14 on Halloween certainly put some frost on the pumpkins. Overall, October ended slightly

above normal (+2.5 degrees, 51

warmest) with a mean of 50.4 degrees.

A trace of sleet on the 9

was the first

solid precipitation of the season.

November was a strange month.

While the first week of the month

featured a mean temperature of 34.8

degrees, the last seven days averaged

41.1 degrees. This occurred during a

time when the average temperature

sees a drop of around 15 degrees,

instead of an increase of over 6

degrees. The five-day period from the

to 30

was the warmest on

record, which included a record high

temperature of 67 degrees on the 27

. November 2017 ended 3.2 degrees above normal, 36

warmest

on record. The other noteworthy occurrence for November was actually a lack of occurrence – of

precipitation. It was quite dry, with a paltry .03 inches of precipitation over the month. This placed

November 2017 at the 5

driest November on record and the driest month since Oct. 1988. The

greatest precipitation (0.02”) was actually the first measurable snowfall (0.2”) of the year on the 6

As conditions dried out during the mild and

snowless month fire danger became an almost

daily concern with increased winds and lower

humidity. Many days were more critical than the

, but it was that evening that saw a grass fire

erupt near Tea, SD. Nearly 160 acres burned very

rapidly, but avoided damaging any structures.

With the proximity of the fire, the smoke plume

was clearly visible on the radar.

Grass Fire near Tea on the evening of

November 16. Courtesy of Maria Kramer.

Three months of modestly ranked above normal temperatures made the fall season the 21

warmest on

record with a mean temperature of 50.4 degrees, 3.2 degrees above normal. The soggy October was

more than enough to offset the extreme dryness of November and well below normal September to

tally the 34

wettest fall with 6.93 inches of precipitation.

December was just another month of extremes. The start of the month continued the unseasonable

warmth of the end of November, with four days more than 10 degrees above normal. The final day of

this streak would bring a first cold blast accompanied near whiteout conditions in snow and blowing

snow for several hours around the evening rush. The wind reached 60 mph to outpace any other of

2017 and become the strongest wind

gust of the year. Snowfall on the 4

was the first of the winter season to

exceed an inch, just over a couple

weeks later than the long term

average. Temperatures would settle

to a little either side of normal from

the 5

to the 9

with some occasional

flurries. From the 10

through the

, the dry weather and mild

temperatures would return along

with periodic fire concerns. Right on

schedule, the next snow storm arrived on the first day of winter, blanketing the area with 3 to 5 inches

of snow. With the pattern change, frigid air would invade the tri-state area through the end of the year.

Three days (26

, 30

and 31

) failed to break zero, the most number of below zero days since 1996.

The high of 9 below zero on New Year’s Eve tied a record low maximum. In fact, for the last week of

the year from Christmas through New Year’s Eve, the mean temperature (-3.0 degrees) was the coldest

on record.

Wind chills at the end of the year made for a dangerous time for celebrating New Year’s Eve, plunging to

25 below to 40 below zero.

Sitting at over 10 degrees warmer than normal at the winter solstice, temperatures would battle to the

final minutes of the year to remain just above normal. Overall, December was the 60

warmest on

record, with a departure from normal of +1.9 degrees. It was the 52

wettest month, and the third

month with above normal snowfall for the year (+2.2 inches).