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NOUS45 KTFX 011512
PNSTFX
MTZ008>015-044>055-031815-
Public Information Statement
National Weather Service Great Falls MT
912 AM MDT Wed Sep 1 2021
...PUBLIC INFORMATION STATEMENT...
...August 2021 and Water Year Weather Summary for North Central
and Southwest Montana...
A ridge of high pressure was centered over Montana during July,
which is normal for the month. However, the ridge was stronger
than normal which resulted in above normal temperatures and below
normal precipitation. Wind speeds averaged below normal.
August started warm, as much as 10 to 15 degrees above normal.
Some daily record high temperatures were tied or set on the 1st.
Thunderstorms with heavy rain brought some localized flash
flooding to Bozeman on the 2nd. Severe thunderstorms produced one-
inch hail over eastern Great Falls on the 4th. Thunderstorms on
the 5th brought high wind gusts. Helena had a gust to 63-mph,
which was their highest August gust since 1976 and 4th highest for
August overall. Strong thunderstorm gusts occurred again on the
8th. Bannack had a gust to 60-mph and Logan recorded 67-mph. Heavy
rain fell along the Rocky Mountain Front and northern portions of
the area. One to 1.5-inches of rain fell. Temperatures warmed
again and on the 14th, some record high temperatures were set. Cut
Bank tied their daily record. This occurred again on the 16th,
when Helena tied their daily record. Thunderstorms with a cold
front produced strong and gusty winds on the 17th. Dillon recorded
a gust to 69-mph, which was their second highest gust of record
for August. As the cold front pushed through Bozeman, 63-mph gusts
were recorded. Cooler air and precipitation settled over the area
from the 17th-18th. Great Falls recorded 1.61-inches in a 24-hr
period, which was their 9th highest 24-hr amount of record for
August. On the 18th, Great Falls reached only 48F for a high
temperature. This was their earliest high of less than 50F of
record. The previous record was August 22, 1992 when the high was
only 38F. This also occurred at Lewistown. Record low maximum
temperatures were set across the region on the 18th. From the
17th-19th, 1.5- to 2-inches of rain fell from the southwest
through central portions of Montana. Isolated thunderstorms with
heavy rain dropped over one inch of rain near Boulder and Monarch
on the 22nd. On the 30th, a thunderstorm produced downburst wind
gusts of 79-mph at Bozeman airport. This was a new all-time high
gust at the airport. The old record was 78-mph set July 30, 1957.
At most locations, August was wetter than normal. West
Yellowstone had their 6th wettest August of record, while it was
11th wettest at Bozeman.
#### Temperature
In August, temperatures averaged near normal. Yellow Mule
(Madison) recorded the coldest average temperature of 51.7F. The
coldest temperature of the month was 21F at Gates Park (Lewis and
Clark) on the 24th. The warmest was 101F at Valentine (Fergus) on
the 1st. The range in temperature departures was from only 0.3F
below normal at Dillon to 0.9F below normal at West Yellowstone.
The areas warmest average temperature was 69.8F at Armells Creek
(Fergus). This was the 68th coolest August of record at across the
area. At most spots it was the coolest August since either 2016
or 2018.
The water-year-to-date temperature averages are 1.1F above
normal, averaging 42.2F. This is the warmest since 2016. The areas
calendar-year-to-date temperature average is 45.6F, which is 0.9F
above normal. This was also the warmest such period since 2017.
Summer season average temperature was 67.0F, the sixth warmest of
record and warmest since 2007. This was 3.8F above normal.
#### Precipitation
Precipitation amounts were mostly above normal. The heaviest
precipitation was over southwest Montana. The Madison Plateau
SNOTEL (Madison) reported 5.0-inches and an observer just south of
Bozeman reported 3.76-inches. Regular rains brought the 11th
wettest August of record at Bozeman and wettest since 2014. West
Yellowstone had their 6th wettest August and wettest since 2014.
The area-average water-year precipitation is 80-percent of normal
and 15th driest of record. A composite of 10.66-inches is
2.62-inches below normal. This is the driest water year since
2003.
Area calendar-year-to-date precipitation averaged 8.23-inches,
2.37 below normal and 78-percent of normal. This was the 13th
driest such period and driest since 1996.
Summer season average precipitation was 2.94-inches, the 11th
driest of record and driest since 2012. This amount was
1.83-inches below normal.
#### Wind
Wind speeds averaged below normal most areas. At airport
locations, Cut Bank recorded the highest monthly average of
11.1-mph. The highest average at other locations was 13.6 mph at
Deep Creek RAWS /Glacier County/, which is 1.3-mph higher than
normal for August. The highest wind gust for the month was 79-mph
at the Bozeman airport on the 30th.
The area average speed for August was 8.0-mph, the 23rd windiest
of record and 0.4-mph above normal for the month. This was the
strongest average since 2008.
The areas average wind speed for the water-year is 9.4-mph, the
24th calmest of record, but windiest since 2008. The calendar-
year-to-date average wind speed was 9.4-mph, which is 0.7-mph
above normal. This was the windiest since 2002.
The summer season average wind speed was 7.9-mph, which was 11th
calmest of record. This was the normal wind speed for the season.
###############
During August, the average sky cover at Great Falls was
2.1-octas. The average is 1.8-octas. Air quality PM2.5
concentrations (courtesy of Montana Department of Environmental
Quality) averaged 16.7 micrograms per cubic meter at Great Falls.
This was the 7th highest of a 22-year period of record, and
highest since 2018. The average for August (since 2000) is 6.6
micrograms per cubic meter.
At Great Falls, the July high and low temperatures were 98F and
35F, for a range of 63F. This was 6F above normal. The August
average diurnal range of 29.5F was 3F smaller than normal, and
smallest in August since 2014. The average monthly relative
humidity was 49.9-percent, which was 24th highest of record
(records began 1942).
For the area, severe convection occurred on five days, which is
one day more than normal. The strongest convective gust was 79-mph
at Bozeman airport on the 30th. Hail to 1-inch hail fell over
eastern Great Falls on the 4th.
Smoke continued to affect the visibility during August. Following
is a table showing the number of hours of smoke with visibility
less than 10 miles and less than 6 miles at locations across the
area in August. The second table shows the cumulative number of
hours with visibility of less than 10 miles for the
season...through the end of August.
Hours of visibility Hours of visibility
Location <6mi record <10mi record Records began
Bozeman 101 139...2000 223 235...2000 2000
Cut Bank 161 294...2018 315 450...2018 2000
Dillon 132 226...2000 251 369...2000 1998
Great Falls 72 167...2015 152 213...2015 1995
Havre 51 141...2018 142 256...2018 1995
Helena 101 183...2015 170 330...2017 1995
Lewistown 27 51...2018 74 142...2018 2000
W Yellowstone 15 64...2016 126* 72...2020 2000
Seasonal through August
Hours of visibility
Location <10mi record Began
Bozeman 406* 333...2017 2000
Cut Bank 735* 480...2018 2000
Dillon 513* 441...2017 1998
Great Falls 388* 271...2017 1995
Havre 317* 259...2018 1995
Helena 436 515...2017 1995
Lewistown 80 143...2020 2000
W Yellowstone 141 147...2020 2000
* New record set this year
Rankings are shown below for individual locations if ranked within
the 15th highest or lowest of the respective element.
Average temperature...degrees Fahrenheit...
Aug Nrml Rank Oct-Aug Nrml Rank
Bozeman.......65.3..65.8... 42.8...41.7...14th warmest
Bozeman MSU...65.3..66.4... 44.3...43.6...
Cut Bank......63.4..63.9... 41.7...40.7...
Dillon........63.0..63.4... 41.9...40.7...
Great Falls...66.2..66.7... 44.5...43.0...
Havre.........68.0..68.4... 44.0...42.3...
Helena........68.9..68.8... 46.4...44.3... 7th warmest
Lewistown.....65.0..65.4... 42.8...41.9...
W Yellowstone.56.7..57.5... 33.8...33.8...
Area Avg......64.6..65.0...68th coolest 42.2...41.1...33rd warmest
Average temperature...degrees Fahrenheit...
Jun-Aug Nrml Rank
Bozeman.......68.1..64.0... 3rd warmest warmest was in 2007
Bozeman MSU...68.8..64.5... 2nd warmest warmest was in 1988
Cut Bank......65.5..62.1... 4th warmest warmest was in 1961
Dillon........65.9..61.6... 6th warmest warmest was in 1961
Great Falls...68.3..64.7...13th warmest warmest was in 1936
Havre.........70.3..66.8... 4th warmest warmest was in 1936
Helena........72.0..67.0... 1st warmest prev warmest in 2007
Lewistown.....67.4..63.2... 4th warmest warmest was in 1961
W Yellowstone.58.6..56.1... 9th warmest warmest was in 1936
Area Avg......67.0..63.2... 6th warmest warmest was in 1961
Precipitation...Inches...
Aug Nrml Oct-Aug Nrml
Bozeman.......1.92..0.94...11th wettest 9.68...12.43... 8th driest
Bozeman MSU...1.04..1.25... 13.29...16.87...
Cut Bank......1.67..0.96... 8.93....9.69...
Dillon........0.37..0.87... M....8.92...
Dillon WMU....0.97..0.88... 7.39...10.04...11th driest
Great Falls...2.18..1.23... 12.71...13.43...
Havre.........1.03..1.06... 7.36...10.76...14th driest
Helena........1.98..1.04...15th wettest 9.75...10.44...
Lewistown.....2.19..1.69... 11.13...15.78... 7th driest
W Yellowstone.3.21..1.05... 6th wettest 20.72...20.58...
Area Avg......1.88..1.21...21st wettest 10.66...13.28...15th driest
Precipitation Jun-Aug
Jn-Ag Nrml Rank
Bozeman.......2.84..4.56...10th driest driest since 2012
Bozeman MSU...5.47..5.75...
Cut Bank......2.36..4.98...10th driest driest since 2007
Dillon........ M..3.67...
Dillon WMU....1.54..3.69... 5th driest driest since 1996
Great Falls...2.95..5.17...
Havre.........1.67..4.94... 4th driest driest since 2017
Helena........2.48..4.31...
Lewistown.....4.65..6.80...
W Yellowstone.4.79..4.57...
Area Avg......2.94..4.77...11th driest driest since 2012
Average Wind speed...mph...
Aug Nrml Rank Oct-Aug Nrml Rank
Bozeman.......5.9....6.0... 5.6.... 5.7...15th calmest
Cut Bank.....11.1...10.4... 13.3....13.3...
Dillon....... 8.1... 7.5... 9.4.... 9.1...
Great Falls.. 9.4... 9.0... 11.9....11.5...
Havre........ 9.4... 8.7... 10.5.... 9.9...
Helena....... 6.7....6.3... 6.8.... 6.7...
Lewistown.... 8.0... 7.7... 9.3.... 9.4...
W Yellowstone 5.1... 5.1... M
Area Avg..... 8.0... 7.6...24th calmest 9.4.... 9.0...24th calmest
Average Wind speed...Jun-Aug
Jn-Ag Nrml Rank
Bozeman...... 6.2... 6.0...
Cut Bank.....11.0...11.2...
Dillon....... 7.9... 7.7...
Great Falls...8.9... 9.3...
Havre.........9.4... 9.1...
Helena........6.8... 7.0...
Lewistown.....7.6... 8.0...
W Yellowstone.5.5... 5.8...
Area Avg......7.9... 8.0...11th calmest
Temperature and precipitation records for Bozeman began in
1935, Cut Bank began in 1903, Dillon began in 1939, Great Falls
began in 1891, Havre and Helena began in 1880, Lewistown began in
1896, and West Yellowstone began in 1905. Wind records at Bozeman
and Dillon began in 1948, Cut Bank and Lewistown in 1938, Great
Falls in 1937, Havre in 1889, Helena in 1880 and West Yellowstone in
2010. The normal period for all elements is 1991 to 2020.
These data are preliminary and have not undergone final QC by NCEI.
Therefore these data are subject to revision. Final and certified
climate data can be accessed at the National Centers for
Environmental Information.
$$