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361
NOUS45 KTFX 161551
PNSTFX
MTZ008>015-044>055-170318-
Public Information Statement
National Weather Service Great Falls MT
918 AM MDT Fri Oct 16 2020
PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1000 AM PM MDT FRI Oct 16 2020
...September 2020 and Seasonal Weather Summary for north central
and southwest Montana...
During September, the average upper level flow was generally from the
northwest with a ridge over the west coast. Normal flow is from the
west. Temperatures averaged above normal, with precipitation mostly
below normal. Wind averages were near to above normal.
The first six days of September had generally above normal
temperatures. Highs of 100F were recorded on the 5th at Loma and
Bozeman. The last year in which a 100F value was recorded in
September in the area was in 2001, when Fort Benton reported the
latest ever 100F in Montana on the 25th.
A somewhat cooler period persisted for the next week, lows dropping
into the 20s most aras, and Yellow Mule reported the areas lowest
on the 8th (14F). Some snow was reported at higher elevations.
Warmer conditions returned, with most of the rest of the month
recording above normal temperatures and little precipitation.
Many areas recorded their first seasonal freezing temperature on
September 8. At Great Falls, this was the 6th earliest of record and
earliest since the late August snows and cold of 1992. The freeze-
free season was 107 days at Great Falls, the 9th shortest of record
and shortest since 2009. Their average length is 122 days. At
Dillon, the low of 25F on the 8th was their 2nd earliest with a
temperature of 25F or lower so early in the season. At Great Falls,
their low of 28F was the 2nd earliest low of 28F or lower so early
in the season. The earliest was Sept 6, 1929.
There were several windy periods. Some of the notable wind
conditions are summarized later in this report.
For the area, the composite monthly temperature averaged 57.1F,
which was 2.4F above normal, which was the 29th warmest of record
and warmest since 2013. The coolest average was 48.4F at Yellow Mule
RAWS while the warmest was 61.7F at Little Bullwhacker Creek
(Blaine). Area monthly extremes were 100F at Bozeman and Loma on
the 5th and 14F at Yellow Mule RAWS on the 8th.
For the growing season period (April - September), temperatures
averaged cooler than normal. The average temperature of 55.7F was
0.4F below normal and the 50th coolest of record.
For the water year to-date (Oct-Sep), the areas average temperature
was 42.1F, 0.3F below normal. This is the 65th coolest of record.
#############
For precipitation, below normal values were observed over all but
portions of Hill County. The highest amount reported was 3.20-
inches at Rocky Boy SNOTEL. As in the past three months, dry areas
were very dry. Bozeman and Helena had their driest September since
2012. For the period from July through September, this was
the 6th driest at Cut Bank (0.99). Dillon received only 0.92,
which was their third driest. At Great Falls, the Jul-Sep period
produced 1.19-inches of rain. This was the driest since 1979.
Normal is 4.49-inches. Helena had their driest past three months of
record, picking up only 0.58. This was their driest such period
since 1919. Normal is 3.49. The area composite of 0.62-inches was
the 26th driest, driest September since 2011 and was 0.47 below
normal.
For the growing season period (Apr-Sep), above normal precipitation
fell over much of Chouteau County. Other areas had below normal
precipitation. At Dillon, they received 3.74-inches of rain, which
was their driest of record. Their previous driest such period was
4.03-inches in 1974. The areas composite of 7.42-inches is 2.68
below normal...the 14th driest of record. This is the driest such
period since 2012.
For the water year (Oct-Aug), the area composite of 11.94-inches is
2.31 below normal and the driest since 2003. Bozeman has had their
driest water-year since 2012, and Dillon has had their driest of
record. With only 5.49-inches for the period, this was 5.01-inches
below normal. The previously driest water year was in 1979 when
5.73-inches of precipitation fell. They have seen their driest
calendar year-to-date of record, recording only 4.27-inches. The
previous record low was 4.78-inches in 1942. Average is 9.16-inches.
For the area composite, this is the driest water year since 2001.
###############
Wind speed averages were generally near to slightly above normal
across the region. The strongest area average wind speed was 15.6-
mph at Deep Creek RAWS, while Cut Bank had the highest average at an
airport (12.1-mph). The highest gust was 70-mph near Browning on
the 24th and Deep Creek on the 25th.
There were some very windy days during September. On the 2nd,
Bozeman had a daily wind average of 13.9-mph, which was their
windiest September day since 1999. Cut Bank averaged 30.1-mph on the
24th, which was their windiest September day since 1984. A peak
gust of 69-mph on the 24th was Cut Banks third highest September
gust of record and highest since 1960. Dillon's daily wind average
of 21.7-mph on the 7th was their windiest September day since 1954
and second highest daily September average of record.
The area monthly average wind speed was 8.6-mph, the 11th windiest
September of record, and windiest since 2005.
For the growing season period (Apr-Sep) and for much of the water
year, winds have been persistently strong. The area wind average for
the growing season of 8.8-mph was near normal, but the strongest
average since 2005.
The average wind speed for the water-year (Oct-Sep) was 9.3-
mph, the 27th calmest of record, but windiest since 2002. Cut Bank
had their windiest water-year since 1990, while Havre had their
windiest since 2002.
###############
During September, the average sky cover at Great Falls was 1.6-
tenths. The average is 2.5-tenths. This was the lowest sky cover in
September since 2012. Air quality PM2.5 concentrations (courtesy of
Montana Department of Environmental Quality) averaged 12.7
micrograms per cubic meter at Great Falls. This was above an
average of 7.7 micrograms per cubic meter over a 21-year period of
record, ranking 2nd highest of this period. Concentrations on the
5th and 15th-19th set new daily record highs. Visibilities dropped
to the 3-4 mile ranges at times during these periods. The continued
abudance of clear skies and lack of moisture produced the largest
average diurnal temperature range at Great Falls since 2012. The
mean diurnal temperature range of 32.7F ranks as the 13th largest.
The largest was 35.8F (1923) and the average for September is 27.5F.
Severe convection occurred on zero days, which is one less than
normal for September. Hail to one-half inch was the largest for the
month. This was reported at Grant on the 19th.
In some areas, there has been an extended period over which much
below normal precipitation has fallen. Southwest Montana is
particularly dry. The table below shows the threshold
precipitation accumulation over the period of days of the
accumulation, along with the record length.
Threshold precipitation totals...no more than the given amount
accumulated over the number of days...(through October 8)
Amount Location Days Record length
0.75 Helena 101 days...longest since 2004 165 days 1930-31
4.00 Dillon 215 days...longest since 2014 325 days 2003-04
5.00 Dillon 249 days...longest since 2012 362 days 1965-66
6.00 Dillon 313 days...longest since 2011 408 days 1965-67
Ranking given if within the top 15.
Average temperature...degrees Fahrenheit...
Sep Nrml Rank Oct-Sep Nrml Rank
Bozeman......57.2..57.2... 43.1....42.8...32nd warmest
Bozeman MSU..58.6..56.9... 44.2....44.8...
Cut Bank.....56.5..53.9... 41.3....42.0...51st warmest
Dillon.......56.8..54.9... 41.8....42.7...22nd warmest
Great Falls..58.9..56.1 .. 44.4....44.5...
Havre........58.6..56.5... 43.3....43.4...
Helena.......61.3..68.3...13th warmest 46.6....45.3...12th warmest
Lewistown....57.8..54.9... 42.7....43.0...
W Yellowston.49.7..48.0... 34.4....34.3...
CWA/Area.....57.1..54.7...29th warmest 37.9....38.8...52nd coolest
Precipitation...Inches...
Sep Nrml Rank Oct-Sep Nrml Rank
Bozeman.......0.44..1.08...14th driest 10.22...13.93... 6th driest
Bozeman MSU...0.63..1.40... 15.39...19.71...
Cut Bank......0.65..1.22... 9.45...10.85...27th driest
Dillon........0.40..0.84... 5.49...10.05... 1st driest
Great Falls...0.49..1.42... 14.06...14.75...
Havre.........1.62..1.12... 9.95...11.20...
Helena........0.25..1.10... 9.12...11.22...
Lewistown.....0.63..1.35... 14.81...16.85...
W Yellowstone.0.47..1.09... 18.99...21.32...
CWA/Area......0.41..1.15...14th driest 10.91...12.01...42nd driest
Average wind speed...MPH...
Sep Nrml Rank Oct-Sep Nrml Rank
Bozeman.......5.8....5.6... 5.8.... 5.6...
Cut Bank.....12.1...10.9... 13.7....12.6...17th windiest
Dillon....... 8.6... 8.1... 9.6.... 9.0...
Great Falls..10.8...10.6... 11.9....12.1...
Havre........ 9.7... 8.3... 10.6.... 9.1... 8th windiest
Helena....... 6.5....6.6... 7.0.... 7.0...
Lewistown.... 8.8... 8.3... 9.4.... 9.2...
W Yellowstone 6.1... 5.3 6.2.... 5.9
CWA/Area..... 7.5... 7.6...11th calmest 9.4.... 8.9...25th calmest
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...and Lewistown began in 1896. West Yellowstone records began
in 1905...winds began in 2010. Bozeman MSUs records began in 1868
for precipitation and 1892 for temperature and snowfall. The normal
period for all elements is 1981 to 2010.
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 at www.ncei.noaa.gov
315
NOUS45 KTFX 161555
PNSTFX
MTZ008>015-044>055-170318-
Public Information Statement
National Weather Service Great Falls MT
918 AM MDT Fri Oct 16 2020
PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1000 AM PM MDT FRI Oct 16 2020
...September 2020 and Seasonal Weather Summary for north central
and southwest Montana...
During September, the average upper level flow was generally from the
northwest with a ridge over the west coast. Normal flow is from the
west. Temperatures averaged above normal, with precipitation mostly
below normal. Wind averages were near to above normal.
The first six days of September had generally above normal
temperatures. Highs of 100F were recorded on the 5th at Loma and
Bozeman. The last year in which a 100F value was recorded in
September in the area was in 2001, when Fort Benton reported the
latest ever 100F in Montana on the 25th.
A somewhat cooler period persisted for the next week, lows dropping
into the 20s most aras, and Yellow Mule reported the areas lowest
on the 8th (14F). Some snow was reported at higher elevations.
Warmer conditions returned, with most of the rest of the month
recording above normal temperatures and little precipitation.
Many areas recorded their first seasonal freezing temperature on
September 8. At Great Falls, this was the 6th earliest of record and
earliest since the late August snows and cold of 1992. The freeze-
free season was 107 days at Great Falls, the 9th shortest of record
and shortest since 2009. Their average length is 122 days. At
Dillon, the low of 25F on the 8th was their 2nd earliest with a
temperature of 25F or lower so early in the season. At Great Falls,
their low of 28F was the 2nd earliest low of 28F or lower so early
in the season. The earliest was Sept 6, 1929.
There were several windy periods. Some of the notable wind
conditions are summarized later in this report.
For the area, the composite monthly temperature averaged 57.1F,
which was 2.4F above normal, which was the 29th warmest of record
and warmest since 2013. The coolest average was 48.4F at Yellow Mule
RAWS while the warmest was 61.7F at Little Bullwhacker Creek
(Blaine). Area monthly extremes were 100F at Bozeman and Loma on
the 5th and 14F at Yellow Mule RAWS on the 8th.
For the growing season period (April - September), temperatures
averaged cooler than normal. The average temperature of 55.7F was
0.4F below normal and the 50th coolest of record.
For the water year to-date (Oct-Sep), the areas average temperature
was 42.1F, 0.3F below normal. This is the 65th coolest of record.
#############
For precipitation, below normal values were observed over all but
portions of Hill County. The highest amount reported was 3.20-
inches at Rocky Boy SNOTEL. As in the past three months, dry areas
were very dry. Bozeman and Helena had their driest September since
2012. For the period from July through September, this was
the 6th driest at Cut Bank (0.99). Dillon received only 0.92,
which was their third driest. At Great Falls, the Jul-Sep period
produced 1.19-inches of rain. This was the driest since 1979.
Normal is 4.49-inches. Helena had their driest past three months of
record, picking up only 0.58. This was their driest such period
since 1919. Normal is 3.49. The area composite of 0.62-inches was
the 26th driest, driest September since 2011 and was 0.47 below
normal.
For the growing season period (Apr-Sep), above normal precipitation
fell over much of Chouteau County. Other areas had below normal
precipitation. At Dillon, they received 3.74-inches of rain, which
was their driest of record. Their previous driest such period was
4.03-inches in 1974. The areas composite of 7.42-inches is 2.68
below normal...the 14th driest of record. This is the driest such
period since 2012.
For the water year (Oct-Aug), the area composite of 11.94-inches is
2.31 below normal and the driest since 2003. Bozeman has had their
driest water-year since 2012, and Dillon has had their driest of
record. With only 5.49-inches for the period, this was 5.01-inches
below normal. The previously driest water year was in 1979 when
5.73-inches of precipitation fell. They have seen their driest
calendar year-to-date of record, recording only 4.27-inches. The
previous record low was 4.78-inches in 1942. Average is 9.16-inches.
For the area composite, this is the driest water year since 2001.
###############
Wind speed averages were generally near to slightly above normal
across the region. The strongest area average wind speed was 15.6-
mph at Deep Creek RAWS, while Cut Bank had the highest average at an
airport (12.1-mph). The highest gust was 70-mph near Browning on
the 24th and Deep Creek on the 25th.
There were some very windy days during September. On the 2nd,
Bozeman had a daily wind average of 13.9-mph, which was their
windiest September day since 1999. Cut Bank averaged 30.1-mph on the
24th, which was their windiest September day since 1984. A peak
gust of 69-mph on the 24th was Cut Banks third highest September
gust of record and highest since 1960. Dillon's daily wind average
of 21.7-mph on the 7th was their windiest September day since 1954
and second highest daily September average of record.
The area monthly average wind speed was 8.6-mph, the 11th windiest
September of record, and windiest since 2005.
For the growing season period (Apr-Sep) and for much of the water
year, winds have been persistently strong. The area wind average for
the growing season of 8.8-mph was near normal, but the strongest
average since 2005.
The average wind speed for the water-year (Oct-Sep) was 9.3-
mph, the 27th calmest of record, but windiest since 2002. Cut Bank
had their windiest water-year since 1990, while Havre had their
windiest since 2002.
###############
During September, the average sky cover at Great Falls was 1.6-
tenths. The average is 2.5-tenths. This was the lowest sky cover in
September since 2012. Air quality PM2.5 concentrations (courtesy of
Montana Department of Environmental Quality) averaged 12.7
micrograms per cubic meter at Great Falls. This was above an
average of 7.7 micrograms per cubic meter over a 21-year period of
record, ranking 2nd highest of this period. Concentrations on the
5th and 15th-19th set new daily record highs. Visibilities dropped
to the 3-4 mile ranges at times during these periods. The continued
abundance of clear skies and lack of moisture produced the largest
average diurnal temperature range at Great Falls since 2012. The
mean diurnal temperature range of 32.7F ranks as the 13th largest.
The largest was 35.8F (1923) and the average for September is 27.5F.
Severe convection occurred on zero days, which is one less than
normal for September. Hail to one-half inch was the largest for the
month. This was reported at Grant on the 19th.
In some areas, there has been an extended period over which much
below normal precipitation has fallen. Southwest Montana is
particularly dry. The table below shows the threshold
precipitation accumulation over the period of days of the
accumulation, along with the record length.
Threshold precipitation totals...no more than the given amount
accumulated over the number of days...(through October 8)
Amount Location Days Record length
0.75 Helena 101 days...longest since 2004 165 days 1930-31
4.00 Dillon 215 days...longest since 2014 325 days 2003-04
5.00 Dillon 249 days...longest since 2012 362 days 1965-66
6.00 Dillon 313 days...longest since 2011 408 days 1965-67
Ranking given if within the top 15.
Average temperature...degrees Fahrenheit...
Sep Nrml Rank Oct-Sep Nrml Rank
Bozeman......57.2..57.2... 43.1....42.8...32nd warmest
Bozeman MSU..58.6..56.9... 44.2....44.8...
Cut Bank.....56.5..53.9... 41.3....42.0...51st warmest
Dillon.......56.8..54.9... 41.8....42.7...22nd warmest
Great Falls..58.9..56.1 .. 44.4....44.5...
Havre........58.6..56.5... 43.3....43.4...
Helena.......61.3..68.3...13th warmest 46.6....45.3...12th warmest
Lewistown....57.8..54.9... 42.7....43.0...
W Yellowston.49.7..48.0... 34.4....34.3...
CWA/Area.....57.1..54.7...29th warmest 37.9....38.8...52nd coolest
Precipitation...Inches...
Sep Nrml Rank Oct-Sep Nrml Rank
Bozeman.......0.44..1.08...14th driest 10.22...13.93... 6th driest
Bozeman MSU...0.63..1.40... 15.39...19.71...
Cut Bank......0.65..1.22... 9.45...10.85...27th driest
Dillon........0.40..0.84... 5.49...10.05... 1st driest
Great Falls...0.49..1.42... 14.06...14.75...
Havre.........1.62..1.12... 9.95...11.20...
Helena........0.25..1.10... 9.12...11.22...
Lewistown.....0.63..1.35... 14.81...16.85...
W Yellowstone.0.47..1.09... 18.99...21.32...
CWA/Area......0.41..1.15...14th driest 10.91...12.01...42nd driest
Average wind speed...MPH...
Sep Nrml Rank Oct-Sep Nrml Rank
Bozeman.......5.8....5.6... 5.8.... 5.6...
Cut Bank.....12.1...10.9... 13.7....12.6...17th windiest
Dillon....... 8.6... 8.1... 9.6.... 9.0...
Great Falls..10.8...10.6... 11.9....12.1...
Havre........ 9.7... 8.3... 10.6.... 9.1... 8th windiest
Helena....... 6.5....6.6... 7.0.... 7.0...
Lewistown.... 8.8... 8.3... 9.4.... 9.2...
W Yellowstone 6.1... 5.3 6.2.... 5.9
CWA/Area..... 7.5... 7.6...11th calmest 9.4.... 8.9...25th calmest
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...and Lewistown began in 1896. West Yellowstone records began
in 1905...winds began in 2010. Bozeman MSUs records began in 1868
for precipitation and 1892 for temperature and snowfall. The normal
period for all elements is 1981 to 2010.
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 at www.ncei.noaa.gov