...A STATISTICAL PREVIEW OF DENVER'S SEPTEMBER WEATHER...
CLIMATOLOGICALLY, AFTER FAIRLY STABLE TEMPERATURE VARIATION DURING THE WARMEST MONTHS OF JULY AND AUGUST, DAILY TEMPERATURE SPREADS ACROSS THE MONTH OF SEPTEMBER BEGIN TO WIDEN. AS PACIFIC DISTURBANCES BEGIN TO PASS ACROSS THE NORTHERN U.S. ROCKIES IN SEPTEMBER, DRYER AND COOLER AIR FROM THE NORTHERN HIGH PLAINS AND CANADIAN REGION PERIODICALLY PUSH ONTO THE HIGH PLAINS OF EASTERN COLORADO.
DENVER'S MONTHLY MEAN TEMPERATURE FOR SEPTEMBER IS 63.4 DEGREES (1981-2010 AVERAGE) AND IS DENVER'S FOURTH WARMEST MONTH OF THE YEAR BEHIND JULY, AUGUST AND JUNE RESPECTIVELY, THE MONTH STARTS WITH A NORMAL HIGH OF 84 DEGREES AND ENDS WITH A NORMAL HIGH OF 72 DEGREES. FOR LOW TEMPERATURES, THE MONTH BEGINS WITH A NORMAL OF 54 DEGREES AND FINISHES WITH A NORMAL OF 42.
THE WARMEST TEMPERATURE EVER RECORDED FOR THE MONTH OF SEPTEMBER, SINCE RECORDS BEGAN IN 1872, WAS 97 DEGREES AND OCCURRED FOUR TIMES. THE FIRST OCCURRENCE WAS ON THE 5TH DAY OF 1899, THEN FOLLOWED BY THE 4TH DAY OF 1960, THE 4TH OF 1995 AND ON THE 1ST OF 1995. THE COLDEST TEMPERATURE EVER RECORDED IN DENVER FOR AUGUST WAS 17 DEGREES AND OCCURRED ON THE 29TH DAY OF 1985.
SEPTEMBER: DENVER'S TOP 10 WARMEST (MEAN TEMPERATURES):
68.3 DEGREES 1948
68.2 1981
68.2 1931
68.0 1998
67.7 1933
67.6 1947
67.2 2005
67.2 1994
67.0 2010
67.0 1939
SEPTEMBER: DENVER'S TOP 10 COLDEST (MEAN TEMPERATURES):
54.7 DEGREES 1912
55.6 1965
56.3 1961
57.5 1971
58.1 1918
58.8 1985
58.9 2006
58.9 1929
59.2 1999
59.3 2003
AS THE NORTH AMERICAN MONSOON SEASON GRADUALLY WEAKENS THROUGH LATE SUMMER, SEPTEMBER BEGINS TO RECEIVE A PORTION OF IT'S PRECIPITATION FROM QUICK MOVING PACIFIC TROUGHS OF LOW PRESSURE WHICH SWING ACROSS THE STATE AS THE SUMMER RIDGE OF HIGH PRESSURE WEAKENS. PRECIPITATION IN SEPTEMBER CAN STILL ARRIVE IN THE FORM OF HEAVY RAINFALL FROM LATE CONVECTIVE SEASON THUNDERSTORMS.
ALONG WITH JUNE, JULY AND AUGUST THE POSSIBILITY OF SEVERE WEATHER STILL EXISTS FOR THE MONTH OF SEPTEMBER, HOWEVER THE CHANCES GREATLY DIMINISH AFTER THE FIRST HALF OF THE MONTH.
SEPTEMBER: DENVER'S WETTEST
5.61 INCHES 2013
4.67 1961
3.78 1909
3.70 1902
3.42 1938
2.95 2012
2.89 1936
2.89 1918
2.89 1875
2.85 1973
SEPTEMBER: DENVER'S DRIEST
T INCHES 1944
T 1892
0.01 1992
0.01 1956
0.02 1921
0.02 1879
0.05 1893
0.06 2010
0.06 1920
0.06 1882
SEPTEMBER IS THE FIRST MONTH OF THE SNOW SEASON IN DENVER. SNOW IN SEPTEMBER OFTEN ARRIVES AT AN INCONVENIENT TIME AS THE TREES ALONG THE FRONT RANGE OF COLORADO TYPICALLY STILL HOLD LEAVES. THE FIRST SNOWFALL ARRIVAL IS ASSOCIATED WITH THE PASSAGE OF THE SEASONS FIRST STRONG PUSH OF COLD AIR FROM CANADA. IN THE 131 YEAR HISTORY OF DENVER’S RECORD KEEPING FOR SNOWFALL, SNOW HAS OCCURRED 45 TIMES. OF THE 45 OCCURRENCES, 28 YEARS HAD MEASURABLE OF 0.1” OR HIGHER. THE OTHER 17 YEARS RECEIVED A TRACE.
SEPTEMBER: DENVER'S SNOWIEST
17.2 INCHES 1971
16.5 1936
12.9 1959
11.4 1895
8.7 1985
6.5 1908
5.8 1961
5.5 1965
5.4 1993
5.2 1984
SEPTEMBER: DENVER`S LEAST SNOWIEST
Numerous years with
0.0" snowfall (87).
...THE OUTLOOK FOR SEPTEMBER 2015...
AFTER AN AUGUST WITH ABOVE NORMAL TEMPERATURES AND BELOW NORMAL PRECIPITATION, THE SHORT RANGE FORECAST MODELS INDICATE THE GRADUAL DEVELOPMENT OF A TROUGH OF LOW PRESSURE OVER THE WESTERN SECTION OF THE UNITED STATES ALONG WITH A SLIGHT WEAKENING OF THE DOMINANT RIDGE OF HIGH PRESSURE WHICH HAS BEEN PERSISTANT OVER THE SOUTHERN STATES. THIS WILL BRING A BIAS TOWARD SLIGHTLY COOLER TEMPERATURES ALONG WITH A SLIGHTLY BETTER THAN EQUAL CHANCE TOWARD ABOVE NORMAL PRECIPITATION. THE CLIMATE PREDICTION CENTER'S LONG RANGE OUTLOOKS, LOOKING BEYOND EARLY TO MID SEPTEMBER, INDICATE A CONTINUATION OF SLIGHTLY COOLER TEMPERATURES AND THE POSSIBILITY FOR NEAR TO ABOVE NORMAL PRECIPITATION.
...SEPTEMBER STATISTICS...
...TEMPERATURES (1981-2010 NORMALS)...
AVERAGE HIGH........................... 78.5
AVERAGE LOW............................ 48.3
MONTHLY MEAN........................... 63.4
DAYS WITH HIGH 90 OR ABOVE............. 3 (3.4)
DAYS WITH HIGH 32 OR BELOW............. 0 (0.0)
DAYS WITH LOW 32 OR BELOW.............. 1 (0.8)
DAYS WITH LOWS ZERO OR BELOW........... 0 (0.0)
...PRECIPITATION...
MONTHLY MEAN........................... 0.96 INCHES
DAYS WITH MEASURABLE PRECIPITATION..... 7 (6.5)
AVERAGE SNOWFALL....................... 1.3 INCHES
...MISCELLANEOUS SEPTEMBER AVERAGES...
HEATING DEGREE DAYS.................... 125
COOLING DEGREE DAYS.................... 76
WIND SPEED (MPH)....................... 8.0*
WIND DIRECTION......................... SOUTH*
DAYS WITH THUNDERSTORMS................ 8* (7.9)
DAYS WITH DENSE FOG.................... 1* (0.6)
PERCENT OF SUNSHINE.................... 74*
(NOTE: SUNSHINE DATA ARE NO LONGER COLLECTED AS OF OCTOBER 1, 2009)
* = 1971-2002 NORMALS
...SEPTEMBER EXTREMES...
RECORD HIGH............................ 97 DEGREES ON 9/1/1995
9/4/1995
9/4/1960
9/5/1899
RECORD LOW............................. 17 DEGREES ON 9/29/1985
WARMEST JULY........................... 68.3 DEGREES IN 2011
MAXIMUM COOLING DEGREE DAYS............ 143 IN 1999
MINIMUM COOLING DEGREE DAYS............ 20 IN 1986, 2006
COLDEST................................ 54.8 DEGREES IN 1912
MAXIMUM HEATING DEGREE DAYS............ 345 IN 1912
MINIMUM HEATING DEGREE DAYS............ 19 IN 1981
WETTEST................................ 4.67 INCHES IN 1961
DRIEST................................. TRACE IN 1892, 1944
SNOWIEST............................... 17.2 INCHES 1971
LEAST SNOWY............................ 0.0 INCHES NUMEROUS YEARS
(86)
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