A Statistical Preview of Denver's May Weather

        ...A STATISTICAL PREVIEW OF DENVER’S MAY WEATHER...
 
JUST ABOUT ANYTHING CAN HAPPEN IN THE MONTH OF MAY WHEN IT COMES TO DENVER'S WEATHER. ALTHOUGH MAY IS TYPICALLY KNOWN FOR IT'S WETTING RAINS, IT CAN ALSO BRING HEAT INTO THE 90'S, COLD DOWN TO THE 20'S, SEVERAL INCHES OF SNOW, AND CERTAINLY THE BEGINNING OF THE SEVERE WEATHER SEASON. THE WETTEST MONTH IN DENVER HISTORY BROUGHT 8.57 INCHES OF PRECIPITATION IN 1876.
 
MUCH LIKE APRIL, FAST CHANGING WEATHER IS COMMON IN MAY OVER THE DENVER METRO AREA AND EASTERN PLAINS. AS COLD FRONTS OCCASIONALLY CLASH WITH WARM AND MOIST GULF MOISTURE, SEVERE WEATHER TYPICALLY ENSUES AS GOOD DAYTIME HEATING PROVIDES GOOD SURFACE INSTABILITY.
 
DENVER'S MONTHLY MEAN TEMPERATURE FOR MAY IS 57.1 DEGREES (1981-2010 AVERAGES) AND IS DENVER'S 5TH WARMEST MONTH OF THE YEAR BEHIND JULY, AUGUST, JUNE AND SEPTEMBER RESPECTIVELY. MAY STARTS THE MONTH WITH A NORMAL HIGH OF 66 DEGREES AND ENDS WITH A NORMAL HIGH OF 77 DEGREES. FOR LOW TEMPERATURES, THE MONTH BEGINS WITH A NORMAL OF 38 DEGREES AND FINISHES WITH A NORMAL OF 48.
 
THE WARMEST TEMPERATURE EVER RECORDED DURING THE MONTH OF MAY, SINCE RECORDS BEGAN IN 1872, WAS 95 DEGREES ON THE 26TH DAY OF 1942. MAY'S COLDEST TEMPERATURE EVER RECORDED IN DENVER WAS 19 DEGREES AND OCCURRED ON THE 3RD DAY OF 1907.
 
MAY: DENVER'S TOP 5 COLDEST (MEAN TEMPERATURES):
 
48.7 DEGREES 1917
50.0         1995
50.2         1935
50.3         1907
51.4         1983
 
MAY: DENVER'S TOP 5 WARMEST (MEAN TEMPERATURES):
 
64.6 DEGREES 1934
63.2         1994
61.9         1886
61.7         1958
61.6         1879, 1974
 
FOR DENVER'S NINE MONTH SNOW PERIOD OF SEPTEMBER THROUGH MAY, MAY RANKS AS THE LEAST SNOWIEST MONTH AND ONLY ACCOUNTS FOR APPROXIMATELY 2 PERCENT OF THE ANNUAL SNOWFALL OF 53.8 INCHES. DENVER NORMALLY COLLECTS 1.1 INCHES OF SNOW IN MAY BASED ON AVERAGES FROM FORMER STAPLETON INTL AIRPORT (1981-2010 AVERAGES). AT LOWER ELEVATIONS, INCLUDING THE EASTERN PLAINS, FRONT RANGE AND METRO DENVER, MAY STORMS TYPICALLY BRING RAIN. SNOW IN MAY WILL OFTEN OCCUR IN THE OVERNIGHT AND EARLY MORNING PERIODS WHEN THE DAILY TEMPERATURES ARE THE COLDEST.
 
MAY: DENVER'S SNOWIEST
 
15.5 INCHES 1898
13.6        1950
13.5        1978
13.2        1921
12.0        1917
 
THE END OF THE WINTER AND ONSET OF SPRING ALONG THE FRONT RANGE AND HIGH PLAINS OCCASIONALLY EXPERIENCE EXTENDED DROUGHT-LIKE CONDITIONS. THESE DRY PERIODS ARE OFTEN ASSOCIATED WITH LA NINA PHASES OF THE PACIFIC OCEANIC REGION. LIKE MARCH AND APRIL, THE DRIEST MAYS USUALLY START THE MONTH WITH ABOVE NORMAL MONTHLY TEMPERATURES MAINLY DUE TO WINDY, CLOUD FREE, DOWNSLOPE WINDY DAYS COMBINED WITH WARMER NIGHT-TIME LOW TEMPERATURES.
 
MAY: DENVER'S LEAST SNOWY
 
NUMEROUS YEARS WITH NO SNOWFALL (42)
 
MAY CAN ALSO BE CONSIDERED THE FIRST MONTH OF THE SEVERE WEATHER AND THUNDERSTORM SEASON IN THE DENVER AREA. TROUGHS OF LOW PRESSURE OFTEN USHER IN RELATIVELY COLD AIR ALOFT IN NORTHWEST FLOW. THIS CAN CREATE PERIODS OF INSTABILITY IN COMBINATION WITH SURFACE AIRMASS COLLISIONS OF COLD AIR AND WARM MOIST GULF AIR. AS THE YEAR MOVES INTO THE WARM AND CONVECTIVE MONTHS OF SPRING AND SUMMER, MONTHLY PRECIPITATION TOTALS BECOME A MEASURE OF INTEREST. AGAIN, AS NOTED ABOVE, DENVER'S WETTEST MONTH IN HISTORY OCCURRED IN MAY OF 1876 AND BROUGHT 8.57 INCHES OF PRECIPITATION. THIS IS OVER HALF OF THE AVERAGE ANNUAL PRECIPITATION OF 14.92 INCHES.
 
MAY: DENVER'S WETTEST
 
8.57 INCHES 1876 *** WETTEST MONTH IN DENVER HISTORY
7.31        1957
6.12        1969
5.06        1973
4.95        1935
 
MAY: DENVER'S DRIEST
 
0.06 INCHES 1974
0.09        1886
0.15        1899
0.22        1919
0.34        1966, 1977
 
                    ...THE OUTLOOK FOR MAY 2013...
 
AFTER AN APRIL 2013 WHICH EXPERIENCED ABOVE NORMAL PRECIPITATION, WELL ABOVE NORMAL SNOWFALL AND WELL BELOW NORMAL TEMPERATURES, THE SHORT TO MEDIUM RANGE MODEL INDICATE A PERSISTENCE TO THE COLDER AND WETTER THAN NORMAL BIAS. LOOKING BEYOND THE FIRST 10 DAYS, THE CLIMATE PREDICTION CENTER'S LONG RANGE MONTHLY FORECAST INDICATES A BIAS BACK TOWARD PRECIPITATION BEING SLIGHTLY BELOW NORMAL WITH NEAR NORMAL TEMPERATURES EXPECTED FOR MAY 2013.
 
                       ...MAY STATISTICS...
 
...TEMPERATURES (1981-2010 NORMALS)...
 
AVERAGE HIGH........................... 71.5
AVERAGE LOW............................ 42.7
MONTHLY MEAN........................... 57.1
DAYS WITH HIGH 90 OR ABOVE.............   1 (0.8)
DAYS WITH HIGH 32 OR BELOW.............   0 (0.0)
DAYS WITH LOW 32 OR BELOW..............   2 (1.9)
DAYS WITH LOWS ZERO OR BELOW...........   0 (0.0)
 
...PRECIPITATION...
 
MONTHLY MEAN...........................   2.12 INCHES
DAYS WITH MEASURABLE PRECIPITATION.....   9 (9.4)
AVERAGE SNOWFALL........................ 1.1 INCHES (9TH AND LEAST SNOWIEST MONTH)
 
...MISCELLANEOUS MAY AVERAGES...
 
HEATING DEGREE DAYS.................... 265
COOLING DEGREE DAYS....................   21
WIND SPEED (MPH).......................    9.3*
WIND DIRECTION......................... SOUTH*
DAYS WITH THUNDERSTORMS................    6* (6.4)
DAYS WITH DENSE FOG....................    1* (0.5)
PERCENT OF SUNSHINE....................   64*
(NOTE: SUNSHINE DATA ARE NO LONGER COLLECTED AS OF OCTOBER 1, 2009)
 
* = 1971-2002 NORMALS
 
...MAY EXTREMES...
 
RECORD HIGH............................ 95 DEGREES ON 5/26/1942
RECORD LOW............................. 19 DEGREES ON 5/3/1907
WARMEST................................ 64.6 DEGREES IN 1934
MAXIMUM COOLING DEGREE DAYS............ 60 IN 1994
MINIMUM COOLING DEGREE DAYS............   0 1971, 1995
COLDEST................................ 48.7 DEGREES IN 1917
MAXIMUM HEATING DEGREE DAYS............ 506 IN 1917
MINIMUM HEATING DEGREE DAYS............ 102 IN 1934
WETTEST................................   8.57 INCHES IN 1876
DRIEST.................................   0.06 INCHES IN 1974
 
FREDIN


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