Monday, September 15, 2014

Snowtember Recap - the Snow and Cold Weather

Unless you weren't paying attention at all to the weather last week you have heard about the snow in the Rockies and northern Plains as well as the unseasonably cool weather that followed for much of the eastern three-quarters of the country. So how bad was it?

The snow forecasts were pretty much on target, though amounts in a few places (notably mountain areas) were a little higher than expected.  The CoCoRaHS observer at WY-SH-33, Sheridan 15.7 W on the east slopes of the Bighorn range measured a storm total of 19.0 inches of snow. Snow fell along the Front Range in Colorado as far south as Denver, with a half inch of accumulation in Boulder northwest of Denver. The accumulating snow reached as far east as Rapid City, SD with 3.5 inches, the earliest measurable snow on record. The old record for Rapid City was 2.8 inches on September 15, 1903. Six to 8 inches of snow fell in the Black Hills during this storm. North Platte, NE picked up a trace of snow, the earliest on record there.

72-hour snowfall accumulation for the period ending 7:00 a.m. local on September 12

From the National Weather Service:


CASTLE ROCK 5.2 SW                    1.0                   
HORSETOOTH MOUNTAIN 3.2 NNW           1.0                   
NEDERLAND 4.8 ENE                     0.9                   
ASPEN PARK 5.2 ESE                    0.7                   
BOULDER 1.6 S                         0.5                   

HEART BUTTE                           8.0                   
MELVILLE 4.7 W                        7.5                   
RED LODGE 4.2 W                       6.0                   
WYOLA 17.3 WSW                        6.0                   
ZORTMAN                               6.0                   
LIVINGSTON 6.6 ESE                    3.5                   


DOWNTOWN CUSTER                       8.0                   
MOUNT RUSHMORE                        7.0                   
HILL CITY 5 S                         6.0                   
LEAD 5.5 SSW                          6.0                   
RAPID CITY 6.9 W                      3.5 -- EARLIEST ON RECORD

LITTLE GOOSE                         18.0                   
SHELL CREEK                          14.0                   
STORY 0.8 W                          14.0                   
SHERIDAN 15.7 S                      13.0                   
BIG HORN                             12.0                   
BURGESS JUNCTION 4 NW                12.0                   
SOLDIER PARK                         11.0                   
BUFFALO 1 E                          10.0                   
BANNER                                7.0                   
CODY 5 ESE                            7.0                   
SUNDANCE 1 ENE                        6.0                   
DOUGLAS 6 S                           3.0  

Obviously that snow would not have been possible without some pretty cold air for this time of year. The cold air spilled south behind this storm system. On Friday, September 12 Cloud Peak, WY in the Bighorn Mountains recorded the nation's lowest temperature of 4°F.  By Saturday morning, September 13 the cold air had pushed as far south as central Texas and New Mexico.

Minimum temperatures for the period from 7:00 p.m. CDT September 12 to 7:00 a.m. September 13

Temperatures for September 12-14 were as much as 20°F below normal in the Central Plains, with much of the middle third of the country from 10°F to 15°F below normal.

In the northern tier of states the first freeze of the season was recorded from Wyoming east into northern Kansas and northwestern Wisconsin and northern lower Michigan.

Map of locations recording first 32°F freeze

Fortunately, a hard freeze (28°F) was limited to Wyoming, Colorado. the far western Dakotas, western Nebraska, and scattered areas in northern Minnesota.

Map of locations recording first 28°F freeze

For most areas the first occurrence of 32°F was about two to four weeks early.

Median date of first occurrence of 32°F in the fall.

The weather will gradually warm this week and it looks like we'll enjoy some "normal" September weather for the next week to ten days

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