Frost on the Roses

Temperatures at 6:00 a.m. PST January 1

Those arriving early this morning in Pasadena, CA to find good viewing spots for the Rose Bowl parade contended with record cold. The temperature bottomed out at 32°F in Pasadena, and the low at the Los Angeles International Airport dropped to 36°F, a new record. The old record was 38°F set in 1972. A winter chill was common throughout southern California and the southwestern U.S. this first day of 2015. Temperatures were in the single digits in the Ventura Mountains and in much of the mid 20s in many of the interior valleys. The cold also was common across most of the Desert Southwest. Tucson, AZ reached a maximum temperature today of only 41°F, a new record low maximum temperature. The previous record was 43°F in 1960.

The same system that ushered in the cold weather also dropped snow on most of Arizona, with up to 20 inches reported in the mountains in northern Arizona, with 20 inches at Mountainaire and 17.3 inches reported at Flagstaff. 

24 hour snowfall ending at 7:00 a.m. local time January 1, 2015

 The CoCoRaHS observer at Pine 0.9 SW in Gila County reported 14.5 inches of new snow, with six other Arizona observers reporting 10 inches or more of snow.

CoCoRaHS snowfall for the 24-hour period ending at 7:00 a.m. PST

The strong upper level wave that brought a chilly start to 2015 became closed off over southern California on December 31 and moved into Arizona last night. It tapped into the cold air being fed into the Rockies and Plains both at the surface and aloft resulting in the uncharacteristic winter weather for the southwestern U.S.

500 millibar map for 4:00 p.m. PST on December 31, 2014.

Cold weather will continue across southern California and southwest Arizona again tonight and Monday morning. Hard freeze and freeze warnings are in place for large portions of these areas. Winter weather advisories and winter storm warnings are in effect for eastern New Mexico and northwestern Texas as precipitation spreads into the cold air with freezing rain, sleet, and snow expected.

Watches, warnings, and advisories in effect as of 8:39 p.m. PST January 1.

The upper low will continue to move slowly east across Arizona and New Mexico the next 48 hours. Precipitation will spread from the Southwest through Texas and eventually into the Midwest and the eastern U.S. over the weekend. Precipitation will be more than a half inch in much of the eastern U.S. By Monday snow is likely across the upper Midwest and the Northeast.

Quantitative Precipitation Forecast for the 72-hour period ending 6:00 p.m. CST Sunday, January 4

24-hour, 2 inch snow probability for period ending 6:00 p.m. CST January 4.