National Weather

NATIONAL WEATHER SUMMARY

DECEMBER 2011

11^th-17^th…The main weather feature for Tuesday was the storm system off Southern California that brought cold and wet weather across the southwestern U.S. Rain and mountain snow continued over Southern California and the Four Corners. Some heavy snow fell over the Four Corners mainly areas above 6000 feet. Snow accumulations were expected 4 to 12 inches, with locally greater amounts on south facing slopes. Precipitation coverage extended eastward into the Great Plains, from central Texas northward to South Dakota, southern Iowa and southern Illinois in the afternoon. Most places saw rain as temperatures warmed up, but Kansas and South Dakota saw snow showers instead. In the Pacific Northwest, a cold front passed southern British Columbia and become nearly stationary. As a result, clouds covered much of the region Tuesday, with light rain over southern Vancouver Island only. Moving to the East, a large ridge of high pressure dominated across the region Tuesday. Mostly clear skies prevailed with temperatures running into 40s and 50s in the afternoon. The Southeast saw temperature rising into the 60s and 70s.

1th-24^th…Snow developed in parts of New Mexico and western Texas on Friday, while another system brought light snow to the Northeast and Great Lakes. A low pressure system that produced heavy snow to Colorado and New Mexico the past few days started to advance eastward into the Southern Plains. Extremely cold air associated with this system allowed for snow showers to persist as it moved off the Southern Rockies and into northern Texas. Snowfall totals have ranged from 4 to 6 inches in southwestern New Mexico and 1 to 3 inches in northwestern Texas. High temperatures behind this system ranged in the 20s and 30s for the Northern and Central Rockies. Further west, a trough of low pressure dipped into the Pacific Northwest from British Columbia. This produced light and scattered rain showers with snow in the Cascades. A few clouds spread southward into northern California, but precipitation has not developed. Meanwhile in the Northeast, a cold front dropped in from eastern Canada and stretched from the Northeast, over the Great Lakes, and into the Upper Midwest. Due to prevailing cold temperatures, this triggered areas of light and scattered snow showers. Most areas saw less than an inch of snow.

25^th-31^st…The biggest weather producer in the country on Monday was a developing storm that produced widespread rain and some thunderstorms in the Lower Mississippi Valley. High pressure system over the East kept dry conditions dominant. Cold air plunged into the Northern Plains from a dry storm in Canada, while the Pacific Northwest remained dry ahead of what is shaping up to be a wet week. California continued its dry and cold streak with agricultural areas of the Central Valley experiencing sub-freezing morning temperatures once again. The Northeast rose into the 30s and 40s, while the Southeast saw temperatures in the 50s, 60s, and some 70s. The Northwest rose into the 30s and 40s, while the Southwest saw temperatures in the 50s and 60s, except for higher elevations that only rose into the 30s.

Unsettled weather conditions continued in the Northwest on Wednesday as the strong Pacific jet stream directed disturbances from the Pacific across the Northwest. A vigorous Pacific cold front reached the Pacific Northwest coast and brought rain showers, periods of heavy rainfall, and strong wind to the region through the afternoon. A High Wind Warning remained in effect for the Oregon coast as south winds of 30 to 50 mph were expected along the beaches and headlands with gusts to 70 mph. High Wind Advisories were also in effect for locations in the lee of the Cascades in anticipation of locally strong winds. To the east of this activity, areas of rain, high elevation snow, and strong winds spread across Idaho, Montana, northwestern Wyoming. Winter Weather Advisories, Winter Storm Warnings, and a variety of Wind Advisories remained in effect for parts of these states through the afternoon. In the East, the deep low pressure system affecting the Northeast moved near the mouth of the Saint Lawrence River this afternoon. A cold front associated with this system extended southward through the Northeast and southwestward through the Mid-Atlantic. A few light snow showers and rain showers continued to form ahead of this front in parts of Vermont, New Hampshire, and Maine. The front also brought in much colder air on gusty west and northwest winds as it crossed these regions. Cold winds sweeping across the warmer Great Lake waters lead to moderate to heavy lake effect snow showers downwind of the Lake Ontario in New York and Pennsylvania. Strong winds and snowfall in these areas created periods of reduced visibilities, blowing and drifting snow, and hazardous driving conditions for travelers. Meanwhile, light snow formed in the Upper Midwest as a clipper system advances toward the region.