Severe weather is currently breaking out across a large area of the Southeast today ahead of a low pressure area pulling eastward out of the Southern Plains where numerous severe thunderstorm warnings and a couple tornado warnings have been in effect. The large area of of rain and thunderstorm ahead of the cold front and draped across northern Florida and southern Georgia will help to reduce the amount of solar heating and instability across this region. However, a moderate risk for severe thunderstorm, some of which can produce tornadoes, remains in place across much of northern Mississippi and Alabama and Tennessee for later this afternoon and into tonight where forcing and instability will remain the greatest as the low pressure center moves eastward. The severity of these storms later this afternoon and tonight is highly dependent upon the level to which the atmosphere can destabilize following this morning’s large convective complex currently moving into Alabama.

Meanwhile, yet another late season blizzard is on the heels of the system across the east, which will bring heavy snows across Colorado, eastern Wyoming and the Great Plains. An upper-level trough of low pressure will remain across the Pacific Northwest today bringing a continued chance for below average temperatures and persistent rains and mountain snows from Seattle to Portland. The central Cascades will likely see another 1-2 feet of snow on top of what has already fallen over the past week. However, the region begins to dry out and warm up to normal by the weekend.

Destructive Winter Storm

The weekend will start out fairly quiet Saturday morning across the majority of the country as the Northeastern storm departs. However, things will quickly become active as the next storm system can already be seen developing across the middle part of the country where snows are falling across the northern Plains and western parts of the Great Lakes region. Additionally, light rain and mist is occurring across the Tennessee Valley along and just north of a warm front draped across the region. Very warm temperatures are expected again south of this warm front across the Deep South.

Additionally, a major and potentially destructive winter storm is starting to make its effects felt across the Pacific Northwest this morning where light snow was falling across the Portland, OR metro area. Temperatures are also bitterly cold across western Washington where lows dipped into the middle teens as far south as the Seattle metro area, with single digits farther north just east of Everett and Bellingham. The region will become very active this afternoon as the strong Pacific storm system slowly moves eastward. Overrunning precipitation ahead of the system will be in the form of snow, and very heavy snow in some locales such as the Hood Canal, the northwest Washington coast and eastern slopes of the Cascades where very high easterly up-sloping winds increase snowfall. Blizzard warnings are currently in effect for most of these areas. The Seattle metro area can expect anywhere from 3-8″ of new snowfall with the storm. Due to the extremely high pressure differences between the arctic high pressure across southern Alberta and the deep Pacific storm system,  very strong winds in excess of 70mph are likely through the Casacade passes east of Seattle, especially Snoqualmie pass. Farther south into parts of northwest Oregon, snow will likely change to sleet and/or freezing rain later Saturday evening and night as warmer southwest winds scour out some of the arctic air currently entrenched across the region. With the potential of very heavy snow, significant ice accumulation and extremely high winds, the storm has the potential to cause widespread damage and power outages across part of the region, especially western Washington and the Cascades. Winter storm warnings and blizzard warnings are currently in effect through Sunday morning.

Weekend Outlook

Just as the Pacific Northwest weather calms down a little by late morning Sunday, the next storm will be rapidly intensifying across the Great Lakes and Northeastern regions, where heavy snows are also possible in many of the same areas that were pummeled by Friday’s storm. The major cities, especially New York City and Boston, will receive several inches of additional snowfall, with lesser amounts farther south as the snow eventually changes over to rain especially near Philadelphia and along the New Jersey coast. Windy conditions will also accompany the storm system, especially behind the front where gusts above 40mph are likely.

A lot of wild weather can be expected across much of the Western and Central US as a the longwave pattern finally reverses and a deep trough digs across the West, locking the region into a deep freeze through at least the next week.

The Northeast storm is departing into the maritimes of Canada and the snow is winding down. Lighter snow showers will be left in its wake near the usual lake-effect prone areas around the Great Lakes. Much quieter weather can be expected throughout Friday as the storm quickly pulls out of the region. However, many reports of power outages and downed trees across the Northeast continue due to the ice accumulations from yesterday through this morning.

Taste of Winter

As the Northeast storm departs, the next system is explosively developing just west of Vancouver Island this morning and will move inland along the western Washington coast later this morning while continuing to rapidly intensify. This is the storm that will spark the dramatic weather changes for much of the west as it pulls in arctic air from north-central Canada down into the region. The Cascades from Washington south into northern California will receive very heavy snows with blizzard conditions possible across parts of the central Cascades as the system causes very windy conditions to develop. Gusts will easily approach hurricane force in the Cascades. Blizzard warnings have been issued for parts of the Washington and Oregon Cascades today along with high wind watches along the coast. As for the Seattle and Portland metro areas, precipitation will primarily be rain until the storm center passes to the east and winds turn more from the north, pulling in much colder air behind it. Snow elevations in the Washington Cascades will start at about 7000ft this morning and quickly drop to around 300-500ft by this evening, possibly lowering to even sea level later tonight. Modified arctic air will begin spilling into the region through the Fraser and Willamette Valleys from the northeast on Saturday, bringing very cold air into Seattle and Portland metro areas. Snow showers can be expected as the arctic boundary moves southward and another disturbance passes the region along the coast on Sunday.

Weekend Outlook

As the Pacific Northwest storm system moves eastward, it will bring heavy snows and bitter cold to a large portion of the West where numerous winter storm warnings and watches have been issued. On Sunday the system will once again begin intensifying across the Northern Plains bringing heavy snow and very high winds to eastern parts of Montana and Wyoming, North and South Dakota, and western parts of Minnesota. Blizzard watches have been issued for this region and will likely be upgraded to warnings later today. Much of the central US will be affected by this system on Sunday with a mix of rain, ice and/or snow expected along and just behind the front across the Midwest and Central Plains, and a chilly rain out ahead of the front.

Pattern Reversal

This weekend’s storm system across the West initiates a major pattern change across North America that will force the ridge that has been over the West for the past few weeks to retrograde West and strengthen northward into Alaska, which in turn will force a very deep trough to dig across the West, causing arctic air from north-central Canada to spill south and westward. The pattern will hold through much of the week with many areas, including the Pacific Northwest, to struggle to get above freezing for high temperatures. A reinforcing shot of arctic air is also expected by midweek to further the cold spell.

Weekend Outlook

A clipper system will dive south out of Canada and then shift east across the Midwest and Great Lakes region, bringing scattered light snow showers beginning Friday afternoon across western areas and gradually moving east into the Northeast by Sunday. Snow amounts will remain light, generally 1-3 inches, with heavier amounts across northern and western Michigan due to lake-enhanced snowfall. Meanwhile, a low pressure system will rapidly strengthen just off the Mid-Atlanta coast by Saturday and then move towards the north and into the Canadian Maritimes by late in the day Sunday. The bulk of the weather will remain just off the coast, however some wrap-around moisture may override the colder air in place and bring some light accumulation of snows to parts of New England. Eastern Maine will likely see heavier amounts as the system approaches late on Sunday. New York City and Boston may see some snow as well, although accumulations, if any, will remain generally 1-2 inches.

Much of the West will continue to remain quiet except for the Pacific Northwest where a frontal system will dive southeastward towards the coast of British Columbia and Washington. Light to moderate rain showers will accompany the front across much of western Washington and northwestern Oregon, while snow showers are likely east of the Cascades in the colder airmass.

Arctic Intrusion

Looking ahead to the coming week, the big story will be the bitterly cold air surging south out of central Canada aimed for the Northern Plains and Great Lakes regions. High temperatures only in the teens and single digits will accompany this arctic airmass for a large area beginning on Tuesday and lasting through the end of the week. While the center of the coldest air will remain just north of the Canadian border, where highs won’t get above zero, many locations across the Northern Plains will struggle to reach the teens for highs after early morning lows hovering just below zero degrees.

Finally, models are beginning to agree that a major longwave pattern change is underway beginning next weekend, which will likely bring an end to the very cold air across much of the Eastern U.S. and a breaking-down of the persistent Western ridge. However, at this point it appears the core of the cold will retrograde westward slightly into the Northern Plains.

Weekend Travel Troubles

Two storm systems will combine this weekend to create many travel headaches on Sunday across much of the Midwest and East, causing delays in major cities from Atlanta north into Chicago, New York and Boston. Heavy rain and thunderstorms will continue across the Deep South where the new storm system is taking shape. Some light snow will fall farther north near the secondary low pressure center across portions of Nebraska and Iowa.

Sunday will bring the most travel headaches as the storm system intensifies across the Ohio Valley and Appalachians. Heavy rain will continue across the Southeast and will extend north along the eastern seaboard, affecting the major cities like Washington, D.C., New York, Philadelphia and Boston. Farther west and north around the Great Lakes region, heavy snows will be possible as colder air is drawn into the system from the north. Major airports in Chicago and Detroit will likely experience long delays as up to 6″ of new snow may accumulate. However, the heaviest snowfall of one foot or more will remain farther north into Quebec and Ontario. Between the rain and snow areas, a wintry mix of rain and snow or rain changing to snow is likely, especially across the Appalachians of West Virginia and central Pennsylvania.

Meanwhile, much of the West will remain quiet and mild with a some light rain Saturday morning across Seattle metro northward. Some light snows are also possible Saturday across portions of the central and northern Rockies. Southern California will likely see strong gusty winds Sunday morning for another brief Santa Ana wind event, though any travel trouble spots are unlikely.