That persistent “polar vortex,” also known historically as the Hudson Bay low, is beginning its brief hiatus. During the next several days, the warmest temperatures in weeks will spread across much of the eastern U.S.
Computer model and human forecasts show that this trend is going to take a sharp reversal before the end of the week. In fact, the “polar vortex,” will be back in position, albeit not as intensely, by week’s end.
The unfolding “vortex” scenario shows that two storms systems will begin to merge across the Midwest by late Wednesday (Fig. 1). By late Thursday (Fig. 2), the storm should intensify dramatically as it moves into the Great Lakes region. Due to the increased pressure gradient associated with storm deepening, look for storm force winds (sustained and/or frequent gusts to 55 mph to 73 mph) across most the Great Lakes. To the east of the storm system, locally heavy rainfall and possible thunderstorm activity is on tap. Locally heavy rainfall and warmer temperatures (and associated snow melt) could lead to some local flooding, especially in the Ohio Valley and parts of the Appalachians (Fig. 3). There is a slight risk that severe thunderstorms could develop from the Ohio Valley southward to near the Gulf Coast on Thursday (Fig. 4). To the west of the storm system, locally heavy snowfall can be expected from Iowa northeastward into the Upper Peninsula (UP) of Michigan. Amounts could easily reach into double-digits because the system will contain ample moisture from the Gulf of Mexico.
California and much of the Desert Southwest will remain rainless. As a Pacific high-pressure system moves into the inter-mountain west, a strong pressure gradient may set the stage for Santa Ana winds to develop across parts of southern California (Fig. 2). Already, locally gusty winds have prompted the issuance of high wind watches across some southern California coastal ranges.
Once this potpourri of weather elements (rain, snow, temperature swings, strong winds and dry weather) winds down by Friday, the exiting storm system will move toward Hudson Bay where it will become the next so-called “polar vortex.” The north and northwest winds in its wake will allow another arctic high-pressure system to advance southward. By early next week, that high should have again dropped temperature readings to below average values across much of the eastern two-thirds of the U.S. (Fig. 5).
In keeping with the balancing of weather extremes theme, look to southern California and Arizona to again see above average readings. Due to warm, dry and windy conditions, grassland and/or forest fire danger will be high tomorrow (Feb. 19, 2014) across parts of the western Kansas plains; the risk will reach elevated to critical levels across most of New Mexico and parts of Arizona and Texas on Thursday (Fig. 6).
Throughout the entire week-long period, a series of storms will pummel the Pacific Northwest. There is the potential for rainfall totals during this period to reach six to seven inches especially along the west-facing slopes of the Cascades (Fig. 7). Heavy snowfall at higher elevations will be falling on recent snowfall that has not sufficient settling time. This has prompted the issuance of an ongoing avalanche warning (meaning that avalanches are likely at any time) for the Olympic and Washington Cascade Mountains and the region near Mount Hood. After a slow start due to the lack of snow across parts of the western U.S., the U.S. has seen nine avalanche deaths in the past 10 days. So far, the winter season (2013-2014) has returned to average (15) in this deadly category (Fig. 8).
© 2014 H. Michael Mogil