So much weather is on tap for the U.S. today (Fig. 1), and then for the whole week, that it’s impossible to cover the scenario in depth. Instead, look at these brief summaries of impending events.
- Major severe storm outbreak across the Central U.S.: A strong upper level storm system over the Rocky Mountains (Fig. 2) will interact with a warm and humid air mass that is rapidly advancing northward (Fig. 3). As a surface low-pressure system moves toward Omaha, NE today, dew points (already rising 6 to 8 degrees in two hours this morning across northern Kansas and southeast Nebraska) will rise into the mid and upper 60’s. Long-lived, large tornadoes are possible across southeast Nebraska and southern Iowa. Elsewhere throughout the Central Plains, severe weather, including large hail, high winds and torrential rainfall, is possible. During the next few days, severe weather, albeit less intense, is probable.
- Heavy rainfall: The air mass to the south and east of the upper level storm system is quickly becoming very humid through a deep atmospheric column. This Mother’s Day morning, precipitable water values were above the seasonal average, some significantly, from Iowa and Nebraska to the Gulf Coast (Fig. 4). With training thunderstorms (repeated storm movement over a particular location) due to expected slow overall weather system movement (Fig. 2 and Fig. 5) during the next few days, two to six inches of rainfall (locally much higher) can be expected (Fig. 6). By the end of the week, heavy rains will spread to the East Coast and New England as the upper level weather system “cuts off” and slows its eastward progression (Fig. 7). Hence, across the eastern half of the Nation, rainfall amounts for the week could total 5 to 7 inches in many places (Fig. 8). Locally, amounts will likely exceed 10 inches.
- Heavy snowfall: The same upper level storm system, responsible for the aforementioned storminess, will also bring significant snowfall to Colorado. One to one and a half feet of snow has fallen across western Wyoming so far. Heaviest amounts (measured in feet) will fall in the higher Colorado mountain elevations. Low-level northeast winds blowing upslope on the east-facing Front Range, will add to the potential for heavy, wet snow (Fig. 3). Even Denver and the eastern Colorado Plains will see significant snowfall (up to a foot in places).
- Warmth: To the west of the upper level storm system, a strong upper level ridge will be developing across the western states. Upper level ridges have sinking air that fosters significant compressional warming. Coastal locations from San Francisco south to San Diego could warm to record-breaking levels early in the week. The warmth will last only a few days and temperatures will then quickly return to more seasonal values. Across the coastal areas and through large parts of the interior Desert Southwest, heat and gusty winds, along with the ongoing drought, will lead to high wildfire fire danger.
- Coolness: Chilly air will spread eastward from Colorado the next several days (balancing the warmth in the west). Then the Northeast and parts of the Mid-Atlantic get a double-whammy. First, a back-door cold front moves southwestward from Canada and helps establish a northeast wind flow. Cool and damp air from the Atlantic will ensure a cloudy, drizzly regime. Then, as the major upper level system arrives and “cuts off” (Fig. 7), an extended period of rainy weather will set in.
With a menu filled with almost every weather event imaginable (at least, tornadoes, severe storms with high winds and hail, heavy rainfall, heavy snowfall, excessive warmth and extended coolness), there’s more than enough weather for everyone.
By next week, the weather pattern is expected to calm down. However, there are indications that a series of storm systems will be moving across the Nation, each of which would be capable of generating some severe weather and/ or heavy rainfall.
© 2014 H. Michael Mogil