1:15 PM | ***Powerhouse storm to slam Pacific NW...significant storm coming to Great Lakes, Mid-Atlantic, Northeast US...multiple cold shots on the way central/eastern US***

A “blocky” type of weather map across North America in coming days with intense upper-level ridges of high pressure and deep troughs of low pressure. This pattern will result in a powerhouse storm system across the Pacific Northwest and a significant storm system later in the week to impact the Great Lakes, Mid-Atlantic and Northeast US. Map courtesy NOAA, tropicaltidbits.com

Overview

The weather map is quite busy currently across North America with intense high pressure ridges combined with deep troughs of low pressure and on top of that we have some tropical moisture on the playing field as well. A deep trough over the northeastern Pacific Ocean will help to spawn a rapidly intensifying storm system that will slam into the Pacific Northwest from later today through tomorrow with hurricane-force winds, tremendous rainfall in low-lying areas, and substantial snowfall in the inland, higher elevation locations that will be on the order of several feet in some spots. This storm system will become a slow-mover and there will be lingering effects from northern California to Oregon and Washington all the way through the second half of the week.

Another upper-level trough will slide south and east during the next couple of days from the north-central states and deepen markedly as it reaches the Mid-Atlantic/Northeast US by later Thursday. An initial low pressure system will head to the Great Lakes while a secondary forms near the northern Mid-Atlantic coastline. This unfolding storm system will also become a slow-mover during the latter part of the week and will bring with it beneficial rains, accumulating snows across inland, higher elevation locations, and a prolonged period of strong NW winds.

Looking ahead, there are signs for multiple cold air outbreaks to make their way from northern Canada into the central and eastern US as we push through the remainder of November and into the early part of December...quite a winter look to the overall pattern that should include threats of snow as well.

Snowfall can be significant in some parts of the nation during the next five days in an overall very active weather pattern. One such area of concern for substantial snowfall in coming days includes the Cascade Mountains of Washington and Oregon and the Sierra Nevada Mountains of eastern California (left circle). The higher elevation locations of the northeastern states from West Virginia to New England (right circle) can also receive significant snowfall in coming days. Map courtesy NOAA, tropicaltidbits.com.

Pacific Northwest “bomb cyclone”

Intense upper-level ridging currently over the Aleutian Islands (Alaska) and a deep upper-level trough of low pressure off the west coast of Canada will combine to produce a long-lasting impactful storm in the region from Northern California-to-Oregon-to-Washington. Low pressure that is currently well off the Pacific Northwest coast will under explosive intensification during the 12 hours or so as it slides south and east featuring as much as a 40 millibar drop of central pressure by this evening to around 941 millibars (27.79 inches). This kind of dramatic drop of its central pressure would easily classify this storm system as a “bomb cyclone” that will soon have strength equivalent to a “category 4” hurricane (a storm is defined as a “bomb cyclone” if it has at least a 24 millibar drop of its central pressure in a 24-hour period…credit Dr. Ryan Maue, X).

The “bomb cyclone” headed towards the Pacific Northwest will feature a very tight pressure gradient (black lines on this map represent lines of equal pressure or isobars). The result is likely to be hurricane-force winds along coastal sections and high mountain passes potentially as high as 75-80 mph. Map courtesy NOAA, tropicaltidbits.com

This intensifying storm system will feature hurricane force winds, flooding rains in low-lying areas, and substantial snowfall on the order of several feet across the interior, higher elevation locations from the Cascade Mountains of Washington and Oregon to the Sierra Nevada Mountains in eastern California. The main impact of this unfolding storm will be from later today through tomorrow; however, precipitation and strong winds will likely stick around right through the week in the region from northern California to Washington...thanks to the intense blocking high pressure to the north. All types of severe weather impacts are on the table with this powerful storm system from flooding in low-lying areas, power outages with 70+ mph winds, and significant travel disruptions in the “snow-filled” higher elevation locations.

Significant late week storm in the Great Lakes/Mid-Atlantic/Northeast US

High pressure will continue to dominate the scene in the Mid-Atlantic/Northeast US during the next couple of days, but then a complex low pressure storm system will take control later in the week. An upper-level trough of low pressure will push into the central US by tomorrow and then deepen markedly by later Thursday as it slides into the Mid-Atlantic/Northeast US. At this point, the deep upper-level trough will become quite a slow-mover and “forced” to rotate around the northeastern states thanks to intense blocking high pressure to the north that will be centered over the northeastern part of Canada. At the surface, an initial low pressure system will push into the Great Lakes, and then a secondary low will form somewhere near the northern Mid-Atlantic coastline during the latter part of the week and become the main player on the field.

A forecast map for early Friday features snow (shown in blue) in upstate PA and southern NY as well as across portions of West Virginia. Map courtesy NOAA, pivotal weather

The end result in the Mid-Atlantic/NE US will be occasional (beneficial) rain from later tomorrow into early Thursday and there can be a thunderstorm or two mixed into the picture as a strong cold front pushes through the area. In fact, this is likely to be the most significant rainfall event in several weeks for many spots of the Mid-Atlantic region in what has been an extended period of very dry weather. Rainfall estimates in the Mid-Atlantic’s I-95 corridor are 0.50” to 1.00” from Philly to NYC and 0.25” to 0.50” in the DC metro region. Occasional “instability” rain showers will be likely from Thursday afternoon through Friday as the atmosphere remains quite unstable given the strong upper-level trough that will rotate around the northeastern states for awhile.

The moisture field of what was Tropical Storm Sara has pushed northward into the northern Gulf of Mexico in the form of a cluster of thunderstorms (circled region). Image courtesy NOAA/NESDIS, Meteorologist Joe Bastardi (X)

In terms of temperatures, after a mild day on Wednesday ahead of the cold front, it turns noticeably colder on Thursday and it’ll remain quite chilly on Friday and Saturday as well with below-normal temperatures for this time of year. The winds will become quite strong later tomorrow as the cold front approaches and then will stay strong on the storm’s back side from a northwesterly direction. In fact, those strong winds to follow will likely last through at least Saturday and perhaps even into Sunday across much of the northeastern US given the expected slow movement of the overall storm system.

As far as snow is concerned, it should become cold enough on Thursday for accumulating snow to fall across interior, higher elevation locations of the Mid-Atlantic/Northeast US all the way from West Virginia to interior New England. The most significant amounts of snow are destined for the higher elevations of central/eastern West Virginia, western Maryland (Garrett County), central and northern PA (e.g., Poconos), upstate New York (e.g., Adirondacks, Catskills) to interior New England. In the DC-to-Philly-to-NYC corridor, it is quite likely that enough cold air wraps into this storm system that the “wrap-around” rain showers mix with or even change over to snow and/or ice by Thursday night or Friday; especially, in the northern and western suburbs where small accumulations cannot be ruled out.

There are signs for a “stretched” polar vortex by early December extending from Greenland to southern Canada and this may be a favorable position for cold air outbreaks from Canada into the central and eastern US. Map courtesy NOAA, weathermodel.com, BAM Weather (X)

Signs for additional cold air outbreaks into the central and eastern US

Looking ahead, there are signs for multiple cold air outbreaks to make their way from northern Canada into the central and eastern US as we push through the remainder of November and into the early part of December...quite a winter look to the overall pattern that should include threats of snow as well. Signs point to the stretching of the polar vortex by late November or early December which can put it in a favorable position for cold air outbreaks to make their way from Canada into the central and eastern US.

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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