11:30 AM | **An active and unusual weather pattern across North America...”bomb cyclone” to slam into Pacific Northwest...significant late week storm to impact Great Lakes/Mid-Atlantic/Northeast US**
Paul Dorian
Kind of an unusual upper-level weather pattern across North America by later this week with multiple intense ridges of high pressure (orange, purple) and deep troughs of low pressure (blues). Map courtesy NOAA, tropicaltidbits.com
Overview
Quite an active and somewhat unusual weather pattern is developing across North America and one that will feature multiple intense upper-level ridges of high pressure and deep troughs of low pressure. One result of this overall pattern will be a powerful storm system that will slam into the Pacific Northwest from later tomorrow into Wednesday. This storm will feature explosive intensification with as much as a 70 millibar drop in 24 hours of its central pressure yielding the strength of a “category 4” hurricane and easily classifying it as a “bomb cyclone”. Another significant storm system will develop in this active weather pattern during the late week bringing with it rain, accumulating snows, and a sustained period of strong winds across the Great Lakes, Mid-Atlantic, and Northeast US.
A powerhouse storm system and one that will classify as a “bomb cyclone” will bring tremendous coastal rains, substantial higher-elevation snows, and hurricane-force winds to much of the region from Northern California-to-Oregon-to-Washington by the middle of the week. Map courtesy NOAA, tropicaltidbits.com
Pacific Northwest “bomb cyclone”
Intense upper-level ridging near Alaska and a deep upper-level trough of low pressure off the Pacific Northwest coast will combine to produce a long-lasting impactful storm in the region from Northern California-to-Oregon-to-Washington. Low pressure off the Pacific Northwest coast will likely under explosive intensification during the next couple of days on the order of as much as a 70 millibar drop in its central pressure in a 24-hour period to around 943 millibars (27.85 inches). This kind of quick drop of its central pressure would easily classify this storm system as a “bomb cyclone” that will have strength equivalent to a “category 4” hurricane (“bomb cyclone” defined as a 24 mb drop in 24 hours…credit Dr. Ryan Maue, X).
This unfolding 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 tomorrow into Wednesday; however, precipitation can stick around right through the week in the region from northern California to Washington. 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.
A significant storm system supported by a deep upper-level trough will bring rain, accumulating snow, and sustained strong winds late this week to the Great Lakes, Mid-Atlantic and Northeast US. Map courtesy NOAA, tropicaltidbits.com
Significant late week storm in the Great Lakes/Mid-Atlantic/Northeast US
High pressure will generally dominate the scene in the Mid-Atlantic/Northeast US during the first half of the week, but then a complex low pressure storm system will dominate the scene later in the week. An upper-level trough of low pressure will push into the central US by mid-week and then deepen 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 for a few days thanks to intense blocking high pressure to the north that will be centered over the northeastern part of Canada. At the surface level, an initial low pressure system will push into the Great Lakes region, and then a secondary low will form somewhere near the northern Mid-Atlantic coastline during the latter part of the week.
The end result in the Mid-Atlantic/NE US will be occasional rain from later Wednesday 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. Preliminary rainfall estimates in the I-95 corridor are 0.50 to 1.00 inches from Philly to NYC and 0.25 to 050 in the DC metro region. Occasional “instability” rain showers will be possible from Thursday afternoon through Friday as the atmosphere will remain quite unstable given the strong upper-level trough that will rotate around the northeastern states for awhile. It is not out of the question that some snowflakes and/or ice pellets mix in with the rain showers from later Thursday into Friday all the way into the I-95 corridor.
An active weather pattern during the next week or so will produce substantial snowfall amounts over the higher elevation regions of the Cascade Mountains and Sierra Nevada Mountains from Washington and Oregon to Northern California and there can be significant snowfall in portions of the Northeast US including upstate New York State. Map courtesy NOAA, tropicaltidbits.com
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 Wednesday 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 given the expected slow movement of the overall storm system.
As far as snow is concerned, it should become cold enough on Thursday for some accumulating snow to fall across interior, higher elevation locations of the Mid-Atlantic/NE US from upstate PA to interior New England with perhaps the most significant amounts falling across portions of upstate NY.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com
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