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Meteorological
“bomb” threatens eastern New England, Canadian Maritimes
24
March, 2014
A
modest storm that will bring some light rain and snow to the
Mid-Atlantic will transform into the most intense cyclone off the
East Coast since Superstorm Sandy. Between Tuesday and Wednesday
afternoon, the storm is forecast to strengthen explosively or undergo
what meteorologists call “bombogenesis.”
Blizzard
watches have been hoisted for eastern Massachusetts, which is
forecast to receive over 6 inches of snow and 50 mph winds. Areas
farther west, from New York City to Boston, may just experience a
glancing blow but a small shift in the storm track back towards the
coast would raise the specter of more significant impacts.
Storm
track forecasts from different simulations of the Canadian and GFS
(GEFS) model ensembles. (Stony Brook)
An
astonishing rate of strengthening
Computer
models have consistently forecast this storm to intensify at an
exceptional rate. Meteorologists consider a drop in pressure
of 24 millibars in 24 hours “rapid intensification.” Some
models have predicted this storm’s pressure will drop up to 50
millibars in 12-24 hours.
A
general consensus is that the storm’s minimum central pressure
will plummet from around 1,000 millibars Tuesday to 950-960
millibars Wednesday. Bear in mind, a pressure of 950 millibars
is equivalent to what we see in category 3 hurricanes and not far
off the minimum pressure of Superstorm Sandy (940 mb) at peak
intensity.
How
is this happening?
(National
Weather Service)
The
National Weather Service office serving New York City posted a nice,
concise explainer – complemented by an excellent graphic (above) –
on why this storm is set to intensify so quickly. In short,
the storm explosively develops due to the collision of cold Canadian
air with warm, moist air from the south – in a region of rising
air and strong high altitude winds:
To promote the rapid strengthening (or deepening) of surface low pressure, we need air to rise up from the ground. How does that happen? Well, one way is thanks to zones of stronger wind, called “jet streaks,” many thousands of feet above the ground. If positioned correctly, they create a relative void of air aloft, forcing air from below to rise and fill it back up (think of it as the atmosphere’s vacuum). This helps low pressure form closer to the ground.
Another important ingredient is a strong change (or gradient) in temperature across the developing low pressure. As the low “spins up,” it can pump warmer air to its north and east, and pull in colder air from the west and down to the south. This makes the gradient even stronger, which energizes the overall system even more. The whole process feeds into itself and causes rapid strengthening of the low pressure
Impacts
expected
A
general rule for this storm is that the farther east you are, the
closer you’ll be to the storm center and the more severe
conditions will be. The National Weather Service currently
forecasts the worst conditions in eastern Massachusetts, including
Cape Cod and Nantucket – where the Blizzard
Watches are
in effect.
CONFIDENCE IS RELATIVELY HIGH FOR HIGH IMPACT OVER THE CAPE AND ISLANDS AND FOR RELATIVELY LOW IMPACT ACROSS SOUTHWEST NEW HAMPSHIRE…NORTHWEST CONNECTICUT AND MASSACHUSETTS NORTH AND WEST OF WORCESTER. CONFIDENCE IS CONSIDERABLY LESS IN THE GRADIENT REGION IN BETWEEN.
Areas
under the blizzard watch could see in excess of 6 inches of snow and
wind gusts to 55 mph.
Farther
south, the National Weather Service office serving New York City
conveys a similar message to the Boston office, stressing its
easternmost areas – such as Long Island – are most likely to be
affected by disruptive snow and wind. Some computer models suggest
significant snow (of at least a couple inches) could reach New York
City, others do not – as the National Weather Service explains:
[THE FIRST CAMP] SPELLS A POTENTIALLY SIGNIFICANT IMPACT FOR EASTERN ZONES. THE SECOND CAMP … SUGGESTS THAT THE TRI-STATE [NY/PA/NJ] WILL RECEIVE AT MOST A GLANCING BLOW…AND THERE IS SOME CHANCE THAT AREAS NW OF NYC COULD EXPERIENCE LITTLE IF NO IMPACT.
2 RETWEETS 2 FAVORITES
The
Canadian Maritimes – directly in the storm’s path – are
likely to be ground-zero for this storm. A foot or more of
snow is forecast in many areas (although somewhat less may fall in
some coastal areas where rain mixes in), along with wind gusts to 75
mph, around hurricane-force. Power outages are expected along
with coastal flooding.
The
storm is likely to generate incredible offshore winds of up to 75-85
mph (sustained) and waves to 40-50 feet according to some models.
Interested in what this storm (in its tamer phase) will mean for D.C.? Stay tuned for a detailed update between 1 and 2 p.m. …
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