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Requirements for a Major Snowstorm That Incorporates Heavy Snow Event (HSE) Criteria in the Philadelphia Metropolitan Area


Title: 50-50 Low Author: ASD Last modified by: ASD Created Date: 12/23/2005 3:35:22 PM Document presentation format: On-screen Show Company: ASD Other titles – PowerPoint PPT presentation

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Title: Requirements for a Major Snowstorm That Incorporates Heavy Snow Event (HSE) Criteria in the Philadelphia Metropolitan Area

Requirements for a Major Snowstorm That
Incorporates Heavy Snow Event (HSE) Criteria in
the Philadelphia Metropolitan Area
  • Widespread Snowstorm in the Delaware Valley
    (southeast PA, southern NJ away from the coastal
    regions, northern DE, and northeast MD) of 8
    inches or more in a 24 hour period

Thank You
  • Very special thanks to two prominent figures in
    the meteorological businessGlenn Hurricane
    Schwartz and David Tolleris. Without them, this
    work would NOT be possible. I hold these
    gentlemen in high esteem and admire their work
    and expertise immensely. NBC-10 Chief
    Meteorologist Glenn Hurricane Schwartz
    initiated the idea of a major snowstorm decision
    tree for the eastern seaboard (checklist) in the
    1980s. Meteorologist David Tolleris expanded on
    the original prototype and has applied such
    checklists to his forecasts. The professional
    feedback I received from them during this
    research endeavor was greatly appreciated. Their
    continued support and collaboration in reference
    to ongoing meteorological issues is priceless and
    I am extremely grateful for their contributions.
    Additionally, thanks also to Larry Cosgrove, Paul
    Kocin, Louis Uccellini, Henry Margusity, Rob
    Guarino, Norman Wes Junker, HM, Bill Conlin, Joe
    Bastardi, and Kathy Orr for their peer review and

Storm Checklist
  • State of the NAO
  • 50-50 Low
  • Polar Vortex
  • Character of 500 hPa Trough
  • Character of Surface Low Pressure
  • Character of Surface High Pressure
  • 850 hPa Low Strength
  • 850 hPa Low Track
  • Low Level Cold Air
  • Other Factors (700 hPa Low Track, 700 hPa Low
    Strength, PNA Pattern, MJO Phase, EPO Index,
    ENSO, Southeast Ridge, Ocean Temperatures, Moon
    Phases, Weekend Rule, Phases of a Snowstorm, and
    Local Climatology)

State of the NAO
Positive phase of the NAO is not conducive for
HSEs in the Delaware Valley. Snowstorms can
happen during a positive phase, but it is rare
for PHL to receive a HSE during a NAO (January
2000 was an exception to the rule). A positive
NAO usually exhibits a fast west to east zonal
flow and/or ridging east of the Mississippi
State of the NAO
A negative NAO in conducive for East coast
snowstorms because it usually allows for cold air
to spill into the eastern United States. It also
allows for a blocking to take place in Eastern
Canada, a subsequent trough to develop over the
eastern United States, and coastal cyclogenesis
to sometimes occur. A negative NAO is by far the
most important factor in East coast snowstorm
development. Negative NAOs and their associated
blocks usually last 10 to 14 days. Models
sometimes break them down too early.
Major Snowstorms and the NAO Index
Most big snowstorms for Philadelphia occur during
periods of negative NAO when it is trending
sharply towards neutral or positive. Sometimes
they occur when the NAO is positive or neutral
trending sharply negative. Click here to see
current NAO values http//
Major Snowstorms and the NAO Index
The NAO index at times can be deceiving. For
example, the NAO can be negative (good for
snowstorms) yet there could be no classic
Greenland block (High Pressure over Greenland).
The block is instead situated elsewhere or not in
the most favorable position for northern
Mid-Atlantic snowstorms. Also, the NAO index can
be extreme negative which can prompt a
suppression of storms. In this case, the lower
Mid-Atlantic and/or southeastern states could
receive the heaviest snow. Therefore, when it
comes to the NAO, the following must be taken
into consideration. 1. Negative or positive?
2. Trend? 3. How negative or positive? 4.
What type of NAO? Where is the block?
NAO Index (Blizzard of 2006)
  • NAO was weak negative prior to the storm, but
    trending sharply positive (this is called
  • This NAO trend of negative to neutral of positive
    is often key in the development and propagation
    of East coast snowstorms.

Other Factors NAO and EPO Index
  • The NAO, basically, is the dominant upper wind
    flow pattern over the North Atlantic influenced
    by the ocean. While in a negative phase, the NAO
    sometimes tends to act as a block (or dam) to the
    upper wind flow over the eastern half of North
    America. This blocking effect, in turn, tends to
    deliver the polar/arctic air into the eastern
    half of the country and Great Lakes more readily.
  • Click here for current EPO index and forecast

Other Factors NAO and EPO Index
  • The Eastern Pacific Oscillation (EPO) is the
    upper wind flow over the Eastern Pacific
    influenced by the ocean. When in a positive
    phase, the EPO generally is reflected by dominant
    stronger zonal flow and/or troughing along the
    West Coast of the U.S. This combination, in turn,
    tends to funnel milder Pacific air well inland
    into the country and thus, limits arctic
    outbreaks by holding them at bay up in Canada.
    When the EPO is dominated by a negative phase (as
    with the NAO), more ridging develops along the
    West Coast as higher pressure extends from the
    Gulf of Alaska south along the West Coast of
    Canada (opposite of the positive phase). This, in
    turn, encourages a northwesterly flow from Canada
    into the middle and eastern sections of the US
    and thus, the delivery of polar or arctic air.
  • Click here for current EPO index and forecast

Blizzard of 2006 (EPO Index)
50-50 Low
  • The 50-50 low is put in place by a negative NAO.
    This low is called such due to its location about
    50 longitude and 50 latitude. This low is
    important because it blocks coastal storms along
    the East coast against a wedge of arctic high
    pressure to the storms north This high pressure
    is usually located south and/or west of the 50-50

50-50 Low
  • According to Dave Tolleris, the 50-50 Low
    affects the overall pattern across eastern North
    America in several ways.
  • Enhances the intensity or amplitude of the
    negative NAO in general and the Greenland Block
    negative NAO in particular.
  • Keeps cold air source (high pressure) in place.
    Trap and lock example. Thus, more precipitation
    falls as snow due to the prevailing NW, N, or NE
  • 3. Prevents systems in Plains/Midwest from
    passing west of the Appalachian Mountains.

High (Greenland Block), Low (50-50 Low), High
(Arctic High) Configuration
February 2003 Presidents Day Storm (50-50 Low,
PV, and High Pressure)
Blizzard of 1996 (January 6-8, 1996) 50-50 Low,
PV, and High Pressure
Polar Vortex
  • The polar vortex is analyzed at 500 millibars.
    The polar vortex occurs above the core of the
    coldest polar air. Since frigid air is dense,
    heights are lower aloft because cold air has a
    lower thickness than warmer air.
  • At the surface of the polar air mass will be high
    pressure, but low heights will occur aloft at 500
    mb since the air is compacted due to high density
    air near the surface.

Polar Vortex cont.
  • The polar vortex can often be located over Canada
    since the coldest surface air is often found over
    high latitude icy/land locations. The polar
    vortex aloft propagates toward where the polar
    air mass moves. The vortex often moves very
    slowly or is stationary, and its position
    determines what part of the USA the Arctic air
    will invade.
  • When the vortex is centered over the Hudson Bay,
    as shown above, arctic air usually plunges south
    over the Dakotas and the northern Plains. If the
    vortex center shifts to the east, the core of the
    Arctic air invasion usually shifts east with it.

Polar Vortex cont.
  • There are many regions where the polar vortex can
    be located for it to be marginally conducive for
    East coast snowstorms. Most important is that
    the PV is on our side of the northern hemisphere
    and away from the pole (displaced).
  • However, in my opinion, the polar vortex is best
    situated in southeastern Canada just prior to an
    East Coast snowstorm. However, for a storm to
    come up the coast the PV needs to weaken and/or
    move out of the way (northward,northwestward, or
    backwards diving south and east of the pumping
    PNA ridge). Otherwise the storm will be
    suppressed to the south. North Hudson Bay,
    Canada is also a favorable position just prior to
    a snowstorm.

Polar Vortex cont.
  • Just keep it away from the Great Lakes region or
    just above it. In this position, short waves
    have trouble slowing down and digging (thoughts
    courtesy of Dave Tolleris).

Polar Vortex cont.
Polar Vortex and 50-50 Low (Blizzard of 2006)

Character of 500 hPA (mb) Trough
Cutoff Low. Low remains closed at 500 mb. This
setup gave Philadelphia 30 inches of snow.
Character of 500 hPA (mb) Trough
Open wave that evolves into a closed wave at 500
mb. This setup gave Philadelphia over 12 inches
and areas to the north and west over 30 inches.
Character of 500 hPA (mb) Trough
Open wave that remains open at 500 mb. This
setup gave Philadelphia over 20 inches of snow.
Character of 500 hPA (mb) Trough
In addition to there being a trough in the first
place, the trough must exhibit specific
properties to be conducive for heavy snow fall in
the Philadelphia region. The 500mb vorticity
maxima needs to be south of Philadelphia and
propagate in a northeastward direction near to
the East coast. If the vorticity maxima
propagates northeastward too far west and away
from the coast, it is likely that the
precipitation associated with the storm will NOT
remain all snow or even mostly snow.
Click here for current 500mb chart (Chart
1) Click here for current 500mb chart (Chart 2)
Character of 500 hPA (mb) Trough
Blizzard of 2006 (Vorticity Maximum)
Note the energy transfer. Vorticity maximum
(violet) just SE of Philadelphia. Note the light
blue shading over Harrisburg, PA and NNEthe best
snows are in between the two.
Other Factors Upper Level Signatures Prior to
Heavy Snow Events
Character of Surface Low Pressure (Miller A or
Gulf Atlantic Low)
Character of Surface Low Pressure (Miller A or
Gulf Atlantic Low)
Miller A Surface low tracks in a general
northeast direction from the southeastern United
States or the Gulf of Mexico. For us to have a
good chance at receiving heavy snow, the low
needs to stay to our south and east and
preferably stay off the Delmarva Peninsula. It
is also beneficial for the low to be just off the
Virginia Capes while deepening and moving slowly
in a NE or ENE direction.
Storm Track (Blizzard of 2006)
Character of Surface Low Pressure (Miller B or
Atlantic Redevelopment Low)
Character of Surface Low Pressure (Miller B or
Atlantic Redevelopment Low)
Miller B Surface low tracks from Northern
Plains or Canada and dives southeast. This low
weakens while a secondary or coastal low
redevelops off the East coast. For Philadelphia
to receive a heavy snow fall from a Miller B low
requires a unique set of characteristics. The
secondary (coastal) low must form to the south
and east of Philadelphia. This low must also
intensify, preferably in a rapid, bomb like,
fashion yet be moving slowly. This low unlike
the Miller A, is best for heavy snow when it
moves in a more northerly direction rather than a
NE or ENE direction.
Character of Surface High Pressure
An arctic high pressure is key for heavy snow to
fall in Philadelphia. An arctic high pressure,
if positioned correctly, and with enough
strength, will aide in keeping the storm mostly
snow or all snow. In addition, an arctic high
pressure with good position and strength will
also slow down the movement of the coastal low
allowing for precipitation to fall for a longer
period of time. For heavy snow events to occur
in PHL, the best position for a high pressure is
to the west of Maine and to the north of the
PA/NY border. The high can also be located in
the Northern Plains/Midwest. As far as strength
goes, pressures above 1020mb are adequate enough
to provide decent low level cold air.
For current surface data, click here
850 hPa Low Strength and Track
The strength of the upper air low, the 850hPa
(mb) low, is one of the factors that aides in the
rapid development of a coastal low. Thus, an
intensifying 850 mb low, or an already strong 850
mb low, greatly aides in the development of heavy
snowfall near the Philadelphia region. This is
especially true in Miller B systems. For a
Miller B storm to be deemed a heavy snow event
for Philadelphia it is crucial that the 850 low
goes through a rapid intensification cycle.
However, even more important than strength is
track. The 850 hPa is best to the south of
Philadelphia, yet north the NC/VA border moving
in an easterly direction.
850 hPa Low Track
Click here for current 850 mb data
850 hPa Low (Blizzard of 2006)
  • Heaviest snow band over the I-95 corridor at this
    time. Rates of 2 to 5 inches per hour. Phase 3
    of the storm (wrap around).

Low Level Cold Air
  • One factor often overlooked during a heavy snow
    event, even when the event is going full
    throttle, is the amount of low level cold air.
    Philadelphia is a major boundary area due to its
    proximity to the Atlantic Ocean, Gulf Stream
    Current, and Appalachian Mountains. Thus, even
    if an arctic high pressure is in perfect
    position, the precipitation can still change to
    sleet, freezing rain, snow pellets, or rain.
    Thus, temperatures throughout all layers of the
    troposphere need to be analyzed in real time and
    by using numerical model guidance.

Click here for local data from upper air soundings
Other Factors Local Climatology
Note how the cities along the I-95 corridor are
often along the boundary between frozen and
liquid precipitation. This makes winter weather
forecasting one of the toughest forecasting
aspects in ALL of meteorology.
Other Factors Interior Snowstorm
Characteristics A Miss for Philadelphia
The cyclone track is further west, usually
crossing the Delmarva Peninsula. The cyclone
also tracks in a more northerly direction going
west of Cape Cod, Mass. Also, the high pressure
is either too far north or too far east.
Other Factors Characteristics of All Snow Cases
Versus Changeover Cases
All snow cases. High pressure west of the state
of Maine and north of PA/NY border. Changeover
cases, high pressure is on top of the state of
Maine or eastward.
Other Factors Characteristics of All Snow Cases
Versus Changeover Cases
To remain all snow, it is best if the low tracks
NE or ENE staying away from coastline of the
Northeast U.S. Why? If the low rides right up
the coast, it pulls in too much low level warm
air from the Atlantic Ocean. Therefore, the
precipitation has a difficult time staying frozen
throughout the entire atmosphere. Philadelphia
can receive heavy snow from a changeover event,
an interior event, and/or a moderate event.
However, the chances of a widespread 8 inches or
more across the entire Delaware Valley is very
Other Factors Characteristics of Moderate
High pressure systems are in a wide variety of
locations. Many cyclonic redevelopment cases
from the west and from the Gulf of Mexico. Wide
variety of surface low tracks as well. However,
all low tracks are south of Philadelphia.
Moderate snowstorm events are the most capable
events, outside the heavy snow events, to give
Philadelphia an 8 inch or more snowfall.
Other Factors PNA Pattern
A negative PNA pattern favors a trough along the
West coast of the United States and ridging along
the East coast of the United States. Thus, when
the PNA is negative, the pattern is not extremely
conducive for East coast snowstorms. Can
snowstorms still occur along the East Coast?
Yes, but the storm track still has to be south
and east of Philadelphia. Best option here for
snow is a negative PNA pattern with a split flow
jet stream and other conducive factors in place
like the 50-50 low, negative NAO, and position of
surface high pressure.
Other Factors PNA Pattern
Other Factors Positive PNA Pattern
A positive PNA pattern favors a trough along the
East coast of the United States and ridging along
the West coast of the United States. Thus, when
the PNA is positive, the pattern is conducive for
East coast snowstorms. However, many other
factors must be in place as well. This is the
case with every single one of these points. Just
one will not make a snowstorm. Having all of them
in place does not mean a snowstorm will happen.
However, the more you have, the better chance
that exists for a heavy snow producing storm over
the Delaware Valley.
Click here for current PNA index values
Other Factors Positive PNA Pattern
Other Factors PNA Pattern
Major snowstorms have occurred in the Delaware
Valley during times of a negative PNA. However,
it is more of a rare occurrence when compared to
times of a positive PNA. If a snowstorm does
develop along the East coast during a time of
negative PNA, there has to be some evidence of
ridging to the south and/or west to promote the
digging of a trough near the East Coast. This
ridging may be displaced just east of the West
coast (Rockies/Plains) or sometimes as far east
as the Deep South, thus the PNA remains in a
negative state.
Click here for current PNA index values
Other Factors PNA Pattern
Also, just as is the case with the NAO, look for
which direction the index is trending. A
negative PNA trending sharply neutral or positive
is a good sign during times of a potential
developing snowstorm. Additionally, the state of
the PNA (positive or negative) when evaluating
snowstorm potential becomes less of a mitigating
factor during late February, and especially into
March and April due to shortening wavelengths
(courtesy of Donald Sutherland).
Click here for current PNA index values
Other Factors PNA Pattern (Euro forecast for
March 1, 2006)
Too big and too strong to be a 50-50 low, it is a
gargantuan polar vortex (courtesy of DT)
When a negative PNA can be idealhuge vortex in
SE Canada, huge blocking ridge (high pressure)
over Greenland connected with ridge in north
central Canada, closed 500 low in eastern Gulf of
Alaska ejecting energy into California, and
energy undercuts the block in California
(courtesy of DT).
PNA Index (Blizzard of 2006)
  • PNA was strong positive during the storm.
  • A strong positive PNA promotes ridging over the
    West coast and a trough over the East Coast.
    With this setup a shortwave (low) is better apt
    to develop into a storm and then ride up the
    Eastern seaboard.

Time of storm
Other Factors Index Combination
  • The NAO, AO, and PNA are all important indices
    when it comes to forecasting a large scale snow
    event. Some professionals say that a negative
    NAO, negative AO, and neutral PNA are very
    favorable for mid-Atlantic snows because the
    storms crash into the Pacific coast, come east
    and hit a block, which in turn slows them down
    with cold air in place, making it favorable for
    snow. However, I feel the best situation for a
    large snowstorm in the PHL area is the following
  • 1. Negative NAO trending positive or trending
    negative (very steep slope)
  • 2. PNA trending positive (very steep slope)
  • 3. AO negative

Other Factors Index Combination
  • 1. Negative NAO trending positive (very steep
  • http//
  • 2. PNA trending positive (very steep slope)
  • http//
  • 3. AO negative
  • http//
  • According to a senior forecaster at NOAA,
    negative AO and NAO favor big snowstorms
    somewhere in or near the eastern U.S. but the
    chances at a given location are still rather

Other Factors MJO Index
Madden Julian Oscillation (MJO) A 40- to 60-day
period of alternately strong or weak trade winds
that normally blow west. It is named after Roland
Madden and Paul Julian, two scientists from the
National Center for Atmospheric Research who in
1971 were studying wind patterns in the tropical
Pacific. For unknown reasons, these tropical
winds sometimes weaken, and the Sun-warmed pulse
of ocean water that they usually cause to drift
west drifts east. As this pulse of warm water,
called a Kelvin wave, moves east-from the coast
of Africa across the Indian and Pacific Oceans-it
carries changed air patterns above it.

Other Factors MJO Index
When the wave crashes into South America, the
water stops, but the air pattern continues over
land northeastward, into the Caribbean atmosphere
and across the Atlantic Ocean. Before this cycle
is complete, another pulse has already started in
the Indian Ocean. Scientists are still studying
the MJO. Most agree, however, that when the MJO
cycle speeds up and warm Kelvin waves pile up in
the Pacific Ocean, we have the start of an El
Niño. The MJO usually brings flooding rains
(also known as the "Pineapple Express") to the
Pacific Northwest and California. In an active
hurricane season on the East Coast, it can mean
several hurricanes within a few weeks, followed
by a long spell with no hurricanes.

Other Factors MJO Index

For the East coast of the United States, the
impact of the MJO during the winter months is
uncertain. We know the MJO goes through phases,
8 to be exact.

Other Factors MJO Index

Although much is uncertain, phases 8 and 1 of the
MJO appear to be the most favorable for large
scale East coast snowstorms due to the above
heights (high pressures) over and near Greenland
which in turn impacts the negative NAO. Click
here for current MJO Phase

Other Factors MJO Index
According to HM (Eastern US Weather Forum), MJO
does not have to be in Phase 8 all the time to
get SECS (Significant East Coast Snowstorms). It
is one tool to the general equation. It is not
until phase 4-7 when the MJO alignment favors a
ridge back east. Click here for current MJO Phase

Other Factors MJO Index (Thanks to NWJ)

Other Factors MJO Index (Thanks to NWJ)

MJO Phase (Blizzard of 2006)
Other Factors 700 mb Analysis
Many of the same processes analyzed on the 850
chart are also studied on the 700 mb chart. The
trough/ridge pattern becomes more defined at the
700 mb levels as compared to lower levels. A
trough is simply a southern "bulge" in height
contours while a ridge is a northerly displaced
"bulge". This "bulge" can be large (such as in
association with a mid-latitude cyclone) or small
(such as a shortwave).
Other Factors 700 mb Analysis
When examining model data at 700 millibars it is
common for them to show upward vertical velocity.
A good forecast strategy is to look at the 700 mb
forecast panels for the upward vertical velocity
distribution, then determine what forces in the
atmosphere are causing the upward (or downward)
vertical velocities.
Other Factors 700 mb Analysis
(1) Find areas with low dewpoint depressions.
Often this indicates a deep layer of moisture.
Use 700 mb chart in combination with sfc and 850
charts to determine depth of moisture(2)
Determine strength of warm air advection, cold
air advection, and moisture advection. Thermal
advection is a function of wind speed, wind
direction, thermal gradient, and isotherm angle
of intersection with height contours(3)
Determine strength of high pressure/ low
pressure. Strong organizing low pressures tilt
toward the northwest with height.
Other Factors 700 mb Analysis
(4) Locate shortwaves. Determine if shortwave is
barotropic or baroclinic. Baroclinic shortwave is
more likely to produce precipitation. Rain and
storms are generally on exit sector of shortwave.
Compare shortwave with other levels in the
atmosphere. Rain is likely to right of shortwave
especially if dewpoint depressions are low.(5)
Weather is warmer than normal under ridges and
cooler than normal under troughs.
Other Factors 700 mb Analysis
Click on this site for 700mb initialization and
forecasts. http//
(6) Look for the greatest height falls and
height rises these values give clues to how the
trough/ridge pattern will change through
time.(7) 700 mb front is found where height
contours kink kinking height contours may also
be a shortwave (especially if thermal advection
is present). A short wave can be an upper level
Other Factors 700 mb Analysis
According to Henry Margusity of Accu-Weather,
the position of the 700 mb low is critical for
snow in Philly. The 700 mb represents the mid
layer conveyer belt that brings in moisture to
the west of the storm over cold air. It the
700mb low tracks just over, then Philly will be
in good position for snow.

Forecasted 700 hPa Low (Blizzard of 2006)
The RUC was saying watch out. This model is
becoming a great short range model for East coast
snowstorms (courtesy of DT). Rates of 2-5 inches
per hour occurred during this forecasted time
frame. Humidity was over 99 during the time of
heavy snow.
Other Factors Southeast Ridge
  • Always watch out for the Southeast heat ridge.
    La Nina winters can be characterized by a
    persistent southeast ridge (high pressure). They
    can manifest at any time and can be killers for
    major snows in Philadelphia when the rest of the
    pattern is favorable (i.e. negative NAO etc.)

Other Factors El Nino and La Nina
  • Our snowiest winters are usually weak or
    moderate El Nino winters. The phenomena of El
    Nino and La Nina greatly impact the location and
    strength of the Pacific jet stream. This jet
    stream, at times, may have a great influence on
    our weather. For example, January of 2006 was so
    very mild due to the strength of the Pacific jet
    stream (QBO) blasting into the West Coast in a
    west to east fashion. This allowed the air flow
    to be in a primarily west to east fashion across
    the continental United States rather than in a
    cooler north to south fashion.

Other Factors Teleconnections
  • Its not one teleconnection (indices etc.), it
    is all the players on the field that count (Joe
    Bastardi of Accu-Weather).
  • For it drives home a point about broad brushing
    ideas. The negative NAO is a signal for cold, but
    unless everything is just right, it is something
    that drives storms south (Joe Bastardi of
    Accu-Weather on March 22, 2006).

Other Factors Teleconnections
  • In other words, a negative NAO does not make a
    snowstorm. A positive PNA does not make a
    snowstorm. A negative NAO and a positive PNA
    together do not make a snowstorm. Patterns make
    snowstorms. A conglomeration of indices create
    the framework on which a pattern can be built.

Other Factors The Importance of the Ocean
  • The prevailing winds over a region prior to a
    storm, the expected prevailing winds over a
    region during a storm, the temperature of the
    Atlantic Ocean, and the character of the Gulf
    Stream current always play a role in storm
    development, propagation, and precipitation type.
    These factors must always be taken into account
    prior to a storm taking place that is expected to
    propagate and intensify along the East coast of
    the United States.
  • Click here for current ocean temperatures

Other Factors Phases of the Moon (Elliot Abrams)
  • Elliot Abrams of Accu-Weather is a firm believer
    that specific phases of the moon have a
    correlation with East Coast snowstorms.
    Apparently new and full phases of the moon are
    strongly correlated to East Coast snowstorms
  • http//

Other Factors Weekend Rule (Dave Tolleris)
  • There is as interesting rule or oddity that
    exists with Significant East Coast Snowstorms
    that several meteorologists have noted over the
    past several years. If you go back and research
    snowstorm events from 1955 to 1987 and you
    include the recent events you'll find that the
    all snow events (no mixing) along the I-95
    corridor cities Richmond, Washington D.C.,
    Baltimore, Philadelphia, New York City, New
    Haven, Providence, and Boston--- those events of
    all occurred on a weekend.
  • All except for 2 events. Really. I call this the
    I-95 SECS WEEKEND RULE. Now that being said
    let's keep the few criteria or parameters... a
    weekend event would be a snowstorm that started
    on a Friday and ended on a Saturday... OR began
    on a Saturday and ended on a Sunday...OR began on
    a Sunday and ended on a Monday.

Other Factors Weekend Rule (Dave Tolleris)
  • This oddity does not apply to snowstorms in the
    lower-Mid Atlantic -- say Virginia, D.C., Lower
    Maryland, and NC... nor does it apply to interior
    snowstorms. Given those parameters the fact is
    every single major I-95 PURE snowstorm -- has
    occurred on a weekend. Everyone since 1900 except
    for 2....
  • I am sure you recall January 96 blizzard--it was
    a Saturday into Sunday into Monday event...  and 
    the President's Day II snowstorm FEB
    16-17,2003   was also a weekend major east coast
    Snowstorm (MECS).

Other Factors Weekend Rule (Dave Tolleris)
  • December 25-26, 1909 (Sat-Sun) March 1-2, 1914
    (Sun- Mon) April 3-4, 1915 (Sat -Sun) February
    6-7, 1920 (Sat- Sun) January 27-29, 1922
    Knickerbocker Storm (Fri Sat) February 19-20,
    1934 (Mon-Tues) January 22-24, 1935
    (Tues-Thurs) February 14-15, 1940 St.
    Valentine's Day Storm (Wed-Thurs) December
    26-27, 1947 (Fri-Sat) March 18-19, 1956
    (Sun-Mon) February 14-17, 1958 Blizzard of '58
    (Sat-Sun) March 18-21, 1958 (Tues-Thurs) March
    4-5, 1960 (Fri-Sat) December 11-13, 1960
    (Fri- Sat) January 18-20, 1961 (Thurs-Fri)
    February 4-5, 1961 (Fri-Sat) January 12-13, 1964
    (Sun-Mon) January 29-31, 1966 Blizzard of '66
    (Sun-Mon) December 23-25, 1966 (Fri-Sun)
    February 5-7, 1967 (Fri-Sat) February 8-10, 1969
    Lindsay Storm (Fri-Sat) December 26-28, 1969
    (Fri-Sat) February 18-20, 1972 rain in
    I-95 cities (WED-THUR) January 20-21, 1978
    (Fri-Sat) February 5-7, 1978 (weekend) February
    18-20, 1979 President's Day Storm (Sun-Mon)
    April 5-7, 1982 (Mon-Wed) February 10-12, 1983
    (Fri-Sat) January 21-23, 1987 (Wed-Fri) January
    25-26, 1987 (Sun-Mon) February 22-23, 1987
    (Sun-Mon) March 12-14, 1993 The Storm of the
    Century (Fri-Sat) January 6-8, 1996 (weekend)
    February 16-17, 2003 Presidents Day Storm II
    (Sun-Mon) January 22-23, 2005 Blizzard of 2005
    (Sat-Sun) and February 11-12, 2006 Blizzard of
    2006 (Sat-Sun).

Other Factors Weekend Rule (Dave Tolleris)
  • The March 12-13 historical 1888 blizzard was a
    Sunday to Monday event, the Feb 12-14 1899 severe
    East Coast snowstorm that was part of an arctic
    outbreak of historic proportions occurred on a
    Friday to Sunday. The Ash Wednesday severe
    Noreaster of March 5-7 occurred on a Monday to
    Wednesday and it was a rain event for most of
    East Coast I-95 cities.
  • Interestingly this oddity does not apply for
    mid-Atlantic snowstorms. For example the January
    24-25 2000 severe Noreaster which dumped some
    21" snow in Charlotte and greater than 6"  of
    snow in much of South Carolina, 15"- 18"  in
    central Virginia and 12" of snow in DC...only
    dropped 6" in Philly, New York City, and Boston,
    and it was a Monday Tuesday event.
  • Of course there is a reason WHY this "oddity"
    exists. If we include the periods of Friday to
    Saturday, Saturday to Sunday, and Sunday to
    Monday.. that is 3 days out of 7. Even so it does
    seem a little unlikely thing.

Other Factors Local Climatology
One must always know his local climatology.
Computer models do not have an understanding for
the past or a comprehension of a regions local
climate character. When issuing a forecast that
has a possibility of fulfilling an extreme
solution, do some research. Know your areas
complete snow history and know what factors need
to either be in place before the storm, or what
factors need to manifest themselves during a
storm to fulfill such an extreme solution. Take
into account what month it is and what day of the
week it is. Take into account how often, on
average, storms of a certain magnitude occur.
Far too often a computer model(s) is (are) taken
verbatim before the most basic physics,
meteorology, and climatology are ever even taken
into consideration and applied to the possible
outcome. One meteorologist who is fantastic at
doing this in a very thorough and often humorous
manner is Dave Tolleris.
  • http//

Typical Snowstorm 3 Chances at Receiving
Accumulating Snow
  • A typical snowstorm has 3 phases or parts that
    can deliver accumulating snow to a specified
  • Phase 1 overrunning snow
  • Phase 2 storm snow
  • Phase 3 wrap around snow
  • Simply put, the more phases you experience in a
    given region, the higher the likelihood is that
    region x will receive a major snowfall.

Thoughts on this slide courtesy of Glenn
Hurricane Schwartz