50-50 Low

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 business—Glenn “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 1980’s. 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 feedback.
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 HSE’s 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 River.
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 NAO’s 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
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
Also, the NAO index can be extreme negative which can
prompt a suppression of storms. In this case, the lower MidAtlantic 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
• This NAO trend
of negative to
neutral of
positive is often
key in the
and propagation
of East coast
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.
1. Enhances the intensity or amplitude of the negative
NAO in general and the Greenland Block negative
NAO in particular.
2. 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 wind.
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
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
• 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
Polar Vortex cont.
Polar Vortex and 50-50 Low (Blizzard of
Character of 500 hPA (mb) Trough
Cutoff Low. Low remains closed at 500 mb.
This setup gave Philadelphia 30 inches of
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
NNE—the 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
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 I95 corridor are
often along the
boundary between
frozen and liquid
precipitation. This
makes winter
forecasting one of
the toughest
aspects in ALL of
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
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 unlikely.
Other Factors:
Characteristics of
Moderate Snowstorms
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
polar vortex
(courtesy of
When a negative PNA can be ideal…huge 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)
Time of storm
• PNA was strong
positive during the
• 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
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 slope)
2. PNA trending positive (very steep slope)
3. AO negative
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 small."
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
(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
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.
(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 front.
Other Factors: 700 mb Analysis
According to Henry Margusity of AccuWeather, “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
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
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
“It’s 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
Other Factors: Weekend Rule (Dave
• 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
• 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 lowerMid 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 I95 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 Nor’easter 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 Nor’easter 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 area’s
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.
Typical Snowstorm : 3 Chances at
Receiving Accumulating Snow
A typical snowstorm has 3 phases or parts that can
deliver accumulating snow to a specified region.
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