Severe Weather Climatology, Risks and Information

tornado-widescreen-wallpaper-tv00tSevere Weather Climatology

Obviously severe weather can happen all year round, but for the Delaware region most of the threat is usually contained in the late spring and summer months. A severe thunderstorm is one that produces winds 58 mph or stronger and/or hail 1 inch in diameter or larger. Below shows the probability of severe storms in the continental U.S. based on 30 years of climate data. Each frame is one day from March to August.

Majority of the significant threats are wind related and flooding that usually accompanies strong thunderstorms. Tornado activity in the region is not frequent but can occur. A majority of these storms are usually at the low end of the Enhanced Fujita Scale (EF0-EF2). The EF Scale rates the strength of tornadoes in the United States and Canada based on the damage they cause.


The Storm Prediction Center

The Storm Prediction Center (SPC) is part of the National Weather Service (NWS) and the National Centers for Environmental Prediction (NCEP). 2014_SPC-2.1Located in Norman Oklahoma, their mission is to provide timely and accurate forecasts and watches for severe thunderstorms and tornadoes over the contiguous United States. The SPC also monitors hazardous winter weather and fire weather events across the U.S. and issues specific products for those hazards. The SPC uses a suite of products and multiple of specialists from lead forecasters, mesoscale forecasters, outlook forecasters and etc. that continuously monitor the continental US for the potential for severe damaging weather events. (For more info on the SPC go here –> About the SPC)

Risk Categories Associated with SPC’s Outlooks

Here is an example of  a Day One Outlook issued by the SPC and definitions of the categories.



The Difference Between Watch and Warning


Understanding the purpose of a watch is important and should not be confused with a warning. A warning means that hazardous weather is occurring at the moment / imminent and you should take actions to protect yourself. Below is a full list of categories issued by the SPC and NWS Offices.

Winter Weather Patterns

Is Winter Finally On The Way ??

Are we going to begin seeing a more a more winter like pattern as we head into Jan ??

Look at the big Picture

Let us begin to look at the larger state of the climate based on El Nino-Southern Oscillation (ENSO) Phase.  We are currently trending into a  neutral El Nino state which means waters in the Pacific Equatorial region are near normal in temperature.  Below is a  generalistic look of usual conditions for neutral El Nino type pattern:

Now there are multiple on-going factors that need to be taken in consideration, and obvious El Nino conditions differ from West Based to East Based and with other factors that are in play. Forecasting long range are ‘best guess’ based on what current conditions are likely to be.

Here is a reminder of the 2019 – 2020 Winter Outlook from CPC:
(Click either pic to go to the NOAA CPC Page for more detail)

Modiki El Nino 

 Modiki El Nino Is when portions of the ENSO are actually cooler then normal on the West of South America. This usually drives colder temperatures for the East and Mid Atlantic.

However, we have not seen evidence of this to date:


Other major factors are what we call teleconnection patterns. Teleconnection refers to a recurring and persistent, large-scale pattern of pressure / circulation anomalies that spans vast geographical areas in the atmosphere.

So lets try to go through and give you a graphical representation of each, and try to explain how a -NAO -AO and +PNA are the best set up for a Mid-Atlantic / East Coast for winter storm setup.

Below is a look at characteristics of a Negative / Positive Arctic Oscillation (AO)

You can see here in a negative phase that the cold in the stratosphere is basically displaced into Canada and North America.

Here is a graphical representation of a North Atlantic Oscillation (NAO) and its general effects:

NAO2A Negative NAO  is also sometimes referred as the Greenland Block , East Based NAO because high pressure establishes itself there allowing for the strongest flow of cold into the Mid Atlantic. West based NAO where high is positioned move over Canada is little less favorable.

… and Finally A Look at the Pacific North American (PNA) Pattern

ElNino_Mod (1)

Image by Steve Tracton (2010)

Positive PNA is also sometimes referred to as  a ‘zonal flow’ usually brings milder conditions from the west straight along to the east.

So wait then, why did we see snow then here in December of 2013 where the patterns didint match any of these and we still got good snow fall totals ???

There is another pattern called the East Pacific Oscillation (EPO)

 The EPO is the high altitude  wind flow over the Eastern Pacific which is influenced by the ocean temps.. When the EPO is in a positive phase, there is usually troughing on the West Coast, while milder air engulfs the inland and Eastern part of the country. The positive EPO limits troughs in the East.  When the EPO is in a negative phase it has the opposite effect on the East Coast where a -EPO encourages a northwesterly flow from Canada into the Eastern part of the U.S, allowing for cold air to intrude, but without the assistance of a stronger -AO or -NAO we end up with more transient shots of cold air  that usually support snow more west of the coastal plain as we saw in 2013.


Maden Julian Oscillation – MJO can be a strong influences to extreme events our weather. Though we usually talk about this during hurricane season and tropical development it can have a profound influence during the winter including Arctic air outbreaks during the winter months.

MJO is large propagating area of tropical convection (showers and thunderstorms) that has a strong influence in Jet Stream patterns. Patterns can cycle from 40-50 days and travel eastward across the tropical equator.  The MJO is classified in Phases as it moves through each of the regions as dictated in the forecast below. We usually see effects in regions 7 8 & 1. The further away from the circle the stronger the effects.  (Circle is sometimes categorized as the Circle of Death because the effects are minimal.)

Current MJO Forecast

Generalistic Look at the MJO and its effects in each phase.

Sudden Stratospheric Warming (SSW)

A Sudden Stratospheric Warming (SSW) of the atmosphere refers to a swift jump in temperatures in the stratosphere that is sometimes linked to the onset of cold weather in winter.


Water Temperatures – This early into the year, water temps usually dont help us on the coastal plain that much. It is usually not till we get more into the heart of the winter season when water temps get cooler and have a less dramatic effect on potential snow storms.

Finally Storm Track – Inland storms also favor snow to West and rain to the East, with a South to South West wind bring warm temps during the storm, and then cold air as the system moves out with slight chance of snow on the back-end.


Okay so what are we seeing today that may be indication that white winter is coming… ( or NOT coming) ?

AO – Trending Positive (Like to See Negative)
NAO – Trending Positive (Like to see Negative) 

PNA – Negative (Like to see Positive)
EPO – Positive (Like to see Negative)
MJO – Outlook to Phase 4 or 5  (Like to see in 1 & 2 or even 7 & 8)

So in closing.. we have a way to go yet to a pattern that will drive us with good snow results. (That is if you like the snow of course.) A persistent cold pattern is really not there though we can not rule out arctic intrusions with some really cold temps as we head into late January.

Though we are not in the heart of winter yet we still have a way to go and we recommend you prepare for it in any case. Make sure you have a Winter Kit for your vehicle including warmers, de-icer, etc.

You cant go wrong by being prepared !

Hurricanes – What is SAL ?

Today we thought we take you into the different climatological  and environmental aspect of Hurricanes and what effects them in today’s post we will cover SAL

Saharan Air Layer (SAL) – is an elevated layer of Saharan air and mineral dust and occurs during the late spring through early fall over extensive portions of the North Atlantic Ocean between the Sahara Desert, the West Indies, and the United States.

SAL is a dry air mass driven off of Saharan Desert and can sometimes be abundant with dust as seen in the above figure. Dry air will definitely suppress thunderstorm development and weaken tropical cyclones causing downdrafts to occur around the storm.  Below are two images of impacts of Sal.. first showing the current Sal and the second a Water Vapor Loop also showing the extent of dry air in the Atlantic basin.

One thing to Note..  Dry Air is not just a Africa Component.. it exists across the globe and is just as effective in degrading tropical cyclone and thunderstorm development.

Evening sunsets can be enhanced when SAL reaches the East Coast.

Hurricanes an Overview

What is a Hurricane ?

The Atlantic Hurricane Season begins June 1 and ends November 30 of each year.

A hurricane is a Topical Cyclone with sustained winds reaching speeds of 74 mph or higher.

?? Okay.. so whats a Tropical Cyclone..??

Well basically put.. a tropical cyclone has the following characteristics, a warm core low pressure system that develops over tropical (and sometimes subtropical) waters, and has an organized circulation. The categories of these systems are usually based on surface winds and are as follows:

Tropical Disturbance – A discrete tropical weather system of apparently organized convection usually maintaining  itself over period of 24 hours and can be associated with easterly waves off of Africa.

Tropical Depression – When a tropical disturbance develops a closed circulation (e.g., counter-clockwise winds blowing around a center of low pressure), it is categorized as a tropical depression. Tropical depressions contain max. sustained one-minute winds of 38 mph (33 knots) or less, at an elevation of 10 meters.

Tropical Storm – A tropical cyclone is given a name by the National Hurricane Center once it reaches tropical storm status. Tropical storms have maximum sustained one-minute winds of 39-73 mph (34-63 knots).

Current Name List 

Hurricane – Hurricanes have sustained one-minute winds of at least 74 mph (64 knots), at an elevation of 10 meters. Winds in most hurricanes can become much stronger. Hurricanes are categorized on a scale of 1 to 5 based on their wind speed via the Saffir-Simpson Hurricane Wind Scale. (<–See link for types of damage associated each category)

Major Hurricane – A tropical cyclone with maximum sustained winds of 111 mph (96 knots) or higher, corresponding to a Category 3, 4 or 5 on the Saffir-Simpson Hurricane Wind Scale.


Number of Tropical Cyclones per 100 Years

The above chart shows the distribution of the number of storms over a 100 hear period. The  peak of the season is from mid-August to late October. However, deadly hurricanes can occur anytime in the hurricane season.


Below graphic shows also the associated areas where storm originates as the season progresses.


 Whats important to note here is that a hurricane does not necessarily have to originate from Africa.. though those that normally due usually can be more



The figures below show the zones of origin and tracks for different months during the hurricane season. These figures only depict average conditions. Hurricanes can originate in different locations and travel much different paths from the average. Nonetheless, having a sense of the general pattern can give you a better picture of the average hurricane season for your area.

danger     HAZARDS    danger


    • Along the coast, storm surge is often the greatest threat to life and property from a hurricane. In the past, large death tolls have resulted from the rise of the ocean associated with many of the major hurricanes that have made landfall. Hurricane Katrina (2005) is a prime example of the damage and devastation that can be caused by surge. At least 1500 persons lost their lives during Katrina and many of those deaths occurred directly, or indirectly, as a result of storm surge.

    • Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides. Storm surge should not be confused with storm tide, which is defined as the water level rise due to the combination of storm surge and the astronomical tide. This rise in water level can cause extreme flooding in coastal areas particularly when storm surge coincides with normal high tide, resulting in storm tides reaching up to 20 feet or more in some cases.

  • High Winds

    • Tropical storm-force winds are strong enough to be dangerous to those caught in them. For this reason, emergency managers plan on having their evacuations complete and their personnel sheltered before the onset of tropical storm-force winds, not hurricane-force winds.
    • Hurricane force winds of 74 mph or more, can destroy buildings and mobile homes. Debris, such as signs, roofing material, siding and small items left outside become flying missiles during hurricanes. Winds can stay above hurricane strength well inland.

  • Rain / Flooding

    • Tropical cyclones often produce widespread, torrential rains in excess of 6 inches, which may result in deadly and destructive floods. In fact, flooding is the major threat from tropical cyclones for people living inland. Flash flooding, defined as a rapid rise in water levels, can occur quickly due to intense rainfall. Longer term flooding on rivers and streams can persist for several days after the storm. When approaching water on a roadway, always remember Turn Around Don’t Drown.

  • Tornadoes

    • Hurricanes and tropical storms can also produce tornadoes. These tornadoes most often occur in thunderstorms embedded in rain bands well away from the center of the hurricane; however, they can also occur near the eyewall. Usually, tornadoes produced by tropical cyclones are relatively weak and short-lived, but they still pose a significant threat.

We will be posting more on hurricanes as we get closer to the heart of the hurricane season..including the Impediments to Storm Development, NHC  Forecasting Models,  NHC Aircraft Reconnaissance, FEMA;s Role and some information on what occurs locally when we are effected by tropical systems.




National Hurricane Center’s Web Site 

Hurricane Preparedness Week


Hurricane Season Begins on June 1st 

….are you ready ?  

History teaches that a lack of hurricane awareness and preparation are common threads among all major hurricane disasters. By knowing your vulnerability and what actions you should take, you can reduce the effects of a hurricane disaster.

Hurricane hazards come in many forms, including storm surge, heavy rainfall, inland flooding, high winds, tornadoes, and rip currents. The National Weather Service is responsible for protecting life and property through issuance of timely watches and warnings, but it is essential that your family be ready before a storm approaches. Furthermore, mariners should be aware of special safety precautions when confronted with a hurricane.

Download the Tropical Cyclone Preparedness Guide (PDF) or follow the links for more information. But remember, this is only a guide. The first and most important thing anyone should do when facing a hurricane threat is to use common sense.


Click on the Above Image to be brought to the NOAA Site

Fall Seasonal Hazards

Some Fall Hazards to Consider
We have definitely seen an abnormal start to fall, with temperatures way above normal for this time of year.

Now though we seeing changes on the horizon and also seeing more leaves drop from the trees. So now would be a good time to cover some safety tips as we go under this transition to more winter like weather.

    1.  LEAVES – Wet leaves can create a hazard for pedestrians in the fall by making sidewalks slippery. IT can also make roadways slippery as well. Clear leaves from pedestrian walkways and use extra caution when driving on roadways that have wet slick leaves on them.

      Do NOT Drive thru Piles of Leaves. This time of year kids love playing in the fall especially in piles of leaves. Be mindful of the fact that there may just not be leaves in those piles, watch for children.

      Yard Cleanup : Use common sense when it comes to cleaning up yard from fall debris.  Leaf burning in the State of Delaware is prohibited by law.  Keep gutters clear and use caution when utilizing ladders by ensuring your wearing appropriate foot gear and ladders are positioned on flat surface. Use certain tools that are specifically made for removing debris from gutters to make the job easier.

    2. FALL DRIVING – We already mention the obvious of wet leaves on roadways but there are other things to consider as well that we just sometimes take for granted.Bright Sunlight  occurs later in the morning at sunrise, it can also present challenges for drivers. Have a pair of sunglasses in the vehicle to wear when the sun is bright is a good strategy. If it becomes too difficult to see because of bright sunlight or glare, a good strategy is for the driver to pull over until he or she can see again.

      More erratic temperature swings we see as we drive closer to late fall. As the temperatures drop further at night, a driver will need to spend some extra time in the morning scraping frost off his or her vehicle. Shady spots on the roadway may be home to black ice, which a driver may not be aware of until his or her car starts to skid on it.


    1.  CHANGE BATTERIES IN SMOKE DETECTOR – On Sunday November 5th we changed our clocks back an hour but this also servers as a reminder to check batteries on our smoke detectors twice a year.
    2. Fireplaces should be inspected at least once a year to ensure that they are operating properly and chimney is swept. (per the CSIA – Chimney Safety Institute of America.)
    3. Service your furnace before the cold autumn and winter weather sets in, be sure to call your heating and cooling company to service your furnace. A specialist should inspect the furnace to make sure everything is in working order and that there are no leaks.
    4. Use Caution with Space Heaters they can be an effective way to warm up a chilly room, but it’s essential that you read the instructions on the unit before you use it. If your space heater requires venting, make sure you have vented it to the outdoors. Never use your stove or oven to heat your home; only use space heaters that are approved for this purpose. Always allow at least three feet of empty area around space heaters.

    Now is the time to think about restocking the trunk with extra blanket, shovel, hand & feet warmers, de-icer, etc. It wont be long till old man winter is knocking on the door. Start thinking about prepping your vehicle for the winter to come.


    Safely Enjoy the Seasons Beauty

    Reminding you of some of these safety tips hopefully will let ya enjoy the rest of the fall preparing you for those hazards we can avoid.


Madden-Julian Oscillation (MJO)

What is it ??

There are many weather phenomenon that have repetitive variation to them in which we see different states and respectively different outcomes in the environment and atmosphere. One of these is called the Madden-Julian Oscillation, or simply called MJO.  The MJO was actually founded not until the early 1970’s by  Roland Madden and Paul Julian of the American National Center for Atmospheric Research (NCAR) while observing tropical wind and pressure patterns.

The MJO can be thought of as a tropical disturbance that propagates eastward around the global tropics with a cycle on the order of 30-60 days and it consists of two phases. The first phase is the convective phase or enhanced rainfall and the second is the suppressed rainfall. In the enhanced convective phase, winds at the surface converge, and air is pushed up throughout the atmosphere. At the top of the atmosphere, the winds reverse (i.e., diverge). Such rising air motion in the atmosphere tends to increase condensation and rainfall.


In the suppressed convective phase, winds converge at the top of the atmosphere, forcing air to sink and, later, to diverge at the surface. As air sinks from high altitudes, it warms and dries, which suppresses rainfall. In this circumstance Green is upward unstable environment while the Brown is dry and stable.

Measuring and Forecasting MJO

MJO is forecast in phases ( not to be confused with the  wet phase and dry phase mentioned earlier ) according to which the region of the world its unstable.  Below is a forecast of the MJO as of August 8th 2016.


This may look little alien as it were but, its actually pretty straight forward.

History is depicted as the Ref line here beginning around June 29th then continuing getting a little more enhanced in Phases 1 & 2 as it continues to more recent observations (blue line ). The forecast is predicted via the green line. The yellow lines in this instance symbol the  individual ensemble members, which all seem to point to strong Phase 5.

Mathematical methods combine cloud amount and winds at upper and lower levels of the atmosphere to provide a measure of the strength and location of the MJO. When the index is within the centre circle the MJO is considered weak and when it is outside of this circle the index is stronger and will usually move in an anti-clockwise direction as the MJO moves from west to east. For convenience, it is defined in 8 different MJO phases / locations in this diagram.  Below is a look at the 8 Phases and how they correlate to locations.



Why do we look at the MJO ?

Remember, this is really a look at the tropics and the conditions of the environment going forward.  When we see MJO in Phases outside 7, 8 and 1 it would tell us the chance of cyclone development is slight because the instability that is needed to keep thunderstorms alive is just not present. Hence why we have not seen much activity in the Main Development Region so far this year.

The MJO also effects weather and climate outside the tropics, in particularly in the mid-latitudes between 40° and 70° in both hemispheres where the prevailing winds are westerly (from the west) and the atmospheric flow pattern is highly variable with alternating low and high pressure systems.  The impacts to North America  may include heavy precipitation or cold outbreaks over time periods of 1-2 weeks. The MJO impacts the western U.S. through “teleconnections,” a term that refers to climate anomalies having a relationship between each other at large distances (typically thousands of kilometers). For example, rainfall in the Indian Ocean associated with the MJO is often related to cooler and wetter weather in the western U.S.


So the MJO plays just another part of the wonderful world of fluid dynamics that affect our weather. They tend to have usually pretty consistent effects for us here in the east but can be mitigated by other factors as well. As we head into the heart of the hurricane this just one of many items to monitor as indication of more favorable cyclone genesis.