John_Krasting's Blog

I've been getting a lot of questions lately asking me about what the coming winter will be like. The early indications so far are for an "average" winter.

One of the main reasons why our weather varies from week to week or month to month depends on the North Atlantic Oscillation (NAO). The NAO defines the relative strengths of a large area of low pressure over Arctic regions and an area of high pressure over the north-central Atlantic.

Changes in the strength of these areas of high and low pressure can influence the jet stream - which ultimately determines how cold it gets here in Philadelphia and where storm systems move in relation to us.

The NAO index is a way to measure this pattern. There are some solid patterns that develop when the NAO changes. For example, when the NAO index is negative, colder temperatures are more likely along the east coast. When the NAO index is positive, the probability of seeing more storms increases.

The UK Met Office predicts that the NAO index will be near zero this winter or just slightly positive. The translation is that the probability of an exceptionally cold or stormy winter is reduced.





The NAO is only one factor in determining the seasonal climate. It is, however, the most dominant feature in climate system during the winter months and it explains over 40% of the atmosphere's variability during the period from December to March (see the figure below, also see http://www.cgd.ucar.edu/cas/jhurrell/indices.info.html
#naopcdjfm)






Other climate features - such as El Nino/La Nina - also play an important role, and I will look at them further in later posts.

With the memories of Hurricane Gustav starting to fade, I came across this article that was published in the Chicago Tribune on September 1st.

Click Here

The article points out how blog, status update, and social networking sites played a unique role in the evacuation of New Orleans earlier this month.  There are certainly a lot of advantages in letting friends and family know your whereabouts – a task that proved difficult following Katrina.

The sites also allow people staying behind in the storm to get in touch with one another.  I would imagine that if I chose to stay behind, I’d want to know just who would be around during and after the storm to keep me company or to help clean up the mess. 

I just have one question, though – what do you do when the power goes out and your laptop battery dies?

Hurricane Ike rapidly intensified during the last 3 hours.  As of the 5 PM advisory on Wednesday, Ike was a category 1 storm with winds of 80 mph.  A special advisory was issued by the National Hurricane Center at 8 pm where Ike was upgraded to a catergory 3 storm with 115 mph winds.

The rapid strengthening of the storm was shown through substantial drop in the central pressure of the storm.  At 5 pm, the pressure was 984 millibars and had dropped to 960 millibars by 8 pm.

This makes Ike one of the most rapidly intensifiying hurricanes in the Atlantic, along with Hurricanes Charley(2004) and Wilma (2005).

http://en.wikipedia.org/wiki/Rapid_deepening

Flooding in New Orleans has always been problem. J.D. Rogers of the University of Missouri published a paper in May 2008 issue of the Journal of Geotechnical and Geoenvironmnetal Engineering that examined the main flooding threats to the city.

This study reports that since 1559, approximately 172 hurricanes have stuck the Louisiana coastline and 38 of these storms caused major flooding to New Orleans. The main cause of flooding from hurricanes is a storm surge that develops off of Lake Pontchartrain.

In October 1965, Congress approved $85 million dollars to fund a project that would build a system of levees and barriers. The system functioned well for 40 years and spared the city major flooding from hurricanes. The levees kept the city dry during Hurricane Camille, which stuck the Mississippi coast as a category 5 storm in 1969.

During the 1960s and 1970s, the Army Corps of Engineers proposed building tidal gates at the end of the drainage canals. The proposals were halted in the courts, since the Army Corps did not thoroughly investigate the environmental impacts. The Army Corps focused instead on increasing the height of the concrete flood walls. These plans were never fully completed by the time Hurricane Katrina stuck in 2005.

Today, rebuilding of the damaged levees left behind by Hurricane Katrina continues. The project is currently over-budget and running behind schedule. The Army Corps has, however, finished construction of the flood gates that were halted during the 1970s. The threat of flooding from Gustav might be the first test of these gates.

The question remains – is the levee system in New Orleans ready to handle flooding from another major hurricane? If not, then what could have been done differently?

A friend of mine, who recently finished his Ph.D., used to talk about a small study that he conducted back in the 1990s.  He studied the frequency of snowstorms in central New Jersey and found that Thursday was the most likely day to see a healthy accumulation of the white stuff.

Unfortunately, however, my friend’s results weren’t well-accepted by his peers.  Some people argued that his results were “coincidence,” others call them “unscientific.” 

I came across an article a few days ago that reminded me of my friend.  Researchers at NASA used satellite precipitation estimates to determine that it rains more between Tuesday and Thursday than from Saturday to Monday - mainly over the Southeastern United States.  The researchers’ full report can be found in the January issue of the Journal of Geophysical Research – Atmospheres.  This recent report deals with summer rainfall, however, and my friend studied winter snowstorms.  Despite this, there is a similarity between the two.

The main researcher on the study, Thomas Bell, commented to the Bulletin of the American Meteorological Society that local pollution may be enhancing rainfall.  The effects of pollution are similar to cloud seeding, and the pollution may be responsible for the heavier rain.  During the weekends, industrial activity slows down leading to less pollution.  Lower pollution then could eliminate the enhancement of rainfall on Saturday and Sunday.

I decided to take a look the summer rainfall record myself.  I broke down the daily precipitation events at Philadelphia International Airport from 1998 to 2007.  I grouped the results into sets of three days.  Sure enough, it rains more at the end of the week (Wednesday through Friday) than over the weekend.

These results make sense.  Philadelphia is a major city with a lot of industry.  It is entirely possible that pollution could be playing a role in affecting local precipitation here, as well.  More work needs to be completed in order to understand the robustness of this late-week enhancement of rainfall, and also how exactly pollution might be playing a role.

I hope that ten years later, however, my friend is finally feeling a bit justified about his results!

After last night’s rains, I started looking around for a sturdy umbrella. I just happened to come across this excellent piece of umbrella craftsmanship!

CLICK HERE TO LAUNCH VIDEO

A recent article published in this month's issue of the Bulletin of the American Meteorological Society (BAMS) has me thinking more about the vulnerability of our region to a hit from a strong coastal storm.

LINK: Article from BAMS

In this article, the authors discuss a storm surge modeling system developed at Stony Brook University on Long Island, NY. The models accurately reproduced flooding in New York City that resulted from a strong Nor'easter that hit the region in December, 1992. The model also forecasts moderate flooding in NYC and the metropolitan areas of Northern New Jersey, if the region were to be hit with a minimal Category 1 hurricane at high tide.

The authors conclude that more preparations should be made to prevent flooding from tropical systems and coastal storms. In particular, they recommend that storm surge barriers be built in New York Harbor to protect against flooding.

What do you think? Should we be as concerned as NYC? Are we prepared in the Delaware Valley to handle the flooding and surge associated with a hurricane? What do you see as our main threats? Do you think we should be doing more to prepare for coastal storms?

There has been some talk about an active hurricane season, and that the formation and intensification of Hurricane Bertha may be a sign of things to come.

Several reports have been citing El Nino/Southern Oscillation as being partly responsible for the early start to the hurricane season, but there are more factors to consider. One of the modulators of tropical activity is the Madden-Julian Oscillation (MJO).  The MJO is a feature of the climate system that typically influences weather in tropics on monthly to seasonal time frames.

http://en.wikipedia.org/wiki/MJO

In the Atlantic, the MJO can affect the environmental conditions in which hurricanes form.  When the MJO is favorable for hurricane development, wind shear is low and clusters of thunderstorms coming off the African coast become more vigorous.

Right now, the MJO weakly favors hurricane development in the Atlantic.  This might be why we saw the formation and intensification of Hurricane Bertha.  Bertha may not be alone this month as the MJO forecasts are favorable for storm development through the end of the month.   There are already some more strong waves moving off the African coast.

Since the MJO typically completes a cycle in 30 to 60 days, we might expect the MJO to become favorable again in early September.  Hurricane activity might be enhanced in the tropical Atlantic just in time for the climatological peak of the hurricane season.

Stay tuned!

A large brick of cement fell through the roof of a house in Naro-Fominsk, Russia, creating a hole approximately three feet in diameter.

Ironically, the cement was part of a program instituted by the Russian Air Force to create good weather on holidays near the nation’s capital.  A dozen planes were dispatched to drop silver iodide, liquid nitrogen, and cement powder into the clouds.  The project aimed to promote rainfall that would dry the atmosphere prior to important dates.

Weather modification is nothing new.  Many programs to increase rainfall or reduce the size of hailstones are in place here in the United States.  Most of these programs are centered in the Midwest and Desert Southwest where water availability is a concern.

There is some debate, however, around the effectiveness of such programs.  One of the most famous weather modification programs carried out by the United States was Project Stormfury, which ran from 1962 to 1983.  During this time, hurricanes were seeded with silver iodide in an effort to reduce the strength of storms that were close to making landfall.  The program was discontinued in the 1980’s, as there was little evidence to determine if the program had any real impact on the strength of the storms.

What is your thought?  Should we continue to investigate ways to control when it rains?  How would you react to a three–foot brick of cement in your roof?

MORE on the Russian weather modification accident

MORE on the background of weather modification

MORE on weather modification programs (including videos)

MORE on Project Stormfury

This Saturday marks the 4th Annual Great American Backyard Campout.

This event is sponsored by the National Wildlife Federation to encourage people to enjoy the outdoors by camping out in their backyards.  Check out their website for more details and take a look at the map of all the people near you who are planning to camp out Saturday night.

LINK:  http://www.nwf.org/backyardcampout/

It may not be the best weather for camping this weekend.  An upper level disturbance and a cold front to our north could spark some strong thunderstorms Saturday afternoon and evening.  If you decide to camp out, keep and eye to sky.  Here are some lightning safety tips:

LINK:  http://www.lightningsafety.noaa.gov/outdoors.htm

I will be hiking myself this weekend in upstate NY near Lake George.  Unfortunately, I won't be able to escape the storms either! 

A new type of weather radar is literally on the horizon!

The aging NEXRAD weather radar network deployed by the National Weather Service in the 1990's may be replaced in the coming years by a new low-power network of radars.

The main problem with the current radar system is an issue of wave propagation.  Radar dishes are angled slightly upward to avoid interference from buildings and trees.  Although this angle is small (0.5°), the radar waves propagate upward as they travel away from the radar dish.  Over long distances, such as 50 miles, the waves are too far up in the atmosphere to capture rain and thunderstorms that are happening near the surface.  There are gaps in the current radar network where locations are not adequately covered by the current radar systems.

Instead of installing additional Doppler radar dishes, the National Oceanic and Atmospheric Administration (NOAA) and universities across the county are working to deploy a new low-power radar system to fill the gaps in the existing network.  The new radar network - named  CASA or Collabortaive Adaptive Sensing of the Atmosphere - consists of small radar antennas that can be mounted on top of buldings and existing cell phone towers.  They work on the same principles of the current radar systems, but are more numerous and allow for more uniform coverage closer to the surface.

Traditional radars also take on the order of five minutes to make a complete scan of the atmosphere.  The new CASA radars will speed this time up dramatically and provide near real-time information about the weather.

The radar technology was initially developed by the Navy to track ships.  The new CASA radar antennas will also relay their data over a WiFi network.  The radars utilize high-speed wireless internet technology to communicate with each other and send their information back to meteorologists.  The new system is already being tested in parts of Oklahoma.

More on CASA from Popular Mechanics
More on CASA from USAO 1
More on CASA from USAO 2

Image from:  http://mirror.bom.gov.au/weather/radar/about/image_fa
q.shtml

Economists at Austin College and the University of Texas-Pan American studied how earlier lead times affected fatalities resulting from tornadoes.  Kevin Simmons and Daniel Sutter studied over 18,000 tornado cases between 1986 and 2002 and found that earlier tornado warnings were effective in reducing injuries by 32%.

In the severe cases, however, lead times longer than 15 minutes resulted in more deaths than the cases where no warning had been issued at all.  Simmons says the stronger, longer-lived tornadoes that result in the most damage and loss of life are the easiest to warn against.  While earlier lead times may be providing additional time for the public to prepare, there may not be many options for people to seek safety from the most powerful storms.  Simmons also raises the issue that people may make bad choices – such as attempting to outrun a tornado in a car – if the warning is issued with enough of a lead time.  Simmons makes it clear that he does not discourage early lead times; he just cautions that some storms might be too powerful for the increased lead time to matter. 

This raises some interesting questions.  What would you do if you had 20 minutes versus 10 minutes to prepare for a tornado?   Currently, the ability to warn against the strength of a tornado is not very good.  If you knew how strong the tornado was, would you act differently?

Article by LiveScience

With this weekend's temperatures in the 90's for the first time this season, this heat wave might feel particularly bad.

A recent commentary published in the International Journal of Epidemiology argues that there are many factors that determine how much the heat affects how we feel. How much water we drink, the amount of time we spend in air conditioning, our age, and the general state of our health all play a part in how we beat the heat.

The author of this commentary, Jianguo Tan from the Shanghai Urban Environment Meteorology Center in China, discusses how temperatures alone are not a good indicator of how bad a heat wave is. The afternoon high temperature is only part of the story; the amount of humidity, overnight temperatures, and even the amount of air pollution make one heat wave different from the next. While other studies have tried to create other objective ways of measuring all these factors. These measures, however, often fall short of capturing the full impact of heat on the body.

Tan comments that one of the most overlooked factors in the public's response to a heat wave is a tolerance factor. People who live in hot climates become accustomed to the heat. Likewise, as we transition in and out of seasons, our bodies adapt to handle extreme temperatures. While this season's heat wave has come a little early, our bodies have yet to adjust to the summertime heat.

Take it easy this weekend and take care of yourself; there are plenty of good ways to stay cool. While this heat wave may seem like too much heat too soon, it might help us adjust to the hot summer temperatures ahead.

Citation: Tan, Jianguo, 2008: People's vulnerability to heat wave. International Journal of Epidemiology, 37(2), 318-320.

A very close call in terms of snow for the viewers out on Long Island.  Steady precipitation associated with a coastal low now south of Cape Cod came within 50 miles of Montauk Point Sunday afternoon, sparing Suffolk County from any accumulating snowfall.  For the rest of Sunday night, some light flurry activity is possible east of the city, but the majority of the tri-state will be dry.

Monday will feature some sunshine, but with the low still lingering off the coast the winds will be strong.  Sustained winds between 15 and 20 mph are likely in the afternoon and gusts as high as 30 mph are possible out on Long Island.

On Tuesday, a front will approach from the west and bring with it some precipitation Tuesday night into Wednesday.  Temperatures north of city will be close to the freezing mark, so there may be a brief period of freezing rain but anything frozen will quickly change over to plain rain later Tuesday night into Wednesday.

After that, we catch a break on Thursday.  More rain is expected, however, on Friday.  Dig out your raincoats!

Have a good one!

Talk about some wintry weather this weekend.  There was some sunshine behind the  milky white clouds early Saturday, but clouds will thicken later in advance of some snow showers.

The atmosphere is very dry, so if you are looking at Fox 5 Sky Guardian and seeing precipitation over top of where you are and wondering where the snow flakes are, they are evaporating before they reach the ground.  The atmosphere will moisten up after dark on Saturday and most of our area will pick up some flurries or snow showers at times Saturday evening through Sunday morning. The culprit is an upper-level disturbance that is moving through the region.  Most place won't see any accumulation, but the best chance for a coating will be north of the city.

The upper-level trough will merge with an area of low pressure off the coast on Sunday.  As the storm intensifies, it will become breezy across the tri-state.  Late Sunday night, the storm may try to bring in some precipitation from off-shore.  This means that we could see some steadier snows late Sunday night into early Monday morning in parts of eastern Long Island.  Accumulations will be very light, but it may be a good idea to plan some extra time for the commute on Monday morning if you live on Long Island.

Next week, temperatures will warm up in advance of a frontal passage late Tuesday into Wednesday that will bring a chance of rain or snow.  After that, our next chance of rain will come on Friday as a storm system is forecast to lift from the Gulf of Mexico up into the Great Lakes.

Enjoy the taste of winter weather this weekend!