What the, Hail? The Story Behind the Ice Stones

It is officially spring and for everybody it means warmer temperatures, the blooming of flowers, trees, and crops, and, most importantly, severe weather.  A lot of people refer spring to severe weather because that is the prime time of a year for tornades since the majority of tornadoes occur between the months of April and July.  But with this kind of severe weather, there is another kind that happens much more frequently than tornadoes and that is hail storms.

Hail looks to be very simple a piece of ice that falls from the sky, but it is more detailed than that because it has to start off with a nucleus surrounded by water, then it has to grow, and finally fall when it becomes too heavy.  What does a nucleus have to do with a frozen ball of ice?  Everything!  What initiates hail is water droplets that are supercooled, i.e. they are colder than 32°F and not frozen, and they come in contact with what is called a condensation nuclei (sand, dust, salt, etc.)  When this happens the supercooled water droplet will turn into ice because it now has something to attach itself to and freeze.  Once when this part of a hailstones life or water droplets life takes place, the growing step begins to take place automatically.  As people have experienced each hailstone is a completely different size ranging from something as small as a pea to something as big as a softball, grapefruit, or, on extreme cases, bigger.  What causes this is the updraft of a thunderstorm, i.e. winds that are forcing moisture high into the clouds in the sky.  When a frozen piece of ice has formed other supercooled water droplets will collect on it and freeze on contact making the original ice stone bigger and bigger.  Depending on how strong the updraft is will depend on how big the hail stone is when it falls from the clouds.  This is where the final step takes into place.

Believe it or not, the growth of a hail stone is simliar to the growth of a tree.  How so?  Hail stones, just like trees, have growth rings.  With each growth spurt there are rings inside of it that shows how many times it grew.  The biggest difference is that the growth of a hail stone is much quicker than a tree. 
Just looking at these hailstones, you can see that they have at least 3 inner rings and the outer, jagged edges when it was falling to indicate that it grew at least 3 or 4 times in the clouds before it fell.  Amazing huh?

Here are a few interesting facts about hail:

The largest hailstone in diameter and weight ever recorded in the U.S. was 8 inches (20 centimeters) in diameter, circumference of 18.62 inches (47.3 centimeters), and weighed 1.93 pounds in Vivian, South Dakota on July 23, 2010.  To put this in perspective, this is about the size of a training soccerball, which is about 17 inches in circumference, that weighs nearly 2 pounds.  That's pretty big and heavy to fall from the sky!

Although the previous hailstone is the biggest in diameter and size it is not the biggest hailstone in circumference.  The biggest hailstone in circumference is the famous Aurora, Nebrask hailstone on June 22, 2003 that had a circumference of 18.75 inches (47.63 centimeters).  It had a smaller diameter of 7 inches (17.78 centimeters).

The costliest hailstorm in U.S. history occured on April 10, 2001 causing $1.9 billion of damage in Kansas, Missouri, and Illinois giving it the name of the Tri-state Hailstorm.

What is El Niño and how does it relate to Chris Farley?

Several people have heard of it and its sister, La Niña, but what is El Niño?  Some of us may think El Niño is a wrestler portrayed by Chris Farley.  As funny as that is, it is not a wrestler and it is not Chris Farley.  In spanish, it means "The Boy" referring to the Christ Child.  In meteorology, it is an increase in sea surface temperatures over the eastern and east-central Pacific Ocean that is above normal sea surface temperatures while cooling the western and west-central Pacific Ocean below normal sea surface temperatures.  This is a very unique phenomenon has a huge impact on the atmosphere that increases the frequency of precipitation, heat, and othere weather scenarios that can create flooding, droughts, and hurricanes (typhoons).  The sister of El Niño, La Niña, means "The Girl" in Spanish and is the complete opposite of El Niño.  La Niña is the cooling below normal sea surface temperatures in the eastern and east-central Pacific Ocean and the warming above normal sea surface temperatures in the western and west-central Pacific Ocean.

Severe Weather Event March 8-9, 2011

During this time of year it is not surprising to have a severe weather event and then a few days later have another one.  The last weather event was over the weekend where Louisiana got the brunt of it all with 4 tornadoes and a bunch of wind reports.  The only thing about the last storm event is that it was very limited to the instability it needed to create severe weather with the except of Louisiana.  This next event, however, is looking to be a little different than the last.  Here is what SPC is showing so far for the area to keep an eye on. 
A good sized area is highlighted for a slight change of severe weather and this shows even with the probabilities of severe weather occurring, but it is kind of misleading because of the 30% area that is hatched.  The hatched area inside the 30% means that there is 10% or greater of significant severe weather that could occur.  Since that area has a higher probability of seeing severe weather then I would monitor Louisiana, southwestern Arkansas, extreme northeastern Texas, and extreme southeastern Oklahoma.  I would not be surprised to see this area under a moderate risk of severe weather by tomorrow morning which will increase the possibilities of severe weather to occur in that area.  If you would like to read the details on why this area is being monitored heavily then visit http://www.spc.noaa.gov/products/outlook/day2otlk.html.

Since the above convective outlook starts from 12Z Tuesday (6 AM CST Tuesday) and ends at 12Z Wednesday (6 AM CST Wednesday) we will look at the forecast surface charts for that time period to show what is forecast to happen. 
This is at 6 AM CST Tuesday morning and the important things to look for on this is the surface low in the panhandle of Texas, the fronts and dry line connected to it, and the stationary front north of the surface low.  Ahead of the warm front is where the showers and thunderstorms will be occurring and even along the dry line is another area.  Kansas will be under the gun around this time as it is north of the surface low that will enhance precipitation of both rain and snow due various lifting mechanisms and temperature variability.  Lets move 6 hours ahead to 12 PM CST (noon). 
The low has slowly, but gradually moved towards the northeast keeping all of its fronts.  The difference is the moisture distribution.  Now there is a lot of moisture and precipitation being lifted and moved from the Gulf of Mexico into the Southern Mississippi Valley and Central Great Plains regions.  These are the areas that are being heavily monitored for severe weather to occur.  What may cause the chances for the severe weather?  The winds are a big factor for chances of tornadoes.  Winds in the middle layers of the atmosphere are westerly winds while the ones near the surface are from the southeast during this time period.  Two opposing winds can cause rotation and create tornadoes.  Lets move on and see how this event continues to evolve in the next 6 hours. 
This is showing the same situation but further east into Mississippi into southern Illinois.  This will be next area to watch for into Tuesday evening for severe weather that could cause wind, hail, and tornadoes.  The chances will most likely not be as high as the other areas, but are still just as likely to occur.  Finally, lets look on to the last 6 hours of the time period. 
Now into Wednesday morning and the system has pushed into Alabama stretching into Ohio and Indiana.  At this time the system is most likely going to be produce heavy rain with a small chance of severe weather to occur.  Tornadoes are highly not likely to occur at this time because the winds in the middle and low levels of the atmosphere are pretty much parallel which does not favor rotation, but hail and strong winds are still likely to happen.

This may seem like another severe weather event to embrase for, but it isn't all about tornadoes, damaging winds, and hail.  There is another important factor that is just as likely to happen in this event that happened last weekend and that's flooding.  There are a lot of places that are very prone to flooding right now due to them being large cities with no way to handle lots of heavy rain or due to rivers and streams that are at or near floodstage.  Here is the forecasted amount of rain to fall starting from Monday evening at 6 PM CST and ending at 6 PM CAST Wednesday. 
There is a bullseye of heavy precipitation in southestern Louisiana, southeastern Mississippi, and southern and central Alabama along with northern Georgia.  These are all areas with 2.5" and greater of precipitation to fall.  With these amounts flash flooding is possible and flooding from rivers and streams are also very likely which explains why there are so many flood warnings and watches of various kinds already in effect according to the following map that shows the current hazards. 
All of those shades of greens are all pertaining to some type of flood issue that is likely to occur by Wednesday.

Overall, This is something to really watch for and to monitor closely.  I will keep you posted and updated tomorrow as the event draws nearer to the Southeast Region.

Midweek Weather Update and Forecast

The start of this week was exciting for meteorologists and a panic for the public with some severe weather that crossed the Tennessee River Valley and Ohio River Valley.  There are 207 storm reports from the system that pushed through Monday.  15 of those reports are tornadoes, 168 are wind reports, and 24 are hail reports. 
For details on all of the reports, go to http://www.spc.noaa.gov/climo/reports/110228_rpts.html.

Now we are in a calm period where high pressure is really signifying the weather the Southeast is experiencing with calm to light winds, temperatures gradually warming up, and clouds being thin and scattered about.  For the ones that enjoy this kind of weather enjoy it while it lasts because when Friday comes around it will be a similar event as Monday was.  Another cold front will be sweeping through the Southeast region once again making way for some more showers, thunderstorms, and always the possibility of severe weather.  Here is a surface forecast for Friday morning to Friday evening. 
Friday morning some moisture along with some precipitation starts to come in from the Gulf of Mexico ahead of the cold front in the Great Plains and a surface low off the Louisiana Coast.  The moisture and precipitation will continue to be pushed inland from the Gulf of Mexico as the cold front in the Great Plains advances easteward.  It may not seem like much just by looking at these images, but here is something to be concerned with. 
The bubble of slight risk of severe thunderstorms is something to watch out for.  You are probably thinking that this is only a slight risk and chances are not high enough to be concerned about.  This slight risk was issued by SPC in their day 3 severe thunderstorm outlook.  That is 3 days ahead and they are already preparing for the chance of severe weather.  Something to keep an eye out for.  Lets go further ahead into the weekend on Saturday morning and Sunday morning with the surface forecast. 
Saturday morning shows the surface low continuing its eastward movement with a frontal trough, which is the orange dash line ahead of the cold front.  Typically this is where thunderstorms and severe weather will develop if it is ahead of the cold front and cloudy skies behind it before the cold front comes through.  If all of the conditions are right, then we could be expecting an interesting event to unfold for the Southeast.  By the time Sunday morning comes around this is what it is forecasted to look like. 
The low pressure system and its fronts have moved closer to the Atlantic Coast spreading rain, with some chances of mixed precipitation further north, all along the coastline.  Although that concerns the eastern part of the Southeast region, what's behind it is just as important.  The deep trough in the Great Plains is a surge of cold air that will be cooling down the southern parts of the U.S. with cold temperatures that hasn't been seen since the last snow event.  This surge of cold air will continue to move eastward over the Southeast region by Monday morning giving the beginning of next weeks work week to be rather chilly.

Overall, lets just enjoy today and tomorrow and keep an eye on the weather for Friday and Saturday for the Southeast and along the Atlantic Coast as the weekend draws to an end.  Since warm weather is present and spring is practically in place for most of the U.S. severe weather is always a possibility because of the warm, moist air towards the Equator is wanting to push northward and the cold air from the Arctic is wanting to push southward.

Update on Tonight and Tomorrow's Severe Weather Threat

Things are really cooking up in the Southern Mississippi Valley and continuing to push eastward.  First let me go ahead and show you how things are set up right now. 
You can see a thin red line of where the heaviest precipitation is and the strongest storms are stretching from northern LA to western KY.  This line is what is causing all the watches and warnings to pop up right now and isn't anything to take lightly.  Here are the current watches and warnings (these change constantly so keep in mind this is for 7:36 PM CST) 

Tornado Warning

Tornado Watch

Severe Thunderstorm Warning

Severe Thunderstorm Watch

Winter Weather Statement

High Wind Advisory

Flood Warning

Flood Watch / Flood Statement

Fire Weather Advisory

Here are the storm reports as of 7:42 PM CST 
Looking at these you can see a few red dots meaning tornado reports.  These were reported in Arkansas and Missouri.  The green dots represent hail reports and there are only a few of them and thats because there isn't much low-level below freezing temperatures and the updrafts are not strong enough for most storms to really produce much hail.  The rest is all blue dots meaning very strong wind reports.  If you compare this image with the radar you can see that most of the tornadic weather is in western TN and KY.  That long squall line that was lined up with the Mississippi River is predominantly creating very windy conditions where wind reports will be high likely ahead and in the path of the squall line.  That means majority of MS will likely see wind reports for this event and not hail reports and a very possibility of a tornado being reported.  Western TN has already seen several tornado warnings and  they haven't been varified yet, but that part of TN will likely see a few tornado touch downs.

That right there is where the southern states stand at this moment.  Continuous updates will be made and if you want to follow me I do have a Twitter account that you can follow all that is going on.  All images from above are from NOAA and Wunderground.

February 24th & 25th 2011 Severe Weather Threat

Something different this time to talk about for the United States than what I have talked about.  We are getting closer to spring and that means severe weather is knocking at the backdoor.  As a matter of fact, that's exactly what is happening right now for the Southern Mississippi Valley.  There is a potential for some severe weather to be seen in Louisiana, Mississippi, Arkansas, eastern Texas, Tennessee, and Alabama.  Here is the current convective outlook from Thursday 1200Z (6:00 AM) to Friday 1200Z (6:00 AM) from the Storm Prediction Center. 
What this is showing is the risks of severe weather.  The brown line shows the general area where severe weather is possible.  The important lines are the green "slight" risk line and, more important, the red "moderate" line.  The slight risk line is saying that all the states and parts of states within that line are in a slight risk of severe thunderstorms.  The moderate risk line is saying that every portion of the states inside that line are in a moderate risk of seeing severe thunderstorms.  This may not seem like much, but allow me to put this in perspective for you.  The Storm Prediction Center will issue slight risk on the day 2 convective outlook, but it isn't common for the Storm Prediction Center to issue a moderate risk on a day 2 convective outlook which indicates that something in the atmosphere is going to mix just right to create severe weather.  If you are wondering what the percentages or probabilities of severe weather for this region is here is a map to show you. 
The pink 45% line is telling us that the area within that line has a 45% or higher chance of seeing some severe weather.  The same goes for 30%, 15% and 5%.  There is another signifcant color surrounding the 45% line and that's a blue line that's hatched inside.  What this is telling us is that the hatchet area has a 10% or greater chance of significant severe weather which means that cities such as Tunica, MS; Memphis, TN; Texarkana, TX & AR; and Little Rock, AR.  What is the difference you ask?  It is basically the difference between experiencing a severe thunderstorm to just produce lightning and heavy rain to a thunderstorm that could produce strong winds, hail, and the possibility of a tornado.  If you would like to read the discussion on why this could happen and the details to it then visit http://www.spc.noaa.gov/products/outlook/day2otlk.html.

Several NWS offices are showing various graphics on this severe weather threat.  I will show you images from NWS offices from 4 different NWS offices.  Here is what the NWS in Little Rock, AR is showing on the severe weather for Thursday. 

Now an image from the NWS in Shreveport, LA. 

Images from the NWS in Jackson, MS. 

Finally an image from the NWS in Memphis, TN. 

The point of all these is to see the perspective from each NWS office that is going to be experiencing the severe weather for tomorrow.  The highest threat stays around the Memphis area and west TN, northern MS, and most of Arkansa.  Alabama was mentioned at the beginning to get the severe weather and they will, but they will see the highest probability of severe weather on Friday.

I will keep everyone updated on the severe weather threat tomorrow as it progresses on things start to unfold.  I will also post more images tomorrow on an updated blog on this event pertaining to Alabama and other areas that will be effected with this event on Friday.  If you would like to see and read more details of this event from the previous NWS offices here are the thinks to each one for you to look at.  For Little Rock, AR: http://www.srh.noaa.gov/lzk/, for Shreveport, LA: http://www.srh.noaa.gov/shv/, for Jackson, MS: http://www.srh.noaa.gov/jan/, and Memphis, TN: http://www.srh.noaa.gov/meg/.

Spring in Winter

What transition from last week to this week.  Lets have a flash back on last week.  Here is what the setup was in the upper levels of the atmosphere. 

This is a 300mb map for the middle of last week when all of the cold weather was coming through.  The purple colors is what known as a jet streak which is an area of strong winds compared to what is surrounding it.  This map shows where the jet stream is which separates warm air from the south and cold air from the north and is caused by this contrast in temperatures.  Now what this is showing is the path that the cold front travelled that gave the southern states all of the snow.  The winds are significant because they are showing how fast the weather pushed on through which holds strong because the snow lasted less than 12 hours before it completely left Mississippi and rapidly moved across the other southeastern states.  The pink lines are areas of upper level divergence meaning areas that air is being lifted from lower levels of the atmosphere creating some instability which is a key factor for areas of precipitation.  The main point of the map is to show how deep the trough is that was pushing all the cold, arctic air into the Southeast region.

Now lets look at the pattern in the upper levels for today at 00z on Thursday (this is at 6PM CST). 

Can you see the difference?  If not, then allow me to tell you and show you what makes this week so much different, and more spring-like, than last week.  First, I would like to point out the ridge that is visible in the central part of the U.S.  This may not seem like anything special, but what it means is that warmer air is pushing further north and giving the southern states warmer air along with a more stable atmosphere.  The last thing I would like to point out is where the jet stream is.  Much further north than last week which keeps us away from the paths of low pressure systems.

So now you know the reason why this week is the way it is, last week was the way it was, and why it all happened.  For all of you spring lover's, expect the current pattern to persist because these upper level troughs and ridges last much longer than the ones closer to the surface.  Since the ridge is west of the southeast states, this day to day pattern of warm, spring-like temperatures in the upper 60's and lower 70's and some places much warmer will continue to occur until this weekend.  A trough will reach the Mid-Atlantic Region and could spread some showers in for the Southeast Region and with the warm temperatures the possibility of a thunderstorm here and there is not out of the question.  A short ridge will pus the trough out of the way leaving the southeastern states dry for Tuesday and Wednesday.  A deep, slow moving trough will be creeping towards the southern states in the middle of next week giving way for some higher chances of precipitation and cooler temperatures.