Andy_Johnson's Blog

Hurricane names are decided by the World Meteorological Organization. There is a set of 6 names in the Atlantic basin, which includes the North Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico. If a storm is very deadly or costly, the name is retired. This is done for sensitivity reasons, as well as, for historical reference reasons.

The Regional Association IV Hurricane Committee decided this week to retire three names from the 2007 hurricane season - Dean, Felix and Noel. These storms caused extensive damage and many deaths. The new names will be Dorian, Fernand and Nestor in 2013. The other names from 2007 will remain the same in 2013.

 

We have seen an unusally active tornado season in 2008. So far we have had 814 tornadoes across the country with the majority in the southeastern states. Normally, we should have seen just about 380 by this time. The normal average for the entire year is 1270.

Here is a graph comparing this year with recent years and with the average:

 

We are in the drier part of the year now but the rainy season usually begins from late May to mid June. Another event that occurs soon is the beginning of hurricane season on June 1. A tropical wave moved off of Africa yesterday. It's much too early for tropical waves to develop into depressions or storms since the water temperature in the eastern Atlantic is still too cool. But it is a reminder to be prepared for the upcoming season and have a personal plan in place. The plan doesn't have to be elaborate but just think ahead about what you would do should a tropical system threaten us this summer.

The first name on the list is Arthur and the second name is Bertha. Let's hope we do not make it all the way to Wilfred.

Normally, April is our driest month with a total of 1.8 inches of rain. So far we are slighty above normal already for the month due to yesterday's rains. Earlier this week, it almost looked like summer with regular afternoon and evening thunderstorms occurring each day. As I mentioned in an earlier blog entry, it is unusual that we have had a fairly wet winter and spring in Florida since we are in La Nina conditions. Almost without exception until now, La Nina is associated with drier than normal winters and springs in Florida.

Unfortunately, a lot of the rain events have occurred on weekends this year. The good news is that the rains are coming at regular intervals, not all at once. This allows water to soak into the aquifer more instead of just running off. Also, normally this time of year we are worried about the possibility of wild fires. So far we have been fortunate the the regular frequency of rain events has prevented any major forest firest.

What will the rest of the spring bring? Will La Nina act more normally and cause us to dry out or will we continue to get regularly spaced rain events that will help us through the fire season? Let's hope that the latter is the case. It would be better to have regularly spaced rain events in time than the ups and down with droughts and flooding.

After the official start of spring this past week on March 20, temperatures will be heading back down to winterlike values, at least for a day or two. A strong cold front for this time of year will cause temperatures to fall to slightly above freezing on Tuesday morning in inland Hernando and Citrus Counties. Even in the Bay area, mid 40's are a good bet on Tuesday morning. If we see 44 in Tampa that still won't be a record, although it will be close. The lowest temperature in Tampa on March 25 was 36 back in 1968.  There have only been 2 days in April that readings fell into the 30's in Tampa - 38 on April 6 and 7, 1891.

As I have mentioned before in an earlier blog post, the La Nina of 2008 is atypical. Usually, La Nina conditions mean a dry winter and spring for us. We continue to have cold fronts and upper level systems bringing rain every 4 to 5 days. Unfortunately, many of these systems have occurred on the weekend. Yesterday was a washout in many areas. There are signs that some more rain could return next Saturday.

We have already set our clocks ahead (early) this year. Spring officially begins this Thursday, March 20th. With spring you look forward to flowering plants beginning to bloom but also you have to deal with pollen. I have a several oak trees in my yard. This time of the year the leaves fall first and then pollen pods seem to fall like rain for about a week or two. I thought maybe this year that since we have had frequent cold fronts with regular rain events combined with wind the pollen would be quickly washed out of the trees and the air. The wet weather just seems to make the pollen pods stick to everything and they are still falling. So much for not dealing with allergies this year.

At least, plants are beginning to bloom. I noticed my irises blooming this past week. The very light green young leaf growth on the oaks made a great contrast with the bright blue skies yesterday. I look forward to this time of year. It is usually relatively quiet weatherwise and we have some breathing room before we begin the summer thunderstorm and hurricane season. Enjoy it while it lasts, in spite of the pollen and allergies.

El Nino and La Nina are strongly correlated with rainfall patterns in Central Florida. The basic rule is that strong El Nino winters are wet in Central Florida and strong La Nina winters are drier than normal. This is clearly shown in the graph below (the link is http://www.srh.weather.gov/tbw/images/tbw/nino/tpaavgr
ain.png)

But this time all the rules seem to be thrown out. We are in a strong La Nina pattern and yet our rainfall in February was well above normal and we continue to see strong cold fronts with squall lines and severe weather threats in Central Florida fairly often. La Nina is a cooling of a large portion of the equatorial Pacific Ocean. Even though it is far away, its effects on our weather in the past have been fairly consistent. This year is an exception.

That is one reason why meteorology and science, in general, is so fascinating to me. There is always something we can learn that doesn't "fit the patten". It makes us re-evaluate what we think we know and try to further explain it. Does anyone have any suggestions as to the reason why this La Nina is different from the others?

We have suffered a great loss in the recent passing of Dick Fletcher. Even though we work for differerent stations, I frequently see Dick at the monthly American Meteorolgocal Society meetings that I preside over. Dick was a long time member of the national American Meteorological Society (A.M.S.), as well as, a member of the West Central Florida Chapter of the A.M.S. He participated in local meetings quite frequently, even though he would have to rush from work at WTSP in Pinellas County on his dinner break to attend meetings as far away as the National Weather Service in Ruskin and return to do the 11:00 PM Weather. He mentored students and volunteered for our "Teach the Teacher" meetings at U.S.F.  where he demonstrated scientific experiments. Numerous chapter meetings were held at WTSP Channel 10 due to his efforts. He contributed his vast knowledge of meteorology during the meetings and individually with members in casual discussions before and afterward. He held strong opinions about weather forecasting and presentation but always backed them up with his own research and investigation. He really loved every aspect of the weather and wanted to present the most correct information possible. Dick held the AMS Seal of Approval for television weathercasting for many years and was awarded national Weathercaster of the Year by the AMS in 1986 for his coverage of Hurricane Elena in 1985. In addition, he obtained the Certification for Broadcasting Meteorology from the A.M.S. a few years ago. We had several discussions about the new certification program. On behalf of the officers, members and all of your friends in the West Central Florida Chapter of the A.M.S. and all of the meteorologists at FOX 13 we will miss you very much and our thoughts and prayers will be with your family.
 
Andy Johnson
 

I have the leaves falling off of the Oak trees this past week and new green leaves are appearing. We are going to get a brief cold snap this week on Tuesday and Wednesday but as we get into the latter part of February cold snaps become less frequent. It is still possible to have freezing temperatures in Tampa even in late February. For instance, it has been as cold as 27 on February 26th, 1967. We've even had 20's into March but they are very rare. The coldest March reading was 29 on March 2, 1980.  The latest date we have had temperatures of 32 and below in Tampa was 32 on March 5, 1893. No freezes have even occurred in April in Tampa but readings have been cold enough to see some patchy frost. It was as cold as 38 as late as April 7th in 1891.

So, if you are planning on planting a garden or sensitive plants odds are that you are safe if you live from the Tampa area southward if you are near the coast. If you are father inland or in our northern counties you might want to wait a few weeks.

A few days ago I noticed that the temperature in Fort Yukon, Alaska was -61 degrees. We haven't seen readings like that in quite some time. Eventually, as cold air builds over Alaska, it releases into the lower 48 states. That is happening now with bitterly cold air in the Northern Plains.

However, the upper level winds are not favorable to bring the really cold air into Florida. The brunt of the cold blast will move off of the eastern seabord. In order for us to get really cold here ususally the cold  air mass has to enter the country from Canada into Montana. When the cold air mass enters the country in the eastern Dakotas and Minnesota, it usually ends up moving too far east to cause a freeze here.

Since the whole atmosphere is connected, it amazing that we have to look so far away (to Alaska sometimes) to figure out our own 7-day forecast.

 

Yesterday, Punxsatawney Phil saw his shadow and according to legend 6 more weeks of winter will follow. Of course, now we have more sophisticated ways of predicting the weather but it is entertaining to watch the furry little animal look for his shadow.

How did this tradition begin? There used to be a holiday called Candlemas on February 2 which was celebrated in Europe hundreds of years ago. The Europeans had a superstition that if a badger saw his shadow on Candlemas there would be 6 more weeks of winter. Of course, since Europe is in the middle latitudes it didn't really apply to locations farther south such as Florida. On Candlemas people would pray for mild weather for the rest of the winter. There was a much colder period of time called the Maunder Minimum when temperatures were much colder around the globe from about 1645 to 1715. After 1715 the trend of general global warming began. In general, the colder periods in history were associated with more human suffering and less food supply.

When the Europeans came to the New World, they could not find any badgers. So they used the next best rodent, the native groundhog. So actually, Groundhog Day should be called Badger Day.

 

After several mornings with dense fog the weather pattern will be changing significantly this week. A cold front will move through later tonight. The ingredients that are condusive to fog in our area this time of year are warm overnight temperatures, higher than normal dewpoints, dewpoints higher than the water temperature (of the Bay, Gulf and swamps) and light winds. Once the cold front moves through later today all of those incredients will be taken away and will stay away through much of this week .

So, get ready for our turn at some more winterlike weather. It won't be as cold as the freezing temperatures we had about 2 weeks ago but you will definitely notice the change.

Usually when you think of life threatening weather, tornadoes, severe thunderstorms and hurricanes come to mind. There are times when stable weather occurs, however, that can also cause problems. I'm referring to heat waves, cold waves and even fog. Ironically I had written my blog 3 days ago regarding fog in the Bay area in the winter months. I had mentioned that of the 19 days a year where dense fog occurs in Tampa 5 of those days are in January. January has the highest number of fog days followed by December and February.

The tragic incident that unfolded in Polk County this morning with the 70 car pileup occurred in an area known for fog development. There are basically 2 kinds of fog, advection and radiational. Advection involves cold air moving over a warmer surface but radiational fog can develop in place. Since the winds were nearly calm in the area this morning, the fog was likely of the radiational variety.

Fog is essentially a cloud at the ground. It occurs when the air temperature falls to the dewpoint temperature and the relative humidity reaches 100%. In addition, cold air is "heavier" and more dense than warm air. The area around the accident site was in a bowl shaped depression that allowed the cold air to drain into. The temperatures were much colder in Polk County than closer to the coast. For instance, Bartow had a low of 48 but Tampa had a low temperature of 58 with a dewpoint of 56. The temperatures in Polk County fell to the dewpoint at which time the fog formed and then kept falling another 8 degrees or so along with the dewpoint.

Part of the reason, I believe, is that the recent cold snap last week cooled off the Green Swamp and nearby lake temperatures to very low values. This was followed by a rapid warm up where not only the temperature rose but also the dewpoint. The air temperature rises more quickly than water temperature so there was a lag in the nearby water temperatures. The dewpoint temperatures were higher than the water temperatures in some areas yesterday. It was almost as if the air were "super-saturated". From the aerial video that I saw from Randy Powers' flyover there was an area of dense fog that had pooled into a limited area. On either side of this "pool" the visibility was low but not all that bad. The fog did not appear to be very deep either. You could still see the tops of trees poking out from the fog bank. So people driving at 70 MPH or more ran into almost a curtain of  fog.

There is some question and I'm sure that it will be debated in the future as to  what additional influence smoke had regarding visibility reductions. From early aerials, though, you could see the smoke rising from the vehicles involved in the accident but not from a nearby controlled burn that was supposedly 90% contained. Also, the controlled burn was on the north side of I4.

Always use low beams when driving in fog. California's interior valleys have experienced dense fog days involving 100 car pileups. However, today's event involved more vehicles than I can remember in Central Florida.

Our thoughts and prayers go out to the many people affected by today's tragic events.

 

Dense fog blanketed most of the viewing area this morning. We don't get alot of fog days here in the Tampa Bay area. On average we see 19 days a year where the visibility is less than or equal to one quarter of a mile. Of those days, the most (5) are in January, 3.3 in December and 2.8 in February. The average in June is .3 which is due to fog formation the morning after a heavy thunderstorm.

In the winter, we usually see fog after we have a had a cold snap. The reason is that there is a lag between water temperature and air temperature. As cold air moves from the continent across the gulf, the temperature over land drops faster. In this past week, the temperature in Tampa reached 29 on Thursday. As a result the water temperature began cooling and reached 54 in the Gulf Saturday. Now that overnight air temperatures and the dewpoint temperature are above 54 fog forms.

 Remember that to achieve 100% humidity the temperature and dewpoint must be the same. If the dewpoint is higher than the water temperature, the water vapor in the air is easily condensed into fog.

Last Sunday , December 16, we witnessed a tornado move through portions of Pasco County. Skytower HD VIPIR performed well as I was showing it live on air  from about 4:45 AM to 6:00 AM.The radar clearly picked up the circulation of the tornado.  Doppler radar can show wind, as well as, rain. I noted a gust to 100 MPH on air about the time the tornado was hitting the Land O' Lakes area at 5:15 AM. Fortunately, everyone must have gotten the word about the tornado since no injuries were reported. Most of the time weather in Florida is tranquil but we do get our share of severe weather.

The chart below shows all tornadoes in peninsular Florida (including the Tampa Bay area) durin the period 1950 to 1994. From the graph you can see that tornadoes are fairly rare in December but not unprecedented. November and December are the 2 months having the fewest number of tornadoes. June has the highest number of tornadoes but  most of the summertimes tornadoes are very weak and short lived and associated with afternoon thunderstorms. The exception in the summer  is when the tornadoes are spawned by tropical cyclones. In the winter months, tornadoes are caused by squall lines ahead of cold fronts.

 

 

 

 

 Even though the highest monthly tornado totals are in the summer, there is a secondary spring maximum in March. Usually, the spring tornadoes are stronger. The graph below shows that the greatest number of strong tornadoes (F2-F4) is in February, March and June. There have been no recorded F5 tornadoes in peninsular Florida.