Tuesday, April 26, 2011

Take tropical notice of what happened today

The little tropical  swirl that has been evident since the weekend took some very significant action today.  While the center of the low level closed circulation plodded westward through the southern Bahamas heat, humidity and convection spread thunderstorms and heavy downpours inland through the Carolinas and parts of VA.

Did you notice the summertime temperature, steamy humidity, low billowing clouds, and downpours which some occurred with virtually no radar warning.  Could this be a foreshadowing of tropical storms this summer?   Had the center of the storm been stronger and therefore "stacked" higher then it would have most likely followed the same flow which was aimed right at us.

The small swirling low pressure has separated
from the tropical plume. 
Image Source: Univ of Wisc SSEC
There is a risk of severe thunderstorm activity tomorrow and more likely Thursday as an approaching cold front collides with the existing heat and humidity.  This is nothing like the once in a lifetime caliber outbreak over a week ago but caution should be exercised nonetheless. 

Saturday, April 23, 2011

The Travails of an April Tropical Low

April development of a tropical storm system is very rare.  The one attempting to get started in the SW Atlantic has an artistic looking low swirl that has the banded features that one would look for in a storm.  So, even if the winds are great and the water temps are marginal why is the storm failing yet to thrive?

First, let's look at the storm:

Well defined swirl in the SW Atlantic.
Source: Univ of Wisconsin SSEC

The failure to thrive seems to be caused by dry air in the atmosphere which is starving the storm of being able to produce the convective (like thunderstorms) activity needed to deepen the system and expand it's influence.
Driest air exists where the low level swirl is located.
Source: Univ of Wisconsin SSEC

As time passes so does the window of opportunity for the system to strengthen before the return of fast westerlies sweeps it away.

Thursday, April 21, 2011

Storm Formation in the SW Atlantic

No April Fools!  There is a storm system taking shape in the Southwest Atlantic which could acquire some tropical characteristics during the next few days.  WeatherBell Analytics Meteorologist Joe Bastardi has been anticipating this feature for quite some time.  While the storm is interesting it is not expected to play a role in our weather.
National Hurricane Center gives the forming system only a 10% probability
of reaching Subtropical or Tropical storm strength during the next 2 days.
It is important to take notice of the fact that the storm system is forming before the official start of the Atlantic Hurricane Season.  Next week a strong Bermuda High and marginal water temperatures will provide some key ingredients to warm the storm center and give it an opportunity to get a name.

Models seem to agree that the system will weaken and turn SW over the next 3-5 days.  None of them seem to be impressed with the storm's prospects for early notoriety.

Sunday, April 17, 2011

A Sort of ... Green light to plant your summer garden

While I do have some concerns about snowcover in Canada and the Arctic providing a high availability of cold air late this month into May it is time to go ahead and plant your summer garden.  This is not a 100% confident "Green Light", maybe greenish-yellow.  Here are my reasons:
  1. The weather pattern here in NC and Central VA is stormy.  No intrusions of cold air capable of frost is expected during the next 2 weeks.
  2. Despite the availability of cold air there is no guarantee that the eastern US would be the target.  
  3. Seedlings can only be maintained in cups for so long. Some of my plants are consuming their water supply daily.  So, either accept a low risk of an unusual late April/early May front or the plants outgrow their containers.
As always.  I planted some tomatoes and peppers today.  Therefore my plants share the same risk as everyone else.

Coming this week:  Summer and Tropics 2011 preview.

Saturday, April 16, 2011

URGENT: Tornado Watch as Severe Thunderstorms are now INBOUND

Ladies and gentlemen;

      I have never seen the National Weather Service add the phrase "This is a particularly dangerous situation" to a Tornado Watch.  The storms are now crossing the Triad and should reach Chapel Hill near 1:20-1:30 then cross the whole Triangle during the following 45 minutes.

     What has me really worried is the potential for tornadoes that are stronger and cut paths of destruction.  While twisters are not very common in our region they usually are the weak variety that bounce from location to location striking with 75-90 mph winds.  TODAY storms which do not contain tornadoes will often have winds near 70 mph!

     Please be sure to be in a safe shelter away from windows during the storm passage.  Do not bet your life on being caught driving on the road or out in the open.

    Here is a link to the Raleigh Radar: http://radar.weather.gov/radar.php?rid=rax&product=N0R&overlay=11101111&loop=no

Friday, April 15, 2011

How to recognize that a tornado is coming in NC and VA

Source: Univ of Wisc SSEC
Serious thunderstorms are expected on Saturday Apr 16.  The storm system crossing the midwest is a monster.  The front attached to the system has caused a great deal of damage with damaging wind, hail, and tornadoes.

Jackson, MS was damaged by a tornado which cut quite a path.  This dramatic video shows a large twister in action.

Here in NC and VA tornadoes are rare.  Major ones even moreso.  Most of our twisters have winds less than 100 mph and bounce rather than cut a path.  Unlike other regions of the country tornadoes are difficult to see coming because of heavy rain and the fact that they bounce from location to location.

My three experiences of being near a tornado, one actually seeing a funnel featured distinctive clues which can be useful to you.  If you see the following then run to a tornado safe shelter right away.
  • Heavy rain stops suddenly.  Sky might even lighten a bit.
  • Hail is hitting the ground/
  • Lightning is striking close and often.  
Waiting for the sound of a freight train can be too late because the low hills and trees dampen the sound and prevent the funnel from being seen.  So by the time the tornado is seen it is often on top of the person looking for it.  

Fortunately the major tornadoes that blow out walls, flip cars, and cut a path of damage are rare in NC and VA.  Tomorrow's storms have potential to produce the uncommon twisters.

If a tornado warning is issued or the weather conditions described above indicate that a twister is nearby then take the following steps:
  • Go to an interior room , hallway, or bathroom away from windows.
  • Avoid temptation to look for the tornadoes.  Broken glass and pieces of toys can become misslies!
Have a safe Saturday!

Monday, April 11, 2011

Concerned about damaging severe weather Friday-Saturday

It has been interesting trying to figure out what form the amplification signal provided by the March 31 and April 1 surge in the SOI.  Finally there is some model agreement on a scenario that I think fits the current climate's tendency for wild weather events.

An intense storm system is expected to deepen over the central Plains and move NE dragging both upper level cold and a strong frontal system through our region. It is bad enough that a cold front is going to ram into unseasonably warm air.  Upper level cold enhances probabilities of hail, damaging wind, and tornadoes.

Here are 2 projections of what could happen in the Friday evening - Saturday time frame:

  • GFS - Depicts a deepening system headed to the Great Lakes with a negatively tilted, trailing front which would bring the biggest risk of severe weather to VA and points north.

  • ECMWF - Storm follows a track just south of the Great Lakes to the NE US.  This scenario has more cold air behind it.
We will need to keep an eye on the situation this weekend.  Another update will occur as we get closer to the event.

Saturday, April 9, 2011

Spring Bowling Ball ready to strike Central NC-Southern VA

WeatherBell Analytics Meteorologist Joe Bastardi introduced me to a term that best describes a cut-off pool of cold air caught in a low pressure system which is a frequent occurence in Spring, especially during La Nina years.  These systems bring sharply colder temperatures and strong to severe storms as they roll through. Joe calls them "Bowling Balls".

The current bowling ball brought thunderstorms last night then highs in the mid to upper 50's, 20 degrees colder than yesterday.  Now the system is about to hit us from its backside with strong to severe thunderstorms along its warm front!  Take note of the systems comma shape.
Bowling Ball system is cutoff from the jet stream
Source: Univ of Wisconsin SSEC

Thunderstorms early in the evening will feature areas of heavy rain.  Later tonight those in the paths of the frontal storms may see high winds, risk of downpours,hail, and tornadoes.  One storm near Charlotte, NC is showing tornado characteristics.

Current Radar shows the severe thunderstorms in SW NC and areas of moderate to heavy rain/thunder moving through Central NC and Southern VA.  Fortunately Richmond appears to be too deep in the cool pool to get more than rain.  The whole bowling ball is moving SE.
National Weather Service Radar shows storm system
moving SE.  I am concerned about the "tail" on the south and
rear quadrants.  Those areas are experiencing severe weather.
I will send a general alert later this evening if the severe quadrant becomes likely to affect the Triangle/NC or the Richmond area.

Monday, April 4, 2011

Super high SOI signalling dramatic weather ahead?

The Southern Oscillation Index is based on the difference in surface pressure between Darwin, AU and Tahiti related to the tendency up or down.  Negative numbers and/or falling tendency signals a progressive (west to east) weather pattern.  In this case the index soared to 74, the highest I have seen, signaling an amplified (north-south) and often a blocked pattern.  The chart below shows that this occurred on April 1st. 
SOI soars to 74 on April 1st
Data Source: The Long Paddock
Computer models are showing no specific events today here in Central NC and VA on April 14-15.  This is not a surprise as models have been simply terrible through this La Nina episode.  I think that the GFS shows an interesting intense storm in the Plains that would be a headline maker if its true.
April 14 GFS - Very cold airmass dominates the east.
Count the number of sub 1000mb storms on the map!

One clue that the cold air mass affecting the east beginning at the middle of this month has a lot of merit is the strong warming event in the Stratosphere advancing from Siberia to the Pole.  Such an event acts like a plunger pushing arctic air into the middle latitudes.  Unfortunately cold air surging into the the typical gyrations of spring further south is a recipe for severe storms, frosts, and freezes.
Sudden Stratospheric Warming (SSW) advances toward the Pole.
Source: NOAA Climatic Prediction Center

So, interesting days lie ahead.  You can definitely that I will be paying close attention to weather developments and will keep you informed.