This Week’s Severe Weather Opportunities

Originally posted on ZoomRadar

With March just a few days away and signs of spring in the air across parts of the U.S., this week will offer a few opportunities for some spring severe weather to break out. The first opportunity will arise Tuesday, especially into the afternoon through the night, thanks to a strong low pressure center which will strengthen over the border region of Colorado, Nebraska, and Kansas. This low will continue to push off toward the east northeast throughout Tuesday and Tuesday night bringing with it a cold front to its south which will be the main concern for the severe weather area this day. The Storm Prediction Center’s Day 2 Probabilistic Outlook depicts areas with a slight chance of severe weather over the location of the low pressure, between Nebraska and Kansas, as well as where that cold front will meet up with some nice warm and moist air from the south over eastern Oklahoma, Arkansas, southern Missouri and Illinois, and into western portions of Kentucky and Tennessee.

Ignoring where the models believe initiation of storms may occur, from my last few posts you may have seen the models have been doing a fairly poor job this far out lately, I will take a look at a few factors which may help define where this storm threat will be on Tuesday. A major concern on Tuesday will be how much warm and moist air can reach up north, especially to the more northern slight chance bubble. The GFS model for midday Tuesday shows some moist air reaching up north but dew points would still struggle to hit 50°F across that Nebraska and Kansas border region (shown below). Just taking this into consideration I would say the severe threat here will be minimal and really only exists at all due to the large amount of rising air occurring there from the surface low as well as some strong positive vorticity advection and warm air advection aiding in this rising air. Additionally, strong winds aloft due to a large 100 knot plus jet streak could help aid by creating some shear. Best threat over this region would appear to be some hail and potential for some damaging winds.

The larger threat for this day comes into play for the more southern area at risk for severe thunderstorms. Dew points across this region will reach and exceed the 55°F mark, especially across the southern portion of this threat area where dew points could potentially hit the upper 60s (shown below). Additionally, a large jet streak aloft with winds in excess of 100 knots will help aid by creating some shear which will especially be the case for the western half of this slight risk area. This area will also all be under some strong warm air advection and a low level jet will even form overnight across the Arkansas and Missouri area (shown below).

Taking all of this into consideration, I would expect this slight risk area to be the main concern for Tuesday and Tuesday night with a wide array of potential severe weather impacts. However, based on the data currently available I would suspect that the best chances for tornadoes exist in the southwestern zone of this slight risk area meaning a city like Little Rock should keep alert to this potential.

Moving into Wednesday now, the Storm Prediction Center’s Day 3 Probabilistic Outlook shows a large area of slight risk once again along this advancing cold front. I will not go into as many details about the potential threats here as it is still a ways out however I would like to point out the amount of moisture the GFS model is expecting this storm system to be dealing with.

A large area of 55°F and greater dew points will stretch from Mississippi across to the Atlantic Coast and up into North Carolina and even into southern Ohio. This will be quite a bit of moisture for this system to work with and should result in an overall greater severe threat on this day then the day before. The threat will also be enhanced by some warm air advection and a low level jet over Tennessee and Kentucky into Virginia.

Additionally, a jet streak will help aid in strong winds aloft and may really help create for some shear across parts of Kentucky and Tennessee which may be aided by a strong gradient in wind speeds aloft. With all of this in mind, I would expect that the SPC map is a good indication as of right now of where the threat will lie this day and night. Main threats from this event should be damaging winds but a few tornadoes may be possible especially across Kentucky and Tennessee where the severe weather indicators look to be most favorable at this moment.

The last chance for severe weather this week will result from a low pressure system forecasted to from over southeastern Colorado and move east into southern Missouri before beginning to move more northward into Michigan and Ontario. The threat for severe weather from this system could develop during the day Friday over parts of the southeast and continue right through the day on Sunday, pushing slowly to the east. While this event is still a ways out and a lot could change, the GFS model does depict a lot of moisture with this system with dew points hitting some pretty high levels over parts of the southeast and Midwest on Friday as shown below.

It could be a rough week for some, but it is that time of year again. Keep it tuned to this blog for more updates on the severe weather situation this week as they arise.

Strong Storms for the South Thursday and Friday

Originally posted on ZoomRadar

It is that time of year again when many companies as well as states publicize their Severe Weather Awareness Week. After such tragic losses from last year’s tornado season, the first step toward not allowing something like that to happen again is education. Many steps have been taken this past year to try to improve the warning of citizens but it is also equally as important for citizens to be prepared to take shelter when they are told to do so. This should involve more than being surprised by the warning at the last minute and scrambling to find where you can shelter. It is much smarter to know when your area has a chance of severe weather days in advance of the actual event. This allows you the ability to continue to check back in on the situation as it nears as well as being able to make and change your plans accordingly for the day and/or night when the event may occur. In this post I will be giving many of you a first look at a threat which has just begun to really catch the eyes of meteorologists last night into this morning. I will take a look at what the NAM model and the GFS model are predicting and talk about any differences between the two as well as give you what area I think will experience the greatest threat from this two day event. However, as I stated before, it is important to keep up to date on situations like this and two of the best sources for this are the Storm Prediction Center and the National Weather Service.

To this event now, the Storm Prediction Center has just issued its new Day 3 Convective Outlook and its new Day 4 through 8 Convective Outlook this morning. They have highlighted a large area of the south to be under the threat for severe weather on Thursday (Day 3) and Friday (Day 4). Cities stretching from Brownsville to Charlotte and Bowling Green may see a good chance at some severe weather Thursday into Thursday night with cities such as Jackson and Atlanta being placed under the greatest risk currently. Friday, cities from Virginia beach down the east coast into the Jacksonville and Tallahassee areas would have the greatest chance for severe weather at this point.

With those general areas in mind, I am going to look some now at the models and see what they are forecasting as far as processes that may help lead to a severe weather event. First, let’s just take a look at the surface temperatures. Below is the NAM model’s output for Thursday evening showing some very warm air over the south with temperatures well into the 70s across most of Texas, Louisiana, Mississippi, Alabama, Georgia, Florida, and South Carolina. Additionally, the model depicts a nice south to southwest breeze across this area which will allow warm and moist air to flow in off of the Gulf of Mexico.

As you may remember from my Spring Severe Weather Outlook post, I cited above normal Gulf of Mexico water temperatures as one of the things that may help out severe weather this season and looking at the current sea surface temperature anomalies below, one can see that the temperatures in the Gulf are currently above normal in most spots.

Returning to the modeled surface now, by the midnight area, the NAM model really shows this moisture working its way into the Gulf states and temperatures remaining quite warm with many values in the mid and upper 60s. You can also now see the very dry air behind and large temperature gradient along the surface cold front which will be pushing through allowing for lines of thunderstorms to form along and ahead of it. Continuing into Friday which I am not showing here, the NAM continues to show this cold front pushing towards the coast removing the warm and moist air with it. The GFS model, which I did not show here, paints a very similar picture but pushes the cold front through maybe a hour or two earlier than the NAM is.

Looking to the upper air now, the 850 mb NAM model depicting conditions for the early night on Thursday, shows us a few important features. First off, the cold front is still very pronounced at this level both in temperature and moisture differences between ahead and behind the front. Additionally, very warm 850 mb temperatures in the mid 60s are occurring out in front of the cold front across portions of Texas, Louisiana, Mississippi, and Alabama. This is due in part to warm air advection occurring in this area blowing very warm temperatures at this level across southern Texas and Mexico where readings are in the upper 60s and even reaching the 70 mark. Maybe the most important feature though is a very strong low level jet with winds over 50 knots centered over Mississippi and Louisiana. The GFS shows pretty much the same set up but does show the colder air seeping into Texas much faster which may limit the amount of warm air advection that could occur across the Louisiana and Mississippi areas.

Looking towards Friday morning now, the NAM model shows some warm air advection still occurring but most of it is over Florida and not nearly as strong as it was on Thursday night. Also while the low level jet remains fairly strong, it is mostly advecting in cold air now. The GFS shows this same thing happening.

Looking to the upper levels of the atmosphere, the NAM model depicts a large jet streak which will form throughout the day Thursday and into Thursday night. Below is the model output for what the jet streak should look like around noon on Thursday. The jet streak is not very pronounced at this time with basically two smaller jet streaks occurring, one over the Midwest into the mid-Atlantic and another across the south, in a somewhat unorganized jet stream.

This all changes Friday night with the formation of a large 170 knot plus jet streak. This will not only create for very strong winds aloft but the right rear quadrant is located right over the area of concern for severe weather. This will provide for lots of extra uplift and is the one feature that really continues into the next day giving strength to the prediction for severe weather to continue on Friday along much of the southern half of the east coast.

The GFS model has this jet streak in almost the same location, however it never really creates it with such intensity. The GFS maxes the wind speeds out around 150 knots and does not have these strong wind speeds spread out across as great of an area. This can be seen in the image below for Friday morning.

This is just an early look at what may be happening as we head into Thursday and Friday this week across the south. Slight changes in model runs are still occurring and there are some differences between the GFS and the NAM as you have seen. Based on the current information, I would say the Day 3 Convective Outlook issued by the SPC is a very good representation of where the threat areas lie Thursday into Thursday night. However heading into Friday, the Day 4 Outlook may be relying to heavily on the strength of the jet streak to suggest a severe weather threat. While some areas in this area will likely be hit with severe weather, I think it is the southern portion of this Day 4 Outlook that will see the greatest threat. So please stay aware in the next couple days, especially if you live across Louisiana, Mississippi, and Alabama as most of the severe weather affecting these states will hit under the cover of night, providing for even more danger to life. Additionally, besides the lines of thunderstorms that are expected to occur there appears to be some chance for supercells to form with this system.

Here Comes The Rain And Storms!

Originally posted on ZoomRadar

A shortwave impulse lifting out of Northern Mexico on Friday should provide the energy for the formation of a low pressure system to develop along the Gulf Coast. This system could bring two major impacts in the form of heavy rain and the potential for severe thunderstorms across parts of the southeastern U.S on Saturday and Saturday night.

The HPC is currently forecasting a large area of the southeastern U.S. to be affected by some heavy rainfall from this system. Many areas along the Texas Gulf Coast, southern Louisiana, southern Mississippi, Alabama, Georgia, and South Carolina have the potential to see in excess of an inch and a half or rain between now and Sunday morning. It would not be out of the question if some localized areas were to pick up three inches or more of rainfall, with most of this falling on Saturday.

Taking a look at the NAM model’s 850 mb map for Saturday morning, strong southerly winds will be blowing in warm and moist air from the Gulf of Mexico providing for plenty of moisture and the uplift needed to create some heavy rain as well as thunderstorms. With models varying between each other as well as on consecutive model runs on the exact track of this system, there is still uncertainty in the areas for greatest risk of heavy rain as well as greatest risk for severe thunderstorms. Judging from the current NAM model run depicting the 850 mb level, warm air advection would place the greatest uplift across basically the same areas that are forecasted by the HPC to receive the heaviest amounts of rainfall.

That being considered, taking a look at the NAM Model’s 500mb map for the early afternoon on Saturday, shows a large area of positive vorticity located over Texas associated with the upper level trough. However, out in front of this across Mississippi, Alabama, and Georgia we do see varying pockets of vorticity which are being advected downstream of their respective locations. Baring this in mind, I would expect the potential for embedded heavier rain and thunderstorm bands within the large swath of precipitation that will be associated with the surface low as well as the potential for short line segments of thunderstorms outside of this large zone of precipitation. However, keep in mind that the image below is just model output and therefore specific areas of vorticity could easily change miles in one direction or another so try not to get carried away with predicting exact locations of these rain or thunderstorm bands.

Below is the current Day 3 Categorical Outlook from the SPC depicting a large area under slight risk of severe thunderstorms Saturday and Saturday night. The area at risk is pretty much the area the models have defined as being under warm air advection, receiving strong southerly winds from the Gulf of Mexico, and as having those pockets of vorticity go through. I would expect that the SPC will not sway in the area of this forecast too much though slight changes may be needed if the warm and moist air makes it farther north than expected or not as far north. The main threats right now would be damaging winds but also depending on the exact setup, we could end up seeing at least a few tornadoes spawn from this event. The hail threat should not be as large as these two factors just due to the amount of warmer air aloft however this does not mean that in some storms with stronger updrafts, severe hail could not occur.

Another factor that could really narrow down the severe threat area for us is the location of the jet stream. The current NAM model image below shows a large 150 knot plus jet streak centered over Mississippi and Alabama. The main area of concern here will be the right rear quadrant of this jet streak as it will provide for an area of uplift. If you take a look at the model loop, you would see that this area basically carves out a spot across the southern portions of Mississippi, Alabama, and Georgia as well as the Panhandle of Florida.

Taking a look at the SPC’s Probabilistic Day 3 Outlook, this is exactly where the SPC has highlighted an area for a heightened slight risk chance and if things keep progressing the way the models think they will, this area or an area very close to this may well be highlighted as a moderate risk by the SPC as we get closer to the event in my opinion.

The strength of this event will depend on the development of this surface low and how much warm and moist air it can pull in from the Gulf. If the system can pull in a lot of this air and line up nicely will the jet streak aloft, we could be looking at an outbreak of storms across parts of the southeast this weekend. Another factor to consider as this system sets up will be the extent of the storms northward which will be mainly dependent on the track of the low and how far north the warm front can extend. It is definitely something everyone should keep an eye on, especially those that live in these areas. I will do my best to post again on this subject before the event occurs to update everyone on the situation.

Cold Air Invasion!

Originally posted on ZoomRadar

The United States is being invaded by a threat to our people, plants, pets, and pipes. No it’s not some kind of biochemical warfare, it’s just a little gift from the season many of us forgot existed this year, winter! One of the largest blasts of cold air this season is currently affecting temperatures across the United States. After a winter that bottled most of the cold air up north of the United States and Canadian Border, this blast will bring freezing temperatures all the way to the Gulf of Mexico and Mexican border in spots. The current surface analysis shows the big picture with a large cold front now off of the east coast and a secondary cold front trailing this just across the Appalachian Mountains.



Strong north and northwest winds are helping aid in pushing this cold air south and creating for some stinging wind chills, especially later tonight. Current air temperatures as of 18Z show a 31°F reading at Little Rock, 16°F in Chicago, and just 5°F at Bemidji, MN all of which will be dropping much lower tonight. Many areas across the south are under frost advisories and freeze warnings for tonight as cold air like this has not really penetrated into these areas this year. Additionally, the strong winds behind the reinforcing cold front have prompted wind advisories and even a few high wind warnings with gusts up to 60mph in a few areas this evening and tonight in the Appalachians.



Taking a look at the NAM model below, depicting temperatures for 12Z tomorrow morning, one can see the 0°C line sinking all the way into northern Florida, just a little north of the Gulf of Mexico, and even dipping down to the Texas/Mexican border in parts of west Texas. In fact, most of the United States will see temperatures at or below freezing tonight! That is certainly something we have not been able to say this winter.

Taking a look at the 850mb level at 0Z this evening, the NAM model shows the strong cold air advection that is occurring behind the cold front, aiding in dropping those low temperatures tonight.

As mentioned above, wind chills will also be a factor tonight. Below is the apparent temperatures for tomorrow morning as predicted by the National Weather Service. It will feel like it is in the teens for parts of northern Florida, Georgia, Alabama, Mississippi, and Louisiana tomorrow morning. Many of these areas are not well prepared for temperatures of this nature and precautions will need to be taken in order to protect the life of plants and infrastructure such as water pipes. Farther north, temperatures will feel like they are below zero in many spots as far south as northern Texas across to Missouri and in the Appalachians down into northern Georgia and western North Carolina. Not to be outdone though, the typical cold spot up in International Falls, MN will expect to see an apparent temperature of -29°F on Sunday morning.

With all this talk of cold air, snow chances are probably one of the first things everyone is thinking about. As a low pressure system continues to develop over the Rockies, some areas could pick up a few inches of snow as well as some ice accumulations. Considering many areas at risk for this snow and ice have received little, if any winter weather precipitation this season, this could create for some travel issues. This situation will have to be monitored carefully over the next few hours as Winter Storm Watches are just beginning to be issued for parts of Texas, New Mexico, and Arkansas. Stay tuned for future blog posts on this topic!

So will there be more cold air outbreaks for the lower 48 states in the near future. Taking a look at the models, it does not appear we should expect anything of this magnitude at least for the next 10 days which would bring us into mid to late February. However, it does appear there is a lot of cold air bottled up in the polar regions so it will definitely be something to continue to monitor.

Spring Severe Weather Outlook

Originally posted on ZoomRadar

As winter begins to draw to a close and leaves us with all of those memories of Alaska being hit by snowstorm after snowstorm while the rest of the United States wondered when winter was going to arrive, I find myself wondering about what this spring may hold in store after such an abnormal winter. Below is an image produced using data from Rutger’s Global Snow Lab which was featured in the January 2012 State of the Climate issued by NOAA.

The image depicts the January snow cover extent anomaly in thousands of square miles based on the 1981 to 2010 average across the contiguous United States. Unfortunately the years are off by one, as the first year on the right should read 2012 as we are all aware this year was well below normal for snowfall and the previous two years were well above normal. This simple mistake aside, I wondered how might this lack of snowfall affect the forthcoming severe weather season if we were to do a simple test, science aside, and compare other recent years with below average snowfall, like 2006.

The image above shows the last seven years of tornado reports as well as the 2005 to 2011 average and this year’s reports so far. Taking a look at 2006, we see that it was the third highest year for number of tornadoes up to this date with only this year and 2008, a year with above average areal snowfall coverage, having more tornadoes reported. However, we see that 2006 ended up being the second lowest total for the number of reported tornadoes out of these years. While snow cover may not have any direct implications to severe weather likelihood, there may be an argument in how it affects the amount of moisture available and the temperature gradient needed for severe weather. The temperature gradient argument is the stronger of the two, stating that with less snowfall in the north, temperatures would be warmer, typically creating for a weaker temperature gradient and thus less severe weather outbreaks. Taking a look at this logic, we see that 2010 and 2011, years with above normal areal snow coverage, both ended up with higher numbers of tornado reports but they achieved these numbers in very different fashions, with 2010 recording most of its tornadoes much later than 2011. So maybe the below average snowfall this winter has no predictive power on the intensity of this year’s severe weather season. But there are other factors we should also consider.

The ENSO cycle has long been considered to potentially hold some power in predicting severe storms. It is common knowledge among meteorologists that a La Nina tends to slightly favor more storms in the spring, especially across the Southeast, and an El Nino tends to slightly favor more storms in the summer months. Current conditions from the Weekly ENSO Update show that we are currently in a La Nina type pattern which is expected to continue into spring. While this particular La Nina pattern is not nearly as strong as last year’s La Nina, which lasted from the summer of 2010 into the spring of 2011, could it bring typical La Nina associated severe weather patterns to the United States for this spring?

With last year’s record outbreaks occurring during a La Nina, it would be easy to jump to the conclusion that this year would result in more extreme severe weather outbreaks, especially with the pace the season has got off to. However, we must remember that this year’s La Nina conditions are not as bad as last year’s conditions and in fact, what we are currently in has not even been classified as an official La Nina. An official La Nina must have sea surface temperatures in the Pacific region used to measure the ENSO cycle at or below 0.5 degree Celsius below normal for at least 5 consecutive 3 month averages. This means the La Nina conditions would need to persist through the JFM (January, February, March) cycle which they are modeled to do but even so, as stated, it would not be at the intensity of last year’s La Nina. That being said, the ENSO cycle would lead one to believe that we could be looking at a strong severe weather season but this is far from a set in stone prediction.

Returning to temperature gradients and moisture now, the above image depicts the current sea surface temperature anomalies across the Caribbean. Of interest here is the warmer than normal temperatures in the Gulf of Mexico, the source of moisture and strong southerly wind flow during severe weather season. With warmer than usual temperatures in the Gulf, the temperature gradient would be stronger creating for stronger winds and therefore increased chances of severe weather. These warmer temperatures are due to the fact that cold air has struggled to enter the United States this year, allowing the Gulf to remain relatively warm. Temperatures in the Gulf were also above average last year though we did not see this anomaly start occurring until March and by April, sea surface temperatures were well above normal as depicted in the image below for April 28, 2011.

In fact, this time period is exactly when we started to see severe weather reports really take off last year. Investigating this further, it appears that a warmer than normal Gulf does show some correlation with increased storm reports. Monitoring of this area of sea surface temperatures should be continued into severe weather season. If the temperatures continue to remain above normal and even become increasingly above normal, we could be seeing an indicator for strong severe weather outbreaks to occur.

One last measure I will look at is the NAO which tends to be more positive during severe weather outbreaks. Once again, this generalization does not always hold true but it can be useful to look at for short term consideration of severe weather probability. As can be seen in the models below, the NAO is forecasted to remain at least weakly positive through about the end of February, meaning that the track of the jet stream will remain farther north than normal over the Atlantic region. The models do not forecast out farther than this but taking a look at the history of the NAO over most of this winter, and assuming that this trend may continue, we can expect that severe weather outbreaks would be favored in this pattern.

So what can we expect this spring in terms of severe weather?

Well, early indications would point to another active severe weather season thanks to La Nina conditions, the NAO continuing to remain positive, and warmer than normal sea surface temperatures across the Gulf of Mexico. However, it is important to note that severe weather cannot occur without the correct synoptic setup and none of what I have looked at has taken a true look at this due to its inability to be predicted accurately in the long term. Therefore, the predictions above may not pan out this spring if synoptic conditions conducive for severe weather do not form or form often enough. It will be important to remain up to date on the latest conditions of the variables mentioned in this article as well as the synoptic scale conditions across the United States as we continue to inch our way into this year’s severe weather season.

Southern Plains and Gulf Storms

Originally posted on ZoomRadar

While a snowstorm is currently striking the Central Plains, the Southern Plains and the Gulf will be dealing with the warm sector of this same low-pressure system. Strong to severe thunderstorms will ignite in the region ahead of a cold front which will sweep through Texas and Oklahoma today and tonight before continuing through Arkansas, Louisiana, Mississippi, and Alabama tomorrow. Current surface analysis shows this cold front back across western Texas and Oklahoma with dew points ahead of the front in the low to mid 60s across Texas and Louisiana. In addition to these dew points, a nice southerly breeze is occurring across most of central and eastern Texas as well as Louisiana with some southeast winds helping to add to the chances of some tornadoes across this area. However, with no well defined jet streaks and limited shear due to the alignment of the winds aloft, tornado risk should remain low.

The current Day 1 Convective Outlook issued by the SPC shows a fairly large area highlighted under slight risk for today. The main threat across this area is damaging winds, however large hail and tornadoes are also possible. The threat of large hail and tornadoes will be most likely across an area from Oklahoma City south into the Dallas area.



Storms will be aided by the presence of rising air due to some warm air advection occurring across the risk area today as shown in the image below for the GFS model depicting the conditions around lunchtime today. This will continue to be the case tonight with the main area of warm air advection moving slightly to the east, keeping in front of the cold front. The map also shows an ample amount of moisture across the area.


Currently, radar imagery is showing some storms firing up across Texas, Louisiana, and Oklahoma but most are remaining below severe criteria right now. The SPC has recently issued a tornado watch for parts of Texas and Oklahoma across the threat area talked about above for tornadoes and large hail today so storms will likely increase in number and intensity here over the next couple of hours.



While this storm system will not produce a major severe weather outbreak, it is important to remain alert for storms across this area today and tomorrow as a few storms should create for at least some damaging wind reports of which a couple have already been reported in Mississippi and Alabama. Spring is only just beginning across the southern U.S., despite what Punxsutawney Phil sees, so be sure to keep up to date on all the current watches and discussion by visiting the Storm Prediction Center’s site.