Archive for January, 2011

The surface low over south Mississippi is moving eastward along the coastal regions and allowing for heavy rain and the isolated thunderstorm to develop.  A severe thunderstorm warning is in effect for Washington and Mobile Counties in south Alabama this evening for this storm moving out of Greene County, Mississippi.  Reflectivity looks impressive, but not much is showing up on radial velocity as far as winds go.  Some isolated wind damage or small hail can’t be ruled out with this storm.

Rainfall is spreading northeastward across areas mainly south of I-20 and should continue to move across and out of the region later this evening into the overnight.  Clearing conditions are expected tomorrow for a short time ahead of our next eventual system to impact the region Thursday and Friday.

On this Sunday afternoon we are watching a southern stream wave moving out of Texas toward the deep south with rainfall spreading ahead of the trough.  In response to this…slight ridging across the state has allow for conditions to warm considerably into the upper 40’s to mid 50’s across most of our sites this afternoon.  Therefore, most of the snow pack as melted even in our northern communities.  The rain shield, which could be heavy at times, is continuing to spread eastward and is nearing I-55 at the present time over in Mississippi.  Some west Alabama communities could begin to see some shower activity as early as 8pm.  Rainfall will spread across the region and keep most of us wet through your Monday and into the early hours of Tuesday at least.  We currently expect rainfall amounts of 1/2 – 1” respectively with some locally heavier totals. 

Another system will effect the region later in the week with another potential Gulf low impacting the area.  This one doesn’t look to have as much cold air to work with as our system did last week, but it’s something that will definitely need to be watched since it’s still some 5 days away.  We will post some model variations with this system over the next few days.  Enjoy the rest of your weekend.

With the Winter Storm Warning now in place….we decided that it was time to update our forecast accordingly to what we are seeing this evening.  It still looks like a good bit of snow and ice will fall across the viewing area starting late tomorrow and into early Monday.  Here is the latest updated snowfall graphic that we have come up with

Here we are suggesting the major accumulations along and north of the I-20 corridor…..with 2”+ expected north of a Pickens to Shelby to Randolph County line.  The precipitation is expected to remain all snow in northern portions of the forecast area, thus we have adjusted the higher totals accordingly.

Now to the ice.  Areas south of I-20 are in for a potential significant icing event beginning tomorrow afternoon.  Do not be fooled when snow starts to fall at the very beginning.  Trust me…it will be changing over eventually.  Areas closer to I-20 will be the last to change to sleet or freezing rain, but it will happen.  Accumulations of .25”+ can cause a great deal of problems such as tree damage, frozen roads, power outages.  Here are a few tips to think about if you are in these icing locations…

• If you live in the country and rely on well water….when the power goes so does your well.
• Prepare with an alternative heat and cooking source if you are fully electric.  Camping grills and heaters are great for this kind of event.
• Check on the elderly!  Elderly people are very prone to serious health issues and even death during extreme winter events.
• Keep cash on you instead of debit/credit cards.  If you must get out…if the power is out at most locations cards will not work.
• STAY OFF THE ROADS!  We aren’t used to this kind of weather in our area….wrecks will be numerous if you travel.

Stay tuned with us for the latest details with out ever changing forecast as new information becomes available.  Prepare now because you are almost out of time.  Stay tuned…

After looking at everything this morning….I believe that we are still in decent shape with maybe a few changes needed on snow totals and ice accumulations later on this afternoon once we get a full suite and days worth of data.  Current indications are that we may need to adjust our icing totals upward south of the I-20 corridor.  We will get into that later.

We are planning to build a large page with our team members live video cameras from different locations around the state.  If you are interested in possibly helping us out and would like for your camera possibly shown on a local news affiliate during the storm….send me a message to bamastormchaser@gmail.com and we will get you setup and ready to stream the ice and/or snow event at your location.  This will in the process help us with real time views to correlate radar data with what is actually happening.

Our next update will come later in the evening as we prepare our next call on the winter weather situation across the deep south.  Have a great Saturday!

The model above is the GFS.  One of our global models that we look heavily at when it comes to our weather.  Looks as if the model is trying to depict a scenario of some ice/snow potential for Central/North Alabama and maybe even areas to the south like Troy and Andalusia as we enter the late Sunday into Monday time period.  Keep in mind this is just one run of one model.  However, some of the past runs of other model data have depicted a similar scenario. 

This evening a few of our other models have decided to veer from a consensus and show a couple of other possibilities.  The CMC (Canadian) model is now showing a warmer picture with the surface low riding through Birmingham and pulling northeast bringing an all rain event….and maybe some thunder to southeastern counties.  The ECMWF still has the Gulf surface low on schedule and brings it eastward along the coastline.  This model is in track with our GFS model above except it is a tad warmer this run suggesting some wintery precipitation and rain mixing. 

What we can say right now is that we are rather confident that portions of the area will see a winter weather event this weekend.  This definitely has the potential to be a high impact event…..in the form of ice, snow, or both.  We won’t talk potential totals until the Friday/Saturday time frame, but we do expect for some accumulations and travel problems across portions of the area. Stay tuned to later forecasts and analysis from us as the event approaches and more details are brought to light. 

There has been a signal on them models for a while that indicates that the deep south could deal with some pretty brutal cold air in the coming couple of weeks…..along with some winter weather potential.  However, the thing we are going to key in on currently is the cold.  I want to show you a model that does very good in the medium range….the European.

The latest 12z run of the model that we have in indicates at large Polar Vortex to our north swinging a cold front and deep upper trough thru the region.  We have a blocking ridge developing over the west coast at the same time which usually spells for some pretty cold air coming into the country and that’s exactly what we see.  A densely cold 1058mb high pressure system over western Canada has trajectories of pushing very cold low level air into the eastern 3/4 of the country.  If this were to verify…..in the extended range we may very well deal with some record breaking cold air.  Remember….winter is just beginning. 

New Years Eve 2010 will go down as one of the most active weather days on New Year’s Eve ever.  As of 1:30AM on 1/2/2011….7 Deaths have been reported from the tornado event.  6 EF-3’s and 4 EF-2’s have been surveyed across the states of Arkansas, Missouri, Illinois, and Mississippi as well….some of which were long track.  We will get into the analysis of why the event was so much more devastating than forecast along with some shots of the Jackson, MS tornado from the VIPIR/FasTRAC radar systems from Baron Services.

First….I will start with a few images from the morning of the 31st.  The 12z upper air analysis charts revealed a pretty dangerous weather scenario that was about to take shape.

Looking at the above 500mb chart….you can see a very powerful negative tilt shortwave rotating around the upper low across portions of Texas, Oklahoma, and Kansas with the apex of the troughing around Tulsa, OK at 7am CST.   Also indicated is a very fast mid level flow with 50-80 knots across most of OK/KS out of the southwest.  Consistent cooling aloft aided in steepening 500-700mb lapse rates rapidly.  The column was also rather dry at H5.

The 250mb chart for the upper atmosphere indicated that massive divergence was beginning to occur across AR/MO in the exit region of a 110+kt upper level jet max plowed into the region.  This would again be another factor in aiding updraft development with a “vacuum” effect aloft for the storm to feed off of….or enhancing the lift.

And we can’t leave out the low level flow at 925mb….or about 3000ft.  This image indicates a low pressure area just off the surface over portions of NE KS with a major temperature gradient developing.  Winds ahead of this low were backed to the S-SSE at the low levels helping create a very favorable shear profile in the lowest 2km of the atmosphere for tornadoes.  The 14C temperatures also helped in boosting CAPE values to levels sufficient to keep thunderstorm updrafts pumping….which allowed several of these tornadoes to become large, destructive, and deadly.

Here is a vertical profile from the morning of 12/31 from the Springfield, MO balloon launch…

This sounding profile shows a small inversion or cap around 800mb.  However, the inversion is very weak and was broken by forced convection, slight cooling/moistening aloft that brought the profile more toward the wet bulb.  Once the storms got into the area….the shear was more than adequate for significant tornadoes given the 550+ m2/s2 shear values in the 0-1km and 0-3km layers.  You will notice that the CAPE is only 423j/kg on this sounding…..but that slight moistening of the column boosted those CAPE values shortly after this sounding.  I’m sure the 75j/kg 3km or low level CAPE was more like 200 j/kg once the cap eroded.  Still, small difference can cause big changes.  The main tornadic activity took place just to the east and north of this sounding location where the atmosphere was a little more moist. 

Thus, given the conditions stated above….these supercells developed in Eastern Oklahoma and traversed through NW Arkansas into Missouri.  This radar capture if of the tornado that hit the Cincinnati, Arkansas community killing 3 as it ripped through town.  This tornado was given a preliminary rating of EF-3.  These same storms continued and cycled through portions of Missouri producing the killer tornadoes in the Springfield county warning area. 

This is an image captured as the supercell produced a tornado at Fort Leonard Wood in Missouri.  You can see the vortex on the ground doing pretty much total devastation.  Also noted is the horizontal low level vortex just off the ground.  This tells me just how dynamical the system was for this area.  Very impressive….especially for December.

Later in the afternoon we were keying in on the deep south as a dryer than forecast mid levels were across the region along with a more loaded-gun type sounding.  The inversion was quite a bit deeper across the south with isolated showers and convection taking shape and being beaten down by the cap.  However, by about 4-5pm it was game time for the Jackson, MS metro area.  Supercells were developing south and west of town and were developing rapid rotation quickly as the low level jet was beginning to intensify over the region.

The image above in FasTRAC (Baron Services Product) you can see several rotations embedded within the QLCS (quasi-liner convective system) to the west, but one thing sticks out like a sore thumb.  The isolated cell ahead of the line that has a hook structure.  This notch southwest of Crystal Springs was feeding off of an environment that was pretty clear to it’s southeast with the low level, moist flow coming from that direction.  As the storm moved northeastward we watched it gain strength with higher output of lightning and better low level wind values.  As it approached Jackson we began noticing maxing wind velocities.

Reports were coming in that the tornado had touched down just west of I-55 with damage being reported just west of Terry, MS.  The tornado then tracked northeast where it continued it’s path toward the Jackson metro.

The tornado is wrapped up with the higher dbZ values (some purples) wrapping in just before reaching I-55.  This is an indication that either debris is being thrown by the tornado or either it’s becoming rain wrapped.  Given the deep moisture field and radar presentation, I’m pretty sure it was a bit of both. 

This image illustrates the strong inflow to the tornado.  The reds embedded within that green area indicates range folding as the winds were extremely strong and the radar didn’t properly alias the data correctly resulting in no or bad data.  I’m sure those were 80+ mph winds streaming into the tornado just off the surface.

This shot shows the tornado approaching the I-020 vicinity between Jackson and Brandon with many storm chasers all around the cell.  At this point, debris was being reported on I-55 with a 1/2 mile wide damage path and the National Weather Service personnel in Brandon were taking shelter as the tornado crossed just to there west.  This tornado was mighty impressive with EF-2 strength winds and a 26 mile long path.  The downtown area of Jackson dodged a major bullet given that this was during a rush hour period that most folks were off for the holiday.  No one has been reported to be killed from this tornado. This tornado also ran across the runway at the Jackson International Airport.  This was the beginning of the Mississippi tornadic evening.

Since the NWS office took a hit during the hour they normally launch there weather balloon sounding….the 00z balloon was never released.  Jackson did a planned sounding at 04z to see what the atmosphere looked like in the wake of their first tornadic storm. 

The sounding revealed an uncapped environment along with nearly 1700 j/kg surface CAPE still in place.  One of the reasons that you check the sounding data when it becomes available is the models are not always correct.  At this same time….the SPC mesoanalysis page (RUC derived) indicated less than 500j/kg CAPE in this area with building convective inhibition (CINH).  One would think that the weather would have calmed down if that were the case…..wrong.

As a second upper level perturbation and jet max moved into the region….a surface low developed on the LA/MS border and moved northeastward along the surface frontal axis.  More tornadoes in turn developed across Central/East Mississippi during the overnight in Attalla, Holmes, Kemper, Noxubee counties.  More areas are being investigated for ratings as wind or tornado damage.

We will update with more content as needed or if more comes available.

Rainfall amounts of 1-2” are pretty common thus far across Central sections of the state with much greater totals NW of I-20/59.  The severe weather threat for the area has all but ended as the rainfall has saturated us pretty well.  It looks as if the situation potential that we posted last night was pretty true……in terms of our severe weather thoughts.  So, we faired pretty well besides some sporadic wind damage and flooding issues.  The rain is currently ending from a line of Livingston – Tuscaloosa – Birmingham – Gadsden and northwest. 

The cold frontal boundary will push much cooler air into the region later on today.  Dewpoints have already dropped into the low to mid 20’s across Mississippi.  Lows tonight will fall to near freezing NW of I-20/59 with mid 30’s to mid 40’s in the southeast. 

We will have more on yesterdays tornadoes in a post later on.  Preliminary data shows that it was the largest tornado outbreak in New Years Eve history.  More to come…

A significant shortwave is beginning to eject with a jet max across E Texas and Louisiana this evening.  This is setting the stage for some potential intensification of convection as storms continue to form within a deep conveyor of low level moisture.

The sounding that has just returned from Jackson indicates a very unstable and highly sheared environment conducive for not only tornadic development, but some significant tornado potential.  A new tornado warning has just went out for the Mendenhall, MS area with this new convection.

A couple of different things could happen.  We have a low level jet increasing….upper level jet maximum and divergence spreading into the region….along with increased forcing and ascent being indicated by water vapor that is moving into Central Louisiana.  All of this combined could be a major player in the weather for the rest of the night across Mississippi and Alabama.  Here are a few scenarios….

1) The storm across Mississippi continue to be isolated out ahead of a main line and have potential for significant low level rotation and tornadoes.  This is likely to be the case for the next few hours given the current radar presentation.

2) The atmosphere is still unstable, but has began to moisten some aloft.  With the low level jet increasing along with mid level forcing coming into play…..numerous showers and storms could begin to develop and overwhelm the instability thus allowing for more of a heavy rain scenario with isolated occurrences of severe storms.  This is what we expect in the long haul once our surface low pressure begins to pull out to the north with all of the capping gone across the region.

We will continue to watch it through the night, but across Alabama the heavy rain should be the big story if even that.  We are still rather dry with soil conditions in most areas and flooding should be isolated at best.  I can’t rule out a tornado warning or three, but it seems that the threat will be no where as high as it was across Mississippi earlier this evening and the Ozarks earlier this morning.