Archive for January, 2011

Our current high resolution radar shows some lighter showers spreading into the area this hour with the bulk of the rainfall staying south of I-20 where it has remained most of the day.  It looks like some showery activity can be expected for the rest of the night across most of the area with the heaviest rainfall staying to the south.  This will begin to taper off during the day on Monday and give way to mostly cloudy skies.

The Storm Prediction Center in Norman, Oklahoma has issued there latest day 2 convective outlook for Tuesday.  The threat has expanded some to the west and they mention higher instability values potentially being present as temperatures are a big warmer on current model runs for the Mississippi area.  There is now mention of rotating storms with a highly sheared low level environment and the potential for a couple of super cell thunderstorms across LA/MS during this time.  We are going to upgrade our chase status to MODERATE for the likelihood of chasing across the Jackson metro area on Tuesday.  Continue to monitor the blog concerning this as things may change before Tuesday.

Now….we won’t talk much about it but the models are starting to pick up on something pretty big for the weekend.  This is the Canadian model that has performed pretty good in the longer range this winter….and it shows some Winter mischief across Mississippi and Alabama in the form of ice and snow on Saturday.  We will fine tune things before then, but the idea is definitely on the table.

This afternoon….temperatures are in the mid – upper 60’s once again across much of the area.  The shortwave we talked about last night is moving across the Lower Mississippi Valley region with rain spreading eastward somewhat.  The WRF model output from last evening may not have been generous enough on the rainfall totals especially across western sections of the state.  Radar already indicates some 3/4” totals across portions of Pickens County with the activity. 

We still expect some of this to diminish this afternoon as it moves eastward into drier air east of I-65 where dewpoint values are still in the 40’s.  Most of the heavier activity should remain south of I-20 even as the rain continues.  Lows tonight should be in the 40’s with the clouds hanging around.

Still expecting some strong to severe activity on Tuesday into Wednesday as a potent system moves in our direction.  The threat may have actually increased for portions of Alabama.  Stay tuned…

Wow…..what a difference a few days make.  We had high temperatures in the 70’s across much of Alabama today with many places nearing record levels. Yes, I said record heat levels instead of cold!  Enjoy it while it lasts because there is more wintery type temperatures in the forecast.  However, today was picture perfect for a day of fishing at the lake or just playing outside with the kids. 

Now….we will look at the current weather maps…

Tempeatures are running in the 40’s and 50’s across the area this evening with clear skies overhead.  We should radiate down into the 30’s with no problem before too much longer.  You will note the spike in temperatures to our west in the Dallas/San Antonio vicinity ahead of our next storm system.  This is setting things up for parts of the southern plains and Midwest to get a rather significant winter storm that is expected to stretch from Oklahoma City to the Great Lakes by Tuesday and Wednesday.

Radar shows some scattered activity breaking out across parts of Texas ahead of the surface front and associated area of low pressure.  The main shortwave is still back over parts of northern Mexico….so it will likely be later tonight before and real established convection gets going and produces anything of significance. 

The SPC has a convective slight risk in place for portions of the SE Texas area mainly for the potential for some wind and hail later in the overnight hours.  This isn’t expected to translate eastward at this point for tomorrow or Monday because we are too dry for any kind of severe weather.

This wave will effect us with some rain late tomorrow night….likely after midnight.  The totals shouldn’t be impressive as the wave will be shearing out across the area and the main precipitation will be decaying.  Totals of less than .25” are generally expected and are advertised by the NAM above.

Now….we are looking into the idea of the second wave that will bring the winter storm across the plains and Midwest possibly setting the stage for some severe weather across the Lower Mississippi Valley region by Tuesday.  The setup involves a strong trough going negatively tilted while intensifying wind fields overspread the area.  The general downfall for these kind of events in the winter is the lack of instability that is associated.  Dynamics can offset instability at times and this could be one of those cases….

These 500mb wind fields are extremely strong and are divergent across the eastern Ozarks and Mississippi Delta region.  This map is valid at 3pm on Tuesday.  The trough is taking a negative tilt as the surface low is beginning to accelerate out of E AR/W MS.  This is a prime setup for severe storms across the deep south.

These shear values of >45+ knots are indicative of very strong low level turning in the atmosphere.  These values are from about 5000ft to the surface.  This indicates extreme shearing will be present in the lower levels of thunderstorms that are able to develop and that they will likely obtain rotation if an updraft can become sustained.  These dynamics will be moving east and northeast.  From this, I do get the idea that damaging winds and potential for some tornadoes will exist across portions of Mississippi and later into West Alabama.

These are the 3km EHI values.  This is an “energy-helicity index” that indicates where the best shear and instability will be present.  Values over 1 are indicative of the potential for significant tornado development.  You can see a bulls eye of near 2 over Natchez, MS at 4pm on Tuesday.  This has been steadily on the rise for the last few model runs as somewhat higher lapse rates and instability values are coming into play.

Finally…here is the forecast sounding from the Jackson, MS area at 3pm off of the 00z NAM model. This shows a very moist column.  The temperature is steadily falling with height and does so pretty rapidly from about 650mb to 300mb.  There is a dry layer there that indicates some potential instability and faster falling temperatures with height.  We will watch for drier air around the 700-750mb level.  This will be key in the formation of deeper instability values.  More dry air at this level can mean less thick cloud cover and higher temperatures in the lower levels creating a “steeper” lapse rate….or cooling of temperature with height.

So, what are we saying?  Basically….I expect the best severe threat to be west of Alabama due to the time of day and nature of the system.  Sure there will be a threat during the overnight Tuesday into Wednesday morning for some isolated damaging winds and maybe a tornado or two, but the better threat sure seems to be over Mississippi at this point.  We are likely going to chase this system if instability parameters continue to improve across the region.  If we can keep the widespread convection at bay….there could be a few tornadoes over there.

We will post more on our plans over the next few days, but for now back to getting the laptop ready for “chase mode” as well as the truck.  Have a good weekend!

Our ULL is moving out and our forecast thoughts were generally in line with the idea of snow being pretty meager even across North Alabama this morning.  It turns out Huntsville and Monte Sano only received a dusting of snow.  Also, heard reports of freezing rain and sleet in that area.  The idea of the snow growth region being dried out a while was correct too.

As for today….a wind advisory is in effect for eastern sections of our area due to a tightening surface gradient to our east.  This will bring some windy conditions east of I-65 with gusts over 25 mph being possible at times.  At least the sun is coming in with the wind this time. 

We expect a quiet few days with lows in the 20’s during the overnight and highs into the 40’s thru Thursday.  Another big shot of cold air looks to be on the table around the first of February along with some wintery mischief.  We will have to watch that because things change rapidly around here as we have seen this winter in terms of snow and ice.  Have a great Wednesday!

Winter Storm Warnings have been issued by the National Weather Service offices in Memphis, Nashville, and Huntsville for most of there counties.  Memphis covered there western counties with Winter Weather Advisories for lesser amounts of snowfall.  I have some agreements and disagreements with some of these advisories…..and I will get into those after looking at the latest and forecast output.  To the maps….

Our upper level system is still digging to the west over portions of Texas at this hour.  The trough has yet to close over, but with very significant vort surrounding the system and indications of deepening….this should happen over the next several hours to our west.  You can see that the flow out of this level is out of the SW…..which will bring me to another key point.

You can see our developing upper low that I have marked to the west….but this is overlaid on current water vapor imagery.  The yellow colors indicate large mid level drying occurring to our SW and now intruding into Mississippi and west Alabama.  This will play havoc with the moisture column in the mid levels and likely dry out a good portion of the snow growth zone….at least for a while until the main low pressure system moves overhead….if it ends up moving across North Alabama.  The latest high res model runs indicate this happening somewhat. 

Here is the upper level low at 6AM on the WRF-ARW model.  This is a high resolution model that seems to be handling things pretty well in terms of the synoptic and low levels…along with precip fields so I will stick with it.  The core of the ULL goes right along the Tennessee border.  Usually, the highest QPF (accumulated precip.) is to the northwest and southeast of an upper level system.  The heaviest snow axis per this run should run from east of Memphis to Nashville to southern Kentucky.

Here is the 3hr precip forecast for the same time frame.  I have overlaid my “Heavy Snow Axis” over the model where I think the heaviest amounts will occur.  Given the model output and soundings, I think it is safe to say that Nashville could see upwards of 3-6” of accumulating snowfall….with maybe a 7” total somewhere.  The most likely place to see any heavy accumulating snowfall in Alabama will be the highest terrain in Northeast Alabama and the Shoals area.  I’m skeptical about NE AL because they could get dry slotted being in the SE quad of the upper level low as it is pivoting.  In other words….places like Skyline and Jackson County could be left dry.

The old saying is…”Upper Level Low, Weatherman’s Woe” and that could prove to be the case this time.  There is extreme difficulty in forecasting the dynamics and thermal profiles with these kind of systems…..along with precipitation fields.  This forecast looks pretty good as of now and I will stick with it.  So, I just don’t see the Huntsville counties verifying warning criteria snowfall…..but I hope you do!

We will post more updates throughout the evening as conditions deteriorate or warrant…

Latest radar imagery shows the rainfall spreading eastward out of Mississippi at this hour into portions of West-Central Alabama.  Tuscaloosa and Jasper stations are reporting light rain at this hour with temperatures in the mid to upper 40’s.  Frozen precipitation will not be a problem tonight.  It looks like a good soaking is in store for the next 24 hours over much of the area as the upper and surface low pressure systems get their act together to our west.

This evening…..the model data extractions are showing the best snow potential to be north of US Highway 278 with accumulations possible across those areas.  The National Weather Service in Huntsville has a Winter Storm Watch up for the entire area for 2-4” snow totals with locally heavier amounts in the deformation band.  Birmingham has also put the watch up for the northern row of counties. 

I have a few obligations to take care of in the morning….but I will be updating the Bama Cam Network with our new sites just in case a surprise is in order.  It is very likely that I will be traveling northward for the snowfall across northern sections of the area.  Like toward Huntsville. 

This is the rainfall forecast thru late Wednesday…..showing well over an inch south of the I-20 corridor.  I believe that the percentages are high enough for me to forecast mostly rain for the area.  I could see some regions locally seeing 2-3” totals from the heavy rain making surface low due to come out of the Gulf of Mexico.  Someone will probably see a transition to some snowfall in the north, but the main dynamics don’t look as strong on recent model runs and I feel more comfortable saying that most of the area will be too warm for snow accumulations.  There is still some time left for things to change on the model data as the system enters our upper air network, but we certainly don’t need to modify over the next two days very much. 

Expect temperatures in the 40’s during the rainfall falling into the mid 30’s during the overnight periods.  Drier weather for the end of the week…

This evening the American guidance certainly looked different, but still too warm for any kind of significant snowfall across the southeast region.  I will say that the European came in with a similar look to the last few runs of that model….and even looked a bit better in some aspects.

This is the 500mb heights with 700mb vorticity overlayed on the graphic.  This basically displays how much turning and dynamics are available in the atmosphere.  With the mid level cyclone closing off over Mississippi and moving eastward over Alabama….this usually puts us in a good setup for a significant snowfall.  The European model has been the best model in terms of the winter systems that have affected the region this season, so we will lean in this direction with our forecast.  It is still a little warm in the lower levels for a massive snowstorm, but it’s too close for comfort….especially form I-20 northward.  We will continue to watch and update the situation as things warrant.

Another strong winter storm system will plague portions of the southeast region by Tuesday with rain and possibly some snowfall.  Will it be a system like the several we have witnessed over the last few weeks across the state of Alabama?  Well, let’s get to the details.

The short, medium, and long range models are all pegging a major storm system diving out of the plains and developing a surface low down on the Gulf coast.  The problem that we are seeing this time with the setup is the low level temperatures.  We will get into that, but first the synoptic setup of the overall system. 

The 18z SREF (Short Range Ensemble Forecast) mean is a mean of many different short range model members.  This model indicates that the upper trough and dynamics will dive and setup over Central Alabama. 

This basically shows us that the best area of lift and mid level cold pool is directly overhead.  This is a good thing in terms of having the lift for precipitation and cooler temps aloft to support some dynamical cooling in the heavier precipitation.  Heavier bands of precip could be snow in some areas due to this if the low level thermos are a bit warm.  I’m going to display a few of our computer models low level thermal profiles now.

18z NAM at 925mb (2500ft)

18z GFS at 925mb (2500ft)

What we note from each of these models is that by the time the low pressure at this level of the atmosphere is over S GA…..the 0 degree Celsius or 32 degree Farenheight line is WELL to our north.  This basically indicates to me that the low levels are having a hard time cooling with no real cold air source around.  I’m very hesitant to say that anyone in Alabama will see a significant snow in this….in terms of a forecast.  I can not make that assumption based on anything I see.  Here are the surface temperatures from the 18z NAM…

That shows 40’s spiking up through portions of the state……so the low levels are very problematic.  If we had an arctic front moving through prior….I would be all over this.  However, that is not the case.  We need this upper system to close off over central portions to see a good snowfall across the area.  This would allow us to dynamically cool through the process of snow melting through the column aloft as it falls heavily.  That is close to happening on the graphic at the top of the page, but not quite.

So….I can say with confidence that most areas will see some rainfall prior to anything frozen during this event.  Rain could start as early as Monday evening and overnight as the surface low gets together to our south.  The strength of this low pressure will have a lot to do with the amount of cold air that surges in.  The weak pressure gradient to the north of the low as of now doesn’t allow for a major cold air flood.  This could occur in future runs, but all of the models are showing a thermal issue of some kind in the low levels.  That’s why I haven’t posted those.

We will continue to watch this developing situation and post more as things change….but I would say that someone will see snow falling due to the dynamical aspects.  How much and where?  No one could answer that at this point.  Stay tuned…

Tonight on the radar we are seeing some developing flurries across West Alabama with a wave that is passing through.

Not expected to be anything major, but still interesting none-the-less.  Temperatures are in the 20’s so any precip will be in the form of snowfall.

Our next wave is showing up in the NW this hour and will bring us some rainfall by early Monday.

This system will once again be minor, but models are starting to key in on a potential winter weather maker that could bring significant snows to the deep south by late Tuesday into Wednesday.  Here is our short range ensemble model as of the 21z run of the system.

Deep upper trough over portions of Alabama with a lot of spin and lift in the atmosphere.  This is a good setup for falling surface pressures and cyclogenesis.

This NOGAPS chart shows a similar scenario with parts of Alabama getting pounded.  Not much time this evening but will go more into detail tomorrow.  Have a great night.