WAFF Weather

Will it be rain or more freezing rain and sleet?

That continues to be the big question right now.  A cold front will move in tonight and provide a quick round of showers with temperatures in the 40s.  Overnight the temperatures will drop into the upper 20s just before sunrise.  Thursday will be a cold sunny day with highs in the upper 30s and a north wind at 7-12mph.

Clouds will increase Thursday night and that's where the disagreement beings with the forecast model guidance.  Some forecast guidance suggests the shallow cold air that is brought in by tonight's cold front will stay locked in place Friday morning while others suggest a brief period of sleet and freezing rain early Friday morning before changing all over to rain as the warm air from the south takes over.  The key is the dry air at the surface.  This is represented well by the Dew Point.  Basically it's the measure of the amount of moisture in the air.  Rain that falls through dry air cools the air by a process known as evaporative cooling.

Here are three models I'm looking at to put together the forecast.  By far the RPM model is the driest which is the reason it keeps everything as freezing rain and sleet.  This model has been very consistant the past 36 hours and I'm watching to see if the other models begin to trend in that direction.  We probably won't have a better idea until the Thursday morning model run.  That doesn't leave a lot of time for a Friday forecast.



Here is a graphic that explains the warmer air and moisture moving over the top of the shallow cold air at the surface.

Think of the atmosphere as a building.  The bottom floor on Friday will start out below freezing in some areas.  The temperatures on the third floor of the building (atmosphere) will be above freezing.  The rain drops fall into the dry and cold air making freezing rain and sleet possible.

At this point in time it looks like we will see a period of freezing rain and sleet early Friday morning before changing all over to rain.  Until the forecast guidance comes closer to agreement there will remain a lot of uncertainty regarding any possible travel problems.

This is the time frame for sleet and freezing rain that I am expecting as of right now.

Brad Travis
Chief Meteorologist
WAFF 48 Storm Team
We Track Storms

Pinpoint Predictor for Friday morning's threat for winter weather.

We continue to track the potential development of Freezing rain, sleet or snow for parts of the Tennessee Valley early Friday morning.  Everything depends on the the cold air holding in place while the moisture moves over the top of the cold air.  The following graphics represent the RPM forecast model we use in the WAFF 48 Storm Tracking Center. 

The setup will begin as colder air arrives Wednesday night behind a cold front.  This front will also bring a chance for some rain as it moves through.  Temperatures will remain above freezing as this happens so no problems are expected Wednesday night.

The colder air will move in behind the front and the wind will remain out of the north and continue to bring in cold air.  Temperatures drop into the 20s by Thursday morning.

Overnight Thursday into Friday a warm front will begin to lift north into the area.  It doesn't look like this front will make it all the way into North Alabama.  A southwest wind will develop higher in the atmosphere and this will bring moisture over the top of the cold air at the surface over the Tennessee Valley. 

Evaporative cooling will take place as the moisture falls into the Arctic Air.  This process cools the lower levels of the atmosphere and creates freezing rain and or sleet.  There could also be snow.  The red warm front stays south of the area for the duration.

By 10am most of the moisture begins to leave and track east.  This model run shows about 4-6 hours of freezing rain/sleet or snow possible early Friday morning.

 

Keep in mind this is a model run and a trend we will be following.  Some other forecast guidance has it warming considerably more.  However given the extend of the arcitc air to the north at this time a colder solution is more likely. 

We will continue to monitor this developing, potential, winter weather threat.

Stay tuned.

Brad Travis
Chief Meteorologist
WAFF 48 Storm Team
We Track Storms

Winter forecast.

November 15th the Climate Prediction Center released the updated long range forecast for the months of December, January and February.  While it's too early to tell if we will have  rough winter with a lot of snow and ice, this is an early indication that our quite November weather pattern will likely become more active as we head into December. 

We have talked about a developing El Nino for a few months.  We had been considering a weak El Nino for the winter months.  This typically leads to colder than normal temperatures for the Tennesee Valley.  Here is the latest statement from the National Weather Service on the El Nino forecast. 

While the tropical ocean and atmosphere may resemble a weak El Niño at times, it is now considered less likely that a fully coupled El Niño will develop. Therefore, the previous El Niño Watch has been discontinued as the chance of El Niño has decreased. http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.pdf

Keep in mind it takes more than just El Nino or La Nina to affect our weather there are many other circulation patterns that develop over time that can dramatically change our weather.  One of these is the Arctic Oscillation.  (below)

This circulation was positive for much of our winter last year and kept the coldest air locked up to the north.  This year there are signs it could go negative this winter.  For more on the (AO) forecast go here.  http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao_index_ensm.shtml

Another circulation pattern that greatly changes our weather is the NAO.  North Atlantic Oscillation.  This link from North Carolina State University has a great write up about this pattern.
http://www.nc-climate.ncsu.edu/climate/patterns/NAO.html  From North Carolina State (Below)

The forecast from the CPC (Climate Prediction Center) is calling for above normal precipitation in the Tennessee Valley and near normal to slighly below normal temperatures.  If one of the above patterns can establish itself for a few weeks we just might see some active winter weather between December and February.

Here is an example of the weather pattern it would take to produce some problems with sleet or ice in the Tennessee Valley (Below)
An active sub tropical jet stream would bring in more clouds along with more moisture while a strong area of high pressure would bring in the cold air at the surface and keep it locked in.  Lately this pattern has set up in early November.  Patterns can often repeat for months once they establish themselves.  This is something we will be keeping an eye on. 

Just in case you are wondering what the CPC forecast looked like for the winter of 2010-2011 here it is.  (Below)

The temperature forecast was off and many remember an active winter with several rounds of snow.  Even a White Chrismas with many reports of 5 inches of snow on December 25th 2010.

Brad Travis
Chief Meteorlogist
WAFF 48 Storm Team
We Track Storms. 

 

More snow possible Wednesday night.

 

Tuesday will be cold but dry with highs struggling into the upper 30s under clearing skies.  Clouds quickly return, however, as round 2 of snow chances this week, creeps in.  Clouds will hang out a good portion of Wednesday before our atmosphere becomes wet enough to produce snow. We'll reach a high near 40 Wednesday. 

Cold air falls in place by Wednesday night  as temperatures drop into the mid 20s with the next front. Snow should begin to fall here in the Valley late Wednesday afternoon into early Thursday morning. Snowfall totals look like they will be between 1 and 3 inches.  If we get this much snow we will likely have travel problems throughout the day on Thursday.

 Our window of opportunity for snow closes quickly Thursday morning with some clearing by the afternoon as highs only reach the mid 30s.  The cold air sticks around one more day with highs in the low 40s Friday with sunshine through the day.

 The weekend looks great as highs climb into the low to mid 50s with sunshine both days. 

Brad Travis
Chief Meteorologist
WAFF 48 Storm Team
We Track Storms

A busy 7 day forecast. Let's break it down.

 

Changes very possible down the road with the Tue-Thu timeframe.

Friday:  Freezing rain and sleet in the early am.  Changing to rain by 9am.  Overnight into Saturday some light snow possible before it all ends.

Saturday:  Light snow early turning to flurries.  It should be over by Noon with some sunshine in the afternoon.

Sunday:  The best day of the next 7.  Sunshine and highs near 50.

Monday:  A weak disturbance moves through.  A few rainshowers could turn to snowshowers in the afternoon.  Cold front moves through.

Tuesday:  Snow flurries and clouds. (Cold)

Wednesday:  Between storm system.  Rain possible late.

Thursday:  A developing storm system will likely bring rain.  Rain could change to snow late in the day.  Colder weather will follow.  (this storm system could become a big one)

Snow and sleet arrive early. Winter Weather Advisory issued.

 

A 
mixture of sleet,snow and freezing rain is in the Birmingham area and moving north.  There have been numerous travel problems reported from Birmingham to Talladega as of 2pm this afternoon.  An area of sleet and snow is moving north-northeast from near Russellville to Cullman.  Arab is also reporting snow in southern Marshall County.  Initially the moisture will be very light however with time it will get heavier and we could see travel problems develop for the drive home.  The bridges and overpasses will become slick first.   A winter weather advisory has just been issued by the National Weather Service.  The latest WAFF Live Doppler 48 radar image is online at waff.com.

Brad Travis
Chief Meteorologist
WAFF 48 Storm Team
We Track Storms.

 

Another chance for wintry weather.

After the Groundhog predicted an early spring this year it’s hard to believe we are still talking about snow, sleet and cold temperatures. It will be mostly clear and cold tonight with lows around 22 degrees. A developing storm system will increase the cloud cover throughout the day on Thursday and keep temperatures in the 30s again. No rain or snow is expected tonight or Thursday. By Friday morning moisture will move north across Alabama and eventually we will have a mix of sleet and freezing rain falling across the Heart of the Valley. Right now it looks like most of it will be sleet and eventually it will all change to rain during the early afternoon hours. Temperatures will be close to freezing so there could be a few travel problems early Friday. Friday afternoon light to moderate rain will fall and highs will be around 40. Saturday morning light rain could change to light snow. No significant accumulations are expected at this time and temperatures will be at or slightly above freezing during the snow. Afternoon highs on Saturday will return to the lower 40s so any travel problems should stay confined to the early morning hours. We will continue to track this developing storm system and have updates on WAFF 48 News and online at waff.com and Facebook.

Have a great night.

Brad Travis
Chief Meteorologist
WAFF 48 Storm Team
We Track Storms

BELOW  (Friday morning. The area in pink is the mostly likely area for sleet and freezing rain. Temps are in black)

 

BELOW  (Saturday morning chance for snow.  Notice temps in black close to freezing. This just represents snow and not accumulation)

 

To Clear up Snowfall Forecast Graphic Confusion

We have been posting snowfall potential using two different images.  These images also have areal coveage.  All future changes will be on the same graphic so you can see the changes and maybe understand them better. 

It is looking like the heaviest band of snow is going to move along and just north of the Tennessee state line.  So in the latest graphic you will see a shift to the North of the 3-5" band in this update.

Sorry for any confusion.  Brad Travis

Tuesday Afternoon Update

 

Below is the graphic from Last night at 10pm.  This shows the Purple area with the 3-5 inch range into NE Alabama. 

Monday Evening Update.

 

Lastest on the Snowfall Potential

Just a slight shift to the north.  It is looking more and more to me as if the deformation zone (heaviest snow band) will setup across southcentral Tennessee and rotate around the upper level energy into Northeast Alabama.  Heaviest snowfall possible between 3am and 7am Wednesday morning.  If the acutal storm track is farther south than advertised by the latest guidance this area will shift south. 

After old fashion hand analysis here's the latest graphic from the WAFF 48 Storm Team

Brad Travis

 
 

 

Snowmeter update on developing winter storm.

The National Weather Service has issued a Winter Storm Watch for all of North Alabama and southern Tennessee.  Rain will move in Tuesday morning and will be with us throughout much of the day.  Late Tuesday night colder air will begin to move in along with a very powerful upper level storm system.  Rain will begin to change to snow from West to East.  As the storm tracks east it will be intensifying and this will increase the chance for heavier snowfall along with the chance for Thundersnow.  Higher snowfall totals are likely along what is know as the deformation zone.  It is in this area and along the track of the 850mb low and warm air advection pattern that we have placed the potental for higher snowfall totals.  This is the area that could fluctuate the most depending on the exact track.  Most of the snow will come to an end by 10am Wednesday.  Surface temperatures will be at or slightly below freezing during the early morning hours. During this time it is likely bridges and overpasses will become hazardous.  Other less traveled roads could also become slushy with slick spots.  By the afternoon temperatures could hit the upper 30s and lower 40s it just depends on how much snow actually falls.  Stay tuned for changes there will likely be more in store.

Brad Travis
Chief Meteorologist
WAFF 48 Storm Team
We Track Storms