Thursday, January 22, 2015

Thursday Night Forecast Update for Friday, January 23rd

While the forecast still seems to point to mainly rain falling tomorrow, forecast snow totals are slightly higher than I indicated on WBBJ 7 Eyewitness News in our early evening newscasts.


The area of low pressure located farther south of us near New Orleans is slowly moving east-northeast still, but has arrived at this location a little earlier than originally expected. It still means that we should start off with mainly rain in West Tennessee tomorrow morning with temperatures above freezing. However, temperatures will be cool enough to allow rain to mix with snow in northwest Tennessee for the start of our Friday.


The chance for rain will gradually increase throughout the morning and into the early afternoon before dropping off, especially after sunset. Chances for snow to mix in with rain will increase throughout the morning and afternoon but are never significant. Most of the precipitation is still expected to be rain south of I-40 throughout the morning but along and north of the interstate is where snow mixing in with rain could cause light accumulations on lawns and tree branches.


This is what we're currently expecting for snowfall accumulations on GRASS tomorrow. Roads will still just be wet, and shouldn't become icy with ground temperatures still above 40ºF across most of West Tennessee. The bulk of sticking snow is anticipated to accumulate along and north of I-40 with parts of Henry, Benton, and Carroll counties possibly getting up to an inch of snow.

After sunset tomorrow night,
most of the precipitation should come to an end or be very light as low pressure continues to move to the north and east off into the Atlantic Ocean of the coast of the Carolinas. The weekend looks great with warmer weather, so any snow that does stick should melt quickly. Just exercise caution when traveling Friday night around West Tennessee as bridges, especially, could be slippery in a few spots with temperatures dropping below freezing after midnight.



Updated Forecast for Friday January 23rd

At the present time (11:51 a.m. Thursday January 22nd), once again it looks as though West Tennessee will miss a chance at seeing any significantly accumulating snow.

If you read the blog yesterday, you might remember that I mentioned the 3-strikes scenario. On Tuesday (1/20) there were a small number of computer models suggesting the possibility for snow on Friday (strike 1), on Wednesday more models suggested snow (strike 2), but now today models are backing off on snow and suggesting primarily rain - no strike 3.


Basically, here's what's changed - models are coming into better agreement saying that precip will start as rain after midnight tonight (Thursday night) and roughly move from southwest to northeast. The center of the low pressure system in question will be moving from the Gulf Coast into land moving northeast toward Savannah, Georgia.

Rain will continue to move into West Tennessee through the morning but could change to a rain and snow mix by the afternoon. This is going to sound silly because we say it all the time, but Interstate 40 should once again be a rough indicator for where the precip change will occur. After noon on Friday a rain/snow mix will be possible north of I-40 while south of the interstate it should continue as all rain. (In case you're wondering, the answer is no - I-40 has no affect on our weather. It's only merely coincidence.)



Regarding possible accumulation - it's unlikely. At best I think we could get a dusting on grassy surfaces and trees by midnight Friday night in northern and northeastern counties of West Tennessee. If you were wishing for snow here's your hope - the 'Weather Prediction Center' is still indicating a 30%-40% probability for snow to accumulate to greater than or equal to 1" in the 24-hour period ending 6 a.m. Saturday.




Pending future updates to the forecast, here's what you can expect in a nutshell -
  • Wet roads in Friday morning - all rain
  • Rain snow mix after noon in northern West Tennessee but staying all rain roughly south of I-40
  • Uncertainty about early dismissals for schools - keep up with WBBJ 7 Eyewitness News (wbbjtv.com) for more on that
  • Exercise caution when traveling north of I-40 during the afternoon. Roads should continue to just be wet and not accumulate snow since the ground is so warm but be prepared for slower than normal traffic in busy areas.
  • Dropping temps on Friday night could lead to slippery spots on bridges and elevated roads. Especially in areas that see the heavier rain/snow.
We'll keep you updated with more details tonight on the news, and I'll post another update tomorrow morning.

Wednesday, January 21, 2015

Possibility for Snow Friday January 23rd in West Tennessee

WEDNESDAY JANUARY 21, 2015 - 1:12 P.M. CST

These next few days when I talk about the "S" word, I'm really talking about snow.

Recently, the weather has been absolutely gorgeous in West Tennessee with temperatures in the 50s and 60s under plenty of sunshine, but that could change drastically by the end of the workweek.

One of the most important tools meteorologist will use to create a forecast is called a computer model. There are several different types, and when computer models align showing similar information in their forecast, our confidence in our own forecast, based on those models, will increase. In baseball, it's three strikes and you're out but in weather I'm going to tell you that it's three strikes and you're in!


Strike 1
Yesterday, there was a computer model called the NAM (North American Model) suggesting the potential for snow on Friday in West Tennessee. The setup on Friday is relatively clear - an area of low pressure will be placed in the southeast United States with surface winds wrapping around counter clockwise, causing northerly winds and colder air to move into the Mid-South on Friday afternoon and evening. The NAM suggested that moisture associated with this area of low pressure would fall as a rain snow mix.


Here's a rendition of this setup based on the European model -

Temperatures that are blue, are below freezing - they're shown here in degrees celsius.

Strike 2

It's worth mentioning, at this point that today the NAM isn't the only model suggesting a potential for the cold air to interact with moisture present to cause snow to fall in West Tennessee. Now that there are others, there's slightly higher confidence that snow will fall Friday afternoon and evening.

Here's a look at those different models where greenyellow
, and red colors show rain, but purple indicates wintry mix and blue indicates snow.


GFS (Global Forecast System)

GEM (Canadian)

NAM 4km (North American Model)


The NAM 4km has a higher resolution and can pick up on scattered showers more easily than the GFS or GEM models. At this point, all three of these models show a possibility for rain to change to snow or a wintry mix after 12pm Friday and last into the evening.

Strike 3
Tomorrow, we'll revisit some of these computer models and watch for any changes to the forecast. If they continue to show the chance for snow, then that will be strike 3, we'll be more confident with a forecast including wintry weather Friday afternoon and evening, and we'll issue a snowfall forecast map. At this point, while snow is possible, I think if we see any, it will be light and have a fairly hard time sticking at first given the warm weather we've had lately.

I'll keep you posted!

Thursday, January 15, 2015

Quick Timeline for Today's Weather

With light snow coming down in northwest Tennessee today, here's a look at how that could affect your travel at lunchtime, picking kids up at school, coming home from work, and for going out later tonight.


Noon - Going out to lunch? Winter weather advisories will end at 12pm at which point, most of the the light snow in northwest Tennessee should have come to an end or will do so soon after noon. Some roads are snow covered in northwest Tennessee so take precautions if you'll be traveling through those areas. Otherwise most roads are fine, there might be some very light rain falling in southeast West Tennessee, but the worse travel conditions will be points south in Northern Mississippi where a wintry mix was falling earlier.


Picking Kids Up at School - by 3pm most if not all of the precipitation will have ended in West Tennessee and temperatures will be above freezing so roads will be just be wet in northwest Tennessee. Elsewhere, light precip if any fell so roads will be okay outside the red circle shown above.
 


Coming Home From Work - by 6pm all the snow will have melted that fell today, roads will be fine if not just a little wet in northwest Tennessee but no ice is expected anywhere at that time.


Going Out - if you'll be going out at or after 9pm tonight just be aware there could be some very small and isolated patches of black ice in northwest Tennessee in areas that got longer periods of snow at higher intensities. Other areas outside that red circle shown above will have no concern.

Make sure to tune in to the latest forecast from Gary Pickens at MidDay on ABC at 11:30 and at Noon on CBS!