The Evans family formerly of Bossier City and now residing in Memphis awoke to a surprise snow storm earlier today (they have been friends of ours for a while).  Parts of the city were covered in 5 inches of the white stuff!  The airport recorded 3 in about 2 hours.  The liquid equivalent was nearly .3 inches.  So the ratio ended up being 10 to 1.  That’s a wet snow-probably had some huge flakes all sticking together!  The temperature at the time of the onslaught was near freezing.

Unfortunately for the kids shown-this afternoon, the temp is up to 34 and the snow has changed over to rain-very sad!  Late tonight, the rain may turn in to freezing rain, sleet and some light snow.  It will be a crunchy mess by Tuesday morning and that will add insult to injury to the drivers for sure!!  By the way, the Evan’s kids have had the pleasure of 5 snow days in the past few weeks!  Sounds great now until they have to make them up in June!

I couldn’t pull up the sounding for Memphis, but they had roughly the same weather conditions as Springfield MO earlier today:

Here as shown, the air was saturated and below freezing from the ground up to roughly 9000 Feet.  Thus, it was a snow storm.

The ArkLaTex may have a shot of this kind of weather-possibly late tonight (quick change over before ending) and especially Thursday afternoon-night-Friday morning time frame.

Stay tuned for the latest at 5 PM on KTBS 3.

Joe Haynes

500 mb Analysis, Sunday Evening, Courtesy of RAP Real-Time Weather

Showers will begin to move in tonight through Monday morning ahead of a low pressure system that will move through late Monday.  In the upper levels of the atmosphere (see above image) a strong low pressure system is moving into the northern plains and it will continue to move south.  Since the winds flow counter-clockwise around a low pressure system, very cold air will be traveling from Canada to the ArkLaTex.  At the surface, a low pressure and an associated cold front will move through on Monday afternoon. This will cause widespread showers and storms, some producing heavy rain. Then, as the cold air moves in from the north, and the surface low moves to the east, rain will possible change over to snow early Tuesday morning.  Little to no accumulation expected.  The image below is a precipitation type forecast for Tuesday morning, blue indicates snow, green indicates rain. Temperatures will be very cold on Tuesday, with highs struggling to get out of the 30s and wind chill values in the upper 20s.

Precipiation Type Forecast, Tuesday Morning, Courtesy of RAP Real-Time Weather

Looking ahead to Thursday, the cold air will remain in place and another disturbance will move into the ArkLaTex. This one looks to move a little further south than the one that will move through on Monday.  Winter weather will most likely develop with this system, with a rain/sleet/snow mix developing early Thursday.  For now, it looks as though the winter weather will continue through Friday, and if this pans out, we will have to watch for possible icy roads on Friday morning.  The  image below is the precipation type forecast for Thursday afternoon.

Precipiation Type Forecast, Thursday Afternoon, Courtesy of RAP Real-Time Weather

Stay tuned this week for all of the latest updates.

Marcy Novak

Skew T diagram for snow showing saturated 100% humidity air, below freezing, skewed 45 degree lines in blue are temperatures of the atmosphere in celcius, 0 C is freezing or 32 F.

Skew T for Sleet where a large area of the curve is above freezing
and saturated i.e. rain and a large area near the ground below
freezing and saturated thus sleet.

This Skew T shows the majority of saturation above freezing
in the form of rain…near the ground shows saturation below
freezing…the warm rain above freezes on contact with the
ground-freezing rain.

This diagram from the other night in Shreveport is all
rain showing saturation above freezing for roughly
10,000 Feet.

The above Skew T/Log P diagrams should give you an indication how meteorologists can view the atmosphere analyzing data from the weather balloons. The above diagrams show the basic winter weather scenarios that we have experienced in the ArkLaTex this year.

What isn’t shown is a common occurrence around here where the atmosphere is dry and rain is falling into it from high altitude, evaporating and cooling the atmosphere down to freezing and saturation. Thus sleet and even snow can happen with this.

Have a nice weekend.

Joe Haynes

(Diagrams are courtesy of RAP UCAR Weather)

There are a couple of ways to show rain in the ArkLaTex tonight. One way is with Mega 3 Doppler Radar (above). It shoots out microwaves in all directions that when reflected by the rain drops return to the radar set and are amplified. Then, the rain areas are shown on the Radar screen (again-above). Tonight, green coincides with light rain and blue is mist or drizzle.

Another way to illustrate rain is with the standard weather balloon shown here. These are launched out at the Shreveport National Weather Service normally twice a day (morning and evening). The balloons carry instrument packages that record temperature, humidity and pressure as they ascend to the top of the atmosphere. The balloons are tracked with Radar so the wind speed and direction can be measured throughout the atmosphere.

An interesting fact about these weather balloons is that they start out at about 3 Feet in diameter at the earth’s surface and expand to the size of a house about the time they burst high in the atmosphere somewhere over 50,000 Feet up. The reason for this is that near the ground the air pressure is high keeping the balloon small. In the upper atmosphere, the pressure is low and thus the hydrogen-yes hydrogen in the balloon freely expands to the burst point of the balloon material.

The data retrieved is shown below for tonight:

The parameters measured once again are temperature-plotted in red as you go up in the atmosphere; dew point or humidity in green; pressure on the left side of the chart close to the calculated elevations in blue and the Radar calculates the wind speed/direction on the right side in the black barbs.

Tonight in Shreveport and above, the atmosphere is saturated with the temperature and dew point lines touching i.e. humidity=100%. With the saturated atmosphere, we have rain!

There is also a temperature inversion where the temperature actually rises a few degrees over the bottom 3 thousand Feet of atmosphere. That generally means the cloud is warmer and the rain falling to the ground is cooling a little with evaporation.

The SW winds shown on the right side of the chart (barbs point toward the NE or the wind blows from the SW) indicate the upper atmospheric storm is still west of us. Thus we are in the rising air side of the storm which cools and condenses the moisture forming clouds and rain. The rain should last for the rest of tonight.

By morning, the storm passes and the winds become NW and the air sinks. This sinking stops the rain and evaporates the moisture. Tomorrow though, if the surface winds remain light, the sinking air above the inversion may warm it more and keep the low clouds in most of the day.

Have a good night.

Joe Haynes

Mega 3 Doppler Radar (shown above) indicates rain areawide tonight in response to our next upper atmospheric storm system approaching the ArkLaTex. Precipitation amounts so far are mostly on the light side ranging from a trace to a tenth of an inch.

The majority of the rain is still falling out of mid level clouds at 9000 FT above the ground coming from the Pacific Ocean. Some of the precip is actually evaporating before reaching the ground due to the relatively dry lower levels.

At this time, the surface reflection or surface storm system is still trying to form in the western Gulf of Mexico. Once this occurs, incoming low level gulf moisture will complete the job of saturating the atmosphere. This should occur Thursday.

At the point of saturation, expect periods of rain, fog and drizzle on into tomorrow evening. Forecasted amounts become heavier as you go south. Northern areas could see .5 to 1.5 inches. Southern sections may exceed 2.5 inches.

Stay tuned to KTBS 3 First News at 5 AM Thursday with Meteorologist Marcy Novak for an update.

Joe Haynes