It’s still a non-zero chance…which means there IS still a chance for snow to fall in the northern parts of the state for Christmas.  Nothing is certain yet, but it’s not been completely ruled out at this time.

I wanted to share with you a wonderful educational discussion posted by the National Weather Service office in Ft. Worth yesterday evening.  In it, they break down the processes that would need to be in place with this next system for snow to develop.  It’s very interesting and not extremely nerdy.  I did include some definitions in parenthesis where appropriate.  It’s worth a read!

SINCE IT IS A QUIET NIGHT…ITS WEATHER CLASSROOM AND LAB TIME FOR THOSE INTERESTED… THE CHRISTMAS NIGHT FORECAST IS ON EVERYONE/S MIND. WE HAVE BEEN WATCHING THIS SYSTEM IN THE EXTENDED MODELS FOR SEVERAL DAYS…AND CONTINUE TO RIGHTLY ASSESS THAT A POTENTIAL FOR A WINTER EVENT EXISTS. UNFORTUNATELY, MODEL GUIDANCE DOES NOT HAVE THE SKILL IN THAT TIME RANGE TO ACCURATELY PREDICT THE INTENSITY AND LATITUDE THE UPPER LEVEL SYSTEM WILL TAKE BECAUSE OF THE UNCERTAINTY ON EXACTLY WHERE A COLD FRONT WILL BE ON TUESDAY.  AS WE HAVE SAID IN THE LAST 2 AFDS (area forecast discussions)…THIS COLD FRONT IS THE KEY TO THE FORECAST. BUT TO UNDERSTAND WHY…IT IS HELPFUL TO DISCUSS BAROCLINICITY AND ITS AFFECTS ON THE MOVEMENT AND STRENGTH OF WEATHER SYSTEMS.

ESSENTIALLY THESE STORM SYSTEMS ARE BLOBS OF UPPER LEVEL ENERGY…OR VORTICITY…OFTEN CALLED SHORTWAVES OR DISTURBANCES. IN AN ATMOSPHERE WHERE THERE IS VERY LITTLE TEMPERATURE DIFFERENCE FROM LOCATION TO LOCATION…THE MOTION OF THESE DISTURBANCES IS BASICALLY DICTATED BY THE FLOW THEY ARE A PART OF. THEY BEHAVE MUCH LIKE A LEAF WOULD IF IT WERE FLOATING DOWN A RIVER. HOWEVER WHEN HORIZONTAL TEMPERATURE GRADIENTS EXIST…SUCH AS WHEN A COLD FRONT IS NEARBY…THIS SIMPLE RULE GOES OUT THE WINDOW. THIS IS CALLED A BAROCLINIC ATMOSPHERE. A DISTURBANCE THAT MOVES INTO A BAROCLINIC ZONE WILL INTENSIFY. THIS IS BECAUSE LOW LEVEL TEMPERATURE ADVECTION (Transfer of heat by a fluid such as water vapor) BEGINS TO INTERFACE WITH THE UPPER LEVEL SYSTEM. IN SHORT…THERMAL ADVECTION IN THE LOW LEVELS CAUSE HEIGHT CHANGES (Height =  the height in meters above sea level of a specific air pressure level such as 500 millibars of air pressure) IN THE UPPER LEVELS…WHICH IN TURN STRENGTHEN THE UPPER LEVEL VORTICITY CENTER…WHICH IN TURN STRENGTHENS THE LOW LEVEL THERMAL ADVECTION…AND ETC. THE WHOLE THING BECOMES A FEEDBACK LOOP. AN UPPER DISTURBANCE UNDERGOING BAROCLINIC INTENSIFICATION WILL TRANSFORM INTO A CYCLONE AND WILL NO LONGER MOVE WITH THE MEAN FLOW…BUT WILL CURVE TOWARD THE POLE. IN THE PROCESS OF TURNING TOWARD THE POLE THE CYCLONE OFTEN OCCLUDES…MEANING THEY LOSE THEIR ACCESS TO THE TEMPERATURE GRADIENTS AND THEY WEAKEN.

WE HAVE ALREADY SEEN MANY MODEL RUNS OF A BIG WINTER CYCLONE DEVELOPING OVER THE SOUTHERN PLAINS AND CURVING OFF TO THE NORTH. IN THE LATEST MODELS WE NO LONGER SEE THAT SOLUTION AND SEE A WEAK TROUGH MOVING OVERHEAD. THE REASON WHY THE MODELS HAVE BEEN ALTERNATING BETWEEN A POWERFUL WINTER CYCLONE IN THE PLAINS AND A WEAK DISTURBANCE HAS BEEN DUE TO THE LOCATION OF THE BAROCLINIC ZONE /OR COLD FRONT/ WHEN THE DISTURBANCE REACHES THE SOUTHERN PLAINS. THE TREND IN MOST OF THE MODELS HAS BEEN TO MOVE THE FRONT/BAROCLINIC ZONE INTO SOUTH TEXAS. AS A RESULT THE UPPER LEVEL DISTURBANCE TRAVELS OVER TEXAS WITHOUT STRENGTHENING BECAUSE THE TEMPERATURE GRADIENTS ARE WEAK SO FAR BEHIND THE FRONT. THE SYSTEM THUS DOES NOT INTENSIFY UNTIL IT REACHES THE NORTHERN GULF COAST WHERE A BAROCLINIC ZONE EXISTS. THIS SCENARIO…WHICH WE ARE CURRENTLY FORECASTING…IS ONE THAT WOULD ONLY PRODUCE LIGHT AMOUNTS OF WINTER PRECIP. THIS IS BECAUSE THE SYSTEM WILL BE WEAK AND HAS NO ACCESS TO THE THERMAL GRADIENTS IT NEEDS TO INTENSIFY. AN INTENSIFYING LOW WOULD BE ABLE AUGMENT THE WIND FIELDS AND THUS TAP INTO THE GULF FOR MOISTURE.

IN ORDER TO GET A SIGNIFICANT SNOW STORM HERE…WE WOULD NEED THE FRONT TO BE FARTHER NORTH THAN CURRENTLY FORECAST…BUT NOT SO FAR NORTH THAT THE SYSTEM BEGINS ITS POLEWARD TURN AND STAYS NORTH OF THE REGION ALTOGETHER. WE NEED A GOLDILOCKS POSITION OF THIS FRONT.

AGAIN…KNOWING THE PRECISE LOCATION OF A FRONT BEYOND 5 DAYS IS THE DIFFICULTY WITH THIS FORECAST. THANKFULLY THE LEAD SHORTWAVE RESPONSIBLE FOR THE LOCATION OF THIS FRONT WILL BE ONSHORE IN CALIFORNIA SATURDAY AND WILL BE SAMPLED BY THE BALLOON NETWORK. IN ADDITION…WE WILL BE IN RANGE OF THE NAM (North American Model) BY TOMORROW FOR HAVING ANOTHER OPINION ON THIS FRONT/S STRENGTH AND LOCATION MONDAY NIGHT AND TUESDAY…EVEN IF WE DONT GET AN EXPLICIT DEC 25TH FORECAST FROM THE NAM UNTIL SATURDAY.

I’ve included some graphics below from the Ft. Worth, Amarillo and Lubbock weather offices that were produced after their own individual analysis of this potential system.  All this to say…don’t give up hope for some snow just yet!

Christmas snow

NWS Amarillo snow

NWS Lubbock snow

Jenny Brown

Jenny Brown

Blogger & Photographer at Texas Storm Chasers LLC
Howdy! I’m Jenny and I joined Texas Storm Chasers in January 2012. I’m married to my wonderful husband, Paul, and together we have six children…he has two daughters from a previous marriage, I have two sons from my previous marriage and together we have twin daughters.
Jenny Brown