Early Morning Analysis; Upper Air Storm Taking Shape

The cold and rainy conditions continue across Alabama at this early morning hour. This latest hourly analysis shows a deepening upper atmospheric trough to the west. A near 30-degree temperature fall has also been noted over our far northwest communities over the past 24 hours. Today we will be on the lookout for a closed off upper level low to develop as the trough amplifies to our west. This disturbance will be the culprit behind the chance of snow for tonight.

I know we’ve been talking a lot about the term upper level low lately so we wanted to provide a more detailed description of this feature. These types of systems can impact Alabama during several times of the year and they are upper level disturbances spawned by spin (vorticity) in the atmosphere and higher wind speeds (i.e. jet streaks) in the upper atmosphere. In this case, the developing upper low is associated with a mid-latitude storm system.

Notice on the included 500 MB chart that there are height contours at 5,580 meters over Central Mississippi, dropping to 5,520 meters over far West Mississippi. This would translate to a drop in pressure heights resulting from faster winds to the east of the troughs center causing the mass evacuation of air. A core of colder air is also associated with these lowering heights. Check out the frigid temps in the -23 C range at this particular level back over Arkansas. Already temperatures at or below freezing are developing below 5,000 feet over north Mississippi and northwest Alabama. This deep layer of cold air will move over our viewing later today.

Because of the deepening layer of cold air, the environment will become more favorable for snow growth. Therefore, we’re forecasting some snow flakes to start mixing in with the rain over north Mississippi today and then possibly change to all snow. This transition will slowly take place over our state later today. The greatest chance for snow will be underneath this cold pool and north-northwest of the center. Since the center of the low will pass to our north, we’re forecasting the greatest chance for snow over our northwest communities. Temperatures in Marion and Winston Counties have already dipped into the upper 30s. This will further enhance the chance of some snow sticking on grassy surfaces and rooftops. We expect the surface temps to stay above freezing however and given the recent mild weather, most of the wintry precipitation will melt, especially on the wet roads. However, a burst of heavier snow could pull colder air closer to the ground and this could cause a fall in surface air temperatures. That is what makes forecasting these systems challenging. We will be watching the radar closely and we will be posting updates as this complex system makes its march across our state. Mickey will have the plenty of weather updates on Good Day Alabama this morning and we will have plenty of blog updates throughout the day.

(925 MB Analysis Chart, freezing line at this height in blue dipping into central MS)