Monday, November 28, 2011

Light Snow Tonight

UPDATE Below: It appears like there is a chance for some light snow today and tonight across parts of southeast Missouri, western Kentucky, northwest Tennessee and northeast Arkansas.

As first mentioned 7 days ago, cold air is wrapping in behind the cold front/surface low pressure that initially brought rain to the region Sunday. Temperatures at 10am CT are in the upper 30's across southeast Missouri, western Kentucky, northwest Tennessee and northeast Arkansas. Temperatures are likely to hold steady in the upper 30's through the day.

Cold air aloft (a few thousand feet) will be between -1° and -3° Celsius. This will allow moisture to freeze in the form of snow. As the moisture drops to near the surface it will encounter temperatures that will be a couple degrees above freezing. This will allow for the snow to melt slightly. That's what we mean when we talk about a "wet snow". It is falling in to an environment that allows it to start the melting process.

The areas I think have the best chance at seeing accumulation, mainly on grassy and elevated surfaces, will be south and east of a line from Mayfield, Kentucky -- New Madrid, Missouri -- Malden, Missouri -- Jonesboro, Arkansas. That's not to say we couldn't see a little north of that line, but the bulk should be south and east of of that line. (I wouldn't be surprised to hear some reports of snow around Doniphan, Mo, Poplar Bluff, Mo, Van Buren, Mo or even Sikeston, Mo or Charleston, Mo.)

At this point, I don't think it will be a big deal. My "Freak-Out-Meter" is around a 1. (That's on a 10 point scale.) Soil/ground temperatures are still warm so that will allow for snow to quickly melt, especially on roads.

11:42am CT Update:

To give a little more perspective as to the temperature profile of the atmosphere I wanted to show you what temperatures are forecast to be at the surface and at 5,000 feet (850mb).

The following is from NOAA's morning run (12z) Global Forecast model (GFS). All tempertaures listed in Celsius.

CITY | 1pm CT 2-meter/5,000' Temp | 7pm CT 2-meter/5,000' Temp | 1am (Tue) CT 2-meter/5,000' Temp

Cape Girardeau, MO | 3.6°/-0.7° | 2.3°/0.5° | 2.6°/1.6°
Dyersburg, TN | 3.7°/-2.1° | 1.5°/-2.5° | 0.7°/-1.5°
Jonesboro, AR | 4.8°/-4.0° | 3.3°/-3.2° | 1.3°/-1.0°
Murray, KY | 3.3°/0.8° | 2.7°/-0.8° | 2.0°/-2.0°
Paducah, KY | 3.2°/0.6° | 3.1°/1.2° | 3.8°/0.8°
Poplar Bluff, MO | 4.4°/-2.5° | 2.1°/-0.8° | 1.2°/1.6°

Looking at the above data you can see when the colder air aloft strengthens yet temperatures at the surface remain above freezing. You can also see areas where temperatures never get below freezing. Also notice the times when the temperature barely makes it below freezing (0° Celsius). Yes, a few tenths of a degree can make a BIG difference in what type of precipitation falls.

This gives you a look at some of the data forecasters look at when trying to determine what type of precipitation is going to fall. Keep in mind, this is only one model of several we look at. For big snow storms I may look at seven to eight models.

1 comment:

Anonymous said...

Thanks John...! I always look to your forecasts for Poplar Bluff and Harviell area... I appreciate what you do for our area! Karen