Chances for wintry precipitation continue in the Tennessee Valley. This morning and afternoon, another batch of precipitation was moving across areas of the lower to mid Mississippi Valley. Ground reports indicate that much of the precipitation reaching the surface is a mix of snow and sleet in eastern Arkansas and northern Mississippi. Drier air in the lower levels may prevent some of the precipitation from reaching the surface on the northern extent of the precipitation shield. A perusal of SPoRT LIS soil temperatures in AWIPS shows that skin surface temperatures are a little below freezing in much of northern and western Mississippi and in parts of northwestern Alabama (Figure 1). In the image below, white colors indicate temps around 32°F, while deeper blues (lower OH Valley and mid-Mississippi Valley) are below 28°F.
Of course, it is important to point out that these data were valid at 15 UTC (from the 15 UTC analysis). Skin surface temperatures, especially, can exhibit relatively large changes in values during periods of radiational heating/cooling. Thus, today’s breaks in the clouds and resulting insolation will cause further warning in skin surface temperatures particularly in parts of northern Alabama. Next, let’s take a look at the 0-10 cm soil temperatures (Figure 2).
Notice that temperatures in the deeper soil layer are generally above freezing (per the SPoRT LIS) despite air temperatures well below freezing. Air temperatures were warmer across the region during much of the weekend, so the sub-surface is still warmer, but slowly responding to the recent cold air advection over the last 24 hours.
So, the take away here is that any accumulations will probably be immediate (due to the below freezing skin temperatures and snowfall rates), but limited, as warmth from the deeper sub-surface tends to melt precipitation slowly from below.
One of the great features of AWIPS II, is that it allows for the visualization of multiple layers. Following is a time lapse of regional NEXRAD radars (composite) over the SPoRT LIS skin surface temperatures (Figure 3) during the late morning into the early afternoon. The 15 UTC SPoRT LIS soil temperature image is static due to its more limited 6-hourly resolution. These soil temperature data/products are currently being transitioned in a testbed phase to NWS offices in Houston, Huntsville and Raleigh.