KNOXVILLE, Tenn. (WVLT) -We enjoyed a break of sunshine in a few spots this morning, in the area of subsidence, or downward moving air behind a departing convective system. This thunderstorm system brought us a few light showers last night across extreme southern parts of the WVLT viewing area, around McMinn and Monroe counties. A high cloud layer, and even a lower cloud layer were spreading into the region during the early afternoon hours. These clouds are indicative of an atmospheric response to the next mesoscale convective system building east through the mid Mississippi Valley. The southerly flow is pulling moisture off the Gulf, and this flow is helping to maintain that convective system as it shifts steadily east toward middle Tennessee. This area of showers and thunderstorms will advance into southeast Kentucky and east Tennessee late in the day, arriving on the Cumberland Plateau around 4-6 pm CDT and into the Tennessee Valley around 6-9 pm EDT. A trailing upper level area of lower pressure may keep a few showers going across the viewing area, right into sunrise on Memorial Day. The thunderstorms associated with this system should remain sub-severe for our viewing area. Again, the better supply of moisture from the surface through about three thousand feet will be farther south, on the other side of a persistent frontal boundary. When they hang around as long as this boundary has remained in place across northern sections of the gulf coast states, we call them stationary. The boundary also helps with atmospheric lifting, and this zone which extends east into the Tennessee Valley of Alabama is where the National Weather Service Storm Prediction Center has placed an enhanced risk for severe thunderstorms. This enhanced risk extends from just east of Little Rock, Arkansas to near Huntsville, Alabama. Skies will remain cloudy, with the light to moderate showers through the overnight hours. Temperatures will drop to around 60 degrees by daybreak on Monday. Winds will remain light northeasterly, with the occasional variable winds in the vicinity of convective showers.
MEMORIAL DAY: Several of the mesoscale models that we use to predict weather are trying to keep a few showers around east Tennessee during the morning, as the trailing convective system slows down as it approaches the southern Appalachian region. The numerical models produce just enough lift in a moist environment to keep widely scattered light showers around during the early part of the morning. It appears that by mid day these isolated light showers will have faded away. The afternoon still looks quite nice at this time. The next main chance for rain is still on track for Monday night, as yet another convective system rides across the mid Mississippi Valley during the daytime hours, in time to bring some showers and thunderstorms to the WVLT viewing area through the overnight hours. Low temperatures will cool only to the lower and middle 60s, as all that condensation of atmospheric moisture slows down the rate of cooling. Remember from our science classes back in the old days, condensation is a process that releases heat energy; thus slightly milder low temperatures. Winds will be northeasterly at around 5 to 10 mph.
TUESDAY: There still may be some showers around through mid morning, as that Monday night convective system shifts only slowly east across the Appalachians. However, we could see a break in the action around mid day, as we await the arrival of the next atmospheric lifting feature which comes in the form of a well developed low pressure system, riding east northeast out of the mid Mississippi Valley, into the upper Ohio Valley through Tuesday evening. Therefore, our next period of rain will be from late afternoon Tuesday through about midnight. Southwesterly winds in the neighborhood of 10 to 15 mph, ahead of our relatively strong low pressure system will help maintain high temperatures in the middle 70s, on Tuesday…