Two major areas of energy were over the United States on Saturday morning. One piece is an upper level low pressure system over the southwestern United States generally diving southeast along the West Coast. The other is an upper level low pressure system moving into the Mississippi Valley region.
The system in the Western US will cause rain and embedded thunderstorms in the Northern Intermountain region that will spread to the Southwestern US by Saturday night with the thunder ending overnight. On Sunday morning, rain and higher elevation snowfall will occur over the central and northern Rockies. There are equal chances for higher and lower values, or essentially a mean forecast value of around a foot of snow in Southern Colorado and Northern New Mexico and up to 6 to 8 inches of snow possible in portions of the Central and Northern Rockies. By Sunday evening, rain and embedded thunder is possible from central/southern California into the Southern Plains as a result of this system. Also in the southern Plains, moisture from the Gulf will mix with the energy moving east from the West Coast to allow for scattered thunder.
The second system will cause showers and thunderstorms in the Mississippi Valley with the heaviest rain falling in the Lower Mississippi Valley. Around 5 inches of rain is forecast to fall through Monday morning as a result of warm moist flow contributing to above normal precipitable water values and warm cloud layers at around 14000 ft contributing to heavy rain. As a result, flash flood watches have been issued over the Lower Mississippi Valley region.
In addition to heavy rain over the Southern US, heavy rain is possible over the Appalachian Mountain region with up to 2.5 inches of rain possible there. Above normal precipitable water values, large scale ascent and above normal moisture transport into the region all allow for heavy rain to fall in that region. Again, as a result flash flood watches have been issued over this region.
Meanwhile, the strongest thunderstorms are forecast to form over the Lower and Central Mississippi Valley Saturday night along the second system’s attendant frontal system with the threat of strong wind, damaging hail and the possibility of a tornado. As the forcing for the thunderstorms moves east for Sunday, they are forecast to be less intense with marginally severe thunderstorms in the Southern and Southeastern US. Hail is expected to be a threat in both Southern and Southeastern US with damaging winds also a threat in the Southeastern US.