Discussion: One of the most fascinating connections to tropical convection is the interaction between middle latitude jet stream patterns and deep tropical convection. When this coupling of atmospheric dynamics occurs major storms are produced. This weekend brings an intense storm to the U.S. inspired by the tropical East Pacific Madden Julian oscillation (sometimes referred to as “Mojo” because of its capacity to produce major storms). The convection in the tropical East Pacific is made more intense by the warm El Nino waters.
A streak of subtropical jet stream presence is already inviting some of the energy and moisture from the deep tropics into the Gulf of Mexico where low pressure and heavy rain are beginning to evolve. Meanwhile Pacific energy in the middle latitudes is surging east from California and will hook-up with the evolving subtropical rainfall in the Gulf of Mexico to produce a huge weekend storm causing multiple dangerous risks to the U.S.
Entrainment of subtropical moisture into a cold Pacific storm causes a confined area of very heavy snow centered on Nebraska this weekend (Fig. 1). Blizzard conditions will emerge. The ECMWF snowfall forecast indicates more than 2 feet of snow is likely. Heavy precipitation also affects the Mid-South U.S. (where severe weather emerges) and particularly the Florida Panhandle where flash flooding will occur caused by 8-9 in. of rain (Fig. 2).
Tornadoes are likely tomorrow near the apex of a storm system separating colder air to the north from warmer air to the south while inviting a channel of subtropical air from the Gulf of Mexico. The tornado outbreak will be centered on Arkansas (Fig. 3). Severe thunderstorms with additional tornadoes possible shift across the northeast Gulf of Mexico states Saturday (Fig. 4).
In the East the MJO-inspired subtropical environment causes unusually warm weather on Sunday as afternoon temperatures surge well into the 80’s in Florida, 70’s throughout the Gulf and Southeast region and 60’s northward into the Mid-Atlantic States (Fig. 5). Prior to the warm Sunday heavy rain will move across Pennsylvania Saturday night and New England on Sunday. A tail of squalls could ignite Sunday afternoon in the Mid-Atlantic region. Sunday will be very windy across the East U.S. Seaboard.
Fig. 1-2: A Pacific storm entrains subtropical moisture from the south inspired by MJO influence and causing 2+ feet of snow in Nebraska this weekend. The MJO episode also causes up to 8-9 in. of rain over-the-weekend in Florida.
Fig. 3-4: MJO-inspired severe weather outbreak in the Mid-South U.S. to Southeast States to start meteorological winter.
Fig. 5: MJO-inspired very warm temperatures across the East on Sunday afternoon.