Larry Cogrove
"The turn to colder air over much of the U.S. in this past week is really only the start of some major weather changes. Because as we approach Halloween, the threat for a large scale major storm and follow-up cold spell will be increasing.
A prominent Kelvin wave is solidifying over the westernmost Pacific Ocean above Indonesia. As the Madden-Julian Oscillation is expanding eastward, this impulse may link with the polar westerlies (see shortwaves in the PRC and east of Japan), and start the process of amplifying the jet stream with a ridge over Alaska and western/northern Canada. That action would force digging of a 500MB shortwave into the lower Great Plains around Oct 25.
Now this is the important part! At the same time that cold air drainage and central U.S. disturbance is taking shape, the tropical Atlantic Basin may supply a warm-core impulse or moisture fetch into the Gulf of Mexico. There are two viable candidates for warm-core cyclogenesis (Caribbean Sea and Lesser Antilles), and one or both of these systems could get drawn into the deepening extratropical storm as it approaches Appalachia and the Eastern Seaboard Oct 27-29."