Dry vs. Wet Halloween Weather

In the western side of the United States, cooler, drier weather conditions while continue into Tomorrow. Cooler above average temperatures will take place on the back side of an upper level shortwave trough due to an area of high pressure. This area of high pressure will create sinking, compressing air behind the trough, where upper level convergence is present allowing for clear, dry conditions. But, there will be increased hazardous conditions in parts of the Southwest due to very strong winds caused by the trough. Strong santa ana winds will accelerate off the west coast, leading to wind fires, thanks to very low relative humidities. Surface temperatures in the Rockies and Central Plains will be in the low teen's to low 30s whilst temperatures above will range between the upper single digits to low 30s. Dewpoint values will be extremely low where digits between the negative single digits to the upper 20s. Very cool and dry weather will occur as a result.

Meanwhile ,in the east much wetter and unstable weather will occur on the leading edge of the shortwave trough. The water vapor imagery shows the trough in the upper portions of the atmosphere due to a deep volume of cold air sinking from the north. This very cold air aloft will lead to an unstable atmosphere. Also, on the leading edge of the trough, temperatures will be 20 to 30 degrees warmer than temperatures in the west. This very cold air combined with warmer air where dewpoint values are much higher will lead to some snow conditions beneath the cooler portion of the trough while heavy rain will occur further on the leading edge of the warmer, moister airmass. Very strong temperature gradients between the southward moving polar air and moist air from the gulf stream will possibly lead to cyclogenesis,  later as the trough evolves into an occlusion(closed) low pressure cyclone. Heaviest precipitation will form on the leading edge near the left exit quadrant where upper level divergence is present. These diverging air colunms will allow for a large amount of air to rise, as it cools due to expansion, causing a drop in atmospheric pressure. Not only this divergence will cause lifting air, a strong cold front ahead of the trough will also give way to lift. Deep steep temperature gradients will lead to unstable atmosphere Lake effect snow will later form in most of michgan into parts of Canada.

As this energy is released into the atmosphere, some cells may become supercellular due to large changes in wind conditions with height, this is called wind shear. Vertical wind shear will support rotating updrafts and organization. Modals show very strong shear at low- mid levels of the atmosphere where possible rotation may occur where frontal convection is present. This will result in possible rotating funnel clouds. Wind conditions in the east will range between 20 to 40 knots at low levels.