Areas up the Mississippi and Ohio Rivers, from TX to OH, are bracing for flooding from a few inches of heavy rain Wednesday into Thursday. However, that’s not the only concern for trick-or-treaters. Rising motion ahead of this cold front will lead to some severe thunderstorms forming Wednesday afternoon and night, providing some added fright for Halloween night.
The overall culprit of this unsettled weather is the shortwave trough that will make its way across the country this week. Its associated cold front will really form and strengthen over eastern TX. Generally with cold fronts, most of the precip that comes with them is out ahead of the front, raining and storming while still in the warm sector but giving way to clearer skies once the cold air mass is overhead. It’s this difference in temperatures between air masses that creates the circulation necessary for clouds, rain, and storms. Upward motion in the circulation can sometimes be stronger, creating thunder or severe storms. It’s for this reason that there’s risk for thunderstorms Wednesday night from central and southern TX all the way to southern OH.
The greatest instabilities will often yield the greatest chance for severe storms. Daytime heating mixed with low-level convergence is all that’s needed to place the highest instabilities on central Eastern TX. This is where a line of convective storms is expected to develop Wednesday afternoon, moving northeastward into the lower Mississippi Valley by late afternoon. Instabilities and shear should remain favorable ahead of its path, advecting possibly severe storms that could last into the night.
Surface based cells may develop further eastward, which could produce small hail and damaging strong winds. Low level jet formation across east Central TX will increase tornado potential late Wednesday night. The biggest concern with these severe storms is if a squall line develops. Low level convergence and front parallel shear positions squall line formation across central TX during the late afternoon and early evening. Damaging winds from a possible squall line is one of the greater concerns for this system as we get closer.
If you’re thinking that this October has seemed a lot more active than usual severe weather-wise, you’d be right! While TX and LA are generally the most active states for tornadoes in October, the severe weather season is supposed to be slowing down, not ramping up. Only 61 tornadoes generally occur throughout the entire country during the month of October, and 43 have already been confirmed for the first half of October. That number is not including the bout of severe weather and tornadoes seen across the Northeast on Monday, or the 4 tornadoes and waterspouts that occurred last week. An active period Wednesday could put us well above the country average for the month.
Of these 43 confirmed tornadoes, 19 of them have been in the Northeast; all in states that generally have less than one tornado during October on average. Before 2018, Long Island had zero confirmed tornadoes on record. As of yesterday, there have now been two just this past month. MA has had the most active October since 1950, with 7 confirmed tornadoes. Just on Monday, more tornadoes spouted up in CT, RI, and MA, adding to the 19 seen from the October 3rd outbreak earlier this month. It’s unclear whether more tornadoes are occurring each year, or if we are simply getting better at detecting them. Even so, this season has certainly been very active throughout the country, especially in usually quiet parts like the Northeast and New England. We can only continue to gather data as we end October and hope for a quieter November.