Note: Clicking on underlined red text provides links to various weather maps. In bold, italicized font are all of the ingredients necessary for tornadoes to form.

Summary: A rapidly intensifying surface low pressure system over the Great Lakes drove its trailing strong cold front into an unusually warm, moist air mass for this time of year over the Midwest yesterday. This created the “lift” that created upward motion in the atmosphere. Instability in the warm air mass in advance of the cold front was intensified by a pocket of very cold air aloft in an amplifying trough in the jet stream wave pattern, diving to the south. This instability accelerated the upward motion to generate strong thunderstorms in advance of the cold front. The strong meridional temperature contrast also generated a strong jet streak aloft which combined with a strong wind field being generated by the deepening low pressure system to create strong vertical wind shear (change in speed and direction of the wind with height). This wind shear created the rotation necessary to turn many of the thunderstorms into long-lived, rotating thunderstorms called “supercell” thunderstorms that produce the majority of strong and violent tornadoes. As a result, there was a tornado outbreak over Illinois, Indiana and Kentucky yesterday afternoon. The National Weather Service has not had time to “rate” the tornadoes yet but some of the damage in the photos and video is at least EF-4 (wind speeds 166-200 mph) in a few of the tornadoes. As strange as it may seem, tornado outbreaks are not unusual in November. In fact, a devastating tornado outbreak occurred during the “Super Tuesday” primary elections in the Southeast U.S. as recently as 2008. However, this outbreak was farther north than usual for November. Most November outbreaks occur in the Southeast or along the Gulf Coast. However, there have been 60 November tornadoes in Illinois and 50 in Indiana and Kentucky since 1950. I am curious to see the rating for yesterdays tornadoes since there has never been an EF-5 tornado and only 20 EF-4 tornadoes anywhere in November since 1950.

As the surface low departs northeastward into Canada and its trailing cold front moves well off the coast, surface high pressure will once again build into our region and give us fair weather through at least Thursday and probably into Friday. Late in the week, the jet stream wave pattern will again amplify with a cold trough driving south over the Great Plains and Midwest. This will generate a surface low along the eastern edge of the trough (the usual location) on Saturday. It looks like this low will develop to our northwest. As a result, we may get some mixed precipitation as it drags its warm front by on Saturday but we should get mostly rain as we move into the “warm sector” to the southeast of the low. I’ll have a better handle on precipitation type as the week progresses. In any case, after the low moves by it should open the door to what looks like the coldest air of the season as the cold trough moves over us for Sunday and Monday.

Monday Night

Variable cloudiness, becoming mostly cloudy after midnight. There is the slight chance of a snow shower or flurry, predominantly over the elevated terrain to the north. Becoming windy and much colder.

Low temperatures near 30 in the valleys, mid to upper 20s over the elevated terrain. Wind chills in the single digits to teens at times.

West-northwest winds at 10-15 mph in the evening, increasing to 15-25 mph after midnight (highest winds over the elevated terrain) with 30-40 mph gusts.

Tuesday

Some lingering cloudiness through mid-morning, then becoming mostly sunny for the remainder of the day. It will be blustery and colder.

High temperatures in the mid to upper 30s in Pittsfield, North Adams, Adams and Williamstown; upper 30s in Lee and Stockbridge, near 40 in Great Barrington and Sheffield and; low to mid 30s over the elevated terrain and hilltowns, depending on elevation.

Northwesterly winds at 15-25 mph with gusts to 30-40 mph. Winds diminishing later in the afternoon.

Tuesday Night

Mostly clear and cold.

Low temperatures generally in the upper teens with mid teens over the elevated terrain.

Northwest winds at 5-15 mph in the evening, becoming light and variable by morning.

Wednesday

Mostly sunny, calm and not quite as cold.

High temperatures near 40 in Pittsfield, North Adams, Adams and Williamstown; low 40s in Lee and Stockbridge, Great Barrington and Sheffield and; mid to upper 30s over the elevated terrain and hilltowns.

Winds light and variable.