Major storm to impact much of U.S. with snow and severe storm threat; Unseasonably mild here

Weather

A major storm system is set to emerge and bring an abundance of harsh weather for much of the Nation. Winter storm warnings have been hoisted for heavy snow across the Central and Northern Plains while several states are outlooked for a severe weather outbreak.

WARMING UP

We are just forty-eight hours removed form the coldest air of the season and we’ve officially severed ties with the polar branch of the jet stream, and for the time being! Temperatures have surged as much as 20-degrees from the same time Wednesday and much warmer than Tuesday afternoon when we failed to reach 30°.

A south breeze will blow tonight keeping temperatures nearly steady and increasing moist air through the night. A few sprinkles and a passing shower is possible through the night but as the lower levels moisten, areas of fog are possible late night and early Friday morning. Just two morning ago we dipped into the teens, the coldest of the season – come Friday morning temperatures will be at or above the normal high temperature for the this time of year.

RAIN ON THE WAY

Showers will be minimal in coverage as Friday opens and there will be many rain-free hours early in the day but a powerful storm system is taking shape and rain chances are set to surge. Showers are to become downpours by mid-afternoon and the threat of a thunderstorm will be on the rise late day as a warm front lifts north after sunset.

STORM TO BRING SNOW AND TORNADOES?

A low pressure will strengthen over the next 24-hours and take a northerly track across the Midwest ultimately tracking to the southern tip of Lake Michigan early Saturday morning. This is where its central pressure is forecast to drop to a whopping 986 millibars or 29.13″ on your home barometer, nearing category 1 strength of a hurricane.

So what is behind this storm? A large spread in temperatures over a small area of real estate, a temperature gradient – will drive strong winds to blow at the surface and aloft. The jet stream winds will aid in deepening the low pressure while welling up warm, unstable air while at the same time, creating heavy winter weather on the storms cold side while producing a outbreak of severe storms in the warm sector. Indiana will reside in the warm sector and the threat of December thunderstorms are once again in the rise along with an increased threat of potentially severe storms as well.

We sit in the warm air late Friday night and are expecting the warmest temperatures to occur after sunset and around midnight when we will challenge the record high temperature for dates! We could tie or break the record late Friday night and early Saturday morning when we near 66°. Just wild, that the temperatures will be that warm at that time of the night. It will not last, that cold front means business and temperatures will tumble when a cold front sweeps the state around sunrise Saturday.

INGRIEDIENTS ARE GOOD

Strong winds feed the storm and as the storm deepens, those wind are to change direction in altitude and over time creating a suitable environment for potential tornadoes. While it may be December and the timing for the worst storms are late at night, the dynamics with this storm are still supportive of possible tornadoes as far north as central Indiana.

The Storm Prediction Center has placed most of the southern half of the state in a slight risk of severe thunderstorms for Friday night and early Saturday that included the possibility of damaging winds and a few tornadoes.

The most unstable air will arrive along with the warmest temperatures as we see it at this time around midnight through 3/4 a.m. Saturday morning. The buoyant air would support the vertical build (updrafts) bringing thunderstorms to life while entering an environment of high shear, winds changing direction with altitude.

The Storm Prediction Center’s SREF (Short-Range Ensemble Forecast) produces a “tornado ingredients” outlook and it is not good especially for portions of southern/central Indiana, western Kentucky, western Tennessee, eastern Missouri, Southeast Illinois and extends south Mississippi. This area highlighted in the image below for a period of time leading from 1 a.m. to 5 a.m. Saturday. We will have new data tonight and again early Friday to firm up the forecasts so be sure to check back frequently on Friday for updates.

IT’S A WINTER STORM TOO

The same low will deliver severe, winter weather across the upper-Midwest where multiple state are not under a winter storm warming. While the probability of a tornadoes or two rises in the warm sector, the probability of a half-foot of snow is also rising in the storms cold sector. This will be the largest winter storm this season with the highest winter weather impact on portions of southern Minnesota through central Wisconsin.

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