After bringing rain, wind and mountain snows to California, all the way into Baja California with even a tornado sighted between Red Bluff and Chico, that same storm is now pushing across the Desert Southwest bringing nasty conditions to Arizona into New Mexico. The upper low brought donw very cold air and thus snow levels dropped to 2,000 feet overnight allowing snow to accumulate over parts of the Mojave Desert. Las Vegas may get a rain-snow mix through today but there is unlikely to be any accumulation.

With the help of a vigorous southern branch jet, heavy rains are now breaking out over Texas while from central Oklahoma north into southern Kansas, snows are now breaking out. This is despite the main storm still being way back over the Desert Southwest and this is a sure sign of trouble later tonight and throughout Thursday extending into Friday. Later this evening, heavy snowfall will begin across Colorado as the low advances ENE and takes aim at the Central Plains by tomorrow afternoon. It’s really once the storm system makes it across the Rocky Mountains and out over the Plains where things get real interesting as arctic air which is sitting, waiting to get tapped, gets injected into the storm and further arctic air gets wrapped in from Canada while warm, moisture rich air gets pulled north from the Gulf of Mexico. These system tend to be fairly moisture starved once they emerge from the Rockies out onto the High Plains but the Gulf opens up and moisture pours north. The combination of the southern brnach and Gulf, means ample moisture for significant snow accumulations on the north side of the low.

Overnight tonight expect snows to pep up in a corridor from Denver, Colorado all the way to eventually Des Moines, Iowa through tomorrow but the real focus of really significant snowfall from this will be from central Kansas up into central Nebraska where as much as 2 feet of may fall between tonight and Friday morning. A uniform 4-8 inches will be found widely with an ice storm situation developing over Arkansas.

To provide you with some insight into the meteorology behind this event, while we have all the right ingredients converging over the Plains tomorrow with truely arctic air and not just cold, the warm, moisture rich air of the Gulf, perhaps the most important ingredient for a MAJOR, possibly record breaking Plains snowstorm is a potent southern or sub-tropical branch which energises the storm and injects additional moisture.

It’s right on the northern edge of that upper low where we see the biggest snows and on the southeast side is where the strong winds will converge with low level warmth and moisture. So, on that southeastern side of the low, watch out for heavy rains and severe weather breaking out with a chance of localised tornadoes while on the north and northwest side of the low, that is where we see the biggest snows and while it’s heavy snow we see, particularly across Kansas and Nebraska, perhaps extending up into Iowa later Thursday, winds will blow sustained at 30-40 mph with gusts topping 50 mph, well within blizzard criteria. Whiteout conditions are a given with this situation and with the geography of this part of the nation.

With those strong winds I also expect some bigtime snow drifts to develop and the blowing and drifting in itself is likely to force travellers to pull over and for major interstates such as I-70 and I-80 to get shut down. I-40 which runs across Oklahoma looks to be south of the worst weather but we could see snow, rain back to snow with this situation.

Here’s the water vapor showing the southern branch and all the moisture out over the Plains way ahead of the main feature. A sure sign of a SIGNIFICANT snow event on the way tomorrow.

Just how cold is the air out ahead of this system? If you notice in the top infrared satellite imnage the milky colour to the clouds extending from central Canada into the central Plains, that milky colour is representitive of very cold arctic air. Below is late morning temperatures across the Northern and central Plains. Note the teens below zero over Minnesota and North Dakota with single digits across Iowa extending into NE Nebraska while upper teens to low 20s cover much of Kansas, while temperature warm slightly through today, they will drop again as darkness falls and the storm moves in.

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Here’s the very latest NCEP GFS snow projection out at 48 hours. Note the bullseye of heaviest snows centred over Kansas.

As for the latest QPF chart, it has increased the amount of water to fall across the Southeast. A corridor of 3-6, locally 8-10″ of rain is projected to fall from New Orleans to coastal South Carolina over the next 7 days. This is likely to cause some pretty substantial flooding.

Here’s the latest severe risk according to the Storm Prediction Center.

Slight risk over Texas for today.

Slight risk shifts to east Texas and across Louisiana into Mississippi.

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