© 2019 Terry Swails

SNEAKY SNOWFLAKES FOR SOME SATURDAY?

October 12, 2019

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That Cat 5 winter storm is still whipping the upper Midwest with gusty winds and chilly temperatures. The system is stacked and nearly stationary over NW Minnesota as of Friday night. This 3D satellite image shows the moisture coming north from the Gulf of Mexico and then wrapping around the intense circulation all the way into Canada. Some pretty dynamic stuff going on here.

This next graphic depicting water vapor anomalies has the moist air in blue and the dry backside of the storm in reds.

The circular area between the blue and red is the closed circulation which goes all the way from 500mb (jet stream level around 30,000 ft all the way to the surface. This is where the storm has its maximum lift and is venting it up through the atmosphere like a volcano.

 

A look at the thermal profile shows why this system was such a beast. Temperatures in central Mississippi were near 90 while a blizzard with readings in the 20s was raging in the Dakotas. 

Notice too how temperatures drop nearly 20 degrees with the frontal passage. That sharp yellow line is the classic dry line that can often spin up severe thunderstorms when the dynamics are aligned properly. Here's the 24 temperature change around mid-day.

Just as impressive as the temperature drop is the reduction in moisture levels. The dew points in some areas are more than 35 degrees lower Friday night. (38.4 degrees down in Cedar Rapids going from 64.4 to 26)

You can certainly see why moisture levels tanked when you look at the surface isobars Friday evening. Isobars are lines of equal pressure shown in black below. They are out of the west compared to the southerly direction they were oriented Thursday. That cold dry air just sheared the moisture east...literally gone with the wind!

As I write this at least 27" of snow has fallen just north of Devils Lake, North Dakota. Many roads are closed and reports are increasing of 5 foot drifts with trees down and power outages. Many roads are closed in the eastern half of the state. This image was captured Friday in Devils Lake. Whoa baby...

Needless to say this was in interesting event in many ways. The storm has one more little wrinkle that could bring some snowflakes to my northern counties, especially near and north of HWY 20 towards Saturday evening. Due to the structure of apowerful storm such as this, it's common to have bands of lift or vorticity wrap around the upper air low. One of these is set to drive southeast towards my area during the late day hours.

That may actually allow temperatures in the south to approach 50. However the warmth will not find my northern counties and here the lift provided by the vort max should kick up some early evening snow showers. The 3K NAM is consistent in showing this scenario. Below you can see the snow depicted between 5 and 9pm north of HWY 20.

The model even shows some bursts that might be significant enough to bring a dusting to a few spots. Here's what the 3K shows for snow totals. 

I'm hoping a couple of those flakes can make it to my place but that's probably a push. After the disturbance departs it will reinforce the cold air for Sunday and highs will likely hold in the 40s in most areas. Norms are in the low to mid 60s. Crisp for sure. OK, that's all for now. Have a fine Saturday and go Hawks, put the dog on those Nittany Lions! Roll weather...TS  Don't forget I'm on twitter too at Terry Swails

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