Joe’s Weather Blog: Why it couldn’t snow when it was 15° (SUN-2/11)

Good afternoon…skies are clearing out and temperatures are still pretty chilly out there but it will be getting considerably better over the next few days. As is typical around these parts, usually in the winter when things warm-up the price to pay will be in the increasing winds that will be developing, especially Wednesday. Later in the week a strong cold front will send colder weather back to the region on Friday with another nuisance type snow possibly affecting Friday morning rush…then it will improve again next weekend. at this point no significant moisture is expected for the next 7-10 days.



Forecast:

Tonight: Clear skies and cold with lows down to near 10°. One thing to watch for would be perhaps some patchy freezing fog developing in some low lying areas. It’s worth mentioning but will all the treatments on the road from the weekend (whatever this thing was) system…hopefully no road issues. Watch the valley areas however.

Monday: Mostly sunny and not as cold with highs in the 35-40° range.

Tuesday: Somewhat breezy and milder with highs closer to average in the mid to upper 40s.

Wednesday: Partly sunny and windy again. Warmer too with highs well into the 50s



Discussion:

Let’s start with the situation from last night. The expansion of freezing mist/drizzle from the south to the north. It was doing this for a good part of the day yesterday south of the metro…then last night around 5PM or so it started to creep northwards and by 6PM the KC metro area was getting into it. Radar did show something occurring and I started getting reports of very light freezing mist around 5:15 or so. It was mixed in with a few snowflakes for some areas.

Now many of you were probably asking yourself…how the heck can we be getting this weird water/ice when temperatures are so cold…it was about 15° or so here on the ground as this was unfolding.

When the sounding from Topeka came in at 6:30 PM or so…it became clear that we were going to have an issue getting actual snow flakes to start falling from the sky. Why? Well despite the mostly saturated atmosphere towards the surface…there was a void of needed moisture (saturation) up around 7,700 feet up (give or take). This “void” of saturation, as revealed by the balloon launch went up several thousand feet higher up as well.

This is a skew-t diagram. Twice each day (sometimes more) the NWS launches a balloon to take various atmospheric measurements. The RED line is the temperature trace going up through the atmosphere and the GREEN line is the dew point. Both in °C

IN last night’s case we look for several things…1) the atmosphere needs to be below 0°C or 32°F. It was…and you can see that by the 0° line that goes toward the upper right from the bottom ( I should’ve sketched that in better for you). It’s part of the numbers that go from -50 to 50…2nd set of numbers from the bottom.

Where the two lines (red/green) are matched together…that’s saturation…there the two lines spread apart that is a measure of lack of saturation.

Notice the area that I’ve circled in orange…that’s drier air. That is also the area in the clouds where snowflakes typically form (of substance). they can form below that level but typically would have a tough time accumulating. So in the area that we need snowflakes to form..the atmosphere wasn’t allowing them to form. IF that layer was saturated then ice crystals would develop…which the snow flakes would form from. No ice crystals…now “real” snowflakes.

Yet below that layer there was saturation. As a result “super cooled” water droplets we’re developing. These water droplets then formed into a mist that slowly worked down to the ground…almost like a cloud forming from up to down in a sense. These incredibly tiny droplets then froze on contact with exposed surfaces especially at first. Hence the windshields getting iced over.

Super cooled water droplets can actually stay “liquid” all the way down to -40°! How? Well to get something frozen to form…it needs a nucleus to freeze around. That nucleus could be tiny specks of dust…or pollen…or pollutants…really anything. When there is none of this present and the air is clean…super cooled water drops can form and persist. That’s what happened last night.

IF there was saturation up at around 7-10,000 feet…and ice crystals were present..then snowflakes would’ve formed…although with such limited lift in the atmosphere it wouldn’t have been much snow at all…perhaps another dusting or so.

There are still some things we don’t understand about this type of precipitation…and it’s still being studied.

Anyway…when we finally saturated the atmosphere in that critical level(s) we finally got some snowflakes to form early this morning. IN the end…this was yet another “dusting” system for KC in a winter where these dusting to 2″ systems have been all too common (except last Sunday’s 1″-2 1/2″ quick hitter system).

The snow that’s out there is showing up nicely on the afternoon satellite picture via NEXLAB

It’s now been over 775 days since the last Winter Storm Warning for the KC area…issued by the NWS in Pleasant Hill

Now you’re saying to yourself…wait I thought the last 3+” snow in one day was back on 2/4/14 some 1469 days ago…you would be correct…

776 days ago was 12/28/15…and on that day with a Winter Storm Warning issued…we had…wait for it…2.3″ of snow. We can’t win for losing around these parts.

Meanwhile…

and farther northwest…

Whatever…I’m going to take a day or two off from blogging. So much writing lately…I’ve felt that with all these systems coming through…the coulda woulda things that you would want to know about…I needed to keep writing…but I need a break now…there won’t be anything special to write about for a couple of days anyway…so it’s a good time to recharge my batteries a bit.

I’ll leave you with this pretty shot from Tammy Grimmett called “Frost de Fleur”

See you Wednesday or Thursday!

Joe

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1 Comment

  • Richard in Olathe

    Thanks Joe !
    For the blogs and wealth of information you always give.
    I was one of the ones wondering why it did not snow at 15 degrees ! Very weird.
    Have a good few days off from blogging. You deserve it.